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True flatness of diamond hones.
- Thread starter williamsld8
- Start date
- Joined
- Sep 19, 2010
- Messages
- 226
I really enjoy this back and forth and have learned a lot. I appreciate you both for your input. Perhaps my original post was misunderstood. I work in a calibration facility. I work with tool makers flats, granite surface plates, and supermicrometers. We have optical flats here as well. I'm not looking for anything to do with flatness on that precise of a level. I'm more or less interested in knowing which brands of stones I can set a straight edged blade down on, not the belly or any other curve, just the straight edge portion, and move the blade from one end of the stone to the other held in a perpendicular fashion, and have the entire surface of the blade make contact with the stone. The most common I have seen is with a few stones having the outside edges raised, so during this practice the whole center of the stone has no contact. I'm just looking to find out which of these manufacturers can be expected to produce stones that are flat and make contact all at once over their whole surface, with no raised edges or hills or valleys throughout the surface, throwing off the actual contact with the edge as it moves forward across the stone. Thank you for your time.
wilihamsld8. The two diamond sharpeners I know are absolutely flat are Norton and Dianova diamond sharpeners.
Dianova sharpeners are glued on a 100% flat base and the producer have experimented a lot to find just this flat base. Nortons sharpener are also flat, at least those I have used.
Most metal based diamnond sharpeners on metal base are not flat. I think they by the base and that the base are cast in just the correct measures. Cast pieces will get a small “bowl-form” = the shoulders are higher than the middle of the sharpener = they are slightly concave.
Put a steel liner across them, hold them so that you have light behind them – and can you see light between the liner and the sharpener – they are not flat. This is my method to se flatness – and you can do this a lot better then what I can
.
I can also se flatness of sharpeners when I have made a 100% flat edge and change to a new finer sharpener – the scratches it gives on the flat edge informs me how flat this sharpener really are.
Most important is that diamond sharpeners needs to be worn a while before they are flat. In the beginning they are “raw” with very sharp tips on the diamonds. After some grinding those tips in different heights are broken off – and the surface will be flat. If you shall use very fine grits (low micron figures) I think you can get very fine flat surfaces with diamond sharpeners.
Thomas
Dianova sharpeners are glued on a 100% flat base and the producer have experimented a lot to find just this flat base. Nortons sharpener are also flat, at least those I have used.
Most metal based diamnond sharpeners on metal base are not flat. I think they by the base and that the base are cast in just the correct measures. Cast pieces will get a small “bowl-form” = the shoulders are higher than the middle of the sharpener = they are slightly concave.
Put a steel liner across them, hold them so that you have light behind them – and can you see light between the liner and the sharpener – they are not flat. This is my method to se flatness – and you can do this a lot better then what I can
.I can also se flatness of sharpeners when I have made a 100% flat edge and change to a new finer sharpener – the scratches it gives on the flat edge informs me how flat this sharpener really are.
Most important is that diamond sharpeners needs to be worn a while before they are flat. In the beginning they are “raw” with very sharp tips on the diamonds. After some grinding those tips in different heights are broken off – and the surface will be flat. If you shall use very fine grits (low micron figures) I think you can get very fine flat surfaces with diamond sharpeners.
Thomas
- Joined
- Jun 25, 2011
- Messages
- 400
Hi williamsld8,
Wow, cool... You work at a calibration facility!
I've only been a knife enthusiast for about a year; mostly casually browsing BladeForums.com, KnifeForums.com, as well as the forums at WickedEdgeUSA and Spyderco. I haven't seen anyone (as a user) quantify or measure the flatness of diamond stones. And most of the people in these forums are sharpening small folders (say, 5 inches or less) on diamond stones which are much bigger (say 3"x8"). And even then, they are sharpening knives with a rather convex belly, like most spydercos, or tanto/spanto profiles.
So it is possible, I think, that most users here would not notice slightly raised edges in their diamond stones, because:
(1) Their knives are likely to have a convex belly/profile.
(2) Their knives are too short to span the length of the stone.
(3) Maybe their stones started out flat, but over the years the center dished slightly (because it is easier to grind in the center of the stone). What if the dishing is so small and gradual, they didn't notice?
That being said, I would love it if someone with real training/expertise and equipment would measure/quantify the flatness of current diamond stones. Since you work at a calibration facility...
You mention noticing, yourself, that some diamond stones are not flat. Can you tell us anything about how you noticed, and maybe how un-flat they seemed to you? I just mean some eye-ball estimate if that is all you have. If you have any measurements, that would be really cool too.
Also, I'm not sure what level of flatness we actually are talking about. I say that because I'm fairly sure that the diamond stones I have seen (mostly Eze-Lap and DMT), are flat to better than 0.1mm. How sure am I? Not sure at all. I'm just saying this, because subjectively they seem flatter than a sheet of paper to me. Since paper is 0.1mm== 0.0039 inches, well that's already 4 mils! (I'm using so-called 24 lbs weight paper. Lighter weight paper is thinner, for example 20 lbs weight paper.) If you take a machinists-straight edge and lay it across, I'm pretty sure you would notice light passing through a gap the thickness of paper.
So it's conceivable to me, but of course I don't know, that we're interested in flatness on the order of 0.001 inches (1 mil), give or take a small factor maybe. At that point, we are in the realm of granite surface plates (okay, Grade B surface plates for daily use in the workshop, even if not the Grade A plates for calibration/inspection).
Sorry I didn't have much substance to say. How about this: we (you, me, others following this thread) go test the flatness of some diamond stones (whichever ones we have access to) using whatever equipment we have (carpenter rulers or squares, dial indicators, engineer squares or straight edges, 1-2-3 blocks, etc.) and report back?
And/or, maybe you could tell us something about your experience with flat and non-flat stones, so that we have some idea of what you're looking for? We could then go check our diamond stones for what you saw on flat and non-flat stones.
Sincerely,
--Lagrangian
P.S. btw, one question I have, but haven't figured out yet is: How much are we grinding off when we sharpen? For example, we all talk about the Sharpie marker test: cover the knife bevel with a permanent marker (such as a Sharpie brand marker), then do one or a few strokes of sharpening. Look at where the marker is worn away; that's where one is grinding. The other places where the marker remains, were places that were missed. What I wonder is, how thick of a layer did we just grind off? Or, how closely must the two surfaces mate for the permanent-marker to be wiped-off everywhere? Of course this varies with situation, such as stone grit, knife metal, etc. etc. But I think it could be quite thin.
P.P.S. Since you work at a calibration facility, could I ask you about that sometime? And would you be interested and allowed to run some tests for knives and knife sharpening? Sorry, but I had to ask...!
Last edited:
- Joined
- Jun 25, 2011
- Messages
- 400
Err.... I think I would say: At the consumer level, no commercially available knife sharpening equipment is that flat.
