True flatness of diamond hones.

Knifenut1013

We disussed for a year ago in this thread if it is possible to grind an angle as low as 1 hundred part of 1 degree. It is.

I did it for some time ago. It was in fact rather simple to do. I used 30 micron diamond sharpener to do it. This photo shows how it looks:

zslt.jpg


I first grind the total edge as flat as I could do it. I do not know how flat it is – I like to sat perfectly flat – but nothing is perfectly flat so I must try to explain how flat it is – you can see two surfaces, the smaller surface have I grind 0,01 degree higher then the first surface. That means that the first surface is flatter then 0,01 degree and we must measure it ina few thousends part of 1 degree.

I use Norton well used diamond sharpener in 30 micron to do both surfaces. I have grind the diagonally in different angles to make it possible to see them.

I use my sharpening tool EdgePal Chef to do it. It was easy. (Everyone who have a Chef can do this – and also repeat it). There is allways 28 cm between the cutting edge and the pivot point with Chef. The pivot height are demanded by a nut on a long vertical screw. I change that nut 1 seventh of a full turn – 28 cm from the cutting edge, that is 0,01 part of 1 degree on the cutting edge.

What I learned is that I shall do it again, but now shall I change the angle only 0,005 degrees, that is half of 0,01 degree. 5 thousends parts of 1 degree, that is my next goal.

Thomas
 
Hmm. That is not really solid proof that you altered the edge by .01 degree. You see, for solid proof, one must be able to quantify the change by actual measurement, not mere theorization. You theorize that you have altered the angle by .01 degree because that is how much you calculated and moved your pivot point, but you don't have an actual measurement of your finished knife bevels. The same goes for your flatness. Without being able to actually measure the flatness and angle of the bevel, you can't claim to factually state that you were able to grind the bevels .01 degree apart.

I must have somehow missed this post when it originally made its rounds. Interesting. Did anyone ever actually check a few DMT plates for flatness? I recall seeing a comment about the diamond plate wearing away the tip of the dial indicator probe. This can be avoided in a few different ways, the easiest being to lift the plunger when moving to another position. There are also ruby tips available that are much more abrasion resistant than steel. There are probably diamond ones too, but they will not be cheap. A very simple way to avoid it would be to simply place a piece of paper on the diamond stone and run the dial indicator over that. It's easy enough to use a micrometer to make sure the sheet of paper is parallel and it will conform to any bend in the plate.

It is possible to resolve an angle to 1 arc second using proper indexing devices, but this is quite pointless as far as sharpening a knife goes. As another aside, some of the best machinist's setup levels can resolve better than .0005" per foot per division.
 
I do not know if it is 0,01 degree - or if it is 0,0099 degrees. I cannot meassure it. There you are correct. What I know, and I think it is enough, is that I can grind down to this level, I can repeat it, I can grind facets - and I can go between those facets forwrad and back an hit their surfaces perfect. That is enough for me - I can use it practical.

i can go 0,25 degrees (or other numbers) up or down from a specific angle, and test sharpness and retention. i can compqre different qualitys of steel in exactly the same edge angles and becouse of that can I work scientificly with edges - if I like to.

In my mind, this is, by the law of physics, 0,01 degrees, if there is 0,001 part of 1 degree to little, or to much, it do not matter for me. That is only 1 % wrong angle.

When sharpening by free hand you cannot hold a constant angle. 3 degrees is the lowest wobble humans can perform and it needs a lot of experience to come as low as that.

What we are discussing now is some thousends parts of 1 degree. How exact do we need to be?

One hundred part of 1 degree are, in my mind, enough. Lower precision is not needed on knife edges. That is my opinion.

The precision of a sharpening tool must be balanced to its price. If the price is to high, no one will by the tool.

I enjoy precision sharpening. For me precision is about edge angles - not about what sharpener I use, this becouse, if I have precision in edge angles I can use any sharpener I like to use.

So, what are we discussing here? We have the same opinion about that it is, perhaps, 0,001 ( 1 thousend part of 1 degree) to little, or to much and that 0,01 degree is not 100% accurat. What is your suggestion - what we shall compare this with?


