In his book Violin Restoration (ISBN 0-9621861-0-4), Hans Weisshaar has a photograph of a self-adjusting jig that will hold violin bridges while they’re being planed. I was rather taken by the simplicity and ingenuity of the idea and I thought that I’d make one to see if it worked any better than the very basic holder, shown below, that I use at the moment.
The clever part about Weisshaar’s jig is that one side is free to rotate which means that it can adjust itself to fit bridges of different geometry, holding them all equally tightly. It’s easier to show how it works with a few photographs than it is to describe it.
Extra holes allow the swivelling side to be mounted closer to the fixed side to accommodate three-quarter and half size bridges.
A small block glued to the bottom helps to hold the jig against the edge of the bench or in a vice.
Although the device works well, it’s probably not going to be much use anyone except a violin maker. Still, I thought that the idea of using a freely moving arm or jaw to grasp pieces of wood when the sides aren’t parallel had wider applicability. You might be able to use a scaled up version for planing tapers on table legs, for example. And the accessory jaw for holding tapered shapes in a vice that’s shown on the Tools and Jigs page of this site (scroll down to the second item) draws on the same principle.
Larger versions of these photographs are available by clicking on the thumbnails below.
Last week I made a bridge for the guitar that I’m building at the moment. Here’s a photograph taken while it was being French polished. It’s in Rio rosewood and the tie block is inlaid with a strip of spalted beech to echo the rosette that I wrote about a little while ago.
To cut the channel for the saddle and for the recess behind the tie block, I used this very simple router table. The idea came from an article in Fine Woodworking (No 182, February 2006) where Doug Stowe described how he made something rather similar for a full size router. There’s a brief description of his table here where there’s also a link to a full explanation and downloadable free plans.
In my table, the Dremmel is mounted overhead on a cantilever. The table itself is a board of mdf. The adjustable fence is simply a straight strip of wood that pivots at one end and that is clamped at the other – an arrangement that allows a remarkable degree of precision. Depth of cut is controlled by the position of the router bit in the collet. The Dremmel isn’t powerful enough to cut slots to their full depth in one pass so, to avoid the fiddly business of repeatedly having to change the position of the router bit in its collet, I place a shim of 1.5mm thick plywood under the workpiece for each subsequent pass.
The only bit about making the table that’s not straightforward is how to mount the Dremmel firmly and vertically in the cantilever in a way that allows removal. I solved the problem by buying a 3/4 inch diameter 12tpi tap, which matches the thread on the nose of the Dremel when the collar above the collet is removed. Then it was only a matter of drilling an undersized hole and tapping it out.
The table is quick and easy to set up and it doesn’t take up much room in the cupboard when it’s not being used. It isn’t big enough to deal with anything very large, of course, but for making guitar bridges it works fine.
The bridge is made out of Macassar ebony inlaid, on the tie-block, with a flash of laburnum to echo the rosette. Earlier today, I positioned it on the soundboard and glued it into place. The clamps are now off but I’m going to be patient and wait until tomorrow before stringing up the instrument. It’s always wise to let the glue cure completely before putting a lot of tension on the bridge.