There was a recent post on the sculpting list showing how a professional makes a spincast master mold. I found this to be extremely informative and helpful, seeing as how I have recently purchased a vulcanizer, and am about to sit down to make my first vulcanized rubber mold! I thought it also might be helpful for me to document this process, so that the pros can see what a beginner makes of their good advice. Also, so that they may comment on the various stages of the process and tell me what I am doing right, and what I might need to do better, different, or not at all. If the mold I am attempting to make today works, I will feel happy, smart, and vindicated in my decision to purchase this equipment. If not, well, there is a learning curve, I’m sure.
I have been spincasting for a couple years now, but to date all of my molds have been made for me. Jeff Acker of Ackertech Castings has done all my mold-making, and has also been a font of knowledge on topics ranging from moldmaking and casting to Battlestar Galactica. Much of what I am doing here is based on advice Jeff gave me, at least as I remember it. I also gained some insight from the recent “How I make a Master Mold” article on themouldmaker.com. Further knowledge has been gleaned from the yahoo lists 1listsculpting and casting, and from Philip Romanoff’s extremely hard-to-read book, “The Art and Science of Centrifugal Casting.”
Step One: The Work
For my first mold, I am going to be trying a bunch of metal pieces I have lying around, with the hope that they’ll be easier, or at least if I mess up I won’t have to worry about ruining them. The items seen in PIC #1 include:
Step Two: The Materials
I will be making today’s mold from a set of Contenti 700 series rubber, shown in PIC #2. The first thing I attempted to do was pop out the little center hole on the top piece. It didn’t come out real clean, and left lots of stringy rubber behind (PIC #3). I guess I should clean that up, so it’s time to move on to:
Step Three: The Tools
My initial selection of tools includes a couple knives, with Swan Morton #10 blades, a ruler, a cutting board, and some router blades (PIC #4). If I need anything else, I’ll take pictures of the new tools I bring in as I go.
Step Four: Let’s Play!
I’d like to get a feel for how the rubber cuts, delaminates, and tools in general, so I’m going to play for a bit on the little center plug. Once I’ve got that down, I’m going to try to clean up the mess I made in the center hole of the top disk.
Okay, success I guess. The material sure is a bit gummier/stickier/stringier than I expected. I think I’m getting the hang of it, but it will take some getting used to. Time to move on to the serious mold-making.
Step Five: Preparing the Mold Halves
The first thing I’m supposed to do is cut a couple big notches into the rubber to help me align the two mold halves while I’m working on them, so that’s what I do. Jeff has some big scissors that work real good for this apparently, but I don’t, so I just use my knife. Theoretically, these notches will fill back in when the rubber starts to flow when vulcanizing. Neat. I’m even supposed to cut out a couple more after I get everything else done.
Next, I will make a place for my central core to sit. Right now, I don’t have steel core, just one a made from pewter from one of the empty center spaces in one of Jeff’s molds. Since it is just pewter, and I don’t want it to deform under the pressure, I’m going to cut in a space for it. I measure to get it centered, then trace around it with the tip of a file to mark it in the rubber (see another tool! I knew I’d need more!).
I cut through the first two layers and peel them up without any problem. I decide to go down one more, but accidentally start to peal up two. D’oh! I managed to correct myself a little bit into the circle, and just kind of shoved and poked the extra peeled up bit back down onto the mold. I hope that’s okay. :/
Now to cut one layer out of the top. I place the core into the hole I cut…fits great. Then I put the top piece on, and align it using the notches I cut earlier. I then carefully flip the whole thing over, and remove the bottom piece…leaving the core sitting on the top part of the mold in the exact spot it needs to be. PIC #8. I trace it and cut out one layer as before.
Step Six: Placing the Pieces and Planning
Leaving the core in place on the bottom half, I now place all of my bits around it, and decide how they will be gated and vented. I mostly do all this in my head, but for your benefit I may go back and photoshop on my initital thoughts onto PIC #9.
