Thread: How flat is flat for a hone

If you want to know whether your stone is really near true flat, check by placing three equal thickness shims under it between the straight edge and the stone - two at either end and one in the center. If all three aren't tight under the weight of the straight edge, your stone isn't true. For shims you can use new unwrinkled strips of aluminum foil, paper or even duplicate feeler gages.

If the stone is out of true you can use feeler gages to get an idea of the curvature also - just use two shims at the ends and then check the difference between the gap by the shim and in the center of the stone.

What is AFAIC? And if relevant, where is it found? I am not good with acronyms.

Euclid440: An abundance of thanks for the information. Also the diamond lapping plates I found started at around $135. Thought that was a bit much, especially when "How many times will you use it?" question occurs. As for me, I am somewhat cautious about my purchases. I have to figure out if it will pay for itself. If it won't do that then I let it go. Now, admittedly I have gone nuts and bought the item anyway. Why? Who knows. Guess it is the nature of the beast.

Originally Posted by Glock27

What is AFAIC? And if relevant, where is it found? I am not good with acronyms.

As Far As I'm Concerned

What if a shim will not slide under the engineers straight edge? I checked 4 points horizontal to the long edges of the stone, multiple checks perpendicular to the stone and six vertical checks to the stone--3 left and three right. I used a four LED flashlight to shine at the bottom edge of the engineers straight edge and no light passes beneath the straight edge. Does that work.

Checking with a light is not quantitative and it is easy to miss a gap. (I was a machinist and toolmaker for a couple decades before I blew my back out and while training apprentices saw many people miss gaps, trust me).

If a .001" (or even .002") shim won't slide under anywhere I'd personally call it good enough and stop worrying about it. The method of checking with multiple shims is for quantitative measurement of any amount out of true, but if you're better than .002" that's plenty good enough AFAIC (*wink*).

Now I'll plant another seed - are you sure your "straight" edge is straight?

Thank you Kertz. Professionalism. Is my straight edge straight? Is any straight edge straight This is an enigma it seems I run into walls about. Ultimately nothing is perfect, not even NASA. As I have mentioned in other posts I simply have to have faith in the products I receive, other than that which comes from china. Now the straight edge I have is American Made, one recommended to use in assuring that the block and the head of an automotive engine is flat enough to tolerances to prevent tragedy down the road for a block or head. As a former machinist what is it you did to validate all of your equipment. Again the shims used. What is it that makes us sure the shims are at the tolerance they claim (faith). Now I could use my micrometer (American made) but I have no assurance that the micrometer is accurate other than faith in the product.
It is suprising to me there are so many member who "appear" to create doubt in other members mind.

Now. When I did all the checks, diagonal, vertical and horizontal I did indeed use a 4 LED light in a black room. it was expeditious for me as I recently moved and sold my stainless steel two tiered tool chest. All my tools are hither skither, so spending possibly hours hunting down my shims was counter productive. The straight edge I have is "00 heavy duty Stainless Steel, manufactured to DIN 874 standard". In order to get close I use a granite surface Plate 9x12x2 inch with no ledge and a bilateral accuracy of +or- .0001 inches. Used this stuff mostly when I use to work on my own cars or when the technology did not exceed my ability (electronics). Ergo, I think my Chinese hone is as near to flat as I can possibly get it with my limited tools and limited knowledge base. I do the best I can, probably like most of the members here. Now are these tools accurate? I have absolutely no idea. I can only depend upon the producer and seller being honest. All the auto's I had to pull the heads on have all worked with no residual problems. Given this I have to guess my tools are accurate to some degree, but tolerances of .0001 is incredible especially for a hone.

Originally Posted by Euclid440

And… just so you know… glass is not flat.

...

I think it's flat enough for flattening a honing stone. Most modern glass today is made with the float method manufacturing process whereby molten glass is floated on a substrate - usually some tin or alloy metal. Perfectly flat? You're right, probably not perfectly flat but certainly flat enough to lap a hone. I suppose I could lay a piece on my son's granite surface plate (certified flat) and run a dial indicator over it - but I think that's probably big time overkill. I think we might be getting a little crazy on tolerances for a hone. As Lynn says flat enough.... and every razor I've had honed by him has been excellent.

Adam

I think about the effects of flatness quite a bit. From doing the math it appears that variations of radius over short distances would be much worse than radii that stay constant over the length of the hone. When you try to put numbers on the effects, you run into a can of worms such as the amount of bias (heel leading), consistency of each stroke, consistency from hone to hone. In the end, a hone can be not flat enough to do a good job, but it can never be too flat. On the other hand obsessing over flatness results in washing most of the hone down the drain without abrading steel first. With all of that said, it probably makes sense to say that the less experience you have, the flatter your hones should be.

O.K. bluesman--you have gotten rather technical here, especially with me because what you have said is above and beyond my skill set. From that I guess I will never have a flat hone, yet most all my razors are quiet sharp. I can't even imagine our forefathers got that particular with their hones and shaving. My grandfather on my mothers side was a sawyer for a log milling company. He spent a large amount of time sharpening huge circular saw blades among other sharpening tasks required of him. He use a SR and sharpened it on a large, foot peddled sand stone. Every sharp bladed instrument in the house was sharpened on this. I don't know how sharp his SR's were but I cannot imagine that big sand stone wheel had any flatness anywhere to it. So. How flat is flat? And, exactly how flat do we really have to be? This gets really far out of my scope.
My original intent was to learn what others do to flatten their hones.