However, there are laboratory grade things which are that flat, including diamond microtome knives. These knives are small diamond blades used to cut very thin transparent slices for microscopy (for example, tissue samples embedded in wax). They are real knives: they slice by push-cutting, and they are diamond. Some are ultrasonically vibrated to aid the slicing, and some are just used as a straight slicer without vibration. They are sharp to an astounding 0.005 microns. Given that a modern razor is sharp to 0.5 microns, this is literally 100x sharper (just by geometry, I mean, not necessarily cutting performance). Right now, you can buy them for around $2,000.00. And they even come (for free!) with a luxury wood storage box. (I want one!
)"The radius of the diamond knife edge is about 50 Ångstroms (5nm) or 30 carbon atoms and the entire length of its edge must be defect free to the same dimensions. "
--www.TedPella.com
http://www.tedpella.com/diamond_html/diamondk.htm
Optical flats, as mentioned are flat to 1/10th or 1/20th wavelength, and if you really want, to 1/100th wavelength. These have to be ground, lapped, and polished to this level of flatness. So it is conceivable that knives could also be sharpened to this level of flatness. For example, I have no idea how diamond microtome knives are sharpened to 0.005 microns, but I would not be surprised if it was related to how optical flats are manufactured. At this level, we are litterally approaching atomic flatness, which is not perfect, but would be as perfect as one could get.
I _am_ surprised that we are talking about the atomic scale. Some sharpening grits (say from Ken Schwartz) are in the 0.1 micron and 0.025 micron range for particle size. So how big are these? The Van Der Waals diameter of a carbon atom is around 3.4 Angstroms (the Van Der Waals radius of carbon is considered to be around 1.7 Angstroms).
http://en.wikipedia.org/wiki/Van_Der_Waals_Radius
So (0.1 microns)/(3.4 Angstroms) = (0.1*10^-6 meters)/(3.4*10^-10 meters) = about 300. So are current super-fine grits are only a few hundred carbon-atoms wide! If you go to 0.025 micron grits, that's only 75 carbon-atoms wide! Honestly, that blows my mind.
You can buy some of these ultra-fine stropping sprays and pastes from Ken Schwartz at ChefKnivesToGo:
http://www.chefknivestogo.com/kenscorner.html
Here is another way to think about 0.01 degrees: How big of an angle is 2 microns over 1 centimeter? Using the small-angle approximation for trig functions: (0.002mm/10mm)*(180/pi) = 0.011 degrees.
A micron (0.001 mm) might seem so small as to be inconceivable (and thus ignorable), but I disagree. Visible light ranges from about 0.4 to 0.7 microns. So when you are stropping with green chromium-oxide (which is typically 0.5 micron grit), you are already working at the optical level. I think this is why woodworkers say, if you can see a glint off the edge, it is not sharp. But if you cannot see a glint, then it is sharp. My guess is that once the edge gets significantly smaller than an optical wavelength, you cannot see it anymore. (I'm 100% not sure about this, because I don't know enough about the limits of human vision, and although I am a physics major, I don't know all the details of what the surface roughness looks like microscopically, and how the light would bounce off of that in terms of diffraction.)
I do appreaciate your point, though, that very few sharpening tools (outside of a laboratory) that are flat to 1/100 degree or the sub-micron level.
I'm just not into sweeping statements of what is "impossible" when such things are already happening in research and metrology labs, many of which are already doing commercial work in high-end production and manufacturing. The level of precision measuring and manufacturing has been increasing over the last decade(s) at an insane rate. Just ask any machinist who does any work with a CNC mill or lathe (Computer Numerically Controlled), or a CMM (Coordinate Measuring Machine).
Sincerely,
--Lagrangian
P.S. It is easy to buy (say from Amazon.com) ball bearings which are Grade 25. This means they are spherical to 25 micro-inches; ie: 0.000025 inches. Converting, we have 25 micro-inches = 0.635 microns. That's not far from being optically spherical. So there are every-day objects which are ultra-precision, even if they are not camera lenses or computer chips.
http://en.wikipedia.org/wiki/Ball_(bearing)
http://www.amazon.com/Chromium-Refl...4JI4/ref=sr_1_1?ie=UTF8&qid=1336657723&sr=8-1
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- Joined
- Apr 12, 2009
- Messages
- 13,435
This has indeed been an interesting thread. All that aside, the Duo-Sharp hones from DMT were made with something like that in mind. DMT advertises these as 'precision flat', and they seem to be, from what I've seen. I used mine to flatten a ceramic hone. Woodworkers use these for sharpening chisels and plane blades (straight, flat edges are a must), as well as for lapping their other stones. My C/F Duo-Sharp actually came in a box with an 'endorsement' from Scott Phillips, who hosts a popular woodworking show on PBS. I've seen him use one on his show, to sharpen a plane blade.
The point from knifenut1013, about pressure points exerted by the hands, is a valid one. I run into that frequently, when sharpening (re-bevelling) the edges on sheepsfoot blades in my stockman knives. Pressing a little too hard in one area of the blade will flex the blade, which then creates an uneven grind pattern on the bevel. They still get plenty sharp, but may not look as pretty or perfect. So, it's always best to keep pressure very, very light.
BTW, I've also noticed that supposedly 'straight-edged' blades (like a sheepsfoot or wharncliffe blade) are very seldom perfectly so. There's always a little warp or uneven factory grind to them (which varies the thickness of the steel near the edge), and reveals itself more explicitly when a new bevel is put on the edge. Really makes warp or uneven grind stand out, and a new bevel will almost always show at least a little bit of wave or variation in bevel width, because of the imperfection in straightness.
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Knifenut 1013, I agree with you when you wrote that you cannot go under 3 degree wobbling during freehand sharpening, that are also my experience. I cannot do it – and no other experienced knife user I have talk about this with, can do it either. I have never seen it done.
I do not agree with you that it is impossible to make a 100 % flat edge – but I can, of cause, be wrong.
I have done like this. I have a protractor, 28 cm distance between the edge and the pivot point the guide rod slides thru. They are fixed points. I have screws that hold this pivot point in a fixed position.
I can turn this screws a number of turns to move up exact 1 degree on the protractor = 14,5 full turns. I can also move those screws 1/7 of a turn = I have change the sharpening angle with 1/100 part of 1 degree – and I can, if I use a very fine sharpener – se this also on the edge because it will grind a “facet” on the edge (if the edge is perfectly flat to start with).
So, is this 1/100 part of 1 degree – or not? In my mind, it is 1/100 part of 1 degree – or, as close at least I can come to this. Perhaps it is 0,95/100 or 1,05/100 parts of 1 degree. I cannot measure that.
But –how deep into this shall we go – on edges? If we use the temperature, there will be a difference if the temperature are + 25 centigrade compare to if the temperature is 0 centigrade – but do this matter – on edges? (compare with freehand sharpening and 3 degrees wobbling). We are now discussing perhaps 3/100 part of one degree…
If I, with a tight screw, can control the sharpening angle in 7 “steps” on a full turn, this is, for me, 1/100 part of 1 degree. If I engrave 14 parts instead of 7 parts on the screw – in my mind, I can change the sharpening angle down to 0,5/100 parts of 1 degree – but I wonder if I can see this small change on the edge?  I do not think so. Do I have any need for it, no.
