| Brood Brother |
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Joined: Thu Oct 20, 2005 6:32 pm
Posts: 6414
Location: Allentown, Pennsylvania USA
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Howdy folks,
I know there are a few of us who make molds and cast their own stuff. ?To the veterans some of this information may be old, but to the rest who are thinking about casting things, here are a few tips I got from the folks at Smooth-On. ?I showed them the scale of the models we were working with and some of the sticky 'resin dregs' as they have been called lately.
Resin Dregs: while there are times that they can have a bad batch of resin, for the most part the sticky resin is not a result of bad resin but bad pouring.
Most of us are working in very small scales and we are pouring only one mold - somthing that has a volume of about a quarter of an ounce or less. ?Despite the fact that you may be measuring accurately, the 1:1 ratio will immediately be off as soon as you pour it from one cup to the next. ?For the Smooth-On 300 product, for example, Part A is more viscous than Part B, so if you are pouring Part A into Part B you are going to have some liquid still on the bottom and edges of the cup. ?While this amount is nominal when mixing 8 ounces or more, it is a significant percentage of your volume at such small amounts. ?In fact your mixing ratio could be off by as much as 1/3, something that would certainly ruin your cast (and potentially your mold).
Solutions:
Shake Parts A and B very well. ?Not the typical 5 second shake but shake it and turn it for a good 20-30 seconds for each bottle.
Thoroughly scrape the mixing containers.
Pour from one cup to the next to catch all the goodies.
Mix larger volumes (pouring several molds at once).
At extremely small volumes mix your resin by weight, not volume (ratio is 10:9 is memory serves me, but check your instructions).
For cleaning sticky molds, try freezing the mold and sticky resin first.
Also, make sure you are mixing your molds properly. You should not see any striations along your mold. ?The Oomoo 30? doesn't set immediately, so you should have more than enough time to thoroughly mix the parts.
The product they recommended that I use with is the Smooth-On 300. ?There is a 300Q that sets very quickly, but I don't believe you'd have time to shake the bubbles out fast enough and they said it doesn't provide any other benefit of strength, just time. ?If you have a model with a lot of details and places for air bubbles to get trapped, then go with the 300.
Epic Scale: they were saying tha this scale is going to be difficult to get consistent results from just by the nature of pouring molds. ?They made the recommendation that -if I had the means- to get a pressurized container and do make two part molds. ?This has the benefit of 'smashing' the bubbles and pushing the resin into all the little crevasses. ?However, these were some pointers that came with the idea:
1. If you are going to make pressure casts, make pressure molds.
2. Cost of the pressurizer will only be around $50, but the compressor is costly
3. Pressure needs to be up around 60-80psi.
They are going to give me some more information on a company here in Allentown that makes these things (you're on your own for the compressor). ?
Overall, I found them to be friendly, helpful people. ?Scott was the technician I mainly spoke with and you can actually talk to him by calling their tech support line. ?They gave me a free set of 300 for my troubles and then ran out to their cars to shut the windows when the lightning and thunder started. ?Poof they were gone! (like Kaiser Sose).
Hope this helps your folks. ?I am going to try out some of these basic changes this weekend and I'll report back.
_________________ author of Syncing Forward and other stories...It's a dog-eat-dog world, and I've got my Milkbone underwear on.
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