resin casting and pressure pots

[longmc]

I picked up the pressure pot from Harbor Freight over the weekend and got it setup. After solving all my leaking issues, I was able to run a couple test casts. Wow, what a difference. It solved my large air bubbles being trapped in my molds, but showed every tiny air bubble in my master mold.

I have made some custom detail work on my F-15 cockpits that I'd like to cast but I'm a little worried about air bubbles getting trapped in some of the details. How well does painting the RTV over the master as opposed to vacuuming it?

[terryt]

It depends on the working time of your RTV, the longer working time the easier it is to remove bubbles by painting the RTV on. It's a lot better using a vacuum, it causes most of the bubbles to rise to the surface and burst. Release the vacuum before the RTV solidifies. If you don't you will have vacuum caused bubbles.

[longmc]

It depends on the working time of your RTV, the longer working time the easier it is to remove bubbles by painting the RTV on. It's a lot better using a vacuum, it causes most of the bubbles to rise to the surface and burst. Release the vacuum before the RTV solidifies. If you don't you will have vacuum caused bubbles.

I've been using the alumilite HS-3 RTV. I really like it. It's very flexible and picks up details nicely. It has a pretty slow curing time, so I was going to try the painted on method and see how it works out. I guess if it doesn't I can always get the vacuum pump.

Edited March 3, 2008 by longmc

[terryt]

What I use to "paint" on the RTV is a stick like a wooden Popsicle/Coffee stirrer. After you have a few coats of RTV on the master, start pouring a thin stream at the lowest point into the mold box. If you pour right you will see some of the bubbles remove are removed. Don't get in hurry, if you do you will end up with bubbles close to the master. If the bubbles are close to the master, the pressure pot will open them up.

[longmc]

What I use to "paint" on the RTV is a stick like a wooden Popsicle/Coffee stirrer. After you have a few coats of RTV on the master, start pouring a thin stream at the lowest point into the mold box. If you pour right you will see some of the bubbles remove are removed. Don't get in hurry, if you do you will end up with bubbles close to the master. If the bubbles are close to the master, the pressure pot will open them up.

I've been gluing my masters to a pane of glass then building a lego house around it about 1/4 to 1/2 inch from the edges. I wrap it in tape and then seal the bottom w/ hot glue. I pour my RTV into a far corner and let it run down the side and fill the box. I've started setting them on the washing machine to agitate the air out. I haven't noticed any air bubbles around the masters until I started pressurizing it.

[terryt]

I build a foundation from Legos by using the single row to piece the floor together. I then secure the master with Blue Tac. Then I build up the sides to the height desired. No need to use hot glue to seal it. Something you could use is a vibrator to get the bubbles to burst.

Edited March 4, 2008 by terryt

[longmc]

Something you could use is a vibrator to get the bubbles to burst.

I guess you could! My luck, the in-laws would walk in right then... not an easy one to explain -'Oh this? I'm just busting air bubbles"

I need to seal the bottom as the HS-3 leaks under the lego mold - it tends to leak out of the lego blocks as well, so I wrap them in tape - it's very liquidy. But it gets in every corner and crevice.

[PlasticWeapons]

Hand pumps, vacuums, and vibrators...

No I swear, baby, none of those are mine!!!

[terryt]

I have some base plates for the Legos, I haven't tried them yet but I plan to cut them to different sizes for my mold boxes.

Here is a link to the base plates, Toys 'R' Us have them.

http://shop.lego.com/Product/?p=2598

[longmc]

could you use pressure on thinner molding RTV? would that crush some of the larger bubbles and force the mold into the details?

[terryt]

You could try to use the pressure pot to try to burst the bubbles. I haven't tried that approach for my molds, because the vacuum setup I have works fine.

[doctorpepper]

i use plastic playing cards as a base, as most of the mold boxes are around that size. super glue it to the master, tape the lego bricks to it, once done, throw it all away, no mess. you get 52 plastic playing cards for about 2 bucks.

as for the pressured RTV, i do exactly that. it pushes the RTV into all nooks and crannies and the detail pickup is even better. plus, all the bubbles near the master get crushed - no more weird pin prick looking things when your resin is cast in the mold for the first time..

flip side to that is that the mold rubber is much more dense, as a result, tends to wear out a little faster, and is more inflexible (ie, much harder to bend.. ouch)

[dsmith]

Hi guys, I thought I would add my 2 cents.