I think what I have done is an improvement of controlling the sharpening angle. The screws make it possible to make facets – and then I can go between those facets as I like - and find the correct sharpening angle without the use of a white board pen. I think that is pretty nice. Because – what shall we compare this with? Freehand sharpening?
No one needs to use the difference of 1/100 part of 1 degree on an edge of a knife. But 1+1 = 2. A car can go in 1 mile per hour – but few cars do.
With the screws, can I change an edge as low as 1/100 part of 1 degree – but, at least I never do this, I have no practical needs to do it. But, I can change an edge 25/100 parts of 1 degree if I like to, it is just a number of turns on the screw – and - I can go back the same number of turns to find the first surface I did. For me, this is amazing. It is precision grinding on edge angles. I can control the angle! I know exactly what I am doing. The most important thing is that I learn new things from this.
If I do not know the edge angle – and change the edge angle. I do not know where I started. I do not know where I landed. I do not know the distance I have traveled – and, what can I learn from - not knowing?
The first drip of water starts to warn out the stone.
14,5 full turns = 1 degree with Chef. I can measure it and control it, even calculate it because the distance, 28 cm, are fixed. If this is correct (and it is), 7,25 full turns = 0,5 degrees – and so on – and 1/7 of a turn is 1/100 part of 1 degree – at least in my mind. Not scientifically – but this is not science, this is about edges on knifes.
Am I wrong?
Regards
Thomas
I do not agree with you that it is impossible to make a 100 % flat edge – but I can, of cause, be wrong.
I have done like this. I have a protractor, 28 cm distance between the edge and the pivot point the guide rod slides thru. They are fixed points. I have screws that hold this pivot point in a fixed position.
I can turn this screws a number of turns to move up exact 1 degree on the protractor = 14,5 full turns. I can also move those screws 1/7 of a turn = I have change the sharpening angle with 1/100 part of 1 degree – and I can, if I use a very fine sharpener – se this also on the edge because it will grind a “facet” on the edge (if the edge is perfectly flat to start with).
So, is this 1/100 part of 1 degree – or not? In my mind, it is 1/100 part of 1 degree – or, as close at least I can come to this. Perhaps it is 0,95/100 or 1,05/100 parts of 1 degree. I cannot measure that.
But –how deep into this shall we go – on edges? If we use the temperature, there will be a difference if the temperature are + 25 centigrade compare to if the temperature is 0 centigrade – but do this matter – on edges? (compare with freehand sharpening and 3 degrees wobbling). We are now discussing perhaps 3/100 part of one degree…
If I, with a tight screw, can control the sharpening angle in 7 “steps” on a full turn, this is, for me, 1/100 part of 1 degree. If I engrave 14 parts instead of 7 parts on the screw – in my mind, I can change the sharpening angle down to 0,5/100 parts of 1 degree – but I wonder if I can see this small change on the edge?  I do not think so. Do I have any need for it, no.
I think what I have done is an improvement of controlling the sharpening angle. The screws make it possible to make facets – and then I can go between those facets as I like - and find the correct sharpening angle without the use of a white board pen. I think that is pretty nice. Because – what shall we compare this with? Freehand sharpening?
No one needs to use the difference of 1/100 part of 1 degree on an edge of a knife. But 1+1 = 2. A car can go in 1 mile per hour – but few cars do.
With the screws, can I change an edge as low as 1/100 part of 1 degree – but, at least I never do this, I have no practical needs to do it. But, I can change an edge 25/100 parts of 1 degree if I like to, it is just a number of turns on the screw – and - I can go back the same number of turns to find the first surface I did. For me, this is amazing. It is precision grinding on edge angles. I can control the angle! I know exactly what I am doing. The most important thing is that I learn new things from this.
If I do not know the edge angle – and change the edge angle. I do not know where I started. I do not know where I landed. I do not know the distance I have traveled – and, what can I learn from - not knowing?
The first drip of water starts to warn out the stone.
14,5 full turns = 1 degree with Chef. I can measure it and control it, even calculate it because the distance, 28 cm, are fixed. If this is correct (and it is), 7,25 full turns = 0,5 degrees – and so on – and 1/7 of a turn is 1/100 part of 1 degree – at least in my mind. Not scientifically – but this is not science, this is about edges on knifes.
Am I wrong?
Regards
Thomas
- Joined
- Jun 25, 2011
- Messages
- 400
Hi Thomas,
I'm nervous when you say you have 0.01 degree accuracy. Your screw mechanism cannot be perfectly accurate, and any setup cannot be perfectly rigid. So how accurate and repeatable is a given machine? Does it have accuracy and repeatability of a few microns? I don't even think watchmakers have gears that accurate.
If the error of a machine is bigger than 0.01 degrees, then it cannot claim to have an accuracy of 0.01 degrees. For a machine to have an accuracy of 0.01 degrees, it's error must be less that 0.01 degrees (actually less than 0.005 degrees). Otherwise it makes no sense to claim an accuracy of 0.01 degrees.
(1) Error can come from looseness of moving parts (this is also called slack, hysteresis, or back-lash error).
(2) Error can come from non-rigidity (flexing of parts under load).
(3) Error can even come from things like thermal expansion.
If someone is claiming an accuracy of 0.01 degrees, then then need to show that the errors from (1),(2), and (3) cause a total error of less than 0.01 degrees.
I'm asking because a right-triangle which is one centimeter wide, and two microns tall represents 0.011 degrees.
So if your sharpening rig is about 1 cm long, you need it to be precise and rigid to 2 microns. That is a tall order.
If your set-up is about 10 cm long, then you need to be precise and accurate to 20 microns. Now, 20 microns is 0.00079 inches, or 0.79 mils. That is more accurate that many imperial calipers. In other words, even if you measure your machine with imperial calipers, that is not accurate enough to guarantee 0.01 degree accuracy.
So if a machine is accurate to 0.01 degrees, its errors due to slack or gaps in moving parts, and also rigidty, must be smaller than 20 microns (say your machine is about 10 cm). I think 20 microns is very small; it's less than 0.8 mils. How often in machine shop, do you make a part with your own hands, that has accuracy of 0.8 mils (20 microns) ?
