True flatness of diamond hones.

[williamsld8]

I have searched through the forum as best I can as of late, as well as throughout the vastness of the great "google", and have yet to be able to find what I'm looking for. For some time now, the only diamond hones/benchstones I was really that aware of were the DMT line and EZE LAP, with of course fans of each touting their respective positive experiences. But as of late, I have noticed that Lansky offers a line of diamond bench stones, as well as smith's edge, and even Buck offers there own diamond stones now. I'm not sure if Norton offers bench stones but I know they now have a coarse/fine combo diamond sharpener much like the smith's edge travel sharpener. With all these different makers of diamond sharpening equipment now, and their varying prices, there is one thing I'm looking for.

I want to find out which ones can be expected to be extremely flat, and which ones will be a "they tried to compete with the others and failed" type stones with raised edges or valleys along the interruptions in surface. I know DMT hones are extremely flat, they use it as a key part of their advertising, but what can I expect from the other makers?

Norton
Buck
Smith's edge
Lansky
EZE Lap

If they can all be expected to have valleys or peaks or raised edges, then I will keep saving my money and continue being a loyal DMT fan, but certain deals I have found slipping my way, and would like to take advantage of them. On the other hand, I don't want to make a mistake with a subpar quality stone just for the sake of saving a few dollars. Thanks for your time.

 

[Lagrangian]

Don't forget to consider high-end Shapton diamond flat stones from Japan:

Shapton Diamond Reference Lapping Plate (DRLP)
"plus or minus 3.5 micron tolerance"
http://www.jendeindustries.com/mm5/...JENDE&Product_Code=1019&Category_Code=SHARPEQ

Shapton Diamond Glass Lapping Plate (DGLP)
"The result is a flattening plate with a production deviation of ± 5 microns"
http://www.jendeindustries.com/mm5/...JENDE&Product_Code=1037&Category_Code=SHARPEQ

DMT Dia-Flat Lapping Plate (I think this is what you mentioned):
"Precision ground flat to +/- 0.0005" [inches]"
http://www.dmtonlinestore.com/Dia-Flat-Lapping-Plate-P80C15.aspx

Let's convert everything to microns so we can compare.
0.0005 inches = 12.7 microns

So on paper, the Shaptons are flatter.

If you need just super-flatness, but without abrasive, there are machinist granite surface plates, and machinist cast-iron surface plates. They come in various grades. Here is one that is (on paper) flat to 0.0001 inches (about 2.54 microns). Wood-workers often use it with sand-paper to sharpen chisels. Machinists use it to check the flatness of parts, and to do precision layout. There are higher grades of surface plates, which are even flatter. btw, the link below is to cheap made-in-China surface plate, so it's not clear that it actually obeys its specifications on paper. However, if you buy a granite plate from a real company, such as Starrett or Mitutoyo, they can be purchased with certified calibration reports which are tracable to NIST (the National Institute of Standards and Technology http://www.nist.gov/index.html ).

http://www.woodcraft.com/product/2004864/7535/granite-surface-plate-9-x-12-x-2-a-grade.aspx

I have a dial indicator, with a small granite plate that is supposedly flat to 0.00005" inches (1.27 microns), but dial indicator is only accurate to 10 microns (it's a real dial indicator from Mitutoyo). The stand I'll be using is this one, but the cheapo dial-indicator has been replaced by the Mitutoyo dial-indicator:
http://www.amazon.com/gp/product/B002BRUUCI/ref=oh_details_o03_s01_i00

This is a cheapo stand (made in China for sure) and does not come with any certified calibration report, so I don't know if it really is flat to 0.00005 inches. But it's the equipment I have, so I'll try testing with it, although one would have to take the results with at least a few grains of salt.

If there are machinists who are reading this, please consider testing the flatness of some of some diamond stones on real equipment (ie: stuff which is actually of high quality and has certified calibration tests). We would love to get real numbers from real machnists using real measuring equipment. If you have a CMM (Coordinate Measuring Machine), that would be _awesome_.

