Replies

1. 
   jako17 | Apr 24, 2005 04:49am | #1

   Hi there Tony

          I have an eclipse honing jig #36 purchased in the late 60's and on the side is cast ; plane iron projection   1 1/2" =30 deg , 2" =25 deg

            chisel projection  1 1/4"=30 deg, 1 3/4"=25deg Took me a while to find it as it was sprayed with oil and not used for at least 10 years   but it worked well as far as I can remember and taught me to work freehand

2. 
   hammer1 | Apr 24, 2005 04:53am | #2

   Rather than use measurements on the jig, I use a protractor head to check the various angles on my tools. Once the angle is set, I use a straight edge to set the blades in the jig. You hold a straight edge, like a metal rule, on the wheel and hold the jig up to the light to sight the blade angle to fit the rule. This eliminates accidentally setting the blades off a bit and having to hone more than is necessary or changing the bevel slightly. This is the only way I know to set the guide accurately. Moving the blade even 1/32" makes a big difference in the honing angle and how many passes it takes to get the angle sharpened fully.

   After reading Jako's reply, I checked my Eclipse and I'll be darned if there wasn't measurements on mine too, in millimeters. My measures are different than Jackos. Chisel projection for 25° is 40mm or a little more than 1 9/16". The sighting trick does help to keep the honing down to a few strokes instead of many. I suppose you could work out the math when first establishing an angle different than the listed 30° or 25°. On mine the difference between 30° and 25° is 10mm for chisels or 2mm per degree. Plane blades are 12mm for the five degree difference or 2.4mm per degree. I can't honestly tell the difference between 25° and 26° on my chisels.

   Beat it to fit / Paint it to match

   Edited 4/23/2005 10:19 pm ET by Hammer

   
   

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   Edited 4/23/2005 10:32 pm ET by Hammer

1. 
   BG | Apr 24, 2005 01:37pm | #3

   Hammer,
   That is a terriffic idea ...using a straight edge with the jig to determine appropriate lgth. for the correct angle. I cut a piece of scrap to reflect that distance and stick it in the front vise...so that strapping on the jig is quick and easy and honing done quickly.
   Isn't there some Trig or something table that'll confirm the 10,12mm distance equal to a 5 degree decrease/increase angle? 

1. 
   hammer1 | Apr 24, 2005 03:53pm | #4

   The 10mm and 12mm are from the measurements that are on the side of my Eclipse jig. It has a 30mm projection for chisels at 30° and 40mm for 25° listed. I'm assuming that a 2mm change would represent a 1° change, but I could be wrong. Because the Eclipse jig rides on the stone, there is a triangular relationship from the wheel to the blade, out the length of the projection and back down the stone to the wheel. Someone that remembers their geometry better than I do may be able to answer your question. Judging from Jacko's post, all Eclipse jigs are not the same. On my jig there is a rounded side and a straight side, obviously, the rounded side goes toward the user. Differences in the distance of where the wheel is and where projection measures are taken will change the geometry. The important thing for me is getting and keeping the edge sharp without a lot of fuss. I don't use micro bevels and I don't prep all my faces with a Norris smoother. Slight variations in angle don't really seem to affect my use of chisels and planes.There is quite a difference between 30° and 25° but 25° or 26° doesn't seem to matter. When I retire, maybe I'll have more time to play with the finer points of hand work but right now, I'm too far behind.Beat it to fit / Paint it to match

1. 
   jako17 | Apr 24, 2005 10:36pm | #8

   Hi there Hammer,my eclipse jig is as said years old I bought it in England when they thought m.m.'s were candies and the Beatles were clean living guys with short hair and stand up collars.It is totally symetrical  with square corners, neither face radiused.I have seen the version you have and it is more recent and probably improved.Your description of setting using a straight edge and light sounds like the same principle the LV setting jig uses ( from the catalogue pics)

    

3. 
   Peter36 | Apr 24, 2005 04:26pm | #5

   I know this is not what you are asking, but when I used to use my eclispse I just loosly clamped the blade in place and then sat it on a flat surface and increased the angle over the ground bevel. [I use micro bevels].