And how are you sure your rod, or base does not flex by more than 0.8 mils (20 microns) ? Personally, I doubt my own sharpening rig is anywhere near this rigid. I also doubt anything except a precision threaded rod, like that used in a micrometer, has this level of accuracy/repeatibility. Remember, this is more accurate than a standard imperial caliper (which are typically accurate to 0.0016 inches, or 1.6 mils).
http://www.amazon.com/Mitutoyo-500-..._1?s=industrial&ie=UTF8&qid=1336680461&sr=1-1
To be clear, I am talking about accuracy, not resolution. Even though those Mitutoyo calipers have a finer _resolution_ of 0.0005" inches, notice that their _accuracy_ is 0.001" inches. It's worth introducing or reviewing the difference between accuracy, precision, repeatibility, and false precision.
https://en.wikipedia.org/wiki/Accuracy_and_precision
https://en.wikipedia.org/wiki/Repeatability
https://en.wikipedia.org/wiki/False_precision
If the slack and/or flexing is more than 20 microns for your 10 cm machine, then you cannot claim an accuracy of 0.01 degrees. So if one is claiming 0.01 degree accuracy, then one has to demonstrate it by measurement, or at least by showing the system has a rigidity and slack better than 20 microns. At worst, you need to show a calculation that under expected loads, that the steel you are using has enough rigidity to avoid deflections of 20 microns. This can be done either by hand, or as a computer simulation. At best, you can measure the play and flexibility of a set-up using a dial indicator, a test dial indicator, a micrometer, or other high precision measuring device.
If you disagree, then let me ask: How much does your guide-rod bend when sharpening? From physics, we know it must bend; it is just a question of how much. And if you don't know much, how can you be sure it is less than 20 microns? With your own eyes and hansd, can you feel or see something as small a 20 microns difference? Maybe you can; the thickness of aluminum foil is 16 microns. But are you sure you can see or feel it? I am not sure I could see or feel such a small difference.
Similarly, how accurate and repeatable are the adjustment screws? And if you don't know, how can you be sure they are good to 20 microns? I'm sure that most regular bolts and nuts have a slack (backlash error) which is bigger than 20 microns.
A difference of 20 microns is not like the difference between 0.0095 degrees and 0.01 degrees (ie: a 5% error). It is the difference between 0.02 degrees and 0.01 degrees. That's a 100% error.
Don't take the 20 micron part too literally; just scale it to your setup. It's all similar triangles, so you can scale it linearly. ie: a 2x larger setup has a 2x larger allowed slack to achieve the same angular accuracy. If your setup is 30 cm long, then the allowed inaccuracy is 60 microns (which is about 0.002 inches, or 2 mils).
The point is very small errors (flexing, slack in moving parts) easily cause deviations bigger than 0.01 degrees. At this level of accuracy, the ideal geometry is nice, but not sufficient. Not only do you need accurate and rigid parts, but we can calculate how accurate and rigid the parts need to be.
Sincerely,
--Lagrangian
P.S. When I have time, I will actually go measure the slack and flexibility of my sharpening rig. I'll measure that with dial indicators, one which is from Mitutoyo and is accurate to 10 microns (about 0.0005 inches) , the other dial indicator claims to accurate to 2.54 microns (about 0.0001 inches) but it's a cheapo made in China, so I won't trust it without testing. I also have a micrometer from Mitutoyo that is accurate to 2.54 microns. I'll be testing the parts as well (rigidity of 1/4" inch diameter steel rod over 16 inches, etc.). As I mentioned, I can feel, by hand, some play (looseness) in the spherical rod ends. If I can feel it, it must be fairly signfificant.
So, who wants to _place bets_ on how un-accurate, non-repeatable, and non-rigid my sharpening rig is?
I'm nervous when you say you have 0.01 degree accuracy. Your screw mechanism cannot be perfectly accurate, and any setup cannot be perfectly rigid. So how accurate and repeatable is a given machine? Does it have accuracy and repeatability of a few microns? I don't even think watchmakers have gears that accurate.
If the error of a machine is bigger than 0.01 degrees, then it cannot claim to have an accuracy of 0.01 degrees. For a machine to have an accuracy of 0.01 degrees, it's error must be less that 0.01 degrees (actually less than 0.005 degrees). Otherwise it makes no sense to claim an accuracy of 0.01 degrees.
(1) Error can come from looseness of moving parts (this is also called slack, hysteresis, or back-lash error).
(2) Error can come from non-rigidity (flexing of parts under load).
(3) Error can even come from things like thermal expansion.
If someone is claiming an accuracy of 0.01 degrees, then then need to show that the errors from (1),(2), and (3) cause a total error of less than 0.01 degrees.
I'm asking because a right-triangle which is one centimeter wide, and two microns tall represents 0.011 degrees.
So if your sharpening rig is about 1 cm long, you need it to be precise and rigid to 2 microns. That is a tall order.
If your set-up is about 10 cm long, then you need to be precise and accurate to 20 microns. Now, 20 microns is 0.00079 inches, or 0.79 mils. That is more accurate that many imperial calipers. In other words, even if you measure your machine with imperial calipers, that is not accurate enough to guarantee 0.01 degree accuracy.
So if a machine is accurate to 0.01 degrees, its errors due to slack or gaps in moving parts, and also rigidty, must be smaller than 20 microns (say your machine is about 10 cm). I think 20 microns is very small; it's less than 0.8 mils. How often in machine shop, do you make a part with your own hands, that has accuracy of 0.8 mils (20 microns) ?
And how are you sure your rod, or base does not flex by more than 0.8 mils (20 microns) ? Personally, I doubt my own sharpening rig is anywhere near this rigid. I also doubt anything except a precision threaded rod, like that used in a micrometer, has this level of accuracy/repeatibility. Remember, this is more accurate than a standard imperial caliper (which are typically accurate to 0.0016 inches, or 1.6 mils).
http://www.amazon.com/Mitutoyo-500-..._1?s=industrial&ie=UTF8&qid=1336680461&sr=1-1
To be clear, I am talking about accuracy, not resolution. Even though those Mitutoyo calipers have a finer _resolution_ of 0.0005" inches, notice that their _accuracy_ is 0.001" inches. It's worth introducing or reviewing the difference between accuracy, precision, repeatibility, and false precision.
https://en.wikipedia.org/wiki/Accuracy_and_precision
https://en.wikipedia.org/wiki/Repeatability
https://en.wikipedia.org/wiki/False_precision
If the slack and/or flexing is more than 20 microns for your 10 cm machine, then you cannot claim an accuracy of 0.01 degrees. So if one is claiming 0.01 degree accuracy, then one has to demonstrate it by measurement, or at least by showing the system has a rigidity and slack better than 20 microns. At worst, you need to show a calculation that under expected loads, that the steel you are using has enough rigidity to avoid deflections of 20 microns. This can be done either by hand, or as a computer simulation. At best, you can measure the play and flexibility of a set-up using a dial indicator, a test dial indicator, a micrometer, or other high precision measuring device.
If you disagree, then let me ask: How much does your guide-rod bend when sharpening? From physics, we know it must bend; it is just a question of how much. And if you don't know much, how can you be sure it is less than 20 microns? With your own eyes and hansd, can you feel or see something as small a 20 microns difference? Maybe you can; the thickness of aluminum foil is 16 microns. But are you sure you can see or feel it? I am not sure I could see or feel such a small difference.
