Potting Tank

[David Schwab]

I've had issues with crazy glue soaked rags spontaneously combusting in our garbage cans and dumpsters..

I've read that CA reacts with cotton, and is supposed to start smoking if you put them together.

I tried it with a Q-Tip once and nothing happened.

[defaced]

In my copious free time, I work as a candle maker's assistant (translation, my girlfriend's into candle making). The candle people use Fry Daddy deep fryers for melting wax, but they add a spout to theirs which I don't think would be needed for pickup potting. They run 25 bucks at WallyWorld and I'm sure every other big box store out there: Walmart.com: PRESTO FRY DADDY: Appliances

For her setup, we opted for something with more capacity, a 22 qt camping pan, which we set on a 1/2" thick piece of aluminum then onto the stove burner. Her wax is a soy blend, melts at about 170F if I remember right, and we don't have any problem with burring the wax. A candle thermometer comes in handy, I would gather that a candy thermometer would also work and be easier to get your hands on. They look the same to me (glass envelope style thermometer), so I assume they're similar enough this application.

[Bruce Johnson]

Here's a batch of my coils being potted with the MultiWoodPrime. I just pour it and daub it on there until it seems to be saturated. When it cures, it's not brittle-hard like CA glue. It's slightly soft. But, it's very low viscosity and completely saturates the coil.

[tedmich]

It doesn't seem to get hot, but the epoxy sure does. And wax is hot too.

I use MG Chemicals potting epoxy. It has the viscosity of maple syrup.

I don't think it's hot enough to melt the insulation though.

The fast set epoxies (30s-10min) produce all their exothermic heat quite quickly while the 50min-4h slow set release heat slow enough to not get too hot. When I potted my toroid with 1/2lb of 5min epoxy the darn thing got so hot I could barely pick it up to put it into a bucket of cold water. I use PTFE insulation so nothing melts anyway.

[David Schwab]

The fast set epoxies (30s-10min) produce all their exothermic heat quite quickly while the 50min-4h slow set release heat slow enough to not get too hot. When I potted my toroid with 1/2lb of 5min epoxy the darn thing got so hot I could barely pick it up to put it into a bucket of cold water. I use PTFE insulation so nothing melts anyway.

It's a funny thing, I started using a new batch of epoxy in larger containers. The last set of pickups I did, which where the first with this batch, the epoxy got really warm and set up pretty fast. I was surprised because I use a squeeze bottle and could feel hot warm it was in my hand.

It usually takes 24 hours for full cure. I did another couple of sets tonight, and it's working as usual, not getting warm, and taking its time.

[Bruce Johnson]

Yeah, epoxies can be touchy in the way they build up heat. If you have a slightly "hot" mix (a little too much catalyst vs resin than spec), it will tend to heat up faster. But the biggest factor is the volume of epoxy in one place. In a blob of mixed epoxy, the center starts heating up, and causes a chain reaction going outwards. The larger the blob, the faster it will turn into a smoking ball.

One way to reduce the problem is to mix it in a flat pan, instead of a cup. Keep it spread out, and don't let it get into a blob. If you feel it starting to get warm, spread it out more.

When casting epoxy, such as encapsulating pickups, be careful not to create spots in the molds where you're filling large volumes with epoxy. That could cause the epoxy to overheat and cook off. If you have a void to fill, cut a little block of wood to drop down in there to take up most of the space.

I use West Systems epoxy to encapsulate my pickups, the 105 resin and the 206 slow hardener. This mix takes about 12 hours to cure. I've had too many problems with heating using the 205 fast hardener for cast parts.

The Smith's MultiWoodPrime that I use for potting the coils doesn't seem to heat up at all in the small-cup quantities that I use. I haven't felt any heat buildup in the coils.

[David Schwab]

Good stuff Bruce, thanks!

Yes, I had mixed up a large amount, since I had seven pickups to pot. I thought about that too.

Last night I mixed half the amount, and it didn't get warm at all.

I do fill up large voids in the covers. I mainly did it as to not waste epoxy, but now I'm glad I do it.

