Pickup Building: Epoxy Cover?

[MerlinTheWizard]

Hi all

I'm building my own bass pickups. Right now, I have a prototype of humbucker with two bobins and an internal preamp. I now need to put all that in some kind of casing...

I was thinking about molding the bobins in epoxy resin. What do you guys think? I've heard it tends to shrink a little bit while drying, and thus I'm afraid it might damage the bobins. I know some manufacturers use epoxy, but maybe not the same kind as I have. I plan on using this transparent epoxy resin...

I also thought about a wooden case; but it's more work, and I'm afraid of the vibrations (whereas in epoxy, nothing would move at all). Since my internal preamp has kinda high gain, my humbucker is pretty sensitive to vibrations (microphonics) even though I already potted the bobins.

Any other idea?

Oh, and I'll post pictures soon.

[MerlinTheWizard]

Just a quick note: I realized the transparent resin I have is not epoxy (which can't really be transparent), but polyester.

Polyester resin is nice looking, but it might react with some plastic components, and might not be ideal in terms of isolation. So I'm not going to use this.

I'm now thinking of simply building a wooden cover and potting everything inside with wax. Good old method. I don't know if wax will stick to the wood properly, though?

I've found proper black epoxy resin, but it's kinda expensive - and makes any further fixing impossible.

[GodBlessTexas]

I used to do work in composite plastics (fiberglass, carbon fiber, kevlar, epoxy/polyester/vynlester resins), and we made plugs out of wood for molds. Wax will stick to wood if the pores of the wood are left unsealed. Even then, the seal may not last due to heat and other environmental factors.

Remember the Alamo, and God Bless Texas...

[nollock]

I have read that West System epoxy doesnt shrink when it cures, although it would be best to email them to make sure.

http://www.westsystem.com/

[onelastgoodbye]

I wouldn't worry to much about the epoxy shrinking, it's more of a problem with polyester I believe. Epoxy takes about 24 hours to dry completely anyway, so your coils would settle very slowly, so there's really no risk of damaging them.

You have already potted the coils separately, right(or are you potting it alltogether in the casing)? If you haven't, keep in mind though that it's better to pot them while your winding (when using epoxy, that is) if that's in any way feasable. Epoxy is usually pretty thick and it won'tcreep in between the windings that easily, meaning there's a chance of loose windings in the center of the coil.

Also remember that epoxy is very sticky so you need to use some sort of mold release wax to keep it from sticking to your mold (you'll need to make a mold to cast everything, so I'm not sure if a wooden cover is 'more' work).

[MerlinTheWizard]

Ok, well I think I'm gonna use wax instead of epoxy. The problem is that wax won't stick right to wood (it does stick pretty well to metal, though). And I don't want to make a metal cover - I tried covering the bobins with metal just to see how it would sound, and it definitely eats a lot of high frequencies, so it's not an option for me.

So, hmm, not sure what to make the cover of. Any more ideas?

[GodBlessTexas]

I have read that West System epoxy doesnt shrink when it cures, although it would be best to email them to make sure.

Technically, all resins shrink when they cure. Epoxies just shrink a lot less, and West Systems is a good epoxy to go with. With their canisters and ready mix pumps it's almost foolproof to get the right mixture of resin and hardener. And by using the different hardeners you can choose how long you want for the pot to last.

However, I'd be worried about the exothermic reaction of putting enough epoxy into a cover to actually seal a pickup. In coats, resins don't tend to give off enough heat to be a problem, because there's enough surface area to help dissipate the heat. But when you fill a container with it, it can get very hot. I've had West Systems expoxy resin melt plastic when combined with the medium speed hardener.

Remember the Alamo, and God Bless Texas...

[MerlinTheWizard]

GodBlessTexas,

actually, If I decided to use epoxy, I would use something that's used for electronics. It's a black epoxy resin that's just right for that purpose; the temperature rises only slightly while curing, and the isolation is perfect; plus, the mix is already prepared (it's sold in small bags with a clamp on it, you remove the clamp, the two components mix and that's it). Not sure what brand it is, it's sold by Radiospares here in France.

[MerlinTheWizard]

Ok guys. Decided to make a wooden cover. The bobins will be glued inside, then wax potted.

I built the cover with plywood and then some veneer. Here is a picture of it drying in between two coats of lacquer.

It's not perfect, but I guess it's not too bad. Probably more pics once it's all done.

[lovekraft]

Damn, that's pretty! Very nice - I'd buy a set!

[MerlinTheWizard]

Thanks lovekraft, I love this veneer actually. I'm not that good at veneering, though, but I'm getting better. I didn't use plain wood because I couldn't find an appropriate piece of wood that looked the way I wanted; but I guess it would have been much faster to make.

[MerlinTheWizard]

Another new pic. The bobbins are glued in the cover, and then are wax potted as to minimize microphonics and improve reliability.

I simply use off-the-shelf white candles, melted in "bain-marie". Once nicely melted, I let the wax cool off for a couple minutes (so as not to be too hot and damage the bobbins or wires), and slowly pour it down in the cover. It solidifies rather fast, but still has some time to penetrate the windings. If you have potted them first hand, it's of course better yet. The cold wax is pretty hard, so nothing can move at all.

[onelastgoodbye]

I think you've made a good choice going for wood instead of epoxy