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

[Thomas Wilson]

The Lie Nielsen honing guide instructions give a list of the projections for bevel angles of 20, 25, 30, … 50 degrees but not a formula for intermediate values or for jaws other than the standard jaws. I took this problem as a challenge and solved it. My question is whether anyone here is interested in my formula or the derivation.

I did a cursory Google search of the internet to see if someone else had reported a formula. I did not find a formula but I did find another forum on which a person asked the if anyone knew the formula (he called it the protrusion). He only got ways to find it by trial and error or measure it with a protractor or angle gauge.

I will take the time to make a drawing and show the math tomorrow if there is any interest.

[Robert Hayward]

I have an interest, thanks for the offer.

[Jack Frederick]

LN have a link on their site for a…what to call it, a board with assorted dimensions, distances to set reference blocks to set the angle. I made one years ago and it has worked well for me. I just packed it up for the move or I’d post a pic.

[Jack Frederick]

Tried to do a link, but it is an “angle setting jig PDF under sharpening.

[Thomas Wilson]

Here you go.

AFE310C1-7F3D-47DE-805C-E5561DFB2356.jpg
26A47412-6C6E-4DBD-989F-488659D85A83.jpg

[Thomas Wilson]

Tried to do a link, but it is an “angle setting jig PDF under sharpening.

Thanks Jack. I meant a math formula for projections that would be used to set up the jig.

[Derek Cohen]

Just place the blade in the guide and use an angle box or a protractor to set the angle wanted.

Then mark/measure the projection involved.

The blocks in front of the grinder are stops for angles for BU blades ...


Regards from Perth

Derek

[Thomas Wilson]

Tried to do a link, but it is an “angle setting jig PDF under sharpening.

Thanks Jack. I am talking about a mathematical formula to calculate the distances versus bevel angle. The formula I found can be used to set up a similar jig with different dimensions or find the distance for an intermediate angle like 27 degrees. I don’t think many will find a use for the formula. I just like to solve math problems.

[Thomas Wilson]

Just place the blade in the guide and use an angle box or a protractor to set the angle wanted.

Then mark/measure the projection involved.

The blocks in front of the grinder are stops for angles for BU blades ...


Regards from Perth

Derek

Can’t fool me Derek. That's a grinder not a formula.

Since you hone freehand, you may not know about the jig LN gives a plan for to set the projection of the blade in front of the guide.

Never mind. I see your projection setting stop blocks at the bottom of the picture. I am giving a way to calculate the set back if you need one that LN did not provide or for another Eclipse style honing guide.

[Thomas Wilson]

I made a sign error in the derivation above, tried to delete the figures but it did not work. The following pages are correct. Sorry for the error.

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5BEDC7AD-0D7F-4C74-94A9-D57CF7D9A119.jpg

[Rob Luter]

LN have a link on their site for a…what to call it, a board with assorted dimensions, distances to set reference blocks to set the angle. I made one years ago and it has worked well for me. I just packed it up for the move or I’d post a pic.

The link is shown below.

https://d3h1zj156zzd4j.cloudfront.ne...e-062719-1.pdf

[Tom M King]

I didn't read all your post. With that in mind, I don't like projection method of setting a jig by because it doesn't take into account the thickness of the cutter. I made these where the thickness doesn't matter at all, and can be used with any jig. No calculations required, and Very quick to set anything by. Nothing fiddly about them, and repeats the same angle every time.

[Greg Parrish]

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.

[Thomas Wilson]

I didn't read all your post. With that in mind, I don't like projection method of setting a jig by because it doesn't take into account the thickness of the cutter. I made these where the thickness doesn't matter at all, and can be used with any jig. No calculations required, and Very quick to set anything by. Nothing fiddly about them, and repeats the same angle every time.

I like it. There is more than one way to skin a cat.

[Derek Cohen]

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.

Greg, did you read my post (earlier)?

Regards from Perth

Derek