Thread: Calculating the Bevel Angle

Originally Posted by riooso

I may be wrong but think the formula should be

tan theta = (opposite / adjacent)

But they come out right which makes me believe we have been had! Probably an inverse function of arctan is sine. It has been to long since I have had it.

Take Care,
Richard

I always remebered tangent as rise over run like slope. That would be opposite / adjacent which is right, if you calculated the adjacent side which would be the length of the bottom of the triangle that would work as well. You could use pythagorem to get the bottom of the triangle, but I used sine because the values were already known with less math for it.

Some interesting info here.

Regards,
Neil

That's interesting that 18 degrees is the ideal angle, maybe that is why some razors shave better than others not only does the quality of steel matter but also the geometry with which the blade was made, as that ultimately determines the bevel angle when honing, unless the spine is taped which alters the angle. Looking at those pictures I noticed something else as well. Depending on how the razor lays on the hone can change the hypotenuse (long side/blade) of the triangle by making it slightly shorter. Most spines are rounded or something similar so the blade rests on the hone with a point of contact slightly less than the entire length of the blade which will give a slightly steeper angle than if you used the entire blade length in calculation.

Another lame drawing to illustrate

So now I'm curious do our custom razor manufacturers use such information to determine the angle of bevel that will ultimately end up on the custom razor that they're creating?

The traditional calc is blade width divided by spine thickness. Some of the old articles I have read say it should be a 3.5:1 ratio.
My goal is 3.5:1 ratio blade width/spine thickness. I like the greater angle since it results in a smaller bevel width which makes it easier to hone.



3/16"..............5/8"................8.63 degrees...... ratio 3.33
1/4"...............5/8"................11.54 degrees .....ratio 2.5
3/16"..............3/4"................7.2 degrees ........ratio 4.0
1/4"................3/4"...............9.6 degrees .........ratio 3.0
3/16"...............7/8"..............6.2 degrees .........ratio 4.6
1/4"...............7/8"................8.2 degrees .........ratio 3.5
3/16"...............1".................5.4 degrees .........ratio 5.3
1/4"...............1"..................7.2 degrees ..........ratio 4.0

Just my $.02,

Originally Posted by randydance062449

The traditional calc is blade width divided by spine thickness. Some of the old articles I have read say it should be a 3.5:1 ratio.
My goal is 3.5:1 ratio blade width/spine thickness. I like the greater angle since it results in a smaller bevel width which makes it easier to hone.



3/16"..............5/8"................8.63 degrees...... ratio 3.33
1/4"...............5/8"................11.54 degrees .....ratio 2.5
3/16"..............3/4"................7.2 degrees ........ratio 4.0
1/4"................3/4"...............9.6 degrees .........ratio 3.0
3/16"...............7/8"..............6.2 degrees .........ratio 4.6
1/4"...............7/8"................8.2 degrees .........ratio 3.5
3/16"...............1".................5.4 degrees .........ratio 5.3
1/4"...............1"..................7.2 degrees ..........ratio 4.0

Just my $.02,

I see, the numbers I used to calc were all just hypothetical to get an idea of the effect of varying the blade width and spine thickness. If you multiplied the angles by 2 to get the full angle of the edge it looks as though it is about 16 degrees at a ratio of 3.5:1.

If you are interested in this topic, you might enjoy reading thru this thread: http://straightrazorpalace.com/advan...ed-taping.html