1. 
   woodworker418 | Apr 24, 2005 04:50pm | #6

   thanks for all the useful information.  i've done some additional looking around on the web and one method that was described somewhere which makes alot of sense to me is the following jig.  take a piece of scrap plywood and cut it sqaure.  then measure out the exact distances required for all chisels and planes (probably no more than 6 distinct distances, assuming each blade has 3 distinct angles, "grinding" angle (which i do on an extra-coarse diamond stone, i don't own an electic grinder and don't think i see a reason to buy one), primary bevel and micro bevel, and two sets of settings are required, one for planes and one for chisels).  then fix short stops set at exactly 90 degrees at the exact distances from one edge of the plywood.  once this is done, setting the eclipse for any established angle (i'd probably use 25 degrees for grinding, 30 degrees for primary bevel and around 33 degrees for micro bevel for both planes and chisels) is as simple as just lightly setting the blade square against the appropriate stop and camping the eclipse at the edge of the plywood.  this way exact repeatability (even if your measurements aren't exactly correct for your desired angles, so what after the first sharpening) and speed are always achieved.  additional setups might be added for bevel up plane blades set at steeper angles.  and if you really want to make it easy, add a quick clamp to hold the blade in place while setting the eclipse.

   how does this method sound to you guys?  any drawbacks that i'm not seeing?  thx. tony.

1. 
   BG | Apr 24, 2005 09:52pm | #7

   Tony,
   Sounds good...but I'd skip the jigs for the micro/secondary bevels...just shorten the blade in the jig a bit and stroke a few times. 

4. 
   UncleDunc | Apr 25, 2005 08:15am | #9

   I can tell you how to calculate it, but you'll need four measurements from your Eclipse, plus the thickness of the blade you're sharpening. First to define some terms: What I will call the bed is the surface that the blade lies on when it is clamped between the edges. There are two beds, as I recall (I can't find my Eclipse, so I'm working from memory), a wide upper bed for plane irons and a narrower lower bed for chisels. The second term is the mid-plane, an imaginary plane perpendicular to the bed which passes through the axis of the wheel.

   Now, consider the Eclipse resting on it's wheel on a horizontal surface with the bed(s) horizontal and the mid-plane vertical. The measurements you need are: 1) H - The horizontal distance from the mid-plane to the nose of the Eclipse, the point from which you would measure the blade extension. 2) VP - The vertical distance from the axis of the wheel to the plane iron bed. 3) VC - The vertical distance from the axis of the wheel to the chisel bed. [But see messages #12 and #13.] 4) R - The radius of the wheel.

   Let's define some more variables, to keep the formulas from getting too cluttered.
   TAN = tangent of the desired cutting angle (supplied below)
   COS = cosine of the desired cutting angle (supplied below)
   X = blade extension
   T = blade thickness

   For plane irons, the formula is

   X = ((T + VP + (R / COS)) / TAN) - H

   and for chisels, the formula is

   X = ((T + VC + (R / COS)) / TAN) - H [But see messages #12 and #13.]

   angle tan cosine
   20   0.3640   0.9397

   21   0.3839   0.9336

   22   0.4040   0.9272

   23   0.4245   0.9205

   24   0.4452   0.9135

   25   0.4663   0.9063

   26   0.4877   0.8988

   27   0.5095   0.8910

   28   0.5317   0.8829

   29   0.5543   0.8746

   30   0.5774   0.8660

   31   0.6009   0.8572

   32   0.6249   0.8480

   33   0.6494   0.8387

   34   0.6745   0.8290

   35   0.7002   0.8192

   NOTES:

   You don't have to understand any of this to use the formula, but you might be curious.

