How to calculate the projection as a function of bevel angle for LN Honing Guide

[Greg Parrish]

Derek, I did but I think my head was still swirling from trying to understand Thomas' math equation. I see now that you were advocating that exact same thing. Thank you for the clarification.

Greg, did you read my post (earlier)?

Regards from Perth

Derek

[Thomas Wilson]

Could you possibly take Tom's approach and use a protractor/angle finder in the same way, only setting the offsetting angle? So rather than 30, set the protractor/angle finder at 150. In my head that seams to work with the chisel once set into the honing guide, but maybe I'm not thinking of something.

Sometimes there is a problem with width or length of the angle measuring device such that you can’t get it to align with the blade without interference. There are solutions to that as well, like Tom’s custom width and length angle blocks.

I find that measuring small angles is harder to do accurately than measuring small lengths. So I like the projection jig. With a math formula for the projection, I have no need to measure the angle. I also like a good math problem. I’m also great fun at parties.

[Reed Gray]

Well, I guess I could do the math, but for me, I would just divide the difference between 2 settings. Personally, I wouldn't worry about anything beyond about 5 degree increments. Don't see the need for them either...

robo hippy

[Gary Focht]

I tried to stay out of this thread, but as long as we are discussing angle setting jigs…


Here is my version for the Lee Valley Eclipse style jig. It has one board and one fence. Adjustable for angle and micro bevel. Don’t really know microbevel angle, but probably 2-4 degrees depending on which angle I’m doing. It varies, but is consistent for that angle. Both lower and upper settings.

62BB343A-9AD7-445E-BD68-776027371F60.jpeg 419B9475-FF5C-4DC1-96F0-B161365FF74A.jpg

[Thomas Wilson]

I tried to stay out of this thread, but as long as we are discussing angle setting jigs…


Here is my version for the Lee Valley Eclipse style jig. It has one board and one fence. Adjustable for angle and micro bevel. Don’t really know microbevel angle, but probably 2-4 degrees depending on which angle I’m doing. It varies, but is consistent for that angle. Both lower and upper settings.

62BB343A-9AD7-445E-BD68-776027371F60.jpeg 419B9475-FF5C-4DC1-96F0-B161365FF74A.jpg

Gary,

The thread has turned into a thread about jigs for setting bevel angle. I tried to turn the herd but it was a stampede.

Your jig is innovative and compact. Certainly worth sharing. I like it. If you take some measurements of blade projection and dimensions of the Lee Valley honing guide, I can tell you the angles.

[Thomas Wilson]

The initial problem that prompted me to figure out the formula for blade projection was the Veritas sharpening instructions that suggested chisels narrower than 1/2” should be sharpened to a primary of 25 degrees and a secondary of 27 degrees. Chisels 1/2” and wider are recommended to be sharpened at 30 and 32 degrees. The Lie-Nielsen guide does not list 27 and 32. Lie-Nielsen also does not give projections for the other jaws they sell. I wanted to fix that.

Here is a table for all the angles and all the jaws I wanted.
624F37C0-275C-4E8B-9404-EAC628D38549.jpg
Here is how I measured the guide parameters.

G the width of the guide front to back
E52BBFA2-9C34-40F9-866E-EA123466B724.jpg

R+r the height of the guide from top of blade to bottom of roller
DABE33B7-08D7-46E7-AC33-731B58033FDA.jpg

and 2r the diameter of the roller


I got a slight difference between my results and the Lie-Nielsen values so I investigated. The differences are shown in the rightmost columns in the table. The greatest difference occurs at 20 degrees.

There is a problem with measuring angles less than the bevel of this test blade. The back of the bevel touches before the tip. To check angles less than the bevel of the blade of 25 degrees I had to turn the blade upside down in the holder and subtract the thickness of the blade from R. The blade thickness is 0.102”.

Here is how I set up the Wixey angle gauge on the guide to check angles. The bench is level within 0.2 degrees which I account for using the relative angle feature of the Wixey gauge.
B7CB7229-0DC8-46D3-A9B3-321B338194B9.jpg
My formula is accurate. LN is off a bit. I do not know why.

[Thomas Wilson]

I tried to cancel a post that had rotated images without submitting it. Then I started a new post in which the erroneous photos had been deleted. Apparently the images were still there at attached thumbnails.

Here is the correctly rotated measurement of the roller diameter that put the post over the 8 image limit.
EF6F66D9-A96F-4206-824F-75C3368E2772.jpg

[mike stenson]

I'm going to ask a stupid question here. The angles are, IMO, pretty arbitrary. In other words, if you're off a degree or two it doesn't seem to matter. Am I missing something?

[Thomas Wilson]

I'm going to ask a stupid question here. The angles are, IMO, pretty arbitrary. In other words, if you're off a degree or two it doesn't seem to matter. Am I missing something?

