exxos's Atari, Amiga & retro forum

alexh wrote: 24 Mar 2023 11:40 Out of curiosity... how do you intend to remove the cast marks after it has been made?

I am not sure it is achievable without some sort of mechanical ball sanding machine?

Molds like these tend to leave either a line around the circumference or a burr at the point the liquid is poured in.

TBH it is more for experimentation as I am also considering alternative methods of making moulds that are potentially more like those 2 part types used for casting metal components. The RTV I used to create the additional mould is actually not hugely robust and I don't think it'll last more than a few uses. I have more I can use, but I'd rather create something more robust from the get go if I can.

I just want to see what the overall result looks like and at that price the risk is very low. I'm considering that it may be possible to seal the seams before casting to reduce the amount of flash that is seen there, but I'd like to test it first, see how bad it is.

I think that probably it might be good enough to carefully hand sand the seam, I just don't know, all I'm looking for at the moment are possibilities as it seems the balls for these mice are problematic, and a new mouse from CJE (They have new old stock) is £89. I think some experimentation is worthwhile to see what can be done.

It has got my creative juices flowing at least as I really would like to come up with a solution of sorts.

So I used a syringe needle pushed into the RTV mould near to the top to allow air out and did a new pour.

I then used the syringe to create a vacuum to be sure that the mould was full, also taking more care to pour the resin definitely improved the way the mould filled. The sprue is full and did move when I applied the vacuum :)

It looks good so far, I guess we'll know in 24 hrs!

Let us know.

HigashiJun wrote: 24 Mar 2023 22:52 Let us know.

I certainly will :)

OK, so it actually worked this time.


However there may be a problem even before I trim off the sprue, and that is weight.
Turns out that what I've made weighs less than the Delrin ball that was too light in the first place.

I'll trim it up and try it, but I don't think it'll work. I need to find a denser material so the weight falls between the Delrin ball and the steel ball.

Suspend a smaller steel ball inside the mould and fill with resin next?

stephen_usher wrote: 25 Mar 2023 11:55 Suspend a smaller steel ball inside the mould and fill with resin next?

Definitely something I've been considering trying.

It doesn't work, as I thought.

Is there a denser resin that would make a mouse ball having a weight close to a real mouse ball ?

Resins are just plastics, they're not heavy. You have to have them contain something very dense inside. Some sort of self-curing latex may work, but I have no idea what, if anything, is available.

stephen_usher wrote: 25 Mar 2023 13:34 Resins are just plastics, they're not heavy. You have to have them contain something very dense inside. Some sort of self-curing latex may work, but I have no idea what, if anything, is available.

P.S. Have you tried cheap boucey balls and sanded off the moulding ridge? They are reasonably dense, very grippy and dead cheap.