Looks like the 4” diameter core I made was a bit too big for some of the pieces I chose, so Kned and the scorpion have to be tilted at more of an angle than I’d prefer. I have set them up pointed opposite the rotation of my spincaster, so the cavity will still go in the right direction for the metal flow…hopefully. We’ll see. Also, I didn’t want to get too crowded on the mold in case I need to cut more air vents, etc., so I leave off a couple of my initial choices. I leave out one of the gaming tokens, because 1 is plenty, and I leave out the boar, because his leg positions really make me think I will need to build up one side of the mold to make them work right, and Jeff suggested I stay away from build-ups on first time out (which seems very sensible—there are enough other things that can go wrong already). Oops, I also left out the Cyclon, because he fell on the floor and I forgot about him. Oh, well, some other time, toaster!
Step Seven: Cutting the Cavities
Now I trace out all the minis in the positions I’ve decided on (again using the tip of the file to ‘draw’ on the rubber—that works very well), and start to cut out the cavities in the bottom half of the mold. This will surely take some practice, so I’m going to start on the easy ones, and work my way around to the trickier pieces.
Okay, that’s done! Whew! Above is a pic of what the bottom mold half looks like with the figures in place. The material did in fact take some getting used to. Also, despite my best wishes, I did need to do a little build-up around the mephit’s ‘wings’. Hope it works okay.
Step Eight: The Top Half
Now to make the cavity holes on the top half of the mold. I’m a little foggy on this…it seems from the mouldmaker.com article that I could just press the mold now as is, without cutting top cavities, and just letting the heat and pressure do the work. On the other hand, maybe he just skipped showing me that step. Jeff says he does cut the top cavities as well, so that’s what I’m going to do today.
I will take the pieces and insert them into the mold bottom one at a time. With one piece in place, I will then place the top mold half into position, and then carefully flip the mold over. I will then remove the bottom mold half (now on top), and the piece should be sitting on the top half in the position I need it to be in (just like with the center core). I’ll cut out what I think needs cuttin’, and then fit the mold back together with piece inside to test it. Here goes!
IWell, that kind of worked. I think it’s good. Some of the flatter pieces didn’t get cut-outs on the top; I really don’t think they’ll need ‘em. There is one issue, though. The scorpion…I think he needs some build up around his little feet:
Therefore, I’m going to have to try using the lighter fluid as a solvent, and then sticking more rubber there in the proper shape. (I didn’t use the lighter fluid on the build up around the mephit, because I had already peeled up all the rubber in those little areas, and was working with only gooey stuff to gooey stuff. I think that will be okay, but if it doesn’t work, well the mephit I don’t care too much about. The scorpion I would really like to see turn out.). This means I’m going to have to go get some lighter fluid.
Okay, I went out to the store and got some of this stuff. It has Naptha in it, which is as I understand it, the solvent needed to make the rubber really stick to itself. You apply it to both pieces and it dissolves the rubber a little bit, and you can then stick the two pieces together, and they’ll stay.
As you can see here, I tried it. And boy, howdy, it works. Good. I even managed to make not too big a mess of myself or my tools (because it also cleans up the black gunk it makes real good). I also managed to spill a little bit of it on the mold there, but managed to get it cleaned up, I think. Hope that doesn’t do anything bad…
Step Nine: Final Preassembly Steps
Now that all the pieces are cut in, I screw several locknuts in place, and cut a couple more little notches in the side.
Step 10: Talc the Mold
For this step I am using a talc bag which I made out of a bandana. I used liquid stitch (wonderful stuff) to make it into a rectangular bag, and affixed some Velcro to be able to open it and seal it back up. I have filled it up with some Mica Powder, which is apparently a really fine grade of separator, finer than traditional talc. I take all the minis out of the mold, bang it with the talc bag, and then put the minis back. I blow off any excess.
Not shown here is the little metal plug for the top hole of the mold. I made it the same way I made my metal core. Basically, I set one my Jeff-made molds top down onto the concrete floor, just the top part of it, and then poured metal into the top hole. I let it cool, and viola! Instant plug. I had to do it a couple times to get it at exactly the right height. I talc that too, and insert it into the hole in the mold top.