Similarly, how accurate and repeatable are the adjustment screws? And if you don't know, how can you be sure they are good to 20 microns? I'm sure that most regular bolts and nuts have a slack (backlash error) which is bigger than 20 microns.
A difference of 20 microns is not like the difference between 0.0095 degrees and 0.01 degrees (ie: a 5% error). It is the difference between 0.02 degrees and 0.01 degrees. That's a 100% error.
Don't take the 20 micron part too literally; just scale it to your setup. It's all similar triangles, so you can scale it linearly. ie: a 2x larger setup has a 2x larger allowed slack to achieve the same angular accuracy. If your setup is 30 cm long, then the allowed inaccuracy is 60 microns (which is about 0.002 inches, or 2 mils).
The point is very small errors (flexing, slack in moving parts) easily cause deviations bigger than 0.01 degrees. At this level of accuracy, the ideal geometry is nice, but not sufficient. Not only do you need accurate and rigid parts, but we can calculate how accurate and rigid the parts need to be.
Sincerely,
--Lagrangian
P.S. When I have time, I will actually go measure the slack and flexibility of my sharpening rig. I'll measure that with dial indicators, one which is from Mitutoyo and is accurate to 10 microns (about 0.0005 inches) , the other dial indicator claims to accurate to 2.54 microns (about 0.0001 inches) but it's a cheapo made in China, so I won't trust it without testing. I also have a micrometer from Mitutoyo that is accurate to 2.54 microns. I'll be testing the parts as well (rigidity of 1/4" inch diameter steel rod over 16 inches, etc.). As I mentioned, I can feel, by hand, some play (looseness) in the spherical rod ends. If I can feel it, it must be fairly signfificant.
So, who wants to _place bets_ on how un-accurate, non-repeatable, and non-rigid my sharpening rig is?
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Langrangian, how fine shall we be able to adjust the degrees? Is it 10/100, 1/100 , 1/1.000 , or 1/10.000 parts of 1 degree? Or is it 0,5 degrees? Perhaps 1 degree?
What is “flat”? How shall we measure flatness so that we can compare flatness? Shall we measure in Ångström, My - or something else?
What is logical - and necessary - measurements - on knife edges?
And for who?
You like precision, and what I can understand, you are very good to calculate. Calculate this:
If I move the screw 1/7 of a turn – how much do I change the edge angle 28 cm away from this screw? 14,5 full turns change the edge angle 1 degree. 1 degree = 5 mm on the protractor 28 cm away from the edge.
The question is, as I see it, when do the pivot point start to change its position? Is it on 1/7 turn of the screw – or is it half a turn? – or somewhere in between = from the exact starting point will the pivot “jump up” to a specific point – or do the pivot point slowly slide up depending on the fact that I slowly make a part of a turn on the screw?
The fact is, I can change the angle with 1/7 turn of this screw – and make a new surface on the edge if I use a very fine flat sharpener – and – the line between those two surfaces will be straight (If I do the job properly), all the way from the handle out to the tip. I must do it with a lot of care, with only the weight of the sharpener and the sharpener holder – but I can do it. (First, of cause, the edge must be perfectly flat and the blade shall be in exact the same position during the complete grinding). So, I know that it will be a different angle when I move the screw 1/7 part of a turn. How big is then this change of the angle? You tell me, please.
When things are used, things get warned. With time - everything warns out. I have used Chef daily for two years now. It have still the same precision today as for two years ago – in my mind – I am certain that scientifically – it have not - because the screws have, of cause, started to be worn out.
But, we still discuss edges on knifes (I hope). How fine shall we be able to adjust them? Or, compare to cars, shall cars not start to roll in 1/1000 part of 1 mile per hour. Or, shall they always make a small “jump” up to 1 mile per hour directly?
Slack, small vibrations, things who slowly warns out- yes, they exists – and the surface will get those small changes also. That is correct. But, on edges on knifes – does it matter? In my opinion - no.
Once again, what are we comparing with? Freehand sharpening?
or - are we discussing the fact that there is not a thing on earth who are perfectly straight, everything is bended...
Thomas
What is “flat”? How shall we measure flatness so that we can compare flatness? Shall we measure in Ångström, My - or something else?
What is logical - and necessary - measurements - on knife edges?
And for who?
You like precision, and what I can understand, you are very good to calculate. Calculate this:
If I move the screw 1/7 of a turn – how much do I change the edge angle 28 cm away from this screw? 14,5 full turns change the edge angle 1 degree. 1 degree = 5 mm on the protractor 28 cm away from the edge.
The question is, as I see it, when do the pivot point start to change its position? Is it on 1/7 turn of the screw – or is it half a turn? – or somewhere in between = from the exact starting point will the pivot “jump up” to a specific point – or do the pivot point slowly slide up depending on the fact that I slowly make a part of a turn on the screw?
The fact is, I can change the angle with 1/7 turn of this screw – and make a new surface on the edge if I use a very fine flat sharpener – and – the line between those two surfaces will be straight (If I do the job properly), all the way from the handle out to the tip. I must do it with a lot of care, with only the weight of the sharpener and the sharpener holder – but I can do it. (First, of cause, the edge must be perfectly flat and the blade shall be in exact the same position during the complete grinding). So, I know that it will be a different angle when I move the screw 1/7 part of a turn. How big is then this change of the angle? You tell me, please.
When things are used, things get warned. With time - everything warns out. I have used Chef daily for two years now. It have still the same precision today as for two years ago – in my mind – I am certain that scientifically – it have not - because the screws have, of cause, started to be worn out.
But, we still discuss edges on knifes (I hope). How fine shall we be able to adjust them? Or, compare to cars, shall cars not start to roll in 1/1000 part of 1 mile per hour. Or, shall they always make a small “jump” up to 1 mile per hour directly?
Slack, small vibrations, things who slowly warns out- yes, they exists – and the surface will get those small changes also. That is correct. But, on edges on knifes – does it matter? In my opinion - no.
Once again, what are we comparing with? Freehand sharpening?
or - are we discussing the fact that there is not a thing on earth who are perfectly straight, everything is bended...
Thomas
Knifenut1013, what do you like to see in a video?
Do you accept a video that shows a perfect flat surface –and then how I make a new surface 1/100 part of 1 degree? = I adjust the screw 1/7 of a turn?
Dos a video like that change your mind about what’s possible to do with a precision tool? Or, do you also like me to go back again, from the second surface to the first surface – just with the help of the screws?
When I do this, I need to use permanent ink so that it is possible to see on a video – but I can do it in one sequence so that you see that I do everything correct.
I can make a video like that, just for you, here in this thread, just because we have the same opinion about freehand sharpening and the last 3 impossible degrees….:thumbup:
But, when I have shown this video, I like you to admit that what I “clime” above – in fact - is possible.