When I have time, I'll be measuring the flatness of an Eze-Lap diamond plate I own. There is some question about what a fair test should be, though. Should it be a brand-new? Or should I let the surface "break in" a bit by using it? What if I "break it in too much" by over-use? To use the dial indicator, I will be sacrificing a ball-bearing or two as a contact point. This is because whatever contacts the diamond stone will get chewed up (at least microscopically). So what sized ball bearing should I use for which grit? I have some Grade-25 ball bearings (http://en.wikipedia.org/wiki/Ball_(bearing)) with diameters of 0.25, 0.375, 0.5, and 1.0 inches.

The grits I have for the Eze-Lap diamond plates are: Coarse, Fine, and Super Fine (these are 3"x8" double-sided stones: Eze-Lap models DD8SF/F, DD8C/XC). I don't know if one side of these is still viable for a test (the Extra Coarse) because I have seriously over-abused that side trying to sharpen tungsten carbide. The other three sides are completely new, and unused.

I also have a very very old, and very very used "Extra Fine" DMT diamond stone (DMT W6E Diamond Whetstone Extra Fine). But dang that is one very old (more than 10 years) and very abused DMT stone. Parts of the diamond surface seem to have been completely worn away. I can test this, but I don't think it would be fair.

So I don't know what an even and fair test would be, I don't have real equipment to do a scientifically valid test, and I couldn't possibly afford such stuff (and am unlikely to have access to any of that either in someone else's lab or machine shop). But I do have some rather crude tools (except the Mitutoyo dial indicator which I consider to be legit), and I'll try to report back to everyone what I find.

btw, how are you using your diamond stones? For free-hand, I'm not sure that manually one could hold an angle more accurate that 0.1 degrees (or maybe 0.25 degrees at best?). At that point the limiting factor is not the flatness of the stone. If you use a guided set-up, then you can go farther. But one should wonder, at what point is the stone so flat, that the limiting factor is something else, such as the accuracy and rigidity of the sharpeing rig?

I don't know. But it's something I wish I could understand and quantify.

Sincerely,
--Lagrangian

--------------------------------------------------------------
"What grit sharpens the mind?"
--Zen Sharpening Koan

P.S. If you need laboratory-grade flatness, you may consider an optical flat. This is typically a disc of BK7 borosilicate glass, fused silica, or a material called Zerodur that has been flattend to 1/10th of a wavelenth of light, and if you want, you can buy optical flats which are accurate to 1/100th of a wavelength. These ultra-precision pieces of optics have had their flatness checked by laser interferrometry, and typically the good ones also come with some kind of certified calibration test. These are very expensive, and typically are rather small (an inch to a few inches in diameter). Larger ones exist, but become phenomonally expensive. They are used to measure the flatness of precision parts (such as industrial valve fittings, or commercial grade optical lenses) via interferrometry. In astronomy, they are the flat mirrors used in telescopes, and are used to fold or redirect the optical path. Typically the green wavelength used in this type of interferrometry is somewhere in the 0.55 micron range. So at 1/10th to 1/100th wavelength flatness, that means they are flat to 0.055 to 0.0055 microns. Now 0.0055 microns is only about 16 carbon atoms wide (Van Der Waals diameter of Caron is about 3.4 Angstroms).

If you are curious, Edmund Optics sells some.

"Single Surface Optical Flats"
http://www.edmundoptics.com/optics/...try-windows/single-surface-optical-flats/1906

"1/60λ and 1/100λ Single Surface Optical Flat Mirrors"
http://www.edmundoptics.com/optics/...-100-single-surface-optical-flat-mirrors/2746

 

[hank_rearden]

so how do you keep your diamond stone, or any free-hand sharpener, from concaving? orient the knife to different sides with each sharpening?

 

[Lagrangian]

I don't know. I think for general use, the diamond stones wear out of flatness very slowly, so that you mostly don't worry about it? Not sure. Will be interesting to test.

 

[Jason B.]

From my experience diamond hones have been flatter than most everything except a freshly lapped waterstone though that flatness is usually long gone before the sharpening is done.

Holding a tight angle when hand sharpening is not that important, getting the apex to meet perfectly and removing the burr is. My hand sharpened edges have a 5 degree per side angle variation with a average 18-20 degree per side apex, if I hold real tight I can get to 3 degrees per side but that's not easy. My point is its not the bevel angle its the apex angle, everything behind the apex is friction.

