Thread: How did barbers hone a wedge in the olden days?

Is there anyone that sells razor hones already cupped? Tc

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Originally Posted by tcrideshd

Is there anyone that sells razor hones already cupped? Tc

Check the razor hone dept of ebay and you'll find most razor hones to be pre-cupped.

Oh sorry I meant new razors hones , not the ones that are being sold cause the guy wants money to buy a flat one !!!! Tc

Here is a question for someone that is much better in math than I am!

If I have an 8 inch long hone with a 1/4 inch low spot in the middle. How much would the angle of the bevel change for a 5/8 inch razor compared to a flat hone?

I don't think it would be as much as most people think because you are using such a small section of a relatively large arc at any one time.

My math is very rusty but I am quite sure it depends on the geometry of the crater. I guess if it is the only hone you use on your razors the effect may be minimal but if you use other hones as well on the same razors it might cause problems. A dip will cause some rounding of the bevel. If you put a slighlty rounded bevel on a flat hone you will first have to remove the metal that constitutes the belly of the bevel before you start working on the edge.
Lap it out.

Originally Posted by tcrideshd

Oh sorry I meant new razors hones , not the ones that are being sold cause the guy wants money to buy a flat one !!!! Tc

Couldn't stop myself.

Originally Posted by 32t

Here is a question for someone that is much better in math than I am!

If I have an 8 inch long hone with a 1/4 inch low spot in the middle. How much would the angle of the bevel change for a 5/8 inch razor compared to a flat hone?

I don't think it would be as much as most people think because you are using such a small section of a relatively large arc at any one time.

It would add .56 degrees per side, so just over a degree inclusive. One layer of .007" tape is .625 degrees on the same razor for reference. I assumed that the contact points on the hone are the full 5/8" dimension apart and that the arc on the stone is constant.

Edit; Using 6/8" for the contact points the change is .669 degrees and one layer of tape is .535*, so things change quite rapidly as the width of the razor changes.

Originally Posted by bluesman7

It would add .56 degrees per side, so just over a degree inclusive. One layer of .007" tape is .625 degrees on the same razor for reference. I assumed that the contact points on the hone are the full 5/8" dimension apart and that the arc on the stone is constant.

Thank you, I will have to trust your math.

So thinking that my imaginary hone is a perfect curve and the blade is even and held at a 90 degree angle to the hone while in motion etc. etc. The effect of the curve on the bevel is less than a piece of tape on the spine which is a very acceptable thing to do.

Continuing with my line of thought . I have always lapped my everyday hones and will continue to do so. but the next one I find with a dish I will not automatically pass on or flatten without at least considering leaving it as is.

Originally Posted by 32t

Thank you, I will have to trust your math.

The math is pretty simple and straightforward, no need to trust anything:

For small angles (less than 6-7 degrees) sticking with first order (linear) means that within 10% precision the additional angle is w/R, where w is the width of the razor and R is the radius of curvature of the hone
That's on each side, so the total for the razor is 2w/R

Then you want to express the radius of curvature in terms of the depth of the dishing d over the length L that it happens (half of the hone length)
Again to first order you have R=L^2/(2d)

When you put both together you have that the extra angle is 4dw/L^2

If you use d=1/4" w=5/8" L=4" you end up with 5/128 rad = 5/128*180/pi deg = 2.2 degree

(BTW you can't use more digits in the answer because the whole calculation is correct to about 3% which is 0.1 degree in the answer, i.e the higher order math terms that we've thrown away.)