I wanted to make my final model thicker than the bottle so that it can be hollow and perhaps accomodate my grymn troops within the interior with a fold down rear door, or maybe side openings for door gunners. So I cast the bottle in two halves, each half more than half the thickness of the bottle (it makes sense to me!).
You can see from the pictures above that I have problems with air bubbles - these are in the rubber mould itself and not the resin, so I have to take more care with that in the future.
My intent is to detail two halves of the resin casting, add swivel engines to the sides and a front cockpit section where the bottle neck is, add a rear door, and then make a mould for the complete model so that I can cast a number of them. Who knows, I may even put a few on ebay and see if they sell!
Hi Brandlin,
ReplyDeleteRe: Your air bubble problems. I tried to leave as much detail from my casting endeavours on the FoD on your thread but I may have missed some, I gleaned my stuff from so many different sources it was hard to keep track of what I'd told you. So I thought I'd ask (for your future reference) did you vibrate/tap your silicon as it was setting and did you give your bottle a good dusting of talc? Both are supposed to reduce air bubbles sticking to the surface of the form you're moulding. Tapping and talc on your mould also reduce bubbles in the resin too, although the speed the TOMPS stuff sets tapping may be a bit of a waste of time. I do it anyway :)
Caerban
It looks like you suspended the bottle above the frame then poured RTV rubber in to fill it from underneath. That's how the bubbles showed up, they couldn't slide across the bottle easily so they stayed in place.
ReplyDeletePouring the rubber over the master usually works better. There are a couple ways to get the results you were after here. One, cut the bottle in half and glue the half you want to keep to the bottom of your frame. Two, cut a piece of plastic to fit tightly around the bottle where you want the edge of the mold to be, fill the gaps with clay, and put the bottle + plastic shield in the bottom of the frame. Three, embed the bottle in clay to the place where you want the mold edge to be and put the frame together around that.
Once you've done one of those three, mix and pour your RTV into a corner of the mold. Any bubbles will be able to rise to the surface, away from the master, rather than rising up against it and getting stuck. You'll still want to shake it a bit to make sure any bubbles that got trapped against the master during the pour come loose.
Of course, since this is just the beginning of a larger building project, it shouldn't be hard to sand and fill the bumps.
Bill - THANK YOU. what you said makes so much sence i just had a little Doh! moment.
ReplyDeleteYou are right, i suspended the bottle so that i could get (slightly more than) a half bottle cast without having to take one of the options you suggest. I never thought of trapping the air that way! I had thought of cutting the bottle, but its pretty flimsy plastic and wouldn't have any strength when cut.
You live and learn.
This is truly a great read for me. I have bookmarked it and I am looking forward to reading new articles. Keep up the good work!. tarief taxi
ReplyDelete