Epoxy potting

[DialtonePickups]

Hi everyone!

I'm hoping to get some help with a couple of epoxy issues we're having with our pickups. Some quick background: we make an active pickup. We pot the coils in wax and then fill the case with a black epoxy. My husband John designed the pickups, I'm just the one who builds them.

First, and most urgently, I wanted to try one of the new epoxies we're looking at so I potted a couple of pickups late last night, and this morning they are not working. No output at all on either one. They were working just fine before the epoxy so I'm hoping it could be because the epoxy is still a little wet? I'm wondering if I should pull the pickups apart to salvage parts before the epoxy dries. (I'd usually ask John but he's in meetings all day and the epoxy will have dried by the time I can reach him.)

Second, I've been having a really hard time getting the epoxy to flow where I want it to go without making a big mess. The plan was to epoxy the pickups after installing the back plate through a small hole in the plate, but I cannot get the epoxy to flow well through a tip small enough to fit through the hole. Any suggestions on how to manage the epoxy better?

Thanks!

[DialtonePickups]

Here's the back plate, by the way. The holes are under the two outside screws.

[jason lollar]

Not advocating epoxy potting but you might consider switching over to a casting resin or thinner epoxy- they make various viscosities. West stystems makes this - I dont know what you are using. Also i learned from a buddy that makes medical displays that for some applications a pressure tank works better than a vacuum, vacuum will make the potting material froth up and the air bubbles expand, a pressure tank will shrink any air bubbles- its much cleaner and you can make one out of an old portable air tank like you would fill from an air compressor to haul around.

[DialtonePickups]

Not advocating epoxy potting but you might consider switching over to a casting resin or thinner epoxy- they make various viscosities. West stystems makes this - I dont know what you are using. Also i learned from a buddy that makes medical displays that for some applications a pressure tank works better than a vacuum, vacuum will make the potting material froth up and the air bubbles expand, a pressure tank will shrink any air bubbles- its much cleaner and you can make one out of an old portable air tank like you would fill from an air compressor to haul around.

Thanks Jason. We seem to have the pickup building & wax potting part down pretty well, but the epoxy process has been a nightmare. It's needed, though, for the pickup to work and fit together correctly. We'll check out West Systems, I did see them mentioned on another post as well. We'll also check out a pressure tank. I hadn't heard of that before - too bad we didn't look into it before buying the vacuums we recently invested in! I do notice that when I vacuum, there is expansion until I shut the vacuum off, so your explanation is consistent with what I've been seeing. Thanks for the tips!

[big_teee]

http://music-electronics-forum.com/t36769/
Checkout post 7

[big_teee]

Here's some more Bruce Johnson bass building.
He shows Encapsulating on page 4.
Building Scroll Basses- Pickups 1

[DialtonePickups]

Here's some more Bruce Johnson bass building.
He shows Encapsulating on page 4.
Building Scroll Basses- Pickups 1

Thanks Big-Teee! I got some great tips from reading through that, like the glue he uses for the magnet wire connection - seems like it could be better than what we're doing.

By the way, if anyone is curious - I think I solved the problem with these two pups. I'm pretty embarrassed to admit what it was... a bad battery. Replacing it seemed to fix the problem and now the pickups are working great.

[ken]

Jason is right here, you will need not an epoxy but a pourable plastic resin. Epoxies many times are too thick to pour neatly, and it´s too easy to get air bubbles trapped in the pickup coils. IMO the lowest viscosity pourable resin that will solidify clean through the pickup reasonably quickly is what you want. Model railroaders use pourable acrylic resins to model water... maybe that would work.

Maybe a small vibratory table would work for your pours - you can shake the bubbles to the top of the cast that way. If you have a vacuum oven, you may be able to pressurize it a bit to shrink the bubbles too.

ken

[David King]

With any potting resin you really need to watch out for run-away thermal reactions. If the stuff gets too hot as it cures it could build up some internal stresses and that might cause a winding failure down the line. The place that can really set you up for production is Epoxies, Etc. ? Epoxies, Silicones & Urethane Formulator They have various sizes of auto mixers/dispensers that can streamline the process, minimize the mess and save you some time. The have a lot of specific formulations to solve issues with viscosity etc.

[J M Fahey]

Agree.
FWIW my first "commercial" products, when I was 16 , were in the disco lighting area: the "Sonolite" music-to-light converter , straight from Popular Electronics, and a self designed Music triggered flash light.

To avoid certain cloning by others, my "partner" and I encapsulated the electronics in Naval type Polyester resin, which is much thinner (and cheaper) than typical Epoxy .

We were plagued by failing modules

The resin sellers told us that we had to mix less accelerators and catalyzers for it to harden at least in a couple hours, preferrably overnight, or the thermal peak would cook transistors.

On the outside it felt hot but bearable; in the core it was Hell .

After we slowed down, we never ever had a problem again.

We used to add a black paste pigment and later some "ground quartz load" , actually looked looked like fine white sand.

Not for physical strength, but to dull possible Xacto blades trying to scrape resin away, bit by bit, to learn about our "secrets"


Joys of youth

So go get some Polyester resin, it's cheap, plentiful and good for casting.

Some people use the "crystal" pouring type to make those transparent cubes enclosing a butterfly or a dry flower, go figure, that's how liquid it is.

[Bruce Johnson]

Big Tee linked to my web pages above, so you've seen my process. I've been potting and encapsulating my pickups in epoxy for about 12 years, and I can't say I've ever seen a failure related to the epoxy.

You probably already know this, but I'll repeat these basics for other readers:

It's important to understand the difference between "potting" and "encapsulating". They are two different steps in the process, and they require two very different types of materials. You can do both steps with epoxy, but it requires two different epoxies. You can't cheat and do both operations at once with one material. And you don't have to use epoxy for both. You can do wax potting and epoxy encapsulation. Or you can do epoxy potting and wax encapsulation, if you wanted to.