Some how I think that if I can grind down to 1 thousend part of 1 degree - some one will say that it is not enough, it differs, perhaps, 1 or 2 million parts of 1 degree....:)

Thomas
 
I think you may be missing the point! If you cannot be certain that you are grinding to .01 degree accuracy and it doesn't really matter if you are anyway, why not just say .1 degree, which you can say with a fair amount of certainty, and even then it never needs to be that close really. You can go back and hit your facet perfectly with a honing fixture, but so can pretty much any other honing fixture. That doesn't necessarily mean you are grinding your bevel at exactly 15.01°, you see? All you can say with any certainty is that you can change your honing angle by what you think is .01°. Just because your angle cube or digital protractor says your angle is 'x°' doesn't necessarily make it so. As mentioned earlier, any degree of flex or free play in your setup will throw that .01° right out the window. Also when using this device you must take into account the angle of your fixture as well as the angle of the center of the blade it is working on combined. What is the claimed accuracy of the protractor? My bet is there is no claim to be any more accurate than +/- at least 1 of the smallest graduations. When you get into such a small tolerance range even differing pressure can change your angle significantly.

The main thing is this: if you don't have a means to measure it accurately past the accuracy level you are claiming, you can't claim to be honing that accurate of an angle. Be it to 5° or to .005°. I would guess you are able to accurately hit .1° wih that setup...so if I were to ask you to grind an edge to 27.5° with a tolerance of +0.1° and -0.0°, I would be fairly confident you could do that, and I could send it out for an inspection and you'd be pretty darn close. If I asked you to grind an included angle of 27.57° with a tolerance of +0.01° and -0.00°, I don't believe you could do it. If you are so confident I would be more than happy to place a wager, and send the knife to an inspection lab to prove my point.

Just to give you an idea, at .01° the difference from one end of an 1/8" (~3mm) bevel to the other would be 22 millionths of an inch (.000022") or 55 one hundred-thousandths of a millimeter (.00055mm). The mere difference made by your hand touching the knife blade, fixture, and/or honing arm and changing the temperature of any of these is enough to alter the angle more than that. The heat causes the material to expand and there goes your .01°. This is why high precision machining, grinding and inspection are always done in temperature controlled facilities. The tools are sometimes even temperature controlled, as is the cooling fluid used. For inspection, the parts are placed into the same room as the inspection equipment for 24 hours to stabilize the part's temperature. So you see, it isn't quite as simple as you think it is.
 
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I have problems to adjust to, for example, 15 degrees exactly - becouse I cannot meassure it. The closets I can come to 15 degrees is with the help from an Angle Cube or similar equipment. With that tecnical help can I hit 15 degrees +/- 0,1 degrees, that means practical that I can be 0,2 degrees wrong. Perhaps can I hit 15 degrees +/- 0,05 degrees as best. That is oractical 0,1 degree wrong. That is the best this texnical equipment can perform.

To be exact in hitting 15 degrees I need very advanced and very expensive equipment.

So, I cannot hit 15 degrees perfect, that is a fact. Few people can do this.

What I can do is that from a certen point can I adjust the angle down to 0,01 degree. You are correct, I cannot meassure this small angle without expenisve texnical equipment. What I can do is to use other ways to se how accurate this is.

For example, I can asjust the angle with the help of a nut on a standing screw. One full turn of this nut change the angle 0,07 degree - in 28 cm distance from the nut center (the nut center is also the pivot point).

What I can do is to adjust the angle 14,2 full turns of the nut, that is 1 degree, and meassure that. i can go up 5 or 10 degrees and meassure that with, for example, an angle Cube. What the angle cube tells me is that if I change the angle 10 degrees (14,2 full turns X 10) so is the accurity still +/- 0,1 degrees - but now in 10 degrees.

So, the nut is more accurate then the Angle Cube.

I can also test if this small change of the nut really is 0,01 degrees by using a laser pen mounted on the sharpener just above the cutting edge The longer distance i use, the more accurate can I check the change of the angle. In 1 meter distance 1 centimeter is 1 degree, in 25 meter distance can I meassure 0,01 degree change very ackurat, in even longer distance I can be very exact.

Yes, you are correct, when sharpening this small angles the temperature is important, the weight of the sharpener is important - and no pressure at all, just the weight of the sharpener is important for the result, it can differ 1-2 thousends parts of 1 degree becouse of those things - in normal temperatures.

But really... We are talking about knifes here. Do we need to be so accurate in angles as knife users? I do not think so.

What I tryed to acchive is to change an edge angle down to 0,01 degree in that way that it is possible to go back to exact that angle again by using turns on a nut. The user can adjust degrees as he likes to and he can go from different angles/surfaces just by adjusting the nut.

