Just a little update today; I started the preparations for getting some of the parts resin cast.
I made up some MDF boxes with the mitre-saw and nail gun, and embedded the engine and landing gear half way in plasticine.
These will be the first 2 part molds I have made so I'm a bit unsure. But i've VERY (emphasis on VERY) carefully embedded them half way so I can pour the RTV on top and then remove the plasticine to pour the other half. I'll cut breather holes and pouring holes after the RTV is cured.
I was surprised how difficult this process was - its taken me a good couple of hours to get the plasticine smooth and tight to the components ensuring it is in all the detail.
These are the two compionents I'm most worried about, especially the landing gear as it has a few nooks and crannies. The tail plane is smooth and simple so that's OK, and the engine mounts only require a single sided mold.
RTV should be mixed and poured tomorrow, then real life calls, so I'll be unable to do any more until Wednesday next week.
I'm not a professional but have done a bit of home casting, and I am worried that you are setting yourself up with a couple of problems, here.
First, if you have any lego it is the best thing for making boxes for casting; you can make it just to the right size, but, more importantly, you may find it easier to remove the mould halves from the box- your boxes look very stoutly constructed and may prove difficult to work with.
You should dig 2-3 holes in the plastacine so that you have knobs in the first part of the mould you are making; later this will help the two halves locate when you are casting.
You also need a well to pour the resin into, I'd put this on the left of the 2 moulds. The foot will be tricky to cast; you might want to think about using low melt metal). Build up the plastacine here, in a half cone shape; it'll save you having to cut the rubber away, later.
Lastly, later on you'll want to spray with something like a mould release compund to help stop the second lot of rubber sticking to the first half of the rubber you have cast previously. Perhaps a v. light coat of oil would be a substitute.
Bubbles in the RTV can be a problem; I have heard it said that if you put your mould on a washing machine it can shake them out.
Drop me a line if you need advice!
simon.miller ( at ) lineone.net
HI BigRedBat(Simon) - Thanks for your comments.ReplyDelete
I'm Ok with the box xonstruction as they're only held together with a couple of pins so can be pulled apart.
I haven't finished plasticine so haven't dug out the alignment holes yet.... :)
Pouring holes and vent holes - as I said in the blog post I was planning on cutting them from the RTV. I may try one mold with them modeled in plasticine as you suggest and another cutting the rtv, and see which works best.
I have a spray of mold release and a handy tub of vaseline waiting too.
I'm planning on using my domestic vacuum cleaner to help degass the RTV before I pour it (more on this in future posts) but I hadn't thought about a washing machine!
It may be worth making the pouring holes now in plastacine, will save you a little RTV. As you say vents can be cut later. I also used to make a little well under the piece (for metal castings), which the vents came off. I never cast in resin, mind you.
Good luck with the moulds! There is something truly fulfilling about the casting process.