 

[Lagrangian]

Hi knifenut1013: Thanks for your post.

 

[Mahoney]

I'll be interested to see how the testing goes.

That said, I would not stress too much about the flatness of a stone used for knives. I certainly would not buy a NIST traceable granite plate and then use anything abrasive on it...the abrasives will abrade the granite almost as well as they will the steel. That's why you buy the cheap ones for sharpening...

Flatness matters (up to a point) when you are sharpening a tool with a straight cutting edge like a chisel, but many knife blades have a bit of curve to the edge. With a curved edge you will only have a single point of contact between the edge and the stone. Any stone that looks flat is probably flat enough for knife sharpening.

I did get into diamond stones when learning how to sharpen plane irons, I have mostly bought EZE-Lap diamond stones...mainly because I liked the sales guy and the prices were good, and they have held up well over the years. YMMV.

 

[EdgePal]

I have only seen two diamond sharpeners who are absolutely flat (as far I can check it out), that is Norton abrasives diamond sharpeners and Dianova diamond sharpeners (produced in Sweden).

When I work with precision grinding I normally use Nortons diamond sharpeners in the end of the sharpening process, I like, for example, Nortons 9 micron diamond sharpener. I use a tool where I can adjust the sharpening angle down to 1/100 part of 1 degree with full control of the angle, that means that I can make, for example, facets on an edge and then go from facet to facet as I like and find the angle the facet was made in without any problems.

Shot at 2011-07-07

This picture shows two blades. The lower blade have 5 facets. They are 1 mm wide, there is 0,75 degrees between the facets and the borders between the facets are straight all the way out to the tip. I have not polished those facets because if I do, they are hard to see – so - those facets are coarse just to be possible to see.

The other blade have three facets. They are made in 9,10 and 11 degrees, I have let the 10 degree facet coarse of the same reason. (I made another edge like this and polished the facets – and they are very hard to se even when you know that they are there).

Edges shall not, in my mind, have facets like this. I just made them to see if it was possible to do – and it was.

It can be decorative to make one or two very thin facets where the edge begins – but I think it will be hard to sharpen the edge without scratching them for most people – just because of the reason Knifenut1013 gives above – freehand sharpening cannot come under 3 degrees wobbling on the edge.

Thomas

 

[Lagrangian]

I use a tool where I can adjust the sharpening angle down to 1/100 part of 1 degree with full control of the angle, that means that I can make, for example, facets on an edge and then go from facet to facet as I like and find the angle the facet was made in without any problems.
Thomas

Hi Thomas (EdgePal),

Thanks for your post! I would love to see a picture of your set-up that has fine angle control (0.01 degrees). Could you show it to us and explain how it works?

Sincerely,
--Lagrangian

P.S. For setting angles, I've been using a Wixey Digital Angle Gauge. But it only has 0.1 degree resolution and 0.1 degree accuracy. I think the Quint iGaging Angle Cube is probably the most popular in the knife enthusiast community. These digital inclinometers (tilt meters) probably have more than sufficient accuracy for most knife sharpening. But I've recently become curious about fine angle control and general metrology. So short of resorting to crazy-expensive angle gauge-blocks (or machinist sine bars), how do you get to 0.01 degree resolution and accuracy?

0.01 degrees = 36 arc seconds; pretty darn good! Machinist spirit levels from Starrett have a sensitivity of around 10 arc seconds (0.04mm per meter). I wouldn't know, but I hear sniper rifles have accuracies of around 1 minute-of-arc (MOA) to 0.5 minute-of-arc, so around 30 to 60 arc-seconds.

http://www.wixey.com/anglegauge/index.html#wr365

http://www.quintmeasuring.com/index.php?route=product/product&path=35&product_id=71

(If you want to take the discussion to a hyper-technical level, then it may be worth reviewing/introducing the technical definitions for resolution, repeatability, sensitivity, accuracy, and precision.)

 

[EdgePal]

Hi Lagrangian, first, EdgePal is a name off the sharpening tool I construct - and make by hand. So, in a way, I am a sharpening tool producer, but I do not mass produce my tools, I make them by hand, piece by piece.