   1) Where did this formula come from? It is derived from the tangent formula. The tangent of one of the acute angle in a right triangle is the length of the opposite side of the triangle divided by the length of the adjacent side. Tan (a) = opposite / adjacent. The right angle in this triangle is where the bed intersects the mid-plane. The side opposite the cutting angle is the thickness of the blade, plus the distance from the bed to the wheel axis, plus the distance from the wheel axis along the mid-plane to the point where the mid-plane intersects the sharpening stone. The side adjacent to the cutting angle is the blade extension plus the distance from the mid-plane to the nose of the Eclipse. Following are the algebraic manipulations to get from the tangent formula to the formula that solves for X.

   TAN = (T + VP + (R / COS)) / (X + H)
   TAN * (X + H) = T + VP + (R / COS)
   (TAN * X) + (TAN * H) = T + VP + (R / COS)
   TAN * X = (T + VP + (R / COS)) - (TAN * H)
   X = ((T + VP + (R / COS)) - (TAN * H)) / TAN
   X = ((T + VP + (R / COS)) / TAN) - ((TAN * H) / TAN)
   X = ((T + VP + (R / COS)) / TAN) - H

   2) Why is the distance from the wheel axis to the sharpening stone expressed as (R / COS)? Because as you tilt the eclipse forward, the mid-plane (defined in the first paragraph, above) does not intersect the sharpening stone at the same place where the wheel touches the stone. If you had a very long blade in the Eclipse, such that the sharpening angle was only infinitesimally greater than zero, then the distance from the axis to the stone along the mid-plane would be effectively equal to the radius of the wheel, but as the extension gets shorter and the angle gets larger, the mid-plane intersects the stone farther behind the wheel, so the distance from the axis to the stone along the mid-plane is greater.

   
   

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   Edited 4/25/2005 8:57 am ET by Uncle Dunc

5. 
   UncleDunc | Apr 25, 2005 03:54pm | #10

   That sounds right. Like I said, I couldn't find mine, and none of the pictures I could find on the web showed enough detail to be useful.

   In that case, the definition of VC should be "the vertical distance from the axis of the wheel to the down facing bed that the chisel back indexes against," and the formula should be

   X = ((VC + (R / COS)) / TAN) - H

   That also takes care of a concern that I had, but didn't address in my first post, about chisel blades that taper in thickness.

6. 
   woodworker418 | Apr 25, 2005 11:09pm | #11

   any choice you might be able to share your calculations for the different angles with thsoe of us that are mathematically challenged?  i'm just looking for a list of angles and corresponding lengths (both chisels and planes) for non-standard angles (ie, anything other than 25 and 30 degrees).  just in case you happen to have any of this info, i figure can't hurt to ask.  thx, tony.

7. 
   woodworker418 | Apr 26, 2005 04:41am | #12

   thanks much.  i think that i need to sit down and read this thread again and think about it for a while before figuring out how to proceed.  and to do that i need to find some free time!  best, tony.

1. 
   UncleDunc | Apr 26, 2005 07:49am | #13

   If you don't have a bevel protractor or some other way to directly measure the cutting angle, you can use the thickness of the blade and the sine of the desired angle to calculate the necessary width of the bevel. The formula is

   bevel width = blade thickness / sine of angle

   For example, if your blade is 5/64" thick and you want to grind a 22 degree angle on it, the required bevel width is

   (5 / 64) / 0.3746 = 0.208"

   I can't read a scale to 0.001", but with a high quality thin steel rule graduated in hundredths, it's not too hard to read to +/- 0.005".

   Here are the sines of the angles from 20 to 35 degrees.

   angle sine

   20   0.3420

   21   0.3584

   22   0.3746

   23   0.3907

   24   0.4067

   25   0.4226

   26   0.4384

   27   0.4540

   28   0.4695

   29   0.4848

   30   0.5000

   31   0.5150

   32   0.5299

   33   0.5446

   34   0.5592

   35   0.5736

   You can also invert this formula to calculate the angle from the width of the bevel, but you need a trig calculator to do the inverse sine function.

   angle = arcsin (blade thickness / bevel width)

   On some calculators, the arcsin function might be labeled asin or sin [superscript] -1. I looked for an online calculator that would do arcsin, but the only one I could find wanted the angle in radians rather than degrees.

   Edited 4/26/2005 12:51 am ET by Uncle Dunc