When you are pouring your molds, there is a good reason to vacuum the RTV twice. The first time you get most of the air out. As some of you who do this know, it gets very big the first time, so use a big container. Then, I don't find a need to do anything but pour the RTV into the mold box. Then, stick the mold boxes back into the vacuum chamber and pull a vacuum on it again. Once you get down to 30 lbs, just leave the boxes in the chamber overnight (or however long it takes your RTV to cure). This should get rid of all the air bubbles.

Secondly, I had one of those pressure pots just like the one from HF. I hated the thing, and after about 6 months the clamps were so stripped you could hardly tighten them. Then, since they are made of such crap metal, they broke. Then I couldn't get replacement parts, so there was $90.00 down the drain. If you want a nice pot that is easy to use, with a much better setup (regulator etc..), get one from CPO. I have three and I love them! Also, you can order replacement parts.

paint tank

Hope that helps,

-Doug

[longmc]

Hi guys, I thought I would add my 2 cents.

When you are pouring your molds, there is a good reason to vacuum the RTV twice. The first time you get most of the air out. As some of you who do this know, it gets very big the first time, so use a big container. Then, I don't find a need to do anything but pour the RTV into the mold box. Then, stick the mold boxes back into the vacuum chamber and pull a vacuum on it again. Once you get down to 30 lbs, just leave the boxes in the chamber overnight (or however long it takes your RTV to cure). This should get rid of all the air bubbles.

Secondly, I had one of those pressure pots just like the one from HF. I hated the thing, and after about 6 months the clamps were so stripped you could hardly tighten them. Then, since they are made of such crap metal, they broke. Then I couldn't get replacement parts, so there was $90.00 down the drain. If you want a nice pot that is easy to use, with a much better setup (regulator etc..), get one from CPO. I have three and I love them! Also, you can order replacement parts.

paint tank

Hope that helps,

-Doug

Thanks, Doug. I got my pot on sale for $40, so it was worth it to practice around with.

[dsmith]

Thanks, Doug. I got my pot on sale for $40, so it was worth it to practice around with

No problem. If you are just casting for yourself then the pot is fine. However, if you are going to do a lot of casting (i.e. sell to others) then it just doesn't hold up so well. Also, I like the one I have because you can hand tighten it. You have to use a wrench to tighten the HF one. Just let me know if you have any other questions :lol:

Cheers,

-Doug

[longmc]

No problem. If you are just casting for yourself then the pot is fine. However, if you are going to do a lot of casting (i.e. sell to others) then it just doesn't hold up so well. Also, I like the one I have because you can hand tighten it. You have to use a wrench to tighten the HF one. Just let me know if you have any other questions

Cheers,

-Doug :)

Doug,

thanks for the advise and the offer of support! Right now I'm still trying to get a feel for it and doing small scale stuff for myself. Does the Campbell Hauser pot hold up really well for large volume use? I saw alumilite sells one that's supposedly specific to casting, but it looks just like the HF one.

[LIengineerBob]

I've done resin casting for myself for many years, and have heard of the pressure pot to make the castings better. I never bought one, but now reading over this topic, I am nearly convinced into getting one.

This might be a dumb question, but exactly how does one use the pressure pot?? I already have a large 2HP, 2.5 gallon compressor so I think it will work. I just need to pick up one of the pressure pots, but am not sure how to actually use the thing?? Any tips?? THANKS!!!

[longmc]

I've done resin casting for myself for many years, and have heard of the pressure pot to make the castings better. I never bought one, but now reading over this topic, I am nearly convinced into getting one.

This might be a dumb question, but exactly how does one use the pressure pot?? I already have a large 2HP, 2.5 gallon compressor so I think it will work. I just need to pick up one of the pressure pots, but am not sure how to actually use the thing?? Any tips?? THANKS!!!