My sharpening tool Chef can do many things. One of the things is adjusting the sharpening angle down to 0,01 degree. It is easy to understand (I hope) – but sometimes my English is not good an off to describe technical things properly – so perhaps you must help me out .

Chef have a fixed distance between the edge and the “grinding loop” (where the guide rod slides thru). Chef are also adjustable for blade width – so this distance, 28 cm, is always the same. Because of this Chef also have a built in protractor up to 22 degrees, and also half degrees are showed. This means that Chef can sharpen any blade width – and the protractor always shows the correct degrees.

The grinding loop are mounted on a “barr” on two vertical screws. The barr is fixed in its position with two special nuts. The nuts have, on their upper side a marking. One full turn of those nuts change the sharpening angle 7/100 parts of 1 degree, half a turn change the sharpening angle 3,5/100 parts of 1 degree. The standard equipped Chef can do that. If I like to have the possibility to change the sharpening angle 1/100 parts of 1 degree I need an extra equipment, this extra equipment is a wider nut and its upper side is divided in to 7 “parts”. When I screw this nut 1 part – I change the sharpening angle 1/100 part of 1 degree, (Angle Cube cannot measure this).

Did I describe this so that you can understand it? As you understand, I work with distances, measures and angles – not with electronic things.

Chef can also grind convex edges, not only grind them, With Chef can I decide how many degrees I like to have on the convex sphere – and – how many degrees I like to have on the convex cutting edge. For example, If I like to have a convex edge who have 3 degree sphere and have 26 degrees on its cutting edge, I can do that with Chef – and I use the built in protractor to do it. Of cause, I can decide any convex sphere and any degree on the cutting edge.

Chefs standard sharpener holder are adjustable in length up to 6”. The sharpener ho9lder can hold any sharpener up to 6” in length – and if the sharpener are 6 mm thick, the protrtactor will show the correct degrees. As a extra equipment there is also a longer sharpener holder who can hold up to 23 cm long sharpeners or leather sharpeners (strops).

This movie shows how I grind convex edges, I also use the extra long sharpener holder: http://youtu.be/nynku3GQOoY

I show, with the help of the Angle Cube that I grind an edge who have 3,5 degree convex sphere. I do this with a angled (bended) guide rod. I use a ceramic sharpener who are 10 cm long to start with, I make some markings on the edge, take away some parts of those markings with different parts of the sharpener –and then all the markings. I change to the extra long sharpener holder who have a leather stop clamped – but I only use a part of the strop, the stop screws on the guide rod decides how long this part shall be (and the part I use decides also how many degrees the convex sphere shall be).

As you can use, I can use a leather strop also against the edge. This is because of that Chefs “fixed” angles are very exact. The edge cannot slice the leather sharpener because that the knife are fixed in its position with very strong magnets and the knife do not move during the sharpening process.

The sharpening process is not finished yet, I have just use a leather strop with 3 micron paste on it – but the edge push cut paper.
On my homepage you can find 6 videos about Chef. They are in Swedish languish, sorry about that – but I explain in English text what’s happened in the videos.

Thomas

 

[BluntCut MetalWorks]

Thomas - the bow sliding axis for convexing is innovative, perhaps Apex EP could incorporate/collaborate your idea. It's an excellent way to cut a workable & consistence convex edge for folder/short knives. May not work as well for kitchen knives because of small angle change away from perpendicular stone-to-blade.

 

[Lagrangian]

Hi Thomas,

Thanks for the explanation!

I might suggest that you post a photo; a picture really is worth a thousand words. For example, by looking that the images in your YouTube video, I instantly understood. But it very difficult to understand several paragraphs of text explaining a mechanism. It almost does not matter how good a writer you are; you won't easily beat the speed and ease of a picture, photo, or diagram. If you have some trouble with English, then this is even a better reason to use pictures, I think. So thanks for the video!

Your sharpening rig is intriguing. I have a couple of questions about it:

(1) About your "grinding loop" (the sleeve that the guide-rod goes through): Is this a sleeve bearing, or a linear-ball-bearing?
(ie: a bearing with re-circulating ball bearings).