Ok?
Thomas
Do you accept a video that shows a perfect flat surface –and then how I make a new surface 1/100 part of 1 degree? = I adjust the screw 1/7 of a turn?
Dos a video like that change your mind about what’s possible to do with a precision tool? Or, do you also like me to go back again, from the second surface to the first surface – just with the help of the screws?
When I do this, I need to use permanent ink so that it is possible to see on a video – but I can do it in one sequence so that you see that I do everything correct.
I can make a video like that, just for you, here in this thread, just because we have the same opinion about freehand sharpening and the last 3 impossible degrees….:thumbup:
But, when I have shown this video, I like you to admit that what I “clime” above – in fact - is possible.
Ok?Thomas
- Joined
- Jun 25, 2011
- Messages
- 400
EdgePal,
There are scientific instruments which output a voltage. Since voltage is just a real number, these devices have infinite resolution. Even if the instrument were to have infinite resolution, it could be inaccurate and/or imprecise.
We are not talking about resolution. We are talking about accuracy and precision.
https://en.wikipedia.org/wiki/Accuracy_versus_Precision
https://en.wikipedia.org/wiki/Repeatability
https://en.wikipedia.org/wiki/Sensor_resolution#Resolution
https://en.wikipedia.org/wiki/False_precision
I'm not speaking about these terms casually; they are technical terms in science and engineering. In research papers, they are debated, and if one makes a mistake with them, then the science can be bad and the paper will be rejected from publication.
Resolution is not the same as accuracy.
Repeatability is not the same as accuracy.
Precision is not the same as accuracy.
Sensitivity is not the same as accuracy.
Repeatability is not the same as precision.
Precision is not the same as sensitivity.
etc.
Both precision and accuracy are necessary for a good measurement. Either alone, is often not enough.
This serious when doing science: if one were to make mistakes about these, then the resulting science could be flawed, and the paper be rejected from publication. It is as important as statistical significance.
And the rejection would be justified; building a high-tech bridge with significantly flawed science (say, where precision is confused with accuracy) is a bad idea. And false precision has lead to disasters in the past, so this is not anything new.
Sincerely,
--Lagrangian
P. S. I won't belabor the point anymore... If you're curious you can read about it on Wikipedia, and in engineering books, as well as books on how to do experiments and build measuring instruments.
There are scientific instruments which output a voltage. Since voltage is just a real number, these devices have infinite resolution. Even if the instrument were to have infinite resolution, it could be inaccurate and/or imprecise.
We are not talking about resolution. We are talking about accuracy and precision.
https://en.wikipedia.org/wiki/Accuracy_versus_Precision
https://en.wikipedia.org/wiki/Repeatability
https://en.wikipedia.org/wiki/Sensor_resolution#Resolution
https://en.wikipedia.org/wiki/False_precision
I'm not speaking about these terms casually; they are technical terms in science and engineering. In research papers, they are debated, and if one makes a mistake with them, then the science can be bad and the paper will be rejected from publication.
Resolution is not the same as accuracy.
Repeatability is not the same as accuracy.
Precision is not the same as accuracy.
Sensitivity is not the same as accuracy.
Repeatability is not the same as precision.
Precision is not the same as sensitivity.
etc.
Both precision and accuracy are necessary for a good measurement. Either alone, is often not enough.
This serious when doing science: if one were to make mistakes about these, then the resulting science could be flawed, and the paper be rejected from publication. It is as important as statistical significance.
And the rejection would be justified; building a high-tech bridge with significantly flawed science (say, where precision is confused with accuracy) is a bad idea. And false precision has lead to disasters in the past, so this is not anything new.
Sincerely,
--Lagrangian
P. S. I won't belabor the point anymore... If you're curious you can read about it on Wikipedia, and in engineering books, as well as books on how to do experiments and build measuring instruments.
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If I understood you correctly my friend, building bridges with many different parts put together where very small wrongs on each part adds up - and can make the bridge collapse. I understand that and I agree.
If a bridge are built up by knife edges put together – then 1/100 part of 1 degree is very important in precision, accuracy, and so on.( I think that bridge will be very unique)…
But if the knife is just a knife, used by a human being - 17 joints away from his body – then it do not matter if the change on the edge is 1/100 part of 1 degree – or 50% more – or less. The main thing is that we can measure it in some way – and repeat it.
If there is variation on the edge surface, say that it differ 1 /1000 part of 1 inch in flatness – no one will see it - or even feel it – and I can accept that you say that it is not a 100% flat. But for an edge on a knife, used by human beings, that is absolutely flat an off. That is my point.
Thomas
If a bridge are built up by knife edges put together – then 1/100 part of 1 degree is very important in precision, accuracy, and so on.( I think that bridge will be very unique)…
But if the knife is just a knife, used by a human being - 17 joints away from his body – then it do not matter if the change on the edge is 1/100 part of 1 degree – or 50% more – or less. The main thing is that we can measure it in some way – and repeat it.
If there is variation on the edge surface, say that it differ 1 /1000 part of 1 inch in flatness – no one will see it - or even feel it – and I can accept that you say that it is not a 100% flat. But for an edge on a knife, used by human beings, that is absolutely flat an off. That is my point.
Thomas
Jason B.
Knifemaker / Craftsman / Service Provider
- Joined
- Jun 13, 2007
- Messages
- 11,179
First, stop thinking so much about that 3 degrees. None of that means much because the main goal is the apex anyways and at the apex I will create infinite accuracy.
Second, there is no such thing as perfectly flat. That's the equivalent to saying we've found absolute zero. It's not happening as of yet with current technology. Maybe never.
Second, there is no such thing as perfectly flat. That's the equivalent to saying we've found absolute zero. It's not happening as of yet with current technology. Maybe never.
- Joined
- Jun 25, 2011
- Messages
- 400
Would it be okay to say "atomically flat" or "molecularlly flat" ?
Forum member Sek pointed me to the awesome precision of x-ray telescope mirrors:
"ROSAT carries the largest X-ray telescope ever built. Its mirror surfaces have a residual roughness of less than 3 Å, which make them, after a final polishing, the smoothest mirrors ever produced for a grazing-angle telescope."
--Max Planck Institute for Physics
http://www.mpe.mpg.de/xray/wave/technologies/mirror.php
A carbon atom has a Van Der Waals diameter of 3.4 Angstroms. So if the ROSAT mirror is smooth to 3 Angstroms, that is litterally _atomically smooth_. Can't get smoother than that! (Okay, maybe you can, but not as a simple and solid mirror made of atoms.) Don't know about precise or flat though.
Thanks to Sek for pointing this out!
Sincerely,
--Lagrangian
Forum member Sek pointed me to the awesome precision of x-ray telescope mirrors:
"ROSAT carries the largest X-ray telescope ever built. Its mirror surfaces have a residual roughness of less than 3 Å, which make them, after a final polishing, the smoothest mirrors ever produced for a grazing-angle telescope."
