Thread: People who tape their spine, then sell that razor irritate me.

Originally Posted by IanS

Stephan, I've said many times I'm referring to the change that occurs over a long period of use. What you say is true, the change due specifically to the presence of the tape at an individual honing disregarding uneven wear is very small. That's why I'm not really concerned with it.

And while there will be variance in wear due to variations in honers, the end result should be extremely close to the original angle.

Your presumption that equal surface area is necessary is mistaken.

I didn't say they were necessary. If you want the angle to stay the same with equal pressure, then identical surface area would be necessary. This assumes identical material and Rc at all points of contact. That's a big assumption. None of us apply equal pressure anyway, so it's a moot point.

The change that occurs over a long period of use is negligible. This assumes reasonable honing and maintenance. You're Grandson can use the same razors that you do. With no change in comfort. Many members do use razors over a hundred years old, with a high degree of satisfaction.

Disregarding chaff interference, equal pressure, angle and identical surfaces guarantees equal wear for any given point. Calculus applies that across the entire blade (that is in contact) and Geometry guarantees that the angle is therefore maintained. Now the question of maintaining equal pressure raises issues, but even given the disparity in gravitational pressure, due to the hardness of steel and shape of most blades this effect should be minimized (bringing us back to your point about it not being exactly perfect either way).

Calculus applies? Which formula would that be? Which Geometry formula guarantees what angle? There are way too many variables here for either.
Equal pressure on both surfaces? Gravitational pressure? I'm pretty sure you're trying to track quantities that you can not measure, let alone duplicate... You're making this way too complicated. What we're all trying to say is that tape does not mess up your razor. Tape applied to a razor before you buy it will not mess it up, either. Tape doesn't mess up a shaving edge. Only bad honing or damage of some other kind does.

...

Uh-oh, I gotta' go change my signature now. I see I've been spelling my name wrong for months...

EDIT: darn it Jimmy, you almost made me spew V-8 juice all over my monitor...

They don't have compressibility numbers, only "high compressibility".

But the minimum (you could add deformity numbers for a more accurate result) would be ...
scratch that, this is a lot of physics toying that I don't feel like doing. here are the formula's set up.

compressibility * ~cos(bevel angle) * blade length * .007in = { ~cos(bevel angle) * blade length * .007in - ( cos(bevel angle) * blade length * .007 * .8 )} / P

P must be... greater than or equal to what it solves for. Again, this only accounts for compression, Most etapes have 10-30% deformity as well. Which will add
{ cos(bevel angle) * blade length * .007in - ( cos(bevel angle) * blade length * .007 * .8 ) } *(deformity) = P
Note that you don't add the P's so solve eq 1 to = P, then subtract the left side of equation 2 from it.

There are a few other factors, but solving for them is nearly impossible.


Me personally, I'd rather just take their word for it about the high compressibility.

integrate a to b wrt x = (b-a)c where c = the value at that point. This formula applies to both sides. You can then repeat to prove it works in 2d as well.

And geometry, well I'm not really sure how to explain that. Take a wedge(not the razor type), grind = amounts of material from all areas of the hypotenuse and the angle is unchanged. I'm sure there's a formula that proves it, but I haven't taken geometry in 13 years.


edit: Oh, Pythag proves it. You just have to add in the definition of tangent.

edit: My mistake I forgot that if you want to treat it as two independant points (the blade height and 1/2 spine width), you have to correct for the angle of removal. In other words, the material directly facing the razor is relative to angle of direction of motion meeting with the angle of the material. So it would be I believe cos*grind angle * ideal for the material removed from a dead center slice of the razor (plane of exact edge leading back to spine) and sin*grind angle * ideal for the spine width I glazed over that fact. That's why the design of razors works (under ideal conditions) to keep angle constant.

I'm not sure if I misspelled your name and that was a joke or if you were serious. If I misspelled your name, my apologies.

Wow 16 people in here. Makes me sorry I need sleep. I have an 18 hr day in umm 5.5hrs. I may be around another 15 minutes or so, but anything else will have to wait until at least sat, more likely sunday.

Its gone but I can still smell it!!

"razors on an average are at about 16"

Glen are you quite sure that wasn't included angle?

I was being generous with 10-13 if anything. If 10-13 is low than my ruler was made by some child that doesn't know his math because I've got some that without rounding in the favor of a larger angle, come out as low as 8.

My Morris 3/8" sculptor in fact has an angle of ~7.2, to be fair it's a well-used razor, but it shaves excellently and holds it's edge just fine.

Chas F schmidt I bought off classies here and did maybe a total of 5 passes on a swaty... (one of the two I haven't honed)

7.6 degrees.

Anyway, bedtime. Please PM me a link to that thread if it's not too much trouble. Every search I try brings up 500+ threads.

Originally Posted by IanS

...
There are a few other factors, but solving for them is nearly impossible.


Me personally, I'd rather just take their word for it about the high compressibility.

"High compressibility" isn't much of a hard number...

My Engineers' Handbook of Applied Mathematics says your compression formulas are way off, not even close. The actual formulas are much simpler. Some of the parameters are, however, hard to measure; unless you have access to a well equipped machine shop or lab. P in your formula is in what unit of measure? Or, what does it measure as a quantity?

P is force/ area of tape bearing the force(edit: cause Im tired).

Formula is { D(V)/D(P) }*1/V = compressibility Its complex because you have to solve for the portion of the tape that bears the pressure. I assumed an application of force driving at the bevel angle. My solution is purely the force that is exerted downward in the end. The force that is used to actually perform the stroke would need to be tacked on at the end, but we're assuming this is a very bad honing job, so that would be minimal.



I agree it isn't a hard number. I wasn't the one asking for hard numbers. I know Etape compresses easily. It's designed for that. The manufacturer brags about it. It's probably a reason why it's used here. (I'd suspect it helps the tape resist wear, so it needs changed less often). It was requested I perform a calculation that can only be estimated, so I gave the conservative side of the estimate as well as I could, but without the compressibility number it's fairly useless. You can always solve to see what range it would need to be in and then look at similar materials and see if it's in the ballpark. I prefer to accept that my pillow is soft rather than looking for the exact physical properties of cotten stuffing. (Or whatever is in there).

Originally Posted by IanS

P is pressure.

In what units? My compression formulas do not have a single trig term in them.

EDIT: if you really want to work this problem out for us, I can PM or post the real formulas here if you like.

Sorry, edited to explain.


It's F/A

And the trig is to get A.


Sorry, tho, bed now. PM or post any more questions and I'll try to answer them next time I'm on.


May be the sleepiness, but I'm fairly certain that you guys are using angle of inclusion and not grind angle, that's why my angle numbers seem so outlandish to you. I've always refered to the bevel by the angle it was ground at (using stones). That's exactly 1/2 the angle of inclusion. This line may be comepletely unintelligible, I'll fix it next time I'm on to explain it better if so. I'm that tired.

It would also make that 25degree razor a LOT less interesting.

Originally Posted by IanS

...I'm fairly certain that you guys are using angle of inclusion and not grind angle, that's why my angle numbers seem so outlandish to you. I've always refered to the bevel by the angle it was ground at (using stones). That's exactly 1/2 the angle of inclusion.

I think it would be useful if you worked with this Excel spreadsheet. It was discussed at great length in this thread. It might also be helpful to search the forum archives for "tape AND spine". You will find gems like this thread. In the wake of the "fun with Vernier calipers and tape" thread, Glen recently did a survey of edge angles (which I cannot currently find), but you might also find that the results in this thread are quite interesting.

Regards,
Robin