(In case there are some you less familiar with mechanics and machines, here is a picture of a linear ball bearing (re-circulating linear ball bearing)):

(2) Are the two vertical screws just standard threaded rods, or are they precision threaded rods?
For example, I would consider screw bolts to have be standard threaded. Or are they precision threaded (like ACME rods)? Precision threaded rods are specifically designed for accurate positioning. They often show up in ink-jet printers (for moving the print head precisely), or metal-shop machines (lathes, mills) for positioning the workpiece and the cutting head. And of course, various types show up in micrometers, etc. Typically, precision threaded rod have rated accuracies. For example, www.McMaster.com sells "precision Acme threaded rods" which have a rated helical accuracy of 0.15mm per 300mm (that's about an accuracy of 0.0005 inches per foot)
http://www.mcmaster.com/#acme-precision-lead-screws/

(3) I see that you can set the angle with extremely high resolution. I like that you have nicely threaded rods with fine screw-control. Do you have a way to measure or verify the angle independently?
I just ask because at 0.01 degrees, I think the rigidity and tightness of the set-up begin to matter. Consider that 0.01 degrees over 15 centimeters is a change of just 0.026 mm (26 microns, or just over 0.001 inches = 1 mil). Given that paper is about 0.1mm thick, that means 26 microns is about 4x thinner than paper. Or you can take standard aluminum foil, which in the USA, is about 16 microns thick. In this case, 0.01 degrees over 15 centimeters represents something just over 1.6x thicker than household aluminum foil. This is very close to being more accurate that my calipers which are accurate/repeatable to 0.001 inches = 25.4 microns.

If your system has any looseness in the sleeve bearing, knife-clamp, or general rigidity which is bigger than 0.001 inches (1 mil = 25.4 microns), then it's not clear if the setup is accurate and repeatable to 0.01 degrees. In my very limited experience machining just a few parts to make fittings, it is easy for any set-up to be inaccurate, loose, or non-rigid to 0.001 inches (1 mil).

I'm not saying your set-up is not accurate to 0.01 degrees; it very well could be! But it would be very difficult to be sure unless you have an independent way of measuring its angle, or at least checking the rigidity and play of the setup. Consider that 0.01 degrees is more accurate and more repeatable than a sniper rifle. (Sniper rifles have an accuracy of about 1 MOA = 1 arc-minute = 1/60th of a degree = 0.0167 degrees.)

Maybe you could use a machinist level as an independent check on the angle? Or perhaps you could check for the amount of rigidity or looseness ("play") in your setup with a dial indicator (or a test-indicator) which has an accuracy of 10 microns or better (for imperial indicators, you probably need to find one with accuracy/repeatability of 0.0005 inches or 0.0001 inches).

Sincerely,
--Lagrangian

P.S. I also like building things. Not as fancy and precise a yours, but here is my sharpening rig:

http://www.bladeforums.com/forums/s...Inspired-by-WickedEdge-and-ApexPro-Pict-Heavy

 

[EdgePal]

Bluntcut, thanks, yes, the angled (bended) guide rod works perfect – with Chef also for long kitchen knifes. The distance between the edge and the grinding loop is 28 cm on Chef. I have smaller tools, Basic for example, there the distance is about 10 cm – and basic sharpens also convex edges – but only up to 12 cm blade length.

If you have a Edge Pro, bend one of the guide rods just behind the sharpener holder, I think that about 7 degrees bend will work fine – and now you can grind any convex edge. The height of the grinding loop (where the guide rod slides thru) decides the convex curve - in combination of how much of the sharpener surface (length) you are using. It is very easy to see how this works when you see it in front off you.

The best with this way of grinding is that the convex sphere will be the same along the complete edge – and – you can later maintain just that convex edge without any changes what so ever, year after year.

Thomas

 

[Lagrangian]

Another reason to be impressed by 0.01 degrees: If we're spanning a distance of 6 inches, then 0.01 degrees is less than half the thickness of a human hair.

