Epoxy encapsultation for the busy working mum.

[Bruce Johnson]

Here's a link to a series of web pages of mine, showing how I build the pickups for my basses. I cast my bobbins from polyurethane, and then overcast the pickups in black epoxy. You can see how I made up aluminum masters, silicone rubber molds, and do the casting. It's not real high tech. As the other guys have mentioned, the master can be made from almost anything, but it has to be made well. Any scratches and flaws will be precisely duplicated by the molding process.

Building Scroll Basses- Pickups 1

I don't currently use pressure or vacuum during my epoxy pours. With slow-curing epoxy mix and careful stirring and pouring technique, the bubbles can be dealt with. I also deliberately designed my pickups, with the perforated brass shells and ebony caps, so that most tiny bubble won't show. Also, black epoxy can be worked and finished after it's cured. So, if you get a bubble or flaw, you can actually repair it by dabbing in some more epoxy, letting it cure, then filing and polishing it to match.

[Peter Naglitsch]

Jonson: Tnx for the links. I will check them out next time I need to order (got a shipment on its way right now so it will not bee soon...)
Jason: Great looking pickup. When you say that using vacuum will shrink the former (mold?) do you apply vacuum only to the inside of the mold in some way? I cannot really wrap my mind around how a mold placed inside a vacuum container would shrink. But thats only me... I have a few fancy "vacuum injectors" or whatever they are called that creates vacuum through the use of compressed air (got them as a favor through my day job) ans I have been pondering to build a low pressure pot (not really a vacuum pot) to be able to cast pickups in one go and your comments make me a bit hesitant to do that.
Bruce: Thanks for the great tutorial. I remember seeing that quite a while ago but I lost the link. Great stuff and a real inspiration for someone just starting out with this casting business. Expertly machined masters/plugs/bucks and a really thought trough construction and all. Makes me feel really crude thou...

[RedHouse]

heres a pickup I made using a silicon mould etc- its a reproduction of an old supro but that type of construction takes alot of prepwork to make a good mould. You hang the pickup from a jug you make to mate up with the mould and its better to pressurize the epoxy than vacuum- the latter just creates bubbles and the former shrinks them down to nothing.

Nice work Jason.

[jason lollar]

I was talking about when you pour the epoxy around the pickup not making the mould. Of course there are different ways to do it but what I was talking about was removing bubbles and voids. If you put the epoxy under vaccum it will draw bubbles for sometimes 15 minutes + so youll get lots of bubbles if you are using fast set, if you put it under pressure it makes any air pockets smaller so you get fewer bubbles. You could use a lober setting epoxy as mentioned and fill any bubbles later but I preffer not to do that but I have only done this maybe 20 or 30 times which is nothing really.

[Peter Naglitsch]

Duh, shrinks the bubbles down to nothing... I misread that to "shrinks the mold down to nothing". Thanks for clearing that up for me Jason!

[David Schwab]

I've recently started to cast pickups to try to differentiate me from the current vintage clone/PAF market. I have started to get the hang of it but I'm no were close to being an expert. I use silicone for the mold and PUR (poly urethane resin?) with added black pigments as I got too much shrinkage when using epoxy. Watch out for shrinking in the 5-6% range. The PUR I use have only 2% shrinkage and works fine. The trick is to spend a lot of time on the original part that you make the mold from (whats that called in English?). Every tiny imperfection from that will show up in the mold and in the finished product.

Oh, just found the thread Dave were reffering to:
http://music-electronics-forum.com/t13575/
Start there, much info

Watch out, some of those urethane resins get too hot. I've had them ruin molds.

I use this epoxy. It's low shrinkage, pretty much doesn't shrink, because it has nylon filler in it.

Black Encapsulating and Potting Epoxy Compound > RoHS Compliant

It's not cheap, but works great. I use it both for potting in plastic covers and in molds.

[David Schwab]

heres a pickup I made using a silicon mould etc- its a reproduction of an old supro but that type of construction takes alot of prepwork to make a good mould. You hang the pickup from a jug you make to mate up with the mould and its better to pressurize the epoxy than vacuum- the latter just creates bubbles and the former shrinks them down to nothing.

Yeah, vacuum makes it foam up.

Nice looking pickup.

[David Schwab]

AeroMarine Products - Epoxy Resin, Urethane Foam, Silicone Mold Making Rubber is the place to go in the States for this material.

After using this epoxy for a while, I'm going to warn against using it. Even when consistently and carefully mixed, it often does not cure fully. I've had pickups with sections that were soft or totally uncured, and even one that looked fully cured, and then started leaking resin six months later. I had to make a bunch of pickups over because of this stuff.

I also had this epoxy ruin four brand new rubber molds. I still have a liter left and wont touch the stuff ever again.

[Joe Gwinn]

After using this epoxy for a while, I'm going to warn against using it. Even when consistently and carefully mixed, it often does not cure fully. I've had pickups with sections that were soft or totally uncured, and even one that looked fully cured, and then started leaking resin six months later. I had to make a bunch of pickups over because of this stuff.

It may require a mechanical mixer for a complete mix. One can do this by hand with a spatula knife, but it's tedious. People use centrifugal mixers for such things.

