Bass Pickup Shell

[Marko Ursin]

What I have been doing with the molds is to pour enough to get a clean front face cast, and then after that cures, I put the pickup in and fill the mold up.

I thought about making the pickups this way but if it doesn't work it's eight more coil to make and that's something I'd like to avoid. That leaking you mentioned is what I'm worried about. I'd use premade covers if someone made MM covers that were deep enough.
Marko

[Bruce Johnson]

Yes, that does sound like the same type of resin that I'm using. It definitely will heat and boil over. One thing that will help is to mix it quickly in a cup, then immediately pour it out into a larger pan, so it goes into a shallow puddle. Then, pour from that into your molds. Every second that it sits in the cup it will build more heat, which then causes it to build even more heat.

I've been using the urethane resin for casting my bobbins and other parts, but then I use black epoxy for the overcast of the completed coil. Like you, I don't want to risk the heat on the coils.

You should try making a two part mold and casting the cover as a separate part. I regularly cast parts with 1/16" wall thickness without much trouble. Sometimes I'll get bad ones with bubbles, but most are good.

So, this resin that you got does come out a nice dark black? If so, I'll get some and start using it for my bobbins.

I've had the best results not using any mold release when casting the urethane in silicone rubber molds. The parts seem to pop out fine without any damage to the molds. Spraying the mold release in there will actually cause the rough surface. With epoxy, however, you need the mold release.

[David Schwab]

Yes, that does sound like the same type of resin that I'm using. It definitely will heat and boil over. One thing that will help is to mix it quickly in a cup, then immediately pour it out into a larger pan, so it goes into a shallow puddle. Then, pour from that into your molds. Every second that it sits in the cup it will build more heat, which then causes it to build even more heat.

I have been mixing it up in the cup and then pouring into the mold right away. If I wait too long it cures right in the cup! They say the working time is one minute. I haven't seen it boil over, but it did get pretty warm in one of the larger molds. I had to pour it in stages.

So, this resin that you got does come out a nice dark black? If so, I'll get some and start using it for my bobbins.

It's absolutely black. Looks just like the epoxy.

I've had the best results not using any mold release when casting the urethane in silicone rubber molds. The parts seem to pop out fine without any damage to the molds. Spraying the mold release in there will actually cause the rough surface. With epoxy, however, you need the mold release.

I hadn't been using mold release with the epoxy, and it was working fine. The first pickup I did with the urethane came out fine, but the next one didn't have a great surface because the urethane was sticking to the mold. It left a lot of tiny flecks behind.

What's the best way to clean the molds?

[Bruce Johnson]

I think that the tiny flecks left in the mold mean that the urethane got too hot on that particular pour. I got similar flecks when I had epoxy that overheated. Unfortunately, that mold may be permanently damaged. The flecks are probably tiny bits of urethane that have melted into the surface of the silicone. If you knock them out, there may be little pock marks underneath. You can try some alcohol on a cloth.

I haven't had any problems so far with the urethane overheating in the molds, but all of my parts are less than 3/8" deep and have open tops. I have had the urethane smoke off in a cup. It'll make a nice smelly cloud. About half a small Dixie cup is all you can realistically mix at a time.

For epoxy, I'm using West Systems 105 resin/206 (slow) hardener, which takes 12 or so hours to cure one of my pickups. That mix doesn't have any heating problems, but I've found that it wants to stick to the silicone if I don't use the mold release. The 205 (fast) hardener is too hot for most casting applications. It'll get smoking to dangerous levels! I like the 105/205 mix for attaching parts, because it'll cure in 2-3 hours. For example, I use the 105/205 mix for attaching the ebony caps to the tops of my pickups, which is done after the main casting.

[David Schwab]

I think that the tiny flecks left in the mold mean that the urethane got too hot on that particular pour. I got similar flecks when I had epoxy that overheated. Unfortunately, that mold may be permanently damaged. The flecks are probably tiny bits of urethane that have melted into the surface of the silicone. If you knock them out, there may be little pock marks underneath. You can try some alcohol on a cloth.

I was concerned about that. Alcohol doesn't seem to do anything. That's what I use to clean up epoxy. I've been using some packing tape, sticking it in the mold to remove stuff.

I haven't had any problems so far with the urethane overheating in the molds, but all of my parts are less than 3/8" deep and have open tops. I have had the urethane smoke off in a cup. It'll make a nice smelly cloud. About half a small Dixie cup is all you can realistically mix at a time.

I mixed 100 ml. The last mix I did, most ended up curing in the cup because I really only needed so much of it and I mixed too much. That got really hot, but didn't smoke. I stuck it in the sink and ran some cold water on it for while.

For epoxy, I'm using West Systems 105 resin/206 (slow) hardener, which takes 12 or so hours to cure one of my pickups. That mix doesn't have any heating problems, but I've found that it wants to stick to the silicone if I don't use the mold release. The 205 (fast) hardener is too hot for most casting applications. It'll get smoking to dangerous levels! I like the 105/205 mix for attaching parts, because it'll cure in 2-3 hours. For example, I use the 105/205 mix for attaching the ebony caps to the tops of my pickups, which is done after the main casting.

I've been using the black potting epoxy from AeroMarine Products. That takes 24 hours to cure and doesn't get hot. Before that I was using some potting epoxy from MG Chemicals. That works well but was a lot more expensive.

[David Schwab]

Just for an update.. I used more alcohol.. poured some in the mold, and the mold cleaned right up. Thanks for the tip.

[RedHouse]

...I'd use premade covers if someone made MM covers that were deep enough...

Can you incorporate the existing MM cover into mold process so it occupy's most of the mold area, then when you fill, the fill will fill inside the existing cover and a partial on the outside of the pickup near the base. That area would most likely be covered by the mounting ring or cutout in the body anyway.
(or maybe that's what you are already doing?)

[Marko Ursin]

Well that's what I did. Didn't work too well. I got leaks on the seam and the plastic cover needed a lot of cleaning to look even somewhat usable.
Marko

[jworrellbass]

I was using the alumilte, but now I'm using the areo marine. The AM is a much better product IMO. I also use silicone spray before I pour the resin, it helps with the release. After I remove the pup I wipe it with rubbing alcohol and then use plastic spray paint. The plastic spray paint helps to cover any little marks left from the casting.

[Marko Ursin]

I got the covers for my eight coils done. I use Alumilite. It heats really lot, I'm not going to cast the pickups in this resin. I'm going to use hot glue to join the covers to the pickup.
Marko
http://s631.photobucket.com/albums/u...ickupcover.jpg

[David Schwab]

That looks great!

Yeah, that resin gets really hot. What I now do for molds is to start off the top surface with the urethane resin, and then after the pickup is in place, finish with slow set epoxy.

[Marko Ursin]

And finally mounted on the bass. A headless bass with Moses graphite neck. Tuner/bridge also machined by me.
http://i631.photobucket.com/albums/u...-01/pickup.jpg
Now wondering whether I like it passive or with active tone control. I have on-board schematics for Anderton filter based pre so maybe that's the way to go. Or maybe I wait for Davids filter based pre.
Marko