--Max Planck Institute for Physics
http://www.mpe.mpg.de/xray/wave/technologies/mirror.php
A carbon atom has a Van Der Waals diameter of 3.4 Angstroms. So if the ROSAT mirror is smooth to 3 Angstroms, that is litterally _atomically smooth_. Can't get smoother than that! (Okay, maybe you can, but not as a simple and solid mirror made of atoms.) Don't know about precise or flat though.
Thanks to Sek for pointing this out!
Sincerely,
--Lagrangian
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David Martin
Moderator
- Joined
- Apr 7, 2008
- Messages
- 19,520
So, choils are not built on Swedish knives... DM
The apex is the exact spot where the two sides of the edge meets. Apex is, in other words, the cutting edge, just that “point” on an edge who penetrate the material. Am I correct? Or, do we use this word differently?
Apex is a place. The cutting edge various in its angle depending on how I use the edge – and to what. It is the cutting edge who penetrates the material and it the sides of the cutting edge that moves the material aside so that the cutting edge can penetrate deeper in to the material. Material hardness differs a lot.
To balance the cutting edge correct for different materials is, in my mind, very important – it is also important to balance the sharpness on the cutting edge so that the cutting edge also have a good retention = the cutting edge shall both penetrate the material – and hold for the material so that I can work with the knife as long time as possible before it gets to dull for the material I slice, cut or chop.
I can make an edge shaving sharp and shave myself with the knife = I have made a razor knife edge on my knife = the cutting edge is very thin, it must be to be able to shave with. If I use that edge to something knifes shall be able to do, for example whittle in wood for 1 minute – then this edge is not shaving sharp any more = the edge did not hold for anything else but just shaving. But – I can still use this edge for other things, as, for example, whittling. But, the edge was to dull for its mission - who was to shave. In the same way, a edge to dull for whittling can be used for other softer materials.
19 degrees are nice to have on the edge when I work in soft wood, it penetrate the soft wood nicely, I do not need to use big force, and I can work for hours before my fingers and hands will be tired. 23 degrees are nice for harder wood, the 23 degree edge will hold for hard wood, 19 degrees will not hold for hard wood. If I use 23 degree edge on soft wood, it will work – but – to penetrate the material I need to use much more power and the edge will not penetrate as deep into the material a 19 degree edge does = my hand and my fingers will soon be tired – and the job will take much longer time to do.
So, the apex is not just an apex on knife edges, apex angle various depending on how, and to what, I use my knife.
I have never seen any person be able, by free hand sharpening, hold a constant angle = they wobble – and the wobbling is, as “best” 3 degrees.
If I need a edge angle on 19 degrees for work in soft wood – and wobble 3 degrees, the apex (cutting edge) will be something between 17,5 and 20,5 degrees – not 19 degrees.
Now, what happened when I use this edge on soft wood? The weak parts of the edge will not hold, the strong parts will hold. The same problem appears if I like to have an edge on 23 degrees for work in hard wood, the edge will be something between 21,5 and 24,5 degrees – and the weak parts will not hold. If I do not know the degrees on the edge, I can make the edge steeper – so that the lowest angle is above 23 degrees – then the edge will hold – but – I need to use much more power so that the edge can penetrate the material – my hand and finger will soon be tired – and the job takes much more time to do – compare to if the edge holds 23 degrees.
If I can make an edge in 19 degrees without any (or only very small) variations on the angle – the edge will hold – and I can work long time with the knife before it gets dull.
Now, you and I probably do not use knifes in the same way. One of us use more or less force, bend a little more, are more careful with the edge, and so on. That means that for me, 19 degree is a good edge – for you 18,75 or 19,25 is a good edge = the edge must be balanced for its user.
Sometimes some tens of 1 degree can be the difference for an edge to hold - or not hold. To understand that – I must have experience off it = I must be able to make those small changes to the edge with full control of the angle and be able to evaluate the edge and fully understand what I have done to the edge.
If we compare a flat edge in 10 degree with a 2 degree honing edge (draw it on a paper) to a convex edge where the cutting edge holds 12 degrees (draw the convex edge contour)– how much more material is it in the convex edge compare to the flat edge? Not much more, just a little more. The convex edge, if it is slightly convex, penetrate better because the sides of the cutting edge moves the sliced material away better so that the cutting edge can penetrate deeper.
It is still the balance between sharpness and retention who rules. Some tens of 1 degree more on the edge – and I can work much longer with this edge before it gets dull.
This is one of the reason why I use a sharpening angle screw on my tools – and the reason why I have protractor on Chef – and a protractor kit for Basic. The protractor informs what angle is used on the edge – and I can change that angle up or down as I like to do balance the edge so that my knife will be more functional for its purpose. And, from that I can learn - because I know what I am doing to the edge.
Am I wrong?
Thomas
Apex is a place. The cutting edge various in its angle depending on how I use the edge – and to what. It is the cutting edge who penetrates the material and it the sides of the cutting edge that moves the material aside so that the cutting edge can penetrate deeper in to the material. Material hardness differs a lot.
To balance the cutting edge correct for different materials is, in my mind, very important – it is also important to balance the sharpness on the cutting edge so that the cutting edge also have a good retention = the cutting edge shall both penetrate the material – and hold for the material so that I can work with the knife as long time as possible before it gets to dull for the material I slice, cut or chop.
I can make an edge shaving sharp and shave myself with the knife = I have made a razor knife edge on my knife = the cutting edge is very thin, it must be to be able to shave with. If I use that edge to something knifes shall be able to do, for example whittle in wood for 1 minute – then this edge is not shaving sharp any more = the edge did not hold for anything else but just shaving. But – I can still use this edge for other things, as, for example, whittling. But, the edge was to dull for its mission - who was to shave. In the same way, a edge to dull for whittling can be used for other softer materials.
19 degrees are nice to have on the edge when I work in soft wood, it penetrate the soft wood nicely, I do not need to use big force, and I can work for hours before my fingers and hands will be tired. 23 degrees are nice for harder wood, the 23 degree edge will hold for hard wood, 19 degrees will not hold for hard wood. If I use 23 degree edge on soft wood, it will work – but – to penetrate the material I need to use much more power and the edge will not penetrate as deep into the material a 19 degree edge does = my hand and my fingers will soon be tired – and the job will take much longer time to do.
So, the apex is not just an apex on knife edges, apex angle various depending on how, and to what, I use my knife.
I have never seen any person be able, by free hand sharpening, hold a constant angle = they wobble – and the wobbling is, as “best” 3 degrees.
If I need a edge angle on 19 degrees for work in soft wood – and wobble 3 degrees, the apex (cutting edge) will be something between 17,5 and 20,5 degrees – not 19 degrees.
