Saturday, 28 November 2015

Resin casting a guitar fingerboard

Let's get our 28mm miniatures out of the way. They were a first class disaster. Another nerd club failure! We failed to use enough/the right silicone mould release between the two halves when making the mould (so instead of a two-part mould, we ended up with a single, solid lump of silicone rubber, with a lead miniature encased inside!).

And even after cutting the miniature free, the silicone had far too many bubbles in it to make a usable cast anyway - even if the mould had turn out right, we could use it to make duplicates of our miniatures, because the bubbles obscured too much of the fine details.

So another failure on the casting front.
But in other news, we did have quite a success with what we actually wanted to achieve - a resin-cast guitar fingerboard!

To test the mould, we used some (cheaper) "backfill" resin. This costs about £18 per 2kg, compared with about £30 for the clear-water stuff. It's opaque rather than translucent, and sets a sort-of pale baby-poo colour. But for testing out the mould, it's perfect. We're looking to test the playability of our resin-cast neck at this stage, rather than test the LEDs shining through it, so a fully-opaque, caramac-coloured fingerboard will do us just fine.

The cheaper resin also suffers a little bit from shrinkage during setting. You can clearly see around the edges of the mould where the resin has shrunk back from the sides as it has cured.

Luckily, we made the mould/master deliberately too deep, to give us plenty of material to be able to sand the back of the fingerboard flat, and remove this slightly convex surface anyway.

The final cast has picked up some of the discolouration from the mould as we expected. Which is no bad thing. We can always give the resin cast a quick rub over with some fine-grit sandpaper to clean it up a bit - and it also means there's less gunk in the mould now, for when we do the next casting with it!

With the resin cast, we pushed some pre-radius-ed fret wire into the slots, to see how things looked. For some frets, we found that they could be pushed into place using our original sanding block. For a few slots, where the slots in the master had a little dust or debris which made the slots ever-so-slightly tighter, a hammer provided all the encouragement needed

Our fret wire sits snuggly in each slot, without being too tight a fit (which may otherwise have caused the resin to split or crack). A little drop of epoxy will hold the wire in place when it's fitted finally, and ensure that both ends sit snug against the fingerboard.

When placing the frets into the resin fingerboard, it did cause a slight curve in the board, as each of the frets pushed against the sides of the slots. This is easily cured by pushing - and in time, gluing - the fingerboard flat against a hard surface. The photo above shows the tiny, slight deflection in the fingerboard with the frets fitted.

Our pre-curved fret-wire fits in the slots, and sits neatly against the curvature of of the fingerboard.

With all the fretwire in place, our resin-cast fingerboard is starting to look like the real thing. We're waiting on a 30 degree fret file and fret nibblers. Then all we need to do is fit it to an instrument and see if it's actually playable!