longmc Posted February 29, 2008 Share Posted February 29, 2008 I've started molding and casting my own parts. It's worked pretty well except for fine detail items like antennas, etc. I'm getting tiny airbubbles trapped inside the mold and can't get them out. I've tried tapping the mold, and running a wire down to try and "stir" the bubble out, but I can't get them all. I had thought about using a pressure pot to pressure cast the parts, but I have no idea if this would solve my problem or how to do it. Any help? thanks, Mike Quote Link to post Share on other sites
kap64 Posted February 29, 2008 Share Posted February 29, 2008 (edited) Some people vacuum the resin before pouring it and then use pressure after pouring it. Edited March 1, 2008 by kap64 Quote Link to post Share on other sites
terryt Posted February 29, 2008 Share Posted February 29, 2008 I've had that happen before, some resin creates it's own bubbles (chemical reaction). After I started using a pressure pot the bubbles went away. The pressure pot forces the resin into spaces and compresses the resin and keeps the bubbles from forming. You can get a Pressure Pot Here: http://www.harborfreight.com/cpi/ctaf/disp...temnumber=93119 Quote Link to post Share on other sites
longmc Posted February 29, 2008 Author Share Posted February 29, 2008 I've had that happen before, some resin creates it's own bubbles (chemical reaction). After I started using a pressure pot the bubbles went away. The pressure pot forces the resin into spaces and compresses the resin and keeps the bubbles from forming.You can get a Pressure Pot Here: http://www.harborfreight.com/cpi/ctaf/disp...temnumber=93119 Thanks! That's the exact one I was going to get. We have a HF here in town. I've never used one before, any pointers? I've got a 2 HP compressor w/ tank, will that be enough? Quote Link to post Share on other sites
Rdrunner Posted March 1, 2008 Share Posted March 1, 2008 I have tried this technique from Tap plastics instructional videos, and one of the segments, it shows you how to pour your mix to avoid air bubbles. HTH Quote Link to post Share on other sites
doctorpepper Posted March 1, 2008 Share Posted March 1, 2008 pressure pots. i swear by it in my high humidity (easy to get the resin contaminated, and foamy) Quote Link to post Share on other sites
PlasticWeapons Posted March 1, 2008 Share Posted March 1, 2008 (edited) Here's a pic of my casting pot set up (from Harbor Freight). 1 = gas ball valve x2 (left side is air inlet, other valve is air release valve) 2 = end cap attached to blank off outlet for air tools Thanks to Harold (AMS Resins) for getting me going on my casting again, LOL. Edited March 1, 2008 by PlasticWeapons Quote Link to post Share on other sites
terryt Posted March 1, 2008 Share Posted March 1, 2008 (edited) longmc: Your compressor is fine, I'm using a 1 1/2 HP compressor with a small tank. Recommend pressure is 40 PSI. Make sure you print the coupon for the pressure pot, take it with you to Harbor Freight, the regular price is $119.00 in store. Here is my setup: I didn't use the valves, I eliminated the pressure gage and went direct into the pot with a quick disconnect. I use the compressors gage for the pressure setting. The pressure relief valve has the round ring. The blue thing in the picture is a vacuum run by compressed air, I use it to remove air from my molds. I was also purchased at Harbor Freight. Edited March 1, 2008 by terryt Quote Link to post Share on other sites
Harold Posted March 1, 2008 Share Posted March 1, 2008 Here's a pic of my casting pot set up (from Harbor Freight).1 = gas ball valve x2 (left side is air inlet, other valve is air release valve) 2 = end cap attached to blank off outlet for air tools Thanks to Harold (AMS Resins) for getting me going on my casting again, LOL. That's my exact set up....the only thing to be weary of, is the HF tank seals. Some of them were really poor. Make sure you can return it, if you can't hold at least 40 pounds of pressure. Quote Link to post Share on other sites
terryt Posted March 1, 2008 Share Posted March 1, 2008 (edited) Harold: I had a problem with my seal at first, I rotated the cover and once I got a good seal I made an index mark on the pot and the cover. No problems with a seal up to 60 PSI and more. Don't recommend going beyond the pressure indicated on the pot. I also use a 10" crescent wrench to tighten the wing nuts. Edited March 1, 2008 by terryt Quote Link to post Share on other sites
kap64 Posted March 1, 2008 Share Posted March 1, 2008 longmc:Your compressor is fine, I'm using a 1 1/2 HP compressor with a small tank. Recommend pressure is 40 PSI. Make sure you print the coupon for the pressure pot, take it with you to Harbor Freight, the regular price is $119.00 in store. Here is my setup: I didn't use the valves, I eliminated the pressure gage and went direct into the pot with a quick disconnect. I use the compressors gage for the pressure setting. The pressure relief valve has the round ring. The blue thing in the picture is a vacuum run by compressed air, I use it to remove air from my molds. I was also purchased at Harbor Freight. That blue vacuum pump you have there, is it used for de-airing the resin before pouring? What brand of resin are you guys using that has a long enough pot life to get all of this done before it starts to cure? . Quote Link to post Share on other sites
Spongebob Posted March 1, 2008 Share Posted March 1, 2008 Looks exactly like my set-up! Spongebob Quote Link to post Share on other sites
longmc Posted March 1, 2008 Author Share Posted March 1, 2008 That blue vacuum pump you have there, is it used for de-airing the resin before pouring? What brand of resin are you guys using that has a long enough pot life to get all of this done before it starts to cure?. Good question. I was wondering the same thing. I have some white "crafting" resin that takes about 15 minutes to cure, but is sort of soft even after 20 minutes. I was planning to try that being that it's slow curing and a thinner resin. I also have some alumilite tan, but it's pretty quick to set. Quote Link to post Share on other sites