Now, what happened when I use this edge on soft wood? The weak parts of the edge will not hold, the strong parts will hold. The same problem appears if I like to have an edge on 23 degrees for work in hard wood, the edge will be something between 21,5 and 24,5 degrees – and the weak parts will not hold. If I do not know the degrees on the edge, I can make the edge steeper – so that the lowest angle is above 23 degrees – then the edge will hold – but – I need to use much more power so that the edge can penetrate the material – my hand and finger will soon be tired – and the job takes much more time to do – compare to if the edge holds 23 degrees.
If I can make an edge in 19 degrees without any (or only very small) variations on the angle – the edge will hold – and I can work long time with the knife before it gets dull.
Now, you and I probably do not use knifes in the same way. One of us use more or less force, bend a little more, are more careful with the edge, and so on. That means that for me, 19 degree is a good edge – for you 18,75 or 19,25 is a good edge = the edge must be balanced for its user.
Sometimes some tens of 1 degree can be the difference for an edge to hold - or not hold. To understand that – I must have experience off it = I must be able to make those small changes to the edge with full control of the angle and be able to evaluate the edge and fully understand what I have done to the edge.
If we compare a flat edge in 10 degree with a 2 degree honing edge (draw it on a paper) to a convex edge where the cutting edge holds 12 degrees (draw the convex edge contour)– how much more material is it in the convex edge compare to the flat edge? Not much more, just a little more. The convex edge, if it is slightly convex, penetrate better because the sides of the cutting edge moves the sliced material away better so that the cutting edge can penetrate deeper.
It is still the balance between sharpness and retention who rules. Some tens of 1 degree more on the edge – and I can work much longer with this edge before it gets dull.
This is one of the reason why I use a sharpening angle screw on my tools – and the reason why I have protractor on Chef – and a protractor kit for Basic. The protractor informs what angle is used on the edge – and I can change that angle up or down as I like to do balance the edge so that my knife will be more functional for its purpose. And, from that I can learn - because I know what I am doing to the edge.
Am I wrong?
Thomas
- Joined
- Jun 25, 2011
- Messages
- 400
Hi Knifenut1013,
Thanks for your posts. In particular, I very much like two of your points:
(1) Pressure on the knife while sharpening will induce errors (due to flexing of the knife, etc.). It would be interesting to get some idea of how big these are. As you suggest, these could easily be bigger than the non-flatness of the sharpening stone, or precision of the sharpening guide.
(2) You raise a very interesting point about the apex. It would be interesting to compare two cases:
[1] Suppose I sharpen a knife by hand, or whatever method, which does not have good angle control. Then in the end, I get a convex edge of some angle, and of some quality. For argument's sake, let's suppose the lack of angle control is roughly 3 degrees.
[2] Next, I sharpen an identical knife, but with a precision device, so that I get the same angle at the very apex, but is a V-grind (no convexing, or at least, minimal convexing).
Suppose in [1] and [2] everything is the same (identical knives, identical sharpening stones) except for the differences noted above. Then one can ask:
In practice, could one actually notice any performance difference betwen [1] and [2]?
I don't mean notice at the level of "let's do a test in a lab." I mean notice at the level of,"This is my EDC knife which I use for simple cutting tasks." Yes, [1] is more convex than [2] so that is a possible difference one might notice. But the convexing is only around 3 degrees, which is quite small. Would this be noticable when cutting in the field?
It is interesting too, though, to ask if [1] and [2] are different in the lab.
I'm mostly interested in microscope pictures of the very apex of the knife edge. Eventhough [1] has less angle control, maybe the smoothness and refinedness of the edge geometry at the apex would be similar to [2] ?
I don't know!
But if you have thoughts about it, tests, or even experiences/stories, I would love to hear about it.
Sincerely,
--Lagrangian
---------------------------------------------------------------------
"What grit sharpens the mind?"
--Zen Sharpening Koan
P.S. The following is a general comment I would like to address to everyone (and not just to any people in particular):
In engineering there is a saying:
If you didn't measure it, then you don't know it.
Many things look great on paper, with simple and correct mathematics. But in the real world, a lot of imperfections are surprisingly big. Imperfections in the real world have been confusing and thwarting engineers for millenia. This is nothing new.
If you are going to make an technical engineering claim, then it should be tested, in the real world, at the level of modern engineering.
In science, we say:
Extrodinary claims require extraodinary evidence.
So if one makes extraordinary engineering claims, then you should have extraordinary engineering evidence to back it up.
If you cannot reach the standards of modern engineering, that's fine. Just say that right at the start, and be cautious and humble in your claims. That's all.
Thanks for your posts. In particular, I very much like two of your points:
(1) Pressure on the knife while sharpening will induce errors (due to flexing of the knife, etc.). It would be interesting to get some idea of how big these are. As you suggest, these could easily be bigger than the non-flatness of the sharpening stone, or precision of the sharpening guide.
(2) You raise a very interesting point about the apex. It would be interesting to compare two cases:
[1] Suppose I sharpen a knife by hand, or whatever method, which does not have good angle control. Then in the end, I get a convex edge of some angle, and of some quality. For argument's sake, let's suppose the lack of angle control is roughly 3 degrees.
[2] Next, I sharpen an identical knife, but with a precision device, so that I get the same angle at the very apex, but is a V-grind (no convexing, or at least, minimal convexing).
Suppose in [1] and [2] everything is the same (identical knives, identical sharpening stones) except for the differences noted above. Then one can ask:
In practice, could one actually notice any performance difference betwen [1] and [2]?
I don't mean notice at the level of "let's do a test in a lab." I mean notice at the level of,"This is my EDC knife which I use for simple cutting tasks." Yes, [1] is more convex than [2] so that is a possible difference one might notice. But the convexing is only around 3 degrees, which is quite small. Would this be noticable when cutting in the field?
It is interesting too, though, to ask if [1] and [2] are different in the lab.
I'm mostly interested in microscope pictures of the very apex of the knife edge. Eventhough [1] has less angle control, maybe the smoothness and refinedness of the edge geometry at the apex would be similar to [2] ?
I don't know!
But if you have thoughts about it, tests, or even experiences/stories, I would love to hear about it.
Sincerely,
--Lagrangian
---------------------------------------------------------------------
"What grit sharpens the mind?"
--Zen Sharpening Koan
P.S. The following is a general comment I would like to address to everyone (and not just to any people in particular):
In engineering there is a saying:
If you didn't measure it, then you don't know it.
Many things look great on paper, with simple and correct mathematics. But in the real world, a lot of imperfections are surprisingly big. Imperfections in the real world have been confusing and thwarting engineers for millenia. This is nothing new.
If you are going to make an technical engineering claim, then it should be tested, in the real world, at the level of modern engineering.
In science, we say:
Extrodinary claims require extraodinary evidence.
So if one makes extraordinary engineering claims, then you should have extraordinary engineering evidence to back it up.
If you cannot reach the standards of modern engineering, that's fine. Just say that right at the start, and be cautious and humble in your claims. That's all.
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