Eclipse honing guide projection/bevel

Greetings,     Lee's "Sharpening" has a jig for setting blade projection for the Eclipse honing guide. I'm making one. The objective is to easily set the guide for bevel angles other than the standard 25 and 30 degrees. In order to place the pegs, I had to do the trig. Turns out that although the imprinted instructions are in millimeters, the device (mine, anyway) was manufactured in inches. Having been through the trig, and discovering that one doesn't have to account for the changing tangent of the surface to the roller (sigh of relief), I asked my spreadsheet to make a list of projections for various bevel angles. I post it here for y'all to file and forget. Someday, someone will google for the info, and here it'll be. Note that the values in the imprinted instructions differ from my analytical values. The table is free; so what if no one will need some of the extreme angles!
Bevel, degrees Chisel Projection, mm Iron projection, mm 15    83.8    104.6 16    77.0    96.4 17    71.0    89.2 18    65.7    82.8 19    60.8    77.0 20    56.5    71.8 21    52.5    67.0 22    48.9    62.7 23    45.6    58.7 24    42.6    55.0 25    39.7    51.6 26    37.1    48.5 27    34.7    45.6 28    32.4    42.9 29    30.3    40.3 30    28.3    37.9 31    26.4    35.6 32    24.6    33.5 33    22.9    31.5 34    21.3    29.6 35    19.8    27.8 36    18.4    26.0 37    17.0    24.4 38    15.7    22.8 39    14.5    21.3 40    13.3    19.9 41    12.1    18.5 42    11.0    17.2 43    9.9    15.9 44    8.9    14.7 45    7.9    13.5
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Australopithecus scobis wrote:

There's a fundemtal glitch. If ya' wanna be dead nuts accurate you have to allow for the thickness of the blade.
Fortunately the actual angle is NOT critical, but repeatablility between successive sharpenings is very useful.
BugBear
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On Thu, 16 Sep 2004 15:55:52 +0100, bugbear wrote:

Exactly. It matters for the plane iron. The table I provided is for stock 3/32 irons. Your point suggests I should supersede my post to make that clear. Thanks for the reminder.
--
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On Thu, 16 Sep 2004 10:40:34 -0500, Australopithecus scobis

The taper on the body of a chisel makes it very difficult to come up with a chart as you need to know the thickness of the body of the chisel along a line passing from the center of the roller and normal to the top (not upper) surface of the chisel.
My chisels are tapered anywhere from 1.5 to 6 degrees.
If you start out with a blade that's been ground at too sharp an angle, then you could measure the projection of the heel of the original bevel. You could then sharpen until the new heel meets up with the original heel, and the thickness of the blade would not be a factor.
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On Fri, 24 Sep 2004 13:43:09 -0500, Ed Bailen wrote:

Always measure the projection from the cutting edge to the front face of the jig. We don't care about the back of the bevel; it could be hollow ground Kirby-style.
For plane irons, thickness matters. For chisels, it does not matter. The back of the chisel is held in a fixed, known position. The geometry does not change with chisel thickness. The Eclipse doesn't care how thick or tapered the chisel is; the projections work. True, it is a PITA to clamp tapered chisels in the Eclipse. I find that narrow and tapered chisels wobble from side to side, so I do them freehand while dreaming of a Veritas jig.
--
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On Wed, 15 Sep 2004 23:27:25 -0500, Australopithecus scobis

Just as an aside, don't use one of those Eclipse-style "unicycle" guides on a waterstone. Soft stones will develop tramlines faster than the iron gets sharpened.
--
Smert' spamionam

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