[automan]

So the people that i ordered my warmer from called and said they didnt have that model in but they have one from another company they can ship right away. I smelled a bait and switch from a quality product to a knock off, so I canceled the order and ordered from somewhere else. I'll repost when I get the right one in as to how it works.

[Zhangliqun]

I just use the glue pot from Stewmac. Self-regulates on the temperature (145F) and works perfectly fine for me.

[chevalij]

I use the following. Max temp is 180, so no real danger.

Double Head Wax Heater Warmer Facial Body Beauty SPA on eBay.ca (item 230355289168 end time 15-Jul-09 11:00:00 EDT)

[gregyancey]

I've had great luck with this rice cooker:

Rival 6-cup Rice Cooker - Red (RC61) : Target

I put it in the "cook" position to get the wax melted, then to "warm" afterwords. I occasionally kick it back up to "cook" if the wax gets a little cool.

[Possum]

$5 wax pot....

I use what Leo Fender used at G&L, an old fryer with temp control. Using a thermometer I find the right temp and leave it set at that. The good thing is it heats up quick and if you're in a panic to pot something turn it up high and it will melt really fast. You can find these often at Salvation Army/Goodwill stores. I like the temperature control.

[tedmich]

Yeah, epoxies can be touchy in the way they build up heat. If you have a slightly "hot" mix (a little too much catalyst vs resin than spec), it will tend to heat up faster. But the biggest factor is the volume of epoxy in one place. In a blob of mixed epoxy, the center starts heating up, and causes a chain reaction going outwards. The larger the blob, the faster it will turn into a smoking ball.

The epoxy is all producing heat at the same rate, its just that the smaller the surface area to mass ratio, the slower the internal mass can pass its heat outward to the environment. Thus the center of the blob gets hotter cause the edges can lose their heat faster. Spreading it out allows more heat loss from the greater surface area.

Slow cure releases exactly the same amount of heat; it just does it slowly and it can radiate out so the temperature stays lower. Less chance of bubbles too with lower temp and more time for gravity to help the gas escape.

splitting hairs here but hey I am a chemist!

[David Schwab]

The epoxy is all producing heat at the same rate, its just that the smaller the surface area to mass ratio, the slower the internal mass can pass its heat outward to the environment. Thus the center of the blob gets hotter cause the edges can lose their heat faster. Spreading it out allows more heat loss from the greater surface area.

Slow cure releases exactly the same amount of heat; it just does it slowly and it can radiate out so the temperature stays lower. Less chance of bubbles too with lower temp and more time for gravity to help the gas escape.

splitting hairs here but hey I am a chemist!

Well, I do know that if I mix up about 3 Oz in a squeeze bottle it doesn't get warm at all. If I mix up 6 Oz in the exact same squeeze bottle, it gets really hot. It also starts to set faster. This is using the same slow cure potting epoxy.

It got REALLY hot last night, and the plastic bottle started getting soft. It was so hot you could not hold the bottle in your hand.

Didn't get hot in the pickups though.

This was left over from potting three pickups... I had mixed up to much. I had to sit it in a cup of cold water.

[tedmich]

Well, I do know that if I mix up about 3 Oz in a squeeze bottle it doesn't get warm at all. If I mix up 6 Oz in the exact same squeeze bottle, it gets really hot. It also starts to set faster. This is using the same slow cure potting epoxy.

It got REALLY hot last night, and the plastic bottle started getting soft. It was so hot you could not hold the bottle in your hand.

Didn't get hot in the pickups though.

This was left over from potting three pickups... I had mixed up to much. I had to sit it in a cup of cold water.

surface area of a cylinder goes up more slowly than mass:
2x mass can be only ~40% higher SA, so it can't shed heat as fast and the retained heat causes an increase in the chemical reaction of the epoxy hardening: approx a 2x faster rate for every 10C rise in temp.

Epoxy credo: Keep mass small, hardening rate slow and avoid shapes approaching a sphere (min SA:vol ratio)