Saturday, 20 August 2011

Junk guitar - progress - adjustable bridge

I've been working on the bridge. I wanted something adjustable in order to set the action and intonation. As I don't have many tools for metal work (no milling machines here!) it has to be a wood job. Fortunately, I found an old box made from something that seems hard and tropical and decided to use that.

My initial idea was to construct something akin to the bridges found on archtops. After a rummage through my nuts and bolts I realised I didn't have anything that was really suitable, but it then dawned on me that I could use a couple of the saddles fom the ZO-3's original bridge. These are the regular sort with worm-screws for height adjustment that are found on strat-type bridges. There were six on the original bridge, one for each string, but three of them were so badly rusted up that their worm screw couldn't be removed. My idea however only requires two - one at either end of the bridge. I'm not sure if it really provides sufficient strength, but the bridges on a couple of my old Japanese twangers are similarly raised by just two, not so heavy-duty, bolts.

I found some bolts with grippable heads to replace the worm-screws.

Hopefully these photos show how it all works:

side view - the saddles from the original bridge are now upside-down

the wooden blank

as seen from below - two of the original saddles - one at each end

from the front

and from above - the plastic saddle is temporary and will probably be replaced with something like brass. there is still some shaping to do once I see how it works with the body

There was also a tail piece to make, plus a bracket for the scale length adjustment. For these I used some sheet steel from the casing of an old Technics hi-fi amp.

cutting and bending the tail piece

slots for strings

still needs a lot of polishing

testing the bridge

the bridge and tail piece are fitted to a block of cherry wood

there's about 3-4 mm of vertical play at the bridge which means I can get an acceptable action at the 12th fret - hope that's still the case when it's fully strung and up to tension!

checking the alignment down the neck

Next step is to glue the bridge block to the body block, I'll probably add some dowels for extra strength. After that, I'll be routing cavaties in the plywood facade to sit over the bridge. I'm thinking the electroncis will be entirely mounted into the facade - that way it can all be removed as one unit which may make maintenance easier.

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