[peskywinnets]

Whilst not epoxy, I used a funky little manual dispensing system the other day (albeit not for pickups!) ...

Rapid Electronics - Syringe gun

Rapid Electronics - Clear polyurethane resin

Rapid Electronics - Nozzle For 50ml Kit 87-7176 (this is the key bit here - 'helix inside' mixing nozzles - the epoxy comes out already mixed)

Certainly for mixing, I can heartily recommend such a low tech method of dispensing of polyeurethane....though how it would work for casting is debateable.

clean, easy to dispense, well mixed, no faff or mess - obviously the mixing nozzle (aboiut 40p) has to be thrown away each time, but you could arrange it so you did a few pickups at once - the cost per pickup would then be minimal from a nozzle useage perspective.

[Bruce Johnson]

I've been doing all of my epoxy casting with West Systems, with good results. I use the 105 resin with the 206 slow hardener. That mix usually cures in about 12 hours. You can't use the 205 fast hardener with any application thicker than about 1/4", or it'll overheat and cook out, which usually ruins both the part and the mold. You need to spray a mold release into the silicone molds, or the epoxy will bond and pull little chunks out of it.

I color the epoxy black (or whatever) by adding about 5% of Moser's alcohol-based powdered Aniline stain. It's an Aniline dye for woodworking, that comes in powered form. You normally mix it with alcohol to make up a wood stain. I just put a small amount of the powder directly into the epoxy as I'm mixing it. It has very good deep opaque color, and doesn't seem to have any effect on the epoxy's chemistry.

I mix the epoxy in a small plastic Dixie cup, with a wood tongue depressor. The key thing is to force yourself to stir slowly. You want to stir it at about 1 revolution per second, which is a lot slower than you stir your coffee. I typically stir it for about a minute.

The only time I've ever had problems with the West Systems epoxy not fully curing (or really slow curing) is when the Hardener has gone bad. Once you've opened the seal on the can, it starts absorbing moisture and getting darker in color. The darker it gets, the riskier it is to use. An open can of Hardener is good for 2-3 months at best. I do two things to reduce this problem. First, I buy the 105 Resin in gallon cans, because it's cheaper and it doesn't have any aging problems. But I buy the 205 and 206 Hardeners in the little 7 oz cans, so there's less exposed when I break the seal. Second, whenever I open a new can of Hardener, I immediately pour it all into a clear plastic squeeze bottle, with a spout top and a cap (from McMasters). The squeeze bottle seals up with the top on, whereas if you use the little West Systems pump in the can, there's always a small open vent hole. Also, in the squeeze bottle, I can see the color of the Hardener to judge how much it's aged.

Most of the epoxies made for potting electronics, at least the ones that I've tried, are too thick for getting good castings. They're made for putting a blob on top of a circuit board. When you try to get them to ooze down into a mold, they'll capture pockets of air in corners. It's the same with most of the hardware store epoxies. They're made thick so they stay in place when doing repairs. The West Systems is much thinner and easier to pour. The technique of pouring into the mold is also very important in reducing bubbles. I pour from the Dixie cup in a thin stream, walking it around to fill the lowest details and corners in the mold first. I usually pour some epoxy down into the bottom of the mold first, let it settle, then set the coils and components in, let them settle, then gently fill the rest up to the top with a small stream.

I hope this helps! I've been casting epoxy parts and pickups for instruments for about 20 years, and this is the system that's worked for me.

[Peter Naglitsch]

Watch out, some of those urethane resins get too hot. I've had them ruin molds.

Thanks for the hint David. I tested the PUR first several times to get the pigment rate right and I never had any problem with heat. So I guess I was lucky with the brand I use/experiment with (heh, I have only cast 5 pickups up until today, not counting numerous test blocks without electronics, still waiting for the next batch of PUR to arrive). I use Creartec PGB from an arts supply store. Cures hard to a matte black that I really like.

One thing I learned on-line to get a better mix is to pour the tho parts into one container, start mixing it there, then pour it into a second container and do the final mix there. I got much better result that way. But I have like 15 minutes before it starts to set (30 minutes according to the manual but no way!) so I have to move fast.

[Soundfarmer Pete]

This stuff is really good......NFI
Restoration Supplies Black Coloured Polyurethane Casting Resin
It`s a little more expensive than most other brands but gives brilliant results......super detail, low temperature cure and zero bubbles.
There also seems to some form of release agent incorporated - castings seem to have a slippy film that wipes off making this resin very kind to silicon rubber.
Also available in white and ivory, I now use this exclusively on my mando pickups both for potting and components such as bobbins and baseplates on humbuckers.

Not sure how easy this would be to buy outside the UK - may be on some kind of prohibited chemicals list.
CheeryBye!

[Peter Naglitsch]

Thanks Soundfarmer. According to this:
Shipping
they ship to the world, even hazardous stuff

[David King]

My trick for bubble free mixing is to bend a 12AWG or so wire into an "L" shape with the foot just shorter than the radius of mixing cup. It helps to add a little serif at the end sticking up. I chuck that in my portable drill and sink it slowly into my epoxy. As long as it doesn't cavitate you can spin it at 300 rpm all day and not get any bubbles. It does a good job wiping the bottom and the sides of the cup but you have to keep it centered and keep a firm grip on the cup at all times.