Thread: Absolutely, positively the last word on spine taping

This is what mathematicians do when they're bored. I wouldn't swear in court that there are no mistakes here, but this is my first stab at a theoretical approach to spine taping.

Suppose a razor comes out of the factory with height h[0], grind angle 2*theta[0], and thickness 2*t. Because we always hone it with tape on the spine, t does not change, so the razor is ground away to height h[1] and angle 2*theta[1].

First, we solve for the amount of height that we have ground away over the years:

And here is the equation:

Next, let's assume that the razor leaves the factory with a 14 degree edge, and that it ceases to function as a razor when it hits 20 degrees. So we'll set theta[0] and theta[1] to 7 and 10 respectively. Then we use the known height and angle of the razor when new, to solve for thickness.

Substituting eq.2 into eq.1, we can solve for the amount of height which has been ground away by the time the razor reaches 10 degrees, which is the point at which it is trashed.

Conclusion: for any height razor, if you tape the spine, the razor will become unusable when you have ground away about a third of its height. QED.

I am not a math wiz, but let me see if this helps.

A razor is 5/8" high with a taper of 17 degrees. 3m electrical tape is 3.5 mil.

I think at that point you are only adding less that .001 degrees of tilt to the blade increasing the taper to 17.001 or something like that.

Is that what you are saying?

Edit: After posting your other posts appeared. A 5/8 razor = .625 removing a third of that .3/.625 = .48. .625-.48 = .145 which is equal to taking a 5/8" razor to between a 2/8 and 1/8. I would argue that the razor would be useless at about .25 of loss instead of .3 of loss.

No. I am saying that you are wearing away the edge but not the spine, thus making the angle more obtuse. I am calculating how this will affect the lifespan of the razor. I conclude that you will have to grind away 1/3 of the razor before it's trashed, which will probably take longer than you have left to live. So spine taping probably doesn't affect the longevity of a razor significantly.

So if you rerun the equations with the information that I gave you 3.5 mil thickness for tape, 5/8" blade, and a 17 degree angle. Assuming this is a new DOVO or TI and not flea bay razor. What do you get?

Also what about the variant of how much metal is abraded? How do you account for that over a life span say 50 years?

Originally Posted by singlewedge

I would argue that the razor would be useless at about .25 of loss instead of .3 of loss.

Maybe so. These are approximate calculations. I wouldn't swear in court that 14 deg. and 20 deg. are the exact right numbers. Other members (like yourself) are welcome to make refinements

Someone posted (sorry, can't remember who) that they'd discovered on the german forums that the friodurs are at their peak at 18 degrees, & therefore actually benefit from taping. My experience with them has indicated this too. I tape.