Potting involves saturating the wire coil to glue it all together into one mass, for durability and to prevent microphonics. Most pickup makers use wax for potting, but a few of us use epoxy. Potting requires a very thin epoxy called CPES (Clear Penetrating Epoxy Sealant). The brand I use is Smith's MultiWoodPrime.

For encapsulation of the coil into a housing or into a mold, I use West Systems epoxy; the 105 Resin and the 206 Slow Hardener. It works beautifully for casting. I stir it gently to minimize bubbles and pour it directly into silicone rubber molds. No vacuum system or vibrating table required, if you can tolerate a few small bubbles on the back (underside) of the pickup. I use Moser's powdered alcohol-based aniline dye to color it a deep black. It cures in 6-12 hours. With the 206 Slow Hardener, it doesn't warm up perceptibly during curing. It's never caused any harm to my coils or wires that I can tell. Do not use the 205 Fast Hardener for casting with West Systems epoxy.

That's about it. You have to have the right epoxy. The West Systems is viscous enough that it will flow in nicely and surround everything. It cures completely hard, and can be drilled, filed, sanded and polished back up to a gloss. It can be repaired, too. You can fix a hole or bad spot by dabbing on some more, letting it cure, and filing and polishing it back.

I also cast parts from polyurethane resin, such as my pickup bobbins. It cures much faster, like 15 minutes, but there's heat and swelling issues, and it's not as tough as the epoxy. I like the West Systems for the permanent outer shell of my pickups.

Edit: To more specifically answer your question, as related to your pickup design: The West Systems 105/206 mix is thin enough that it squirts very well through a syringe. I use the disposable plastic syringes with the screw-on tips, from McMasters. With a little bit of cleaning, they can be used many times. The epoxy doesn't bond to them.

The West Systems epoxy should work fine for your application. Use the syringe to fill the housing through the hole in the back plate. Over the next 20 minutes, keep checking on it and adding a bit more to top it up, as it settles in.

Wipe the outside of the metal cover with Johnson's Paste Wax (no relation) first, and any epoxy that oozes out won't stick. Don't wipe it while it's wet, let it cure and the blob will pop right off.

[DialtonePickups]

Wow, thanks everyone! This is all really helpful. I cannot tell you how much trouble we've had with epoxy; I wish I'd come here first! Oh, and Bruce - I especially appreciate the Johnson's Paste Wax tip. I hadn't heard of it, but I'm going to pick up a container ASAP. I've spent so much time scrubbing epoxy off of surfaces I don't want it on.

[Bruce Johnson]

If you are having trouble with epoxy leaking out of holes in the top cover, during the encapsulation process, you can make a "mask mold" for it. You make a silicone rubber mold from one of your top covers, using the same process as if you were going to cast the outer shell. Set a waxed cover face down into a rectangle of wet silicone rubber molding compound. This silicone mold will now snap tight around the cover, sealing up openings and holding the epoxy inside. With a bit of cleverness, you can figure how to allow the silicone to stick in slightly through openings in the cover, to create deliberate pockets or open areas where you want them.

For your production process, first wipe the outside of the cover with the wax, and snap it down into the mask mold. Set in the innards and the back plate. Inject the epoxy into the hole and keep topping it up until no more will go in. Let it cure, and pop the whole thing out of the mold. It should be pretty clean, with minimal waste of epoxy. When you get the mask mold idea worked out, make up a bunch of them and line them up. Do the encapsulation on a row of them at a time for efficiency.

[Rodent]

interesting to discover how many other 'SO teams' are working together on pickups these days

my SO has been helping with the marketing, and has been begging to learn how to start working the winding and post epoxy encapsulation detailing. winding 'lessons' start this week with the goal of having her taking ownership of her first pickup model by end of next month (if not sooner)

I have a new model that will be epoxy encapsulated if for no other reason than it being a total PITA to find a reliable source for undrilled Bart sized soapbar covers. What I discovered in the process was the freedom to utilize a more suitable overall size by making my own silicone molds and going the epoxy encapsulation route.

thanks again Bruce J and David K for all your excellent insights here (and elsewhere) - I definitely owe you a both beer or two next time we meet up!

[DialtonePickups]

If you are having trouble with epoxy leaking out of holes in the top cover, during the encapsulation process, you can make a "mask mold" for it. You make a silicone rubber mold from one of your top covers, using the same process as if you were going to cast the outer shell. Set a waxed cover face down into a rectangle of wet silicone rubber molding compound. This silicone mold will now snap tight around the cover, sealing up openings and holding the epoxy inside. With a bit of cleverness, you can figure how to allow the silicone to stick in slightly through openings in the cover, to create deliberate pockets or open areas where you want them.

For your production process, first wipe the outside of the cover with the wax, and snap it down into the mask mold. Set in the innards and the back plate. Inject the epoxy into the hole and keep topping it up until no more will go in. Let it cure, and pop the whole thing out of the mold. It should be pretty clean, with minimal waste of epoxy. When you get the mask mold idea worked out, make up a bunch of them and line them up. Do the encapsulation on a row of them at a time for efficiency.

Thanks Bruce for the mask mold tips!! I really appreciate the help, especially with enough detail to help us do it correctly. We would have never thought of that, and it's really been a frustrating problem I've not known how to solve other than carefully swabbing with a half dozen or so alcohol drenched q-tips per pickup. We have similar issues with our potentiometers, so now I have some fresh ideas on how to approach that issue as well.

Like Rodent said, I definitely owe you a drink or two! Do you guys ever meet up in-person?

Rodent - good luck with the lessons!! I bet she'll pick it up quickly.