Lastly, I place both mold pieces together, aligning them the best I can (the mold lock nuts now get in the way a little bit), and manually squishing it down as good as I can.
Step 11: Preheat the Mold Frame
Next, I slide the mold frame into position in the vulcanizer, and work the pump by hand until it is closed. Then I insert the rod and give it a couple pumps, to get it up to about 1000 lbs of pressure. It doesn’t take as much work as I’d have thought to get it there. I watch the mold frame very closely as I am doing this to make sure the top part is sinking down into the ring like it is supposed to. It does, so everything appears to be seated correctly. I let it warm up at this pressure for 3 minutes before applying any more pressure.
Step 14: Now We’re Cookin’!
Jeff says 90 minutes at 310 degrees at 2500 pounds of pressure will do the job, so that’s what I do! Or, I should say, that’s what I attempt to do…
My first issue is that it took WAY less work to pressure up the jack than I thought it would. I was imagining just having to pump and pump to get to that kind of pressure (it sounds like a lot), but that turned out not to be the case. I gave it two good pumps, and overshot the mark…a lot. I ended up at nearly 4000 pounds. I didn’t know what to do about that, so I just left it.
I was working out in the garage doing some casting while it cooked, so I could kind of keep an eye on it. Twice during the process, once at about 45 minutes and again at about 65 minutes, the guage lost some pressure. It dropped down to about 2000 lbs both times. I didn’t know if that was good or bad, so I pumped it back up both times, thinking consistency was probably best.
Step 15: ‘DeCanning’ the Mold
Ninety minutes later, I take the mold frame out of the vulcanizer (again with the heat resistant gloves on! As expected, it is reluctant to just come gleefully apart, and I must use screwdrivers, a hammer, and a good bit of force to pry off the lids and get my mold out. It comes out alright though, and with less fighting than I could have imagined, and my first thought is that it looks like it might have worked!
Step 16: Demolding the Masters
I take my new mold back up to the studio, and carefully pry out my masters. They pretty much come out okay. The mephit breaks a little bit, and some of the rubber had melted around one of his ‘wings’. I cut a slit into it with the knife, and he comes out fine. My scorpion, Spliffy, also had some minor damage. He delaminated from the penny he was sculpted onto, and one of his little legs broke. Some of the filigree pattern in the pendant also stayed in the mold, and had to be scraped out. All the metal pieces were, unsurprisingly, just fine.
Step 17: Cutting Gates and Vents
Using the surgical blades again, I cut in some gates from the core to take metal to the figures, and some vents to take displaced air from the figures and out of the mold. I’ve seen how Jeff makes his, so I’m pretty sure how I want them to go, but I haven’t had quite as much practice, so mine aren’t nearly as pretty as his. Should work okay, though, I think. There is also a bunch of ‘flash’ and junk around the outer edges of the mold, and around the top hole, and I trim that stuff away too. Now it looks all nice and shiny!
Step 18: Let’s try it!
Back down to the garage! I talc the mold (using regular talc this time, but in the same type of bag as I described for my Mica bag) and put it in the spincaster. I am spinning at around 500 rpms (the only speed my used spincaster reliably operates at…I never mess with the speed setting anymore), and put the mold under about 23 lbs of pressure.
Here’s the result of the first pour. Several of the pieces that I thought would be easy didn’t come out at all, and all the ones I thought would be difficult came out flawless. I probably didn’t just cut the gates big enough, though, and maybe one or two more vents wouldn’t hurt either. I take out the knife and make a few little adjustments, and then try it again.
Step Nineteen: Success!
Woo-hoo! I’ve done it. The second spin and every piece comes out perfectly! Oh, I think I am going to LIKE this!!!
Step 20: Feedback
Okay, now that I’ve done it, here’s where I need your help! All you experienced moldmakers out there, please email me your thoughts, opinions and advice! Anyone else out there trying to get started, thinking about it, or just curious about the process, please send your questions!
What I learned to do here was not easy knowledge to come by…would have been darn near impossible without Jeff! (Thanks Jeff!) Let’s all try to make it easier for the next guy (and help finish my education!!!)!!!