(Assuming that hair is around 60 microns in diameter.)
http://hypertextbook.com/facts/1999/BrianLey.shtml
http://midwoodscience.org/?p=1136

In my own sharpening rig, I bought some "precision hardened steel shafts" which are 0.25 diamter, and 16 inches long. But their straightness rating is only 0.002 inches per foot (or approximately 50 microns per 300mm). So my rig, even if it were _perfectly_ rigid and _perfectly_ accurate in every other way, I would be not too far from being unable to guarantee 0.01 degrees accuracy because my guide rods may not be straight enough. If you do the math, 0.002 inches per foot comes out to be 0.0095 degrees. Which is basically 0.01 degrees. And that's assuming everything in my setup was absolutely perfect, except for the guide rod itself.

In practice, I know that there is some slight play in the spherical rod end, as well as the fit between the guide-rod and the hole in the spherical rod end. And the rod itself easily could have a flex of 0.001-0.002 inches, not to mention the knife clamp and the rest of the rig. At this point, even the surface texture of the rod begins to matter; the surface finish is rated at 9 microns RMS (root mean square).

Sincerely,
--Lagrangian

P.S.
You can find the hardened precision steel shafts I bought at www.McMaster.com. The shafts that I received were manufactured by Thompson, one of the older and respected manufacturers in the area of linear shafts and linear bearings.
"Straightness tolerance is 0.002" per foot for inch sizes; 0.03 mm per 300 mm (unless noted) for metric sizes."
http://www.mcmaster.com/#linear-shafts/=hg54fp
http://www.thomsonlinear.com/website/com/eng/about.php

 

[EdgePal]

Lagrangian, thanks – what do you like to see in the picture? The nuts?

1. I use three two different “grinding loops” on Chef, just a loop of brass are the standard – but I also have a pivot as extra equipment. The loop have a small gap, it need to be there, the gap gives about 1/10 of a degree uncertainty, but, you can decide to let the guide rod slide in the bottom of the loop or in the top of the loop – and the sharpening angle will be constant. The loop has not this gap and the guide rod slides fine thru the “pipe” in the pivot. No balls needed .

2. I do not know how precise those vertical screws are, they are stainless steel M4 = 4 mm in diameter,very sharp cuted and precision made. The two nuts are made in stainless steel, precision made –and expensive to by, about 3 USD each

3. You start to talk over my head my friend, my English are limited. I think I understand your question… Freehand sharpening cannot come under 3 degrees wobbling, that is my opinion after 40 years of free hand sharpening. My goal have been to be as exact I can be in sharpening angles with the construction of Chef. Chef gives 100% flat edges on short blades, and very small changes of the edge angle on long blades – and that was my goal to construct. I can, if you like, build a variation of Chef who have all those things you like to have = extremely exact. But, in my mind, Chef is exact an off. When I made those five facets, I also calculated the height of facet no 2 compare to facet no 1 = the two facets are connected with a “knee”. Both facets are 1 mm wide - How low is the far end of facet no 2 compare to the facet 1 level, I am not sure, but I think it was 3/100 off 1 mm (I think that you can calculate this better than I can do) For me, this in precision an off - at least comparing with 3 degrees wobbling on free hand sharpening… And, with Chef can I go from facet to facet and hit the exact degree on the facets – just using the nuts.

I calculated degrees and angles when I construct Chef. My goal was to build a tool that was as exact as possible – but not cost a fortune to make. That is Chef today. So, I do not know if what I say is 1/100 part of 1 degree, really are 1,05/100 parts of 1 degree or 0.95/100 parts of 1 degree – and - I do not think it matter on edges. At least I cannot feel this small differences.

If I like to go deep and scientifically study edges – I can build a tool who are more exact than Chef are – but it will cost some money to do it…

No, there are no looseness anywhere on Chef. The blades are fixed in position with strong magnets, Chef is very stabile built (weight 1,4 kilo) and everything is fasten distinct with screws. Every pice in Chef are hand made. No vibrations at all, everything is very stabile – and Chef is very nice to work with because off this.

For a sharpening tool, I do not think that it need to be so exact that we need to discuss 0,001 degrees, I think that a possible variation of +/- 0,005 degrees is more than ok for a sharpening tool.


Your sharpening tool looks fine to me. Is it adjustable for different blade width? If not, it can easily be if you want to have that function. It can also, if you change it a little, also sharpen convex edges.