I think your opinion is pretty common. My opinion is that is is pretty easy to get an accurate number. With a combination square and a sharp pencil, you can make a reference mark on a scrap board and set an exceedingly accurate bevel angle. No one else had shared a formula anywhere that I found so I put mine here for anyone who is curious.

Bevel angle does affect cut quality, cutting force, edge durability, and a lot of things. People here do discuss optimum bevel angles for chopping and paring, for planing, for different woods, etc. To share experience or to use experience other people have shared on the effect of the bevel angle in this forum, you need to know what it is. From an engineering perspective, a difference of 25 vs 27 degrees is significant, like 8%. Forces and loads, to a first approximation, are proportional to the angle, so 8% also.

[Tom M King]

Do you use a different formula and stop block for each thickness of cutter? Projection the same for an old Stanley iron and a new thick iron?

I made my setting jigs in about 10 minutes one morning in 2016 (I think it was). I made a quick jig to cut the little blocks at a complementary angle on my miter saw. No calculations were required. I just made them quickly to see if I liked them, with plans to make "better" ones out of Corian if I liked them. They've worked just fine every since for some number of hundreds of sharpening sessions, good enough that I haven't made the Corian ones yet.

They are at least as quick and easy to use as a projection jig. You just loosely put the sharpening jig on the tool well back from where it will end up, hold the cutter in place against the angle piece, slide the jig down until it touches the surface, and tighten it. The same setting jig repeats the same angle every time, for any cutter, any thickness of cutter, and any sharpening jig combination without changing anything. Thickness of chisel or iron matters not.

I haven't ever heard of anyone else making any to try. It seems like everyone thinks the projection method is better somehow. I don't. I did use one for a long time when I only used the original Eclipse, but it's long since been thrown away.

When I had helpers, I hired people that no one else would hire. They never did learn to read a tape measure, but they could sharpen anything as good as I could using my system which included these setting jigs.

[Thomas Wilson]

The Lie-Nielsen jig registers the top of the blade in a wedge shaped grip between the jaws. Hence the top surface of the blade is always the same distance from the centerline of the roller. Thickness of the blade does not affect the relationship between projection and angle. The classic Eclipse must work a bit differently. I do not have one. The Veritas Mk.II references to the bottom of the blade but it comes with a setting gauge.. The Veritas Side Clamping references to the top like the Lie-Nielsen. I could add a parameter for the thickness of the blade to the formula for jigs that reference the bottom of the blade.

Your jig is very clever and easy to use. I can see that and I do like it.

I have no jig at all, just a pencil line on a board. I extend the blade of a combination square to the projection length corresponding to the desired angle and scribe a line across the end of the square on the board. It is even easier to make and I can adjust bevels in fractions of a degree. I maintain that it is easier and more accurate to measure and mark a length on a board and align the blade and guide to it than to cut an angle for your jig's angle block and align the guide and blade to it. Angles are harder to measure than lengths. But I will not argue the point further than that.

I am sure you would have been a great boss to work for and learn from. We need to get together sometime.

[Derek Cohen]

Thomas, it needs to be said that the absolute angle of the bevel is relatively unimportant. You need just to be in the ball park (i.e. close). There are no Bevel Police coming to check your angles. What is most important is repeatability, that is, being able to return to the same setting (on your guide) each time you sharpen. Calculating angles is a waste of energy. Get it close (digital box) and set a projection stop. Done.

Regards from Perth

Derek

[Thomas Wilson]

Thomas, it needs to be said that the absolute angle of the bevel is relatively unimportant. You need just to be in the ball park (i.e. close). There are no Bevel Police coming to check your angles. What is most important is repeatability, that is, being able to return to the same setting (on your guide) each time you sharpen. Calculating angles is a waste of energy. Get it close (digital box) and set a projection stop. Done.

Regards from Perth

Derek

Derek, I solved a woodworking math problem. It was not a hard problem. I thought the work was interesting, useful, and original so I shared it here. I still feel that way. The energy is small. The accuracy is great. Give it a try.

[Patrick McCarthy]

Tom, much appreciated. Thank you. Patrick

[Jim Koepke]

An Eclipse style guide was given to me and is used occasionally. It has the projections for a few angles embossed on the siide.

For a shop rigged guide a much easier way was found.

Shop Made Honing Sharpening Guide.jpg

It was easier to align the angle on a piece of tile by using the bevel already on the blade.

The exact angle of a blade never stopped it from cutting if it was off by a degree or two.

Sometimes it is better to forget about all the calculations and permutations and just get the job done.

There are advantages to being lazy.

jtk

Whenever there is a hard job to be done I assign it to a lazy man; he is sure to find an easy way of doing it.
— Frank B. Gilbreth Sr. (“Popular Science Monthly” in 1920)