11-27-2012, 07:59 PM
#1
  • Kavik79
  • Active Member
  • Albany, NY - USA
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I know it's been done before, but I wanted to share my take on it Biggrin
(go grab a coffee, it's a long post)

  It seems to be commonly accepted that a bevel angle between 15-20 degrees offers the best combination of sharpness and strength; the lower angles being sharper, but more fragile; the higher angles being more durable, but might not slice as easily.
Think of it like the difference between a knife and an axe both trying to cut the same small twig. A knife will make a clean slice (good, sharp), but the edge will wear after a few slices (bad, lots of touch up honing required). The axe isn't going to go dull from a small twig any time soon (good, durable, more time between honing), but it requires more force to chop through the wood rather, than cleanly cutting it (bad, tugging).

  In most cases with modern razors, or even older razors with little hone wear, there is nothing to worry about. If it shaves, it shaves. But the older razors you get into, the more chance you'll run across ones that have uneven wear or even ones that weren't made to an 'ideal' angle.

  The razor that got me looking in to all this was an 1820's(ish) Joseph Elliot, near wedge, slight smile. I could get it sharp, but never great....being almost a wedge I figured I'd try some tape, that made the honing a helluva lot easier, but the results didn't seem to change.
  So I started doing some measurements and calculations and found out 2 things; First, the spine was half a mm narrower in the middle than at the toe or heel, causing over a degree of difference in bevel angle from one point to the next. Second, at the best point the bevel angle was 19.2 degrees, at its worst it was 20.1 degrees. Adding just a single layer of tape changed those numbers to 20.3 and 21.3 respectively.

  Enter the spreadsheet. I started out by making a table that will calculate your bevel angle after you provide the measurements of the spine thickness (measured at the edge of the hone wear closest to the spine) and the distance from the same point on the hone wear to the edge of the blade. There's a diagram in the spreadsheet that shows the points to measure.
  In addition, if you enter the thickness of the tape you have it will tell you the angle you will get with either 1 or 2 layers of tape. This can help you correct for an overly acute angle. Or if you like to tape because you don't like the look of hone wear, or have a gold washed spine, or whatever your reason is....this will help you decide if taping for the sake of vanity is leaving you with an overly obtuse angle.

  Once I had that I created another section for correcting my particular issue of an overly obtuse bevel angle. After entering the measurements from above, and telling it the angle I'm aiming for, it tells me the spine thickness required to hit my target angle as well as 2 half degree increments in either direction, in case the target angle would require more metal be removed than I'm comfortable with.
  This should be considered extreme corrective measures and should be thought about long and hard before doing anything with this information....you can't put the metal back after grinding it down Tongue


  After that I got carried away and figured since I had found all the formulas, I might as well add a sheet to help people who are making a razor from scratch.
  The first table on page 2 will help you choose a blade width if you have already chosen your bar stock and have a target bevel angle in mind. For example: I have a piece of .25" thick bar stock and I want to make a razor with a 16 degree bevel angle, the spreadsheet tells me I need to make a blade that's .8894" (roughly 7/8") wide from the edge of the blade to spine edge of the grind, not including the portion of the spine that extends past the grind point. (again, the diagram inside the spreadsheet will explain it better with visuals than I can with words)
  The second table will help you select the right thickness of bar stock based on the bevel angle and the blade width you want to make. Example: I design a razor on paper that's 7/8" from blade to back of spine, I figure out where the grinding will stop and find that that leaves me with a distance of 6/8" from edge of blade to edge of grind, and I want a 17 degree angle on this one. The spreadsheet tells me I'd need to make it out of 0.2242" thick bar stock

  Now, I've never made a razor or anything like it, so I don't know if there's more involved there or not...if someone else wants to chime in on that section I'd be glad to hear it.


  Anyway, here's the spreadsheet for those who want to play around with it: BevelCalcKavik79_Shared2.xls
The sheets are protected so you can't accidentally delete any of the formulas, the only fields you need to enter data into are the ones with a white background.
All you'll need is a decent set of calipers to measure with, and MS Excel (or a program that can read Excel files, such as OpenOffice)


Hope it helps someone out there Biggrin Happy to hear any questions or comments here, in PM or in the email address found in the file.

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 11-27-2012, 08:40 PM
#2
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Nice write up!
Some people really enjoy the "figuring it out" stuff.
I enjoy it but don't get to crazy about it.
Assuming the grind will be somewhat normal (not the the same as your example 7/8's blade, 4/8 grind) you will almost always be safe to go by this: 1/4 for 7/8- up, 3/16 for 6/8's - down.
That covers the majority of normal sized razors with normal grinds.
On the other hand, if your going to have a non-typical grind, it's best to do a little math (like your spread sheet) before you start Smile

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 11-27-2012, 09:32 PM
#3
  • Kavik79
  • Active Member
  • Albany, NY - USA
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Thanks man
haha whooops. my example was retarded, I was getting to the point where I didn't want to type anymore LOL I meant to account for about an 1/8" for spine past the grind, not 3/8". I'll go back and fix that in a minute

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 11-28-2012, 02:52 PM
#4
  • oscar11
  • Senior Member
  • North Dakota
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Thanks for the info.

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 11-29-2012, 07:20 PM
#5
  • gijames
  • Mile High Soldier
  • TN, USA
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Thanks for sharing Daryl!
Thumbup

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 11-29-2012, 09:01 PM
#6
  • Kavik79
  • Active Member
  • Albany, NY - USA
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you're welcome guys Cool

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