Thread: My bevel angle calculations

Bruce, I've never quite grasped the 30 degree shaving angle suggestion either. If the bevel angle is 20 degrees, does that mean I should lift the razor off my face another 10 degrees, another 20 degrees, or another 30 degrees? Even if I knew, I don't think it would help as I really cannot afford to attempt taking such a measurement while shaving

Originally Posted by BeBerlin

Big fat warning: I hate maths. Always have, always will. It's a truly mutual relationship, by the way.

That said, I am not entirely certain that what you said is entirely accurate. Take a look at the drawing again. We measure B, which is the total spine thickness. Suppose we did not calculate the taped bevel, but just measure the taped spine, in the same fashion as we measure the un-taped spine. Obviously, we are then measuring 2 extra layers (I tried to illustrate that in the drawing as well). So when using the same formula, in the taped version the spine thickness is B+2 layers of tape. It is true that you can easily rewrite the formula (B+2T)/2 = B/2+T. Both are correct. I believe my variant stays closer to what would happen if you were to measure the taped spine instead of calculating it. Quite honestly, I thought that would be simpler.

The rest is, I'm afraid, slightly beyond me. I think that by widening B, also A will become very marginally longer. However, a spine is usually rounded and neither does tape create a sharp corner where it is folded over the rims of the spine. I couldn't think of a formula that completely correlates with how exactly the tape folds around the rim. Moreover, I think this factor will only alter the outcome in amounts far beyond the precision of our measurements (using the Verniers calipers) and far beyond the normal variations in spine thickness and blade width that can be found along the same blade. Variations in thickness of the tape itself will nullify the intended extra precision.

I'm sure this will be an interesting exercise for you mathematicians (and, of course, the Polymaths), but for practical use in real life on real razors, it seems a bit over the top. Personally, knowing the bevel angle within half a degree is more than accurate for my purposes.



I think it would be fun to have that in the Excel spreadsheet for practical purposes.

Thanks a lot!
Robin

Sorry for the late response, haven't checked this thread in a bit! What you mentioned in the first long paragraph could work just fine too. You can easily just measure the width of the spine and the bevel with the tape on and substitute these values into the original (simpler) equation and not have the need for an extra variable (i.e. tape thickness) and you wouldn't even need to know the thickness of the tape in the first place. This is, like you mentioned, simpler and more practical. To be honest I derived the second formula just to see what it would look like and for fun. But it would be more prone to error since you are using a given value of the thickness of the tape when it may not be as exact as if you actually measured the thickness of the tape on the razor. Also, if you added tape you'd be removing some metal from the edge also, shortening A as labelled in your diagram. I'm sure you could find some fancy-dancy (yes, that is a mathematical term) formula that measures the bevel angle but also takes into account the amount of the wear on the edge given the grit used, the weight of the honer, the day of the month, what colour shirt you are wearing.......etc.....etc....

But for all everyday bevel angle calculations (which I honesly don't do or really care about), it would surely be easier to make the measurements with the tape actually on the razor and use a simple equation. But what's the fun in being practical when you can use some convoluted math equation that makes everything more difficult?

So judging by this thread: since I'm a newbie and don't have a degree in mathmatics, I should wrap my razor in my favorite, high-quality electrical tape and send it to my local scientist to have it honed?

I read through this whole damned thread to find a gssixgun post for pure entertainment...and the bastard didn't even post!

You owe me 5 minutes of my life Glen!!...Of course you can always buy me a beer instead.

Originally Posted by JMS

I read through this whole damned thread to find a gssixgun post for pure entertainment...and the bastard didn't even post!

You owe me 5 minutes of my life Glen!!...Of course you can always buy me a beer instead.

LMFAO Mark...
I am waiting for the conclusion to the thread, which from my real life experience, I will guess that each layer of 3M tape will add just barely over 1/2 of one degree of angle change to the average edge, which will accomplish much to save the spine and the stone but little else that is provable...