landman Posted October 30, 2015 Posted October 30, 2015 I'd like to duplicate this transmission along with the 4-speed which goes with it. Am I better to glue the two halves together and make a two part mold or try and cast each half separately?
Ace-Garageguy Posted October 30, 2015 Posted October 30, 2015 It'll be a lot easier your first time to do two molds of the separate halves.Making a two-part mold gets into alignment, mold-filling and possibly air-bubble issues you're better off dealing with AFTER you have some experience with the basic materials.
Mike Kucaba Posted October 30, 2015 Posted October 30, 2015 If you cast these parts as they are you would not need a 2 Part mold. You could also glue and refine the unit and do a 1 piece mold,but the RTV should be VERY flexible. You may get only a few copies.
Kit Basher Posted October 30, 2015 Posted October 30, 2015 If you fill the inside with modelling clay and stick them down to a flat surface, you could pour RTV over them and make a one part mold. The parts you cast would then be solid, not hollow, and you might have to sand the mating surfaces flat. I've heard that you need to put a flat cap on the mold after you pour in the resin or the resin won't cure properly. If you want them hollow you will have to leave them apart and make a two part mold.
landman Posted October 31, 2015 Author Posted October 31, 2015 If you fill the inside with modelling clay and stick them down to a flat surface, you could pour RTV over them and make a one part mold. The parts you cast would then be solid, not hollow, and you might have to sand the mating surfaces flat. I've heard that you need to put a flat cap on the mold after you pour in the resin or the resin won't cure properly. If you want them hollow you will have to leave them apart and make a two part mold.Hugh, that was my original intent but the seam line isn't straight, so that complcates things quite a bit. I've looked at several videos and I will go the two part mold with the two halves glued together.
Kit Basher Posted October 31, 2015 Posted October 31, 2015 Hugh, that was my original intent but the seam line isn't straight, so that complcates things quite a bit. I've looked at several videos and I will go the two part mold with the two halves glued together.That makes sense to me.
landman Posted October 31, 2015 Author Posted October 31, 2015 Now the Million dollar question: How do I figure out the amount of resin/urethane to mix?
Art Anderson Posted November 2, 2015 Posted November 2, 2015 If you fill the inside with modelling clay and stick them down to a flat surface, you could pour RTV over them and make a one part mold. The parts you cast would then be solid, not hollow, and you might have to sand the mating surfaces flat. I've heard that you need to put a flat cap on the mold after you pour in the resin or the resin won't cure properly. If you want them hollow you will have to leave them apart and make a two part mold.A much better way of doing this would be to glue the halves, mating edge down, onto a piece of thick sheet styrene, at least .080" thick. Then build up a mold box from either sheet styrene or even Lego's, deep enough to allow for at least 1/4" of RTV between the highest point of the pieces being molded, and what will become the bottom of the resulting molds (when placed on your bench for pouring), and at least 1/4" on all sides between the sides and ends of the "masters". Next, make another mold box the same length and width, but with just the smooth sheet styrene surface in the bottom of it, and the sides of the box at least 1/2" high.Pour rubber into all three mold boxes (right side of the transmission master, left side of the transmission master, and the plain box, filling each of the mold boxes full, but not spilling over. Once cured, remove the plain rubber block, and pour a second one, same as the first.Once these are all cured, and you've removed the masters from them you can pour resin into each of the molds for the transmission halves, allowing excess resin to flow over the tops of those molds; and gently press the smooth "blocs" (with their precisely flat sides down!) on top of the cavity molds--pressing the smooth blocks down AROUND THE EDGES ONLY (don't just press them in place in the middle of the mold, as they will tend to spring back flat, sucking air into what will be the mating surfaces of your transmission halves.Once the resin is cured, simply remove the castings, and take the flashing off around the edges--with a bit of practice on this, you should have almost micro-thin flash that will simply tear away, and two halves of a transmission that will fit tightly together with no sanding or filing needed to make them mate cleanly!I did this for years with such parts, so I know it works!Art Anderson (formerly All American Models)
landman Posted November 5, 2015 Author Posted November 5, 2015 watched several videos then started by making a clay bed and imbedding the transmission. Then mixed & poured the mold stuff. Supposed to cure in 16 hours.Now about 18 & still not gelled.
landman Posted November 6, 2015 Author Posted November 6, 2015 Dumped it this morning. While it had congealed somewhat there was abviously something very wromg with it. Will have to start again.
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