The ball rod end is nice, I use them in my next sharpening tool, it is named Forest - and I show it on my homepage in some weeks. Forest is a minor Chef in a way, shorter distance between the edge and the grinding loop, 165 millimeter, adjustable for blade width, sharpen both flat and convex edges, convex edges with wanted sphere degrees and wanted degrees on the convex cutting edge – and Forest sharpens both parallel and three shaped blades, also small folders – but not blades over 18 cm long.

Thomas

 

[Lagrangian]

Hi Thomas,

Thank you for answering my questions. Pretty interesting! I think I understood your answers, so thanks.

My setup can accommodate wider blades; I set the angle with a digital tilt-meter (like the Angle Cube etc.).

The problem with my setup is that its geometry is limited to medium and short blades. Once the knife gets too long, my guide-rods will collide with metal frame on the side. I originally choose this design because I thought it would be simpler and more rigid to have such a frame. I'm probably restricted to blades shorter than about 8.5 inches. But for me, that's good enough. If I did have a bigger kitchen knife, I would want to re-design and re-build it.

The spherical rod-ends I've tried, have a tiny amount of play. I don't know how tiny, as I haven't measured it, but now that I have a dial indicator, I'm curious to see how big it is. I have two kinds of spherical rod ends, one is for 1/4" diamter shafts and is manufactured by Heim RBC (model Heim HM4). The other is by FK Bearings, and is for 1/2" shafts (model FK M8SB). With my hand, I can feel some slight axial play in the center ball, but I didn't feel any radial play on these. But the proof will be in the pudding, when I try to measure them with a dial indicator. Hopefully, I'll be able to report back to everyone in a week or two.

So far, I haven't tried convex yet, but maybe in the future

There are a couple of threads on bladeforums.com from people who made their own sharpening rigs. Some of them are pretty interesting!

Sincerely,
--Lagrangian

 

[EdgePal]

Lagrangian, when I constructed Chef I choose to use screws and nuts to fix the barr in its position. I could have use just a blank steel rod – but then I lose the possibility to be very exact and the possibility to go from surface to surface. It was not my goal to be able to adjust Chef as low Chef can be adjusted – it was a spin off effect of the material I used.

How precise shall a sharpening tool be – and how much money are people willing to pay for it? Those things must be balanced to each other.

If I have a knife who I know extremely well and have used for a long time – how many tens of 1 degree can I feel if I change the edge? 1 tens? 2, 3 4 ? Or must I go up to half a degree, or 1 degree? And, to test this I must work with the same part of wood during the complete test.

In my mind, I do not think that very small tolerances matter much. People mostly sharpen by free hand, when they do, they cannot come under 3 degrees wobbling –they are happy with that – and I am happy with that also.

Use a laser pen. Mount it on a magnet. Put it on the knife blade, (or the moving sharpener if the blade are fixed in grinding postion) aim to a paper that are 54 cm away from the edge – and start the sharpening. The red dot shall not move vertically at all. If the red dot go 1 cm up (or down) – you are 1 degree wrong on the edge. It is very simple to check out how the red dot moves… It is a quality check of how much I wobble during the sharpening process. I use this device:

http://imageshack.us/photo/my-images/338/001vwl.jpg/

And sometimes - when people aggressive say that they can hold a 100% fixed sharpening angle by free hand – I use just this device… No one have come under 3 degrees wobbling – yet .

I also use this when I constructed Chef. I am not good in mathematic – but I can calculate distances and angles – and I can stand 54 cm from a wall, have the “target” on the wall – and check out how the red point “dances” on the target. That tells me what I need to do on my constructions. When the red dot do not move vertically, I am happy. (Longer distances then 54 cm - and you can use fractions of 1 degree).

As I say before, I can build a sharpening tool that are extremely exact in sharpening angles. I think, but I am not sure, that it is possible to come down to 1/1000 part of 1 degree – and then, all material I use must be extremely exact with no tolerances at all. A tool like that will be very expensive to make – but I think it is possible to build it. But for what purpose? Perhaps a scientist who makes resurges on edges penetration skill in different materials in combination with different steel quality’s? I think 1/100 part of 1 degree is more than an off for daily use. But that is me…

Do you use Googel’s 3D drawing program: Skethup? If not, download it from Google and I can send you a suggestion for your new sharpening tool…But, for your eyes only.

