Thread: blade width vs, thickness question.

Originally Posted by JDM61

Or in the case of a 1 to 4 thickness to height ratio you can just divide 60 by 4 and get 15. That's math for the liberal arts major.

OK, where did you get 60 from?

My point was for any given blade height you wanted to make, find the width needed for the correct honing angle.

With the Isosceles triangle as you starting point, all three angles are 60 degrees, Divide by the long ratio. 60 divided by 4 equals 15. Not exact science as the angle of each side would actually be slightly more that 8 for a total included angle of like 16.1 on the 1 to 4 ratio but fairly close. Gives you a tiny bit of wiggle room, Like i said. math for liberal arts majors kind of like the "3 pennies tall" sharpening angle for full width chefs knives.

Originally Posted by Hart

OK, where did you get 60 from?

My point was for any given blade height you wanted to make, find the width needed for the correct honing angle.

A 1 to 4 ratio is actually 14.36* inclusive.

I/2 thickness/hyp > A-sin x2

Originally Posted by JDM61

With the Isosceles triangle as you starting point, all three angles are 60 degrees, Divide by the long ratio. 60 divided by 4 equals 15. Not exact science as the angle of each side would actually be slightly more that 8 for a total included angle of like 16.1 on the 1 to 4 ratio but fairly close. Gives you a tiny bit of wiggle room, Like i said. math for liberal arts majors kind of like the "3 pennies tall" sharpening angle for full width chefs knives.

Equilateral triangle is what you mean.

Originally Posted by JDM61

With the Isosceles triangle as you starting point, all three angles are 60 degrees, Divide by the long ratio. 60 divided by 4 equals 15.

The only reason that I can see for this coming close is that a radian is ~ 57.3 degrees

Originally Posted by bluesman7

The only reason that I can see for this coming close is that a radian is ~ 57.3 degrees

You lost me as my only extensive exposure radians was milliradians when trying to get a rough idea of where an artillery shell might fall and even then, we couldn't say the entire word. Just mils. But what happens if you use that "formula" on any of the common 8th widths? 6/8 with a 3/16th spine width should give you pretty much the same result, right? Slightly "scientific" than trying to decide which coins to use and how many when figuring out the angle to use to sharpen your new Shun.

Shuns dont stay sharp at 3 coins...

Tan(1/2desired angle)= (1/2thickness)/height of grind(adjacent)...

tan(-1)(desired angle/thickness/2)=height of grind(adjacent)

Getting my calculator to do this is harder though... trig is a long time ago

Or you could just keep above the 1 / 4 ratio and don't bother with formulae.
That is what vintage makers did and it seems to work well.

This quickly got way too scientific. The thickness of the spine in relation to the edge is built to ensure the correct angle for honing. That is all.

Appreciated... just got confused as if you look at it from a symmetrical grind perspective the slope with a 1:3.5 or 1:4 is somewhere between 1:7 & 1:8... which is a 12.5- 13.5% slope... one sided... which i thought would be larger than 7.5 to 8.5 degree slope... one sided and i am irritable with my maths at the mo...