Post by hypoponera on Sept 5, 2019 13:52:06 GMT -5
I have used Alumilite for many years with mostly good results. But I have never been really good with it. The provided RTV rubber works great with no real trouble. The resin however...
I do find the standard resin in the sets to be too quick. You have to mix the 2 part resin very well and pour into the mold then remove air bubbles. All within about 3 mins. I am just not that fast most days!
I have found that Micro-Mark CR-600 is much easier to work with. While the directions says it begins to harden in about 2 mins, it really takes more like 10 mins in my experience. That gives far more time to mix, pour, and remove air bubbles. Parts can then be removed from the mold in 30-60 mins.
Micro-Mark does sell another 2 part resin that has even longer working time. But it takes even longer to demold.
Post by hypoponera on Sept 5, 2019 15:57:13 GMT -5
I don't think the CO2 would be of much value. Most of the resin would be covered by the rubber mold with very little surface area exposed. Most bubbles in the resin comes from being too rough when mixing... which gets back to needing greater working time.
Post by NickelPlate on Nov 26, 2019 0:08:00 GMT -5
When I was a model maker we had the fast cure resin -- which seems to be what is in these kits -- and the slow cure, which took many hours. The slow stuff was better for picking up fine details or for thin walled, complicated parts, but also required the premium platinum rubber, as opposed to the tin stuff we worked with most of the time. The slow cure urethane would come out with an unusable gummy surface if cast in a tin silicone rubber mold, particularly when the mold was new. I'm not sure if the technology has advanced much in the last 15 years, but from all I've read it's much the same.
I know many model makers just set the tub of rubber on a running belt sander, for e.g., and let the vibrations work out the bubbles before pouring the mold.
Speed was of the essence on the job, so we worked with the fast cure 4 hour tin rubber and fast resin most of the time. We had a vacuum chamber and pump for degassing the rubber before pouring, and pressure tanks in 3 different sizes for casting parts. So it was a matter of quickly mixing the resin, pouring it or injecting it into the mold, then throwing it into a pressure tank, slamming on the cover, and attaching the hose from the compressor to squeeze out the bubbles. That's how we did it in an industrial setting, anyway.
For boiler fronts you really should make a 2 piece mold to properly cast both sides, and set it up so the boiler front is face down so that any bubbles will be in the back of the casting.
If you're casting fronts for the Pacific & Mikado, you'll have to remove the bell because that's going to trap it in the mold, unless you want to attempt making the edge of the bell and bracket part of the parting line for the mold.
2 other tips I've heard for getting bubbles out is banging the table or setting the filled mold on top of a running washing machine.
Yep, any sort of vibration helps the rubber outgas. It's not as thorough as a vacuum chamber, though, which basically makes the rubber boil (the bucket will overflow if you aren't watching carefully and regulating the suction valve) until the head on it finally breaks and it's ready for pouring.
frankenstein: I'm worried about wks now..
Feb 21, 2020 17:52:37 GMT -5
wks: Be afraid. Be very afraid.😜🤪😺😀😆
Feb 21, 2020 23:04:38 GMT -5
wks: Some names to be painted:
Feb 21, 2020 23:06:30 GMT -5
wks: Ohio Fe Railroad
Feb 21, 2020 23:06:49 GMT -5
wks: Penntrak Railroad
Feb 21, 2020 23:07:33 GMT -5
wks: Santa Burlington Railroad🎅
Feb 21, 2020 23:09:00 GMT -5
wks: Penn Baltimore Railroad
Feb 21, 2020 23:12:00 GMT -5
wks: Contrak Railroad
Feb 21, 2020 23:12:37 GMT -5
wks: Probably more but have to go to bed for work tomorrow☹️
Feb 21, 2020 23:15:51 GMT -5
oldtimer52: How about "Santa Pee" Railroad??
Feb 22, 2020 1:11:00 GMT -5
The Jade Fog, formerly: Dave: I hear TK is boogieing up to Allentown already. I’ll be heading out soon. Flamingo tote IS riding shotgun! For practice I went to an antiques mall yesterday to hone my visual acuity to spot deals from 15 yards or more. Hello Allentown!
Feb 22, 2020 8:49:03 GMT -5
wks: See if they have any Penn Fe equipment there for your collection Dave.
Feb 22, 2020 13:29:43 GMT -5