Calculating the bevel angle

Use a straight. You know it makes sense.
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Southbound
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Joined: Fri Oct 06, 2017 2:17 am

Calculating the bevel angle

Post by Southbound »

Hi all,
I know how to calculate the bevel angle on razors, but I was wandering how one would go about a smiling blade. I don't currently have one at the moment, just was curious, but wouldn't the measurements vary on a smiling blades width up to the hone wear bar?
For example maybe 17° in the center, but on the heel and the toe the calculations may be 19°, because the blade naturally curves upward. When we shave sometimes we use the entire blade length and other times we only use the toe, and others we may use the heel and the middle portion on the blade, just depends were we are shaving. So would one average it out the calculations - For example 19+17=36÷2= 18°??
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drmoss_ca
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Re: Calculating the bevel angle

Post by drmoss_ca »

Wouldn't it depend on whether you hone the razor with straight strokes, or with a rolling stroke? In the latter case the bevel angle is properly measured perpendicular to the edge and will be small than if measured perpendicular to the spine. Just to complicate things, old razors with smiles often have swaybacked spines, so my inclination (if I might use the word!) is to test the edge all along the length and see if it is satisfactory. I don't worry much about bevel angles when the razor shaves OK.
"Je n'ai pas besoin de cette hypothèse."
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Southbound
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Joined: Fri Oct 06, 2017 2:17 am

Re: Calculating the bevel angle

Post by Southbound »

I don't really know exactly ? I don't overly worry about the angle either but I like to be at least angle aware. The tape and not taping isn't confusing to me. Depending on the thickness of tape ( I use kapton) it changes the angle about a half of a degree. Some guys seem to think that if you tape the razor, (for a couple dozen or so honings) and you decide you want to untape then you have to put unnecessary wear on the spine to correct and get the geometry back on track, and that is farther from the truth. It only effects the angle by a half or 3/4 of a degree, and one can choose to tape or not taps anytime they want. The only way a razor would start getting noticeably obtuse and not shaving as well - If one only used one straight razor for 30 + years and 'always' taped the spine, 'then' over all those 30 years of removing the metal from width and none from the spine, and say they wore for example 1/16" off the width and always taped the spine then yes the angle will be affected and become more obtuse, because the spine thickness was never reduced in that 30 + years of honing.
Most of us have plenty of razors in our rotation and if we always tape, then its very doubtful in our lifetime that this obtuse angle would even be noticed. I have gotten 70 shaves from one hone, so the stones get revisited not much because of need, but they get revisited because I like to hone. I like to tape my new razors, but I prefer the honing feedback without tape. Yes a new guy tends to lean on the spine and wear it prematurely, but when he learns to use a slight torque towards the edge then that will not become a problem for him if he wanted to hone with no tape. I would say the only person who would start to see and notice a new razor (always honed with tape) getting obtuse would be a barber who shaves more people in a week than we do in a month, because they would have to revisit the hones a lot more than the average Joe.

I would hone heel leading and use × - stroke on a smile the same as I do on a 'straight' blade .
I am not smart enough to do trig - I use a angle calculator. I know on a 'straight' spine and edge razor I measure from top of the hone wear bar to the apex of the edge. I then punch in calculations from the spine thickness and the width of the razor to the hone bar and the apex, then hit calculate.

I just assumed that the width would naturally vary because of the smile 👉) in the blade. So one would have to choose a given point to calculate the angle, I just figured measure all points (of the width) then calculate, then average. I may be wrong though? That's why I asked to get feedback from more experienced people . Still have lots to learn for sure, but I enjoy the hobby. I don't post much on the other forums. To many egos.
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drmoss_ca
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Re: Calculating the bevel angle

Post by drmoss_ca »

You're correct that if you have a straight spine but a smiling edge, the bevel angle will vary, and be a bit larger at the point and the heel, simply because the distance is less between the edge and spine in those places. This will be mitigated if a curving stroke is used for honing, as the edge meets the in a diection of travel more nearlt perpendicular to the edge at those points, and the effective blade width is then a bit wider.
At the end of the day, I don't hone to get a bevel angle just so, and as long as a razor shaves, it doesn't matter what the value is to me. If a razor won't shave as expected, even after much honing, then it's more likely a geometry issue rather than an incorrect bevel angle.
Now I know some people spend much argument on whether this or that angle is preferable. I wish them well, but I'd rather shave than argue!

I'm not so sanguine about tape as you. I recently honed a razor that had been honed with tape (I didn't know it at the outset) and had been overhoned until its edge looked like a serrated knife. To illustrate the bevel change caused by the tape, I had to hone for a very long time as I wore down the shoulder of the bevel before I could get to the edge. (It worried me at first as I thought I was honing the edge which was remaining saw-toothed and must have been crumbling, or so it seemed). I used to play with tape, mostly because it made the razors slide over the hones easier, and seemed to make it simpler to give the blade a smooth, light even stroke across the surface. These days it only comes out when a razor won't come right for me, and often then it will be used on one side or only on part of the spine to correct some mangled geometry.

You'll be very welcome to post all you like here - we don't tend to encourage egos so you'll be safe!
"Je n'ai pas besoin de cette hypothèse."
Pierre-Simon de Laplace
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