ways of making a bobbin

[R.G.]

I was just at a hobby shop and saw some stuff called "Alumilite" casting gook.

There is a pourable silicone rubber for making molds, release agents, and various filled and unfilled catalyzed casting resins.

They showed an example of making a copy of a formed-polystyrene car body by making a two-part mold with the mold making gook, then filling the mold with the casting resin. It worked beautifully in the illustration, of course. But it might, with some practice, be usable for duplicating an existing bobbin.

[David Schwab]

That's basically the route I'm going with my pickups, instead of using covers.

I'm thinking about trying to make bobbins that way too.

The guy I work with was a model maker, so we have the whole vacuum chamber setup, but for bobbin you might not need that.

Right now I cut out the flatwork by hand, and then mill a slot in each for a blade, and epoxy the thing together. It time consuming to say the least.

[jonson]

David nothing wrong with going down that route at all I do lot of molding in silicone but reading previous posts you state you use epoxy for casting and it is best to stay that way. I think I've said before makesure you use an addition cure silicone and not a moisture cure one. Spent alot of time doing Knobs in polyester resin (allways comes out tacky) youv'e got to sand and polish it or coat it with 2 pack lacquer and polish it, and polyurethane resins com out dry but are to soft for the job and take too long to cure. You will probably need a 2 part mold for bobbins and still do some drilling but worth while in the end. Loads of info on mold making on the net and if you are stuck give me a shout and if there is anything I can help with then I will do.

[R.G.]

Polyester resin comes out tacky because of exposure to air. I can't remember if it's the moisture or oxygen that causes the tackiness.

The same people who sell the casting resins sell coatings to seal out air. Polyvinyl alcohol is one of them, I think. From experience, casting polyester with a top covering to seal out air results in a non-tacky surface, given that everything else is correct.

[R.G.]

There is a marine product called "Getz-Rot" that is an epoxy that is water-thin when catalyzed. It's used to soak into partially rotted wood in marine environments, hence the name. I suspect it would infiltrate a wound coil just dandy.

[R.G.]

Polymer clays.

[jonson]

It's oxygen mostly but lots of other factors come in as well. I even resorted to spraying nitrogen into the vacume chamber to stop it but it's all a pain in the arse compared to epoxy so still best route to go.