Archive for August, 2006

Sawdust generator

Tuesday, August 22nd, 2006

I’ve had a few requests to post details of the top carving jig which shows up in some of the progress pics of John’s guitar. It’s a simple project to knock together, and makes roughing out a carved top much faster. It’s also an impressively efficient way off spreading wood chips over a large area…

One of the common techniques for roughing out carved top instruments is using routers to cut a ’step’ pattern into the wood. This technique works well, but is pretty nerve wracking (it’s very easy for the router to tip and cut deeper than you want) so I settled on this solution. The pictures should be pretty self explainitary, but questions and suggestions for improvement are welcomed.

Here a shot of the jig with a roughed out top. This was my first test, so the contours are not at final dimension yet - the edges were later thinned down to .25 inch.


The router is suspended about a little over 2.5 inches above a flat workboard, enough height to carve a top glued onto a body for a Les Paul style instrument. The router is attached to the base with 2 M6 machine screws.

At the moment the jig is attached to the workboard with 2 clamps, and is perfectly stable and solid, but ultimately it will be screwed in place. However it’s done, you must be completely condfident it can’t move *at all* - You really don’t want it getting lose and coming to find your fingers…


The guitar body registers off a wooden guide which runs in the body of the jig. The radius at the end of the guide matches the radius of the cutter in the router; a 1″ dish cutter bit.

This image shows the guide removed from the jig.


This shows the cutter and guide. The guide is adjusted by sliding and clamping with an F-clamp. In time I’ll add thumbscrews and an adjustment slot to the guide piece.


Here’s the body registering off the guide. The depth of cut is adjusted with the router plunge mechanism and depth stop.

With the cutter speed up high, and taking no more than 2mm with each pass there is no tendency for chatter or grabbing, which I think is helped by the rounded edges of the bowl cutter. The steps end up very smooth, though care has to be taken to keep the edge of the body square to the jig, otherwise the width of the rebate created can vary.

The jig is also great for routing binding with a bearing bit.


You can space your contour lines equally, which will create an even stepped surface, but I drew out the curve I wanted to create, and then mapped the steps required to come close to this shape if I removed 2mm each time.

Then, I transferred these measurements to the guide - I line up each mark with the edge of the jig, and drop the cutter 2mm each time.


Here’s the result - hopefully a few minutes with a small carving plane and a spokeshave will get me very close to my final shape. In this shot I’ve planed the neck angle into the top with a jack plane - the jig doesn’t do that bit for you :(