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MARCH: Tip of the Month

 
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jegner
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Joined: 30 May 2003
Posts: 2144
Location: Texas, USA

PostPosted: Thu Mar 22, 2007 10:27 am    Post subject: MARCH: Tip of the Month Reply with quote

Lots of talk about resins and silicones, so I thought I'd drop my 2 cents in.

Resin, there are a couple of options, but currently, my favorite is Smooth-on's SmoothCast 320 in an off white, and if I want to cast dyed color parts, the SmoothCast Color Match 325.

Both are available here: http://www.smoothonsecure.com/store/index.php?cPath=291_1_10&osCsid=4855cbeb4e4f0895eef2628ac70fd12f

As for the mold materials, there are several options, but for me, I like PlaSil 71-20 from http://www.bare-metal.com/polytek/platsil.html This is a 1:1 ratio silicone for easy measuring. Most silicone rubbers are 10:1 and require a gram scale to measure correctly. Yikes!

There are others, and I know Tony uses a more affordable silicone, but I don't know that brand. I think he gets his from ebay. And from the castings I have seen of his, they look great!

Stay away from ureathane base mold materials. That stuff is far less a mold material than silicone, requires a liberal application of mold release, and stinks to high-heaven.

Jim
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Stomper
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Joined: 01 Oct 2005
Posts: 473
Location: Woodburn, Oregon USA

PostPosted: Mon Mar 26, 2007 3:42 pm    Post subject: Reply with quote

LOL... here I was all set to post a tip and you posted this great stuff! Let me add to this since Jim is basically addressing two pertinent topics... resin and silicon for mold making and casting:

I was having issues while pouring black tinted SmoothCast 325 resin and getting a whitish swirling or "marbling' in the color that was NOT acceptable because these pieces were not going to get painted and I needed perfect color. I was going nuts trying to figure out what I was doing wrong... I'd stir the tint and B-part resin VERY thoroughly, then I'd stir the A-part and tinted B-part together for as long as possible before it would start setting up and become useless... same thing getting that white swirling through the blackness.

I was looking real close at my silicon molds to see if there was a residue or something that was causing this and I noticed that my breath was forming condensation on the mold!! (Not because it was bad-breath, but because it was warm, and the silicon was cold as my shop is not climate controlled... ATM) It dawned on me that as the resin is reacting and setting up it gets pretty warm... DUH!! The molds were getting condensation inside them as the resin was curing and the moisture was causing the swirling in the nice black finish I was going for!! Moral of the story... warm up your molds if they are cold! I soak mine in hot water for a little while then dry them off before I make any more casts!

Here's a photo showing that marbling:


Jim is also correct, I get my silicon from a guy off eBay. Its a 10:1 ratio by weight (not volume), but since I have an electronic scale for measuring refrigerants, it does metric (grams) and imperial (pounds, Oz's.) and is not an issue for me. I can buy a gallon of the stuff and it costs $103.00 shipped. The Plat-Sil Jim uses IS terrific stuff, but a mold I made of an M38 scope basically cost me $50 using the Plat-Sil silicon to make!! If you have a scale (preferably and electronic one) I recommend you use the stuff I get, if you don't have a scale take Jim's advice on the Plat-Sil... its top-notch!

The guy I buy my stuff from is an eBay merchant, his name is John and he goes by "aeromarine" on eBay. He sells a 1/2 gallon 1:1 ratio silicon that I have used with excellent results as well!

Here's the link to his eBay store for those interested in getting into this aspect of the hobby: http://stores.ebay.com/AeroMarine-Products

Here are a few photos of parts I have cranked out to give you an idea of what you can produce:







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jegner
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Joined: 30 May 2003
Posts: 2144
Location: Texas, USA

PostPosted: Tue Mar 27, 2007 7:21 am    Post subject: Reply with quote

Thanks for the additional info, Tony!

Any suggestions on a scale for measuring silicone?
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Stomper
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Joined: 01 Oct 2005
Posts: 473
Location: Woodburn, Oregon USA

PostPosted: Tue Mar 27, 2007 8:04 am    Post subject: Reply with quote

Hey Jim,

I recommend an electronic "refrigerant charging/metering" scale as they typically have up to a 200-lbs. capacity... although I seriously doubt any of use would attempt to mix that much silicon or resin on one shot, at least you CAN if you ever had too!! LOL


Here's a few links from eBay that show reasonably priced scales that are IMHO ideal for what we do:

http://cgi.ebay.com/TIF-Electronic-Refrigerant-Charging-Scale-TIF9010A-New_W0QQitemZ110106169487QQcategoryZ66997QQrdZ1QQcmdZViewItem

http://cgi.ebay.com/TIF-9010A-ELECTRONIC-REFRIGERANT-RECHARGING-SCALE_W0QQitemZ260099798210QQcategoryZ109756QQrdZ1QQcmdZViewItem

http://cgi.ebay.com/9010A-Electronic-Refrigerant-Scale_W0QQitemZ170094413758QQcategoryZ11814QQrdZ1QQcmdZViewItem

http://item.express.ebay.com/FJC-Pro-Charge-Electronic-Refrigerant-Scale_W0QQitemZ270102045450QQihZ017QQtrZexpQQcmdZExpressItem

http://cgi.ebay.com/ebaymotors/Pittstop-Electronic-Refrigerant-Scale_W0QQcmdZViewItemQQcategoryZ35625QQitemZ130093238394QQrdZ1

http://cgi.ebay.com/ELECTRONIC-SLIMLINE-CHARGING-METER-SCALE-9010A-R62529_W0QQitemZ250097750142QQcategoryZ66997QQrdZ1QQcmdZViewItem
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