Thomas

 

[Lagrangian]

Hi Thomas,

Thanks!

I agree with you. Ultra-high precision isn't necessary for knife sharpening. I don't know why I'm so interested in high precision mechanisms.... My interest doesn't serve any practical purpose. It's probably just that ultra-high precision parts appeal to the perfectionist in me. Kind of silly, but if I think it's fun, then why not?

I do have a laser-pointer, so I may try out your suggestion of tracking the laser-point on a wall to test the accuracy of the mechanism.

I do use Google's Sketchup 3D, so I would love to see your suggestion!

Sincerely,
--Lagrangian.

P. S. This is off topic, but mentions some uses of lever arms for precise measurement:

Interestingly, atomic-force microscopes (AFMs) also bounce a laser off a small bar. When the bar bends, it changes the angle of the reflected laser. In this way, they can track deflections of the bar which are smaller than one atom. The way it works is the other side of the bar has a very sharp stylus, a needle which is so sharp that it literally has a single atom at its tip. Then they very very carefully drag this stylus over a surface while measuring the tilt of the bar based on the reflected laser. In this way, they can detect the bumps of individual atoms on the surface. By scanning the surface completely, they can create a 3d reconstruction the surface to sub-atomic resolution. A scanning tunneling electron microscope (STEM) also achieves sub-atomic resolution by scanning an atomically sharp needle, but works by quantum-tunneling of electrons rather than bar deflection.

Years ago, I spent a little time in a physics lab where sub-atomic deflections of a membrane were measured using a superconducting film and a quantum magnetic detector (superconducting quantum interference device or SQUID). The idea was to see if a single line of the magnetic field moved, because it was slightly deflected by the magnetic properties of the superconducting membrane. Sounds complicated, but the fundamental idea is the same: use a very very long lever to detect a tiny change of angle. In this case, the lever was a line of the magnetic field instead of a laser beam. And the deflection was caused by a tiny change in magnetism, rather than a change in the tilt of a mirror. (If the super-conducting membrane bulges or moves slightly, it changes the magnetic field a tiny bit.) Pretty darn cool, but also pretty darn hard to do in practice. At the time, only three research groups in the world were working on that problem. There was a joke that your experiment would simply fail to work for five years, and then one day, finally, it would all come together. I myself found working on a problem like that to be too challenging and left the lab. But several years later, I was happy to hear they succeeded! (They were using the membrane deflection to study the pressure and flow of quantum liquids, like liquid helium-3 and liquid helium-4. Such fluids can interfere with themselves, in a way similar to how light interferes and diffracts.)

You might wonder how the position of a membrane can even be well defined to sub-atomic resolution. After all, wouldn't it be jostling about and vibrating from thermal heat? Yes it would be, except that the experiment was done at a around 4 kelvin or colder (4 degrees above absolute zero). When something is that cold, it doesn't move around so much (liquid helium being an exception).

 

[EdgePal]

Lagrangian, thanks for your answer.

Yes, in a way am I interested in exact things – but not in your level, your level is too high for me (or perhaps too low ).

The laser pointer is very nice to use because you see what’s really happen on the edge when you follow the red dot. I recommend that you make a video of the red dot so that you can be fully concentrated on the sharpening and do your absolute best there – and then study the video. Make lines for degrees, or parts of degrees, it helps. It is very visible – and informs you very clear how exact you can hold a sharpening angle, or, how exact your tool is.

In freehand sharpening there is 34 joints involved, 17 in each arm from the shoulder and out. 34 joints, a knife in one hand and a sharpener in the other hand – and both hands, and 34 joints, moves… to come down to only 3 degrees wobbling needs a very long time of practice, years of daily practice. There are no shortcuts in sharpening…

Ok, I made the drawing in Sketchup, send me an email and I send it to you. It is easy to understand.

Regards
Thomas

 

[Lagrangian]

Hi Thomas (EdgePal)

Thanks! I sent you an e-mail.

Yes, in a way am I interested in exact things – but not in your level, your level is too high for me (or perhaps too low ).

lol! I admit to being a little crazy.
I'll be sure to try the laser pointer soon, probably next week.

Sincerely,
--Lagrangian