Thread: How Bevel is Affected by Taping

Gentlemen, Please let's separte fact from opinion.
Everyone is entitled to have his own opinion, but don't start preaching personal opinion as facts.

Keep this discussion respectful and non-inflammatory.

Originally Posted by icedog

Okay, this may not be news for some. I wanted to know how much the application of a single layer of electrical tape to the spine of a razor you are honing affects the angle of the bevel (as compared to no tape). So I took two measurements on the nine (9) razors I currently own:

1. blade width from the thickest part of the spine(which is what contacts the hone) to the edge
2. thickness of the spine

Then I used the following formula to calculate the theoretical bevel angle (I'm not smart enough to work these computers so I am showing a photo of the formula):

Where (still not smart enough, I insert yet another picture of a picture):

Note: I divided the spine width by two to get the actual bevel angle. Otherwise I would have calculated the included angle of both sides of the blade.

I then ran the calculations as above and added 0.007" (the typical tape thickness or TTT for those that dig abbreviating shit) to O to calculate the angle (theoretical) with tape.

Here's the data Oh my God I'm so stupid! I have to put in another picture):



Conclusions:

• Yes, taping the spine will affect the geometry of the bevel (but DUH Icedog! we already knew that!)
• The narrower the blade, the more it's bevel will be affected by taping.
• I need more big razors
• I really need to get back to work!

So what do you think about that?

Icedog, this is what I think: you're an animal! Kinda crazy too - to go through all that, but a great idea.

I also believe that as the spine wears down, coincidentally with the edge (under normal honing) that the angle remains constant for a correct shaving edge. Can you figure a formula for that? Eh?

Or how about this: (and maybe your above data aready has some of what I'm about to suggest)

Assuming a brand new straight razor, the spine has a certain thickness, blade certain width, equals a bevel of X. That bevel would be the intended thickness for shaving for that razor. Yes? Now add the tape. How far off is the bevel with the tape (I guess that is your Delta above), and how would that affect shaving?

Also a rate equation: under normal honing (define) how long will a straight razor blade last before the edge/spine wear will no longer produce a shaving edge?

All in fun, of course.




Scott

Originally Posted by honedright

Icedog, this is what I think: you're an animal! Kinda crazy too - to go through all that, but a great idea.

I also believe that as the spine wears down, coincidentally with the edge (under normal honing) that the angle remains constant for a correct shaving edge. Can you figure a formula for that? Eh?

Or how about this: (and maybe your above data aready has some of what I'm about to suggest)

Assuming a brand new straight razor, the spine has a certain thickness, blade certain width, equals a bevel of X. That bevel would be the intended thickness for shaving for that razor. Yes? Now add the tape. How far off is the bevel with the tape (I guess that is your Delta above), and how would that affect shaving?

Also a rate equation: under normal honing (define) how long will a straight razor blade last before the edge/spine wear will no longer produce a shaving edge?

All in fun, of course.




Scott

tan A= opposite/adjacent=a/b

If the cutting edge is angle A. As hone wear reduces the spine thickness (side "a"), the edge honing also reduces total blade width (side "b"), thus maintaining edge geometry "A".


I think?

If the honing process results in a different wear rate of the spine versus the edge, then I think it is reasonable to assume that the bevel angle will change slightly each time the razor his honed. I recently bought a Hartsteel razor and the note that accompanied the razor said they recommend taping the spine during honing. The razor came shave ready and did give an excellent shave. If they used tape at the factory to set the initial bevel then I probably should continue to use tape every time I rehone it.

First, the honing process does not need to result in a different wear rate. It depends on where pressure is applied. The spine is mean to be an angle guide but it doesn't need to have a lot of pressure applied to it. If the razor is torqued during honing, much less steel is removed from the spine. Next, the taping of the spine is a recent phenomenon, as is the Hart razor. If they honed with tape, then you CAN touch up with tape. If you don't use tape, the very apex of the edge will not touch the hone, but only a minimum amount of steel needs to be removed from the bevel to alter its angle to allow normal, tapeless honing.

Originally Posted by Seraphim

tan A= opposite/adjacent=a/b

If the cutting edge is angle A. As hone wear reduces the spine thickness (side "a"), the edge honing also reduces total blade width (side "b"), thus maintaining edge geometry "A".


I think?

I'm hoping the image came acrsoss on the "quote" as well. It would be more like "B" being the tip of the edge of the blade, and "A" the highest point of the spine where "b" is 1/2 the thickenss of the total spine, and "h" well, it's an imaginary stright line, but it actually curves inward due to the hollow ground process, but it still exists, though not really visible. "a" is the center of the spine to blade edge, as "C" is the absolute center of the thickest part of the spine.

