Thread: proper included angle

I doubt manufacturers actually measured the angle… but throughout the history of making razors, most (if not all) manufacturers adhered to the proportion of the blade about 3.5 times the thickness of the spine.

Thank you! I can work with that --

with a blade that's 3.5x as wide as the spine,

the included angle is 16.3 degrees.

[The arithmetic:
the thickness is 1/3.5 of the blade width, so
the half-thickness is 1/7 of the blade width, so
the half-angle is arctan (1/7) = 8.13 degrees, and

the angle is 16.26 degrees.

Charles

Originally Posted by cpcohen1945

a blade that's 3.5x as wide as the spine

It is the golden razor ratio if there ever was one

Yes, but imagine a circle with centre in the middle of the blade with radius Z (Z to the spine and Z to the edge).

Now, if we place this imaginary circle around the blade and now imagine that it is a disc of height A, we can work out the volume of this encompassing disc as follows:

Volume = area X height

Area of a circle is Pi X (radius squared), which is, in our case,

Pi x Z x Z

So the Volume must be

PiZZA!

Ergo, when thinking of the best angle for a razor, it is best to have a pizza.

Math don't lie.

James.

Should the pizza be 3.5 x as wide as it's crust?

Whilst poking around a couple of weeks ago, I had read that Hart Steel uses a 14.2 degree angle so that it is a 15 degree when using tape. But for the life of me I can't seem to find that on their website. Maybe it was here. Maybe it was something I had fabricated in my own mind

When the Harts were introduced some of the cognoscenti groused about the thickness of spine to width of blade aspect ratio. They noted that the included angle was 13 and change degrees: too thin, too thin they said and unsharpenable with that delicate O1 steel - all of which makes one wonder how the razor makers were able to get such good edges on them.

I think they look just fine and shave very well.

need to add that so far in my testing that SS razors like a bit more angle then there carbon brothers

Originally Posted by KingsRam

Whilst poking around a couple of weeks ago, I had read that Hart Steel uses a 14.2 degree angle so that it is a 15 degree when using tape. But for the life of me I can't seem to find that on their website. Maybe it was here. Maybe it was something I had fabricated in my own mind

The first run of Hart's were 14.2 degrees. That worked great if manufacturing tolerances were kept tight. If the blades got much wider than 3/4" the angle would be too acute and edge holding would suffer.

The current Harts are 16 degrees. That way if a blade is a little too wide, the included angle doesn't go below about 15 degrees.