For me, this works in practical use - and I enjoy precision. For a scientist, it is not accurate an off, it can differs 1-2 thousend parts of 1 degree...

For me, this is a step forward. I can be more exact in what I am doing to an edge. When I know exactly what I am doing - can I also leran from what I am doing. Exatly in my mind is not million parts if 1 degree, not even thousends parts of 1 degree, I am perfectly satisfyed with 1 hundred parts of 1 degree -+/- 1 or 2 thousend parts of 1 degree varaiation, (so far).

Many people, inclouding me, use Angle Cube or similar equipment to meassure the angle, as best this equipment is accurate down to +/- 0,1 degree. My nut can change an angle down to 0.01 degree +/- 1-2 thousend part of 1 degree.

So - I cannot hit the degrees exact - but I can adjust an "unkown" edge angle with 0.01 degrees - +/- 1-2 thousends part of 1 degree.

So, I cannot, with the equipment ai have today, grind an edge in exatly 27,5 degrees. This becouse I cannot meassure it accurate enough. But - I can change an edge in exactly 27 degrees to 27,5 degrees - with the tolerance of some thiusends part of 1 degrees. To hit exactly 27,5 degrees I think is impossible to do, perhaps a very advanced tecnical lab can do it.

As I wrote before. This discussion will allways come. Now we diskuss the accurity of 0,01 degrees, in the future we will probebly diskuss the accurity of 0,001 and later 0,0001 degrees in the same way - and with the same argument. But really, is this discussion accurate? We discuss edges on knifes...

Thomas
 
Well, my original reply about this was because of your claim that you could sharpen to an accuracy of .01°. That is a false statement, and is overstating your accuracy level. If you never know the angle of the edge to start with to any more accurate level than 1/2° or so, then that is your accuracy level. You are limited by your angle checker: its level of accuracy is only +/- .2°, I just checked it out. So your actual ability to grind an accurate bevel angle with that protractor setting the angle is more like +/- .8°. You have to measure the angles twice, first the angle of your workpiece (the blade) then the angle of your honing arm. If both were off by the full .2° you'd be out by .4°, then you'd be doubling the error by flipping the knife to grind the second side. You could also possibly do much better than this, but you have no way of checking.

You must remember not to confuse the terms accuracy and precision. Accuracy relates to an absolute angle in this case, precision to your amount of change of the angle.
 
An absolute angle is decided down to a decided level. If not, then we must talk about trillion parts of 1 degree or more. There is also accurity enough for different things. Miles meassures long distances, and it would be rediciles to argue about that the disance between two cities is not 3 miles, it is 3,0001 miles! Agree?

I talk about changing an edge angle down to 0,01 degree - and be able to repeat it. If I, with my method, is so accurate that this change is +/- 1 or 2 thousend parts of 1 degree, that is fine with me, it is accurqte enough for a edge on a knife - in my mind.

Yes, the Angle Cube is limmited to +/- 0,1degree accurity. That gives a uncertenty of 0,2 degrees on the edge. I have also another "cube" that is limited to +/- 0,05 degrees - they say, I have not checked it out. i often use both to meassure - and they seldom give the same angle...

I have not clamed to be able to make an edge in exact 15,01 degree. I can make an edge flat - and then change that edge with 0,01 degree +/- 1-2 thousend parts of 1 degree.

If, scientificly, this is false, ok, I can accept that :). But in my world, this works practical and it is very useful - and it gives a lot better precisoon then the angle checker I have.

My English is not good enough as you can see. I know that this work in practise, You diskuss from theory. I discuss in a forigin languish an are lack of words. Thanks for the discussion :)

Thomas
 
Sure, I am enjoying the discussion. Your English is quite good actually. Do take note that although the angle cube has a precision or resolution of .05°, the manufacturer states that its accuracy is only +/- .2°. That means that when it reads 15.10°, you could be anywhere from 14.9° to 15.3°. Here is the manufacturer's website with the specs:

http://www.igaging.com/page11.html

Perhaps the earlier misunderstanding arose from your improper use of the term "accurate." I think we are mostly in agreement now that we have that straightened out. It isn't ridiculous to argue the distance between two cities is 3.0001 miles; if someone were to make that claim, I would ask how they measured it. If it was measured with a suitably precise and accurate method from suitably precise and accurate points, the claim could be made. I only responded to your claim because it seemed to me that you were making a claim of accuracy that was beyond your measuring device's precision and accuracy. Anything can be measured to any accuracy desired so long as one has the proper equipment and method.
 
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