Well, I'm no expert as I just started using the pressure pot last weekend. However, it seems REALLY easy. If you read through the post you can see some pictures of setup. I got the pot at harbor freight and picked up some 1/4" ball valves and an end cap. Once I got all the leaking connections taken care of, I just poured my resin into my existing molds, placed them in the pot and pressurized to 40-60 psi. Closed the valves and waited about 15 minutes for the resin to cure. Released the pressure and removed the molds. It was amazing how much better the parts cast.

One thing I noticed was all the pin sized air bubbles that were in my molds. The pressure will force the resin into all of these holes and leave tiny resin balls at the edges of my cast parts. I'm now trying to pressure my molds to get the bubbles out. I just started messing with that so not sure how it will work.

Also, you will need resin that has a longer working time. I'm ordering some from the smooth-on link above in this post.

[doctorpepper]

Well, I'm no expert as I just started using the pressure pot last weekend. However, it seems REALLY easy. If you read through the post you can see some pictures of setup. I got the pot at harbor freight and picked up some 1/4" ball valves and an end cap. Once I got all the leaking connections taken care of, I just poured my resin into my existing molds, placed them in the pot and pressurized to 40-60 psi. Closed the valves and waited about 15 minutes for the resin to cure. Released the pressure and removed the molds. It was amazing how much better the parts cast.

One thing I noticed was all the pin sized air bubbles that were in my molds. The pressure will force the resin into all of these holes and leave tiny resin balls at the edges of my cast parts. I'm now trying to pressure my molds to get the bubbles out. I just started messing with that so not sure how it will work.

Also, you will need resin that has a longer working time. I'm ordering some from the smooth-on link above in this post.

you left them in for only 15 mins? there's a good chance that after that, as the resin hasn't fully hardened, the bubbles will expand and distort your casting

[longmc]

you left them in for only 15 mins? there's a good chance that after that, as the resin hasn't fully hardened, the bubbles will expand and distort your casting

I guess it was a little longer. I usually put it in the pot and then go off to do something else.

[dsmith]

Doug,

thanks for the advise and the offer of support! Right now I'm still trying to get a feel for it and doing small scale stuff for myself. Does the Campbell Hauser pot hold up really well for large volume use? I saw alumilite sells one that's supposedly specific to casting, but it looks just like the HF one.

What do you mean by large volume use? Using it a lot, or putting a lot in it? Since I have owned both pots, I think that the CH pot is a higher quality product, and will last much longer (not to mention you can get replacement parts). It is designed much better, especially all of the fittings that go on the lid (with the HF pot, I could never get a good seal with the regulator assembly, and therefore had to leave the compressor hooked up so that the pressure would stay relatively constant). As far as putting molds in it, the CF pot can hold plenty. When I am pouring wheels, I can fit about 20 - 30 molds in it at one time. I also like the fact that it is easier to tighten.

When I cast, my wife helps me, and she like to do it as little as possible So, here is what we do. I get enough molds preped so that I can do three pours in a row (about 100 molds total if I am doing wheels). This way, I get everything poured in about 15 - 20 minutes. I do not demold until at least 30minutes after pouring (time can vary depending on your resin).

DO NOT buy the Alumilite pot though, as it is the same thing as the HF pot, just 4 times as expensive. However, I do use the Alumilite vacuum chamber. I will try and post a picture of my setup when I get home tonight.

One thing I noticed was all the pin sized air bubbles that were in my molds. The pressure will force the resin into all of these holes and leave tiny resin balls at the edges of my cast parts. I'm now trying to pressure my molds to get the bubbles out.

Vacuuming your RTV will fix that problem. I think we talked about that earlier in the post.

This might be a dumb question, but exactly how does one use the pressure pot?? I already have a large 2HP, 2.5 gallon compressor so I think it will work. I just need to pick up one of the pressure pots, but am not sure how to actually use the thing?? Any tips?? THANKS!!!

