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Thread: How Bevel is Affected by Taping

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    Hi kids! It's been a while since I've checked in on this thread. Wow can one find a more controversial tech question?

    My initial conclusion here was (and still is)that difference of bevel angle ground with the application of tape to the spine or without the application of tape to the spine is incidental. Therefore the only reason to tape the spine is to protect the spine. I want to make a quick point. Some have been proposing the idea that not taping the spine will allow for the edge and the spine to be ground uniformly thus maintaining a constant bevel angle. That is not true. The edge of the razor is going to wear much more rapidly than the spine and (especially in the case of full hollow ground razors) the edge will not wear so much in thickness as it will in width. What I mean is the 6/8 razor will begin approaching 5/8 at the very first stroke on a stone. This will cause the razor (over time) to actually rotate toward the edge with the necessary increase in bevel angle, tape or no tape. I wish I was smart enough to make a computer generated cartoon to show this. But I am hoping you get my drift.

    Brad

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    yoshida (11-24-2009)

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    I get what you are saying.

    What I am saying is that even if you don't tape it, you are going to wear material away from the edge far more quickly than the material on the spine so you aren't really gaining anything know what I mean?

    My friendly argument is, that the effect you are talking about in your above post is going to happen whether you tape the spine or not. It might happen faster if you tape it, but the difference would be negligable, and over a pretty large span of time imo. Great thread.

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    Exactly my initial conclusion. We are on the same page.

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    Senior Member Deryan's Avatar
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    This was a very interesting read good points made and great debates.

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    Quote Originally Posted by icedog View Post
    The edge of the razor is going to wear much more rapidly than the spine and (especially in the case of full hollow ground razors) the edge will not wear so much in thickness as it will in width.

    What is the reason for this? Physically speaking, assuming perfect honing, an untaped wedge should never have it's angle changed. Hollow grounds should perform the same, with the assumption that they are a perfect wedge with a gap. In reality, the shift should be towards the opposite end (the spine should wear slightly faster), as there is additional weight at the back of the razor creating greater friction.

    The only thing that would account for increased friction (and thus increased metal removal) at the edge is if the filings from the edge impair the hone from being effective all the way to the spine or if the user pushes into, rather than along, the hone.

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    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.

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    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.

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    Quote Originally Posted by Seraphim View Post

    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.
    Last edited by Gibbs; 06-04-2011 at 08:30 PM.
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