Wood-fired!

A jig for a jig for a jig

My woodworking colleagues will be familiar with this scenario. You need to build a jig for a particular job. But in order to make the jig you need another jig that you haven’t built yet. In this case I had to make a third jig (albeit a trivial one) so that I could make the second jig so that I could make the jig that I needed for my job.

The job seems simple enough. I need to plane a 45° bevel along the long side of a thin board. Four such elements will make the sides of a long thin box.

Normally in box making the grain runs around the box so that the mitred edges are end-grain. So most jigs such as the one shown here are setup to plane end-grain - usually on the shorter side of the piece.

For several reasons it is difficult to mitre the long side of a board using this jig especially if the board is narrow. Two of my boards are only 25mm wide and around 200mm long.
It is difficult to register the board correctly because the end that must sit against the square fence is so short. And though it seems trivial, the effort to steady and run the plane on this jig detracts from the effort needed to manually hold the board in the correct position.

So I decided to build another add-on to my shooting board. The standard shooting board as used by most woodworkers allows the plane to run on its side on the bench. This works well as long as the side of the plane is roughly square to the sole¹.

The add-on jig will allow me to hold the board to be beveled at 45deg to the bench and run my plane on the bench with all my attention focused on holding the board in the correct orientation.

To make this add-on I needed some thick lumps of MDF cut to precise 45° angles to support the reference surface for the board to be planed. The 32mm MDF stock I found was quite small so cuttting it on my dimension saw was not going to give an accurate result. So I decided to cut it on my large bandsaw.

This is an old bandsaw with great power and accuracy but limited reference fences. I had added a good ripping fence but have no reliable arrangement for crosscutting or indeed cutting at 45°. So I needed a simple jig that I could run against the ripping fence that would hold my small piece of MDF at 45° to the blade.

This jig is also quite small and slightly tricky to cut accurately on the saw so I constructed this trivial jig to do the job safely and well. It’s pushing the definition of a jig because it’s really just a crosscut fence and a trusty magnetic clamp acting as a stop.

So I cut the jig on the table-saw. This allowed me to easily cut the wide blocks at an accurate 45°. I was then able to construct the add-on jig for my shooting board.

The shooting board jig worked quite well. I was able to accurately bevel the long edges of my boards and proceed with the project. Using the jig still requires some concentration and effort. It is not as easy as simple squaring on a shooting board but it is quite managable.

As always as soon as you have a jig you find other uses for it and wonder how you did without it. I find it very handy for putting small bevels (2 strokes of a plane) on the edges of small elements. I would normally do this with a block plane holding the piece in my vise or my hand. The jig gives a more consistent and even bevel.

1. this setup actually allows quite a deal of latitude provided the user is aware of what’s happening and makes minor manual adjustment [↩]

4 comments January 9th, 2009