A Simple Home-made Honing Guide for Plane Irons and Chisels. Part 1 Back to School - Painless Geometry.

All cutting tools should be kept sharp, not only to produce clean cuts in the material but to do so safely and with the minimum effort.

The manufacturers of planes and chisels supply them with the 'business' edge ground to an angle of 25°. It is recommended for optimum cutting of wood that this angle is increased at the tip to 30° and you have to do this yourself using a flat abrasive surface. There are countless sites on the internet that describe this process and offer really sound advice and tips on how to achieve the desired sharpness. Unless you are really experienced with the process it is very hard to attain the desired angle of the blade against the whetstone surface and to this end a honing guide is used. These guides vary in price but all require the blade to be clamped to it.

Very early on on Friday morning I had the idea of making a guide using a flashlight and this is how I made it.

Back to the Geometry Class

Maybe a shudder runs down your spine at the thought of school geometry but there is an elegance in being able to reproduce angles very accurately and with ease. 

I wanted to produce a line that was 30° from the horizontal. To do this I first drew two sides of an equilateral triangle, which as you may remember has internal angles of 60° and then bisected this to produce my 30° angle.


I selected a piece of MDF recuperated from a pallet top. Along what was to become the lower straight edge I drew a straight line about 1cm from the edge and parallel to it.

Now, using a pair of compasses, the point of the compasses firmly on the baseline (the origin), I marked two arcs, one on the base line...
....and one in the approximate position for the second line, it doesn't matter if you draw a quarter circle through the baseline and up instead of the two arcs.

I moved the point of the compasses to the point where the arc crossed the base line and drew another arc. The two arcs drawn above the baseline (or the new arc and the quarter circle) intersect.

I drew a line from the origin to this intersection. This established the two sides of the triangle and the 60° angle.

To produce the 30° angle I needed to bisect this. So, placing the point of the compasses where the arc intersected the base line I drew another arc above the base line.

Moving the point of the compasses to where the first construction arc now intersected the newly-drawn 60° line I drew  the final arc.

A line was now drawn from the origin to the intersection of these last two arcs. 

And that's it! A line inclined at 30° to the base line.

Part 2 follows shortly., after I've had a cup of tea. I will also include a film I made of the process, which takes you though the steps visually. The link for part two is here.   

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All the best, Andy

© Andy Colley 2014

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