Thread: Tape

Mparker,

Sorry, I'm confused:

I'm not completely sure what the definition of the angle of a blade is - is it 2a? From the way your ascii art is drawn, I guess it is.

Another question: if you rotate your picture 90 degrees clockwise, is that the equivalent of resting the blade on its back with the edge in the air? I'm confused about what you call the width of the blade - is it the horizontal distance from spine to point, or is it the hypotenuse of your picture?

If it's the hypotenuse, I get why you use sin. I'm just not sure the width is the hypotenuse - I'd have thought sqrt((t/2)^2 + w^2) should be the divisor in the arcsin calculation.

Or am I getting it all wrong?

James.

It seemed clear to me that what Michael called Width is the hypotenuse and that if you rotate 90 deg clockwise it would be like resting the blade on the spine. And that the blade (edge) angle is 2a.

Unfortunately I remember nothing about sinus, cosinus, etc. - what a shame

Cheers
Ivo

Originally Posted by izlat

It seemed clear to me that what Michael called Width is the hypotenuse and that if you rotate 90 deg clockwise it would be like resting the blade on the spine. And that the blade (edge) angle is 2a.

Unfortunately I remember nothing about sinus, cosinus, etc. - what a shame

Cheers
Ivo

OK, I get it - it is the hypotenuse (sorry). Would you generally verify the assumption of equal angle (in case of uneven hone wear)? Or is this usually minor?

SOHCAHTOA, Ivo!

James, is SOHCAHTOA an insult or something? I guess I deserve it, for not knowing basic things

I would think that uneven hone wear is indeed minor.

However, some razors, for example the TI PI hand forged LE, have weird geometry - different angles on both sides. Then the total edge angle would not be 2a; more like a+b.

Cheers
Ivo

The width along the side of the blade is the hypoteneuse of the triangle, whether it's standing on the spine or not (the hypoteneuse is the side opposite the right angle in a right triangle).

In the case of uneven hone wear or uneven grind (both sadly common) then you're on your own, my trig and geometry are too weak at this point.

Bruno, it's unnecessary to tape the spine. I know some have felt the spine would decrease in size over time but the angle geometry set by the spine and blade edge is an important one. Try this. Under magnification, examine some spines for wear. Tell us what you see.

Originally Posted by izlat

James, is SOHCAHTOA an insult or something? I guess I deserve it, for not knowing basic things

...

Cheers
Ivo

Ivo - no, no, not an insult! Maybe it's just how we learned it in Australia, but SOHCAHTOA is an acronym for remembering the definitions of sin, cos and tan using a right-angled triangle.

Sin - Opposite over Hypotenuse
Cos - Adjacent over Hypotenuse
Tan - Opposite over Adjacent

James.

Originally Posted by Howard

the angle geometry set by the spine and blade edge is an important one.

It's important, but there's a wide range of acceptable angles. Unless your razor is already getting near 20 degrees, taping the spine is unlikely to change the geometry enough to matter.

Now we only need conclusive research on the edge properties and feel in the 15-20 deg range

Might be a good weekend project for the scientifically inclined

Cheers
Ivo