Wednesday, 4 November 2015

Casting a resin guitar neck for display LEDs

After successfully trialling our LED guitar tutor, we looked into putting a fingerboard back over the exposed LEDs and circuit boards. It proved to be more difficult and more fiddly than we'd anticipated. In fact, after drilling the original fingerboard (and making a mess of it in the process) we figured it'd be easier/better to create the entire thing from scratch.

Originally this was going to involve CNC routing a new piece of rosewood, with precision cut holes for the LEDs, perfectly spaced slots for the frets and pockets on the reverse for the PCBs and shift registers to fit into. And then Jake had a great idea....

Jake works with surfboards and has done quite a bit of resin casting. Using resin (and fibreglass sheets, where appropriate, to strengthen the resin) Jake suggested making a cast of the entire fingerboard. Because the resin is completely clear, we could embed the LEDs into the reverse of the resin while it sat in the mould. Once set, simply wire the LEDs and fix to the remaining guitar neck/body assembly.

At first we weren't entirely convinced about an entirely cast, resin neck. After all, we've no idea how quickly resin frets might wear down, nor how they might stand up to repeated pressure from a guitar string. Jake had a second, great idea:

After making the mould, and before pouring the resin, we place the wire frets into the mould (with their tines facing upwards). Then, when the resin is poured over the top, it sticks to the underside of the fretwire and holds it perfectly in place.

After a first layer of resin has been poured, we can place a printed pattern inlay actually inside the fingerboard, with the LEDs behind it (the inlay is not so opaque as to block the LED light when it is illuminated). Lastly, another layer of resin is poured over the top (remember we're working from the front of the fingerboard, towards the back) and the LEDs embedded into the fresh layer, while still wet.

So while all this sounds good in theory, there's only one way to know for sure if it'll work - and that's to give it a go!

We had some silicone left over from an earlier casting experiment. It wasn't brilliant, but would do for a test piece. After all, we're only using a guitar neck we've got lying around, to prove the idea works - we'll probably buy a new neck and fingerboard to make a "final piece" if it does, indeed prove to be workable. So the first thing to do was create an enclosure for our mould. This was made with a few offcuts of wood:

We didn't have a massive amount of silicone to play with, so made the enclosure quite close to the fingerboard. Ideally we'd have liked a bit more room around the fingerboard, to create a larger bulk of silicone, once dried, but this will just have to do!

Then a really critical part - to seal all the edges, to stop the silicone from seeping out while it is drying. We used Play-Doh and squashed it into every join where wood meets wood:

And finally, mixed up the silicone with the catalyst, and poured it in!

Rather than just dump the whole lot over the top, we poured the silicone into one corner of the enclosure and let it slowly spread to cover the rest of the fingerboard naturally. It may have been because the silicone was quite old, but it was really thick and gloopy, took ages to spread, and seemed to have a large number of air bubbles in it.

While pouring, we constantly tapped on the framework, to encourage the air bubbles to the surface (and to pop). The whole pouring process took a good ten minutes. Now the mould is likely to take at least 24 hours to cure properly. More photos to follow......