I tape old and brand new. Just me. Here's why. The spine wears but not necessarily in relationship to the edge. Why? Have you ever studied the process of griding the razors in videos? Wacker and other put the razor blank in a special holder and grind away at the top of the spine getting the curvature that they want. I believe there is some loss in tempering at that point, as there are always plenty of sparks as they grind away. They are not concenerned with the temper of the back of the blade, only the very edge. Therefore, the spine will not wear in the same relationship as the better tempered edge. Also, as Glen pointed out, the steep angle gives strength to the edge. It will be enough to get that 0.45 micron or less edge, but is less prone to bending over as one that has a lot of spine wear, and you hone it "au naturale" and get a really wide bevel and the edge of that long bevel has a really thin edge with not nearly as much metal on both sides to give it strength to prevent bending during cutting whiskers.
A 5 degree edge could get sharp, but be so thin that the first time you tried to cut anyting with it, the edge is gone, bent over. Even stropping agressively would keep bending it back and forth to the point the edge will simple not hold up, like metal that you keep bending back and forth over and over.

Also one of the reasons that I listen to the strop and blade when I strop. It makes a certain sound and if I keep stropping, it looses that sound and I think the fact of the ege going back and forth may degrade the edge, so I strop maybe 10-20 times just before shaving and get a beautiful soft smooth shave.

I think if the electrial tape was as well discussed in bygone days as it is on the internet it may have been more widely used. But, in those days, some had telephone and electrical tape was not invented by Minnesota Mining and Manufacturing (aka 3M) until 1946. Probably didn't get a lot of widespread publicity until 1950, so at that time, it was about the time of the demise of straight razor shaving for those going to single injector or other DE razors. King Gillette is to thank for that. Too bad Gillette doesn't come back into the business with straight razors, but they make too many billions off disposables at this point.

Originally Posted by honedright

Icedog, this is what I think: you're an animal! Kinda crazy too - to go through all that, but a great idea.

I also believe that as the spine wears down, coincidentally with the edge (under normal honing) that the angle remains constant for a correct shaving edge. Can you figure a formula for that? Eh?

Or how about this: (and maybe your above data aready has some of what I'm about to suggest)

Assuming a brand new straight razor, the spine has a certain thickness, blade certain width, equals a bevel of X. That bevel would be the intended thickness for shaving for that razor. Yes? Now add the tape. How far off is the bevel with the tape (I guess that is your Delta above), and how would that affect shaving?

Also a rate equation: under normal honing (define) how long will a straight razor blade last before the edge/spine wear will no longer produce a shaving edge?

All in fun, of course.




Scott

Okay Scott, Seraphim has answered your question, correctly. If the thickness of the spine is reduced in direct proportion to the width of the blade, the angle will remain constant. However, that will not be likely. The reason razors (and other cutting tools) are hollow ground is to expedite stock removal at the edge. Therefore, because of the grind of the blade, the edge is removed much faster than the spine.

Your second question regarding how long a razor can be brought back to usefully sharp is loaded with too many variables. Hey, I see 200 year old razors being used to shave. How many times have they been honed? How have they been honed? Who knows? But they probably haven't been taped for most of their lives.

I happen to be ambivilant on the taping issue. On old razors I've seen with badly honeworn spines, I believe that honewear has likely been caused by gents with little pushcarts equipped with handcranked grinding wheels that used to stroll from block to block sharpening anything that needed an edge. These guys would sharpen scissors, axes, cleavers and razors all on the same stone wheel. The razors would be held against the side of the wheel and ground merrily away with a quick finish on a strop.

Glen has voiced his opinion regarding the durability of an edge. Again, theoretically, I agree that a more obtuse edge is less likely to be damaged (rolled, chipped, whatever) however, when looking at the actual delta between taped vs not taped, we see an average difference of 0.59 degrees. Personally I think that is negligible. But that is a guess.

Hoglahoo,

I used a plastic scale to measure the width to the nearest 1/16th inch and I used a Mitutoyo Absolute Digimatic caliper to measure the spine width and I rounded to the nearest 1/1000th inch.

Brad

Originally Posted by icedog

Okay, this may not be news for some. I wanted to know how much the application of a single layer of electrical tape to the spine of a razor you are honing affects the angle of the bevel (as compared to no tape). So I took two measurements on the nine (9) razors I currently own:

1. blade width from the thickest part of the spine(which is what contacts the hone) to the edge
2. thickness of the spine

Do you have a photo of your measuring device? What did you use to get it so precise without damaging the edge of the blade?

I may be wrong, but isn't the side labelled A the hypotenuse? So wouldn't the correct formula involve arcsin, not arctan?

James.

Originally Posted by Jimbo

I may be wrong, but isn't the side labelled A the hypotenuse? So wouldn't the correct formula involve arcsin, not arctan?

James.

Jimbo,

You are right, you are wrong.

In my measurements I reduced the razor blade down to a right triangle. The diagram I so poorly drew is essentially the same as the way awesome diagram Seraphim somehow posted (except my edge is pointing toward the right and I called my adjacent side A and my opposite side O). The hypotenusala is actually an imaginary line drawn somewhat through the razor from the center of the thickest part of the spine to the edge.

Brad