Routing the control cavity and making a matching cover

Today I planned to get the control cavity for the bass finished, including cutting a matching cover from sapele. I used Inkscape to draw out the shape of the control cavity cover, printed that off twice and on one, drew the shape of the internal cavity freehand.

There were stuck to MDF and cut into templates.

For this job I needed three templates; one for the internal cavity, one for the control cavity cover, and one for the ledge the cavity cover sits on. The last of these two need to match as close as possible. I’m still searching for a way of using the router to create two exactly matching male/female templates, and I spent a couple of hours of experimenting with collets and straight cutting bits, with no success. More research required on this topic. Instead I used the offcut from cutting out the cover’s template, to make myself the template for the cover ledge. Not exact but close enough for me at this stage.

I select a piece of offcut sapele, and planed a couple of millimeters from a portion of it.

I attached the cover template, and routed round it to a depth slightly deeper than I would want for the cover.

I set up a fence on my band saw and sliced the sapele, just slightly thicker than I would need for the cover.

I attached the templates to the body and routed the cavity and cover ledge.

Rather than having a screw on cavity cover I decided to use neodymium button magnets, an idea which I’d seen used to great effect on the Musical Instrument Maker’s Forum (aka MIMF). The magnets are 6mm in diameter and 3mm thick. I drilled a 6mm hole at each corner. Initially these were just 3mm deep. I put pairs or magnets into each hole, put a drop of CA glue (aka superglue) on the top of each, then pressed the cover down. Once the three magnets were glued to the cover I could drill the holes to 6mm deep, put a dab of glue at the bottom of each, and then push in the magnets with a cocktail stick. NB: If you’re doing this then you need to pay attention to the polarity, because you want them to attract the magnets on the cover, rather than repelling.

One the glue holding the magnets had set, I sanded the top of the cover level with the body. I’m really happy with the result of this.

I drilled one small pilot hole through from the back of the cavity and then, making sure the relationship between the two looked OK, drilled the second one through from the front.

I used a 19mm spade bit to drill a “countersink” for each of the knobs. This means that the bottom edge of the knob can sit below the top face of the body, hiding the nut and washer securing the pot.

I drilled the 8mm hole for the pot shaft and then checked that it all fitted together neatly…

…before lightly sanding to round over the edge of the countersink.

Hopefully the pickup and bridge will arrive tomorrow, which means I can get the final routing completed, and glue up the neck. All that will be left to do is the final sanding, applying the Danish oil finish, assembly and set up.

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4 thoughts on “Routing the control cavity and making a matching cover

  1. That’s very neat. I like the magnet idea. Is it still easy to get the cover off when you need to?

    • Easy is probably the wrong word for it. It comes off ok but there is a bit of a knack to it. Once it has got finish on it I’ll be able to use a suction cup.

  2. Assuming you have a suction cup handy. Not that you should have to get in there too often.

    • True, although I’m rarely without one. There’s always my satnav and phone windscreen mounts in my car.

      It is actually relatively easy to pop off with a plectrum – just get it in under the corner and it pops up.

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