Triarius Posted March 1, 2008 Share Posted March 1, 2008 Something I don't think anyone mentioned: good mold release, regardless of what the mold is made from. You also want the lowest viscosity with the longest pot life for fine detail. Quote Link to post Share on other sites
terryt Posted March 2, 2008 Share Posted March 2, 2008 I don't de-air resin before I pour it, just use pressure in the pressure pot. Right now I use Smooth On resin, they have several different formulas when it comes to working time and hardness. This link should help with mold making material and resin: http://www.smoothonsecure.com/store/howto_service.php Quote Link to post Share on other sites
kap64 Posted March 2, 2008 Share Posted March 2, 2008 I went by and bought one today, They were $80, but if you print out the internet sale ad, they sell it to you for $40. Also got a vacuum pump, on sale for $9, the blue one. I don't know if it's strong enough, but it says it will pull 28 inches, only one shy of what's recommended, so maybe it will work. Quote Link to post Share on other sites
longmc Posted March 2, 2008 Author Share Posted March 2, 2008 I'm a little confused as to what the vacuum pump is for? Don't you just pressurize the pot to squash the air bubbles? Quote Link to post Share on other sites
P-38 guy Posted March 2, 2008 Share Posted March 2, 2008 I'm a little confused as to what the vacuum pump is for? Don't you just pressurize the pot to squash the air bubbles? I think it's used when making the mold. Mike Quote Link to post Share on other sites
terryt Posted March 2, 2008 Share Posted March 2, 2008 Vacuum is used when you make molds. When you mix mold material air bubble are created, since it is less viscous than resin the bubbles are in suspension and if left will cause the mold to have thousands of air pockets. Thats when you use a vacuum to de air the mold material. Quote Link to post Share on other sites
BOC262 Posted March 2, 2008 Share Posted March 2, 2008 ... I have some white "crafting" resin that takes about 15 minutes to cure, but is sort of soft even after 20 minutes. I was planning to try that being that it's slow curing and a thinner resin.I also have some alumilite tan, but it's pretty quick to set. I'll echo others in recommending Smooth-On--excellent resin! Choose a low shrinkage, low viscosity formula with a 15-20 minute potlife and it will be fine for pressure casting. Read the specs for the resin you are using--often the specs are given in "potlife"--it will take longer than that for the resin to really cure hard. To accelerate the cure and help prevent warping, make a box out of plywood with a round hole in the top to accept the pressure pot. Place 1 or more 100 watt light bulbs in the box. The box should be deep enough so as much of the pressure pot as possible is in the box. The light bulbs will heat up the pressure pot and will accelerate the hard cure of the resin--even though most resins are supposed to be fully cured in 24 hours, they will actually not develop their full strength for several days. This is a very good techniques when casting thin sections. Turn on the light bulbs and heat up the pressure pot before casting the resin, then leave in the pot for a couple of hours--experiment to find the best/minimal amount of time needed. If you want to get fancy, use a thermometer to monitor the temperature, add adjustable inlet and exhaust vents, and/or a dimmer switch to help regulate the temp. Keep a casting log and take note of all the variables--that way you can fine tune the procedure, learning the most efficient combination of heat, time, etc. Back when I operated a resin casting business, I used an apparatus like that described above and was able to consistently turn out castings with walls as thin as 1/32 inch and 10 inches long (think 1/72 model acft fuselage halves) with no warping or pinholes at all. HTH! Quote Link to post Share on other sites
longmc Posted March 2, 2008 Author Share Posted March 2, 2008 Vacuum is used when you make molds. When you mix mold material air bubble are created, since it is less viscous than resin the bubbles are in suspension and if left will cause the mold to have thousands of air pockets. Thats when you use a vacuum to de air the mold material. do you vacuum the material before pouring your mold or after you've poured it over your master? Quote Link to post Share on other sites
Harold Posted March 2, 2008 Share Posted March 2, 2008 do you vacuum the material before pouring your mold or after you've poured it over your master? I vac the RTV before I pour it into the master. Make sure you have it in a large container. It will swell three times or more. Let it collapse. Then slowly pour it on the bottom of the master and let it rise around it. Then vac it again. On very complex parts with under cuts, I sometimes vac it more than once, just to make sure all the bubbles are pulled. Harold Quote Link to post Share on other sites
PlasticWeapons Posted March 2, 2008 Share Posted March 2, 2008 Cool! I had a feeling the pressure pot could double as a vaccum chamber. Thanks guys! Quote Link to post Share on other sites
terryt Posted March 2, 2008 Share Posted March 2, 2008 (edited) For what its worth, I only vacuum my mold material once, doing it more than once is redundant and it also cuts into working time of the RTV. This also removes air bubbles formed around the master. I typically use RTV with longer working time to ensure the vacuum process removes the air properly. If you don't use vacuum to de-air your mold material, paint a coat of mold material on the master and then pour the material into the mold box. I have a smaller setup to de-air my RTV. Instead of the vacuum jar shown above I got these to use with my hand pump. http://kitchen-dining.hsn.com/rival-seal-a...53&ocm=sekw Edited March 2, 2008 by terryt Quote Link to post Share on other sites
PlasticWeapons Posted March 2, 2008 Share Posted March 2, 2008 I swear, that's not mine baby. Quote Link to post Share on other sites
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