Well, just remember that the pots that everyone uses are designed for spraying paint. So all you need to do is make sure that the outlets for the paint and the srayer are capped off. That way, you turn on the compressor, charge up the tank fast, disconnect, and then the pot should stay pressurized. One thing to keep in mind is the pressure limit of the pot you are using (this is one time you want to read the instructions!). I think the HF pot will go to 70 or 80 psi, but the CF pot only goes to 50. However, I find that 35 - 45 psi is more than adequate for any casting you are going to do. You just need to make sure that you get the resin in the pot in time (another reason I like the CF pot, as you can tighten it faster). My resin has a pot life of about three minutes, so the faster we can go, the better But, like I said, I will try and get some pictures posted tonight.

Cheers,

-Doug :)

Edited March 6, 2008 by dsmith

[longmc]

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

Thanks everyone for the tips and guidance! I've gotten my pot up and working.

terryt, thanks for the pointer to Smooth-on!! I ordered a test set of their 310 and it's fantastic.!! The HF pot is a good starter, but leaks like crazy. Luckily the Iwata aircompressor I bought puts out about 50 psi and has a pressure shutoff switch, so I can fill the pot with my big compressor (too loud to leave connected) and then use the Iwata to maintain about 40-45 psi while the molds cure.

I'm really enjoying mixing and matching parts to make mold sets for all my kits of the best parts and as I progress I'll be looking for a better pot and quieter large compressor.

I'd like to thank everyone in this post for their support and help! You guys are the best!

Mike Long

[terryt]

longmc:

My pressure pot used to leak like crazy. I eliminated the leaks by turning the lid to different positions and used a 10" crescent wrench to tighten the wing nuts. You have to alternate the tightening sequence, tighten one snug then go directly accross (180 degrees) and tighten it with the wrench, then go back to first one and tighten it with the wrench. Next go to one of the loose fittings and snug it then the other, then use the wrench to tighten. Then ensure all the wing nuts are tight, don't use too much muscle or you might break the wing nut. Once I got the pot to quit leaking I made a index mark on the pot and the lid, now when I use the pot I use the index points and only have to hand tighten the the wing nuts to get a good pressure seal. No leaks now even with 60PSI.

I experimented with different pressures and found I got the same results with 25PSI and 40PSI. You might want to try different pressures.

[longmc]

longmc:

My pressure pot used to leak like crazy. I eliminated the leaks by turning the lid to different positions and used a 10" crescent wrench to tighten the wing nuts. You have to alternate the tightening sequence, tighten one snug then go directly accross (180 degrees) and tighten it with the wrench, then go back to first one and tighten it with the wrench. Next go to one of the loose fittings and snug it then the other, then use the wrench to tighten. Then ensure all the wing nuts are tight, don't use too much muscle or you might break the wing nut. Once I got the pot to quit leaking I made a index mark on the pot and the lid, now when I use the pot I use the index points and only have to hand tighten the the wing nuts to get a good pressure seal. No leaks now even with 60PSI.

I experimented with different pressures and found I got the same results with 25PSI and 40PSI. You might want to try different pressures.

Hi Terry.

I had done all that. I got everything where it wouldn't leak, made a mark and it started leaking again. I have a small pipe wrench I use to tighten the wingnuts. It's pretty snug now, but still leaks a little. I've got a bunch of new molds in curing right now. I'm going to leave them in until Saturday afternoon, then I'll take it all apart and redo everything. I'm going to use more teflon tape and remark it. I don't mind using the small compressor to hold pressure - it's very quiet and only comes on about once an hour or so.

thanks again for the point to smooth on! I can't believe the detail it picks up even unpressured and it's super strong! I've cleaned up a set of engine nozzles from the revell F-15E kit and molded. none of the other resins would either fully cast or hold their shape as it's so thin, but the smooth on gets it all and holds perfect shape with just a straight pour.

[terryt]

longmc:

I forgot to mention that I removed the gasket from the lid and flipped it over, that might have helped.

I also used to use Pour-A-Cast Mk2 Resin without a pressure pot. I think its a lot better than any Smooth-On resin I have used, but the working time isn't long enough for my purposes.

Link: http://www.bare-metal.com/Pathway%20Polyme...in-Casting.html

If you look at my pressure pot setup, I disconnect from the pressure pot once it is filled to the PSI I want, no leaking and no need to keep a compressor hooked up to it.