Resin casting questions....

[JasonW]

Was wondering if anybody out there has any tips or could share their experience with using a pressure pot during their resin casting? I have made a few masters of my own for a few things over the years. Mostly warship turrets and other things that are easy to cast without the use of any type of vacuum etc. and still come out looking decent. I was thinking of taking my casting to the next level however and possibly purchasing a pressure pot as I have been told this will help to eliminate a good deal of the air bubbles and ensure that the resin gets into all the smaller crevices, nooks and cranny's of more intricate or detailed molds.

I've found a couple of five gallon pressure pots online, is there anything special I should be looking for when buying something like this?

Does anybody have good experience with a specific model of pot they can recommend?

Is there anything special to keep in mind with regards to RTV molds that I want to use in a pressure pot? Special type of RTV needed or anything special with regards to how I set up my mold?

Any insight, details or stories that anyone could share with regards to pressure pot resin casting or resin casting in general would be appreciated.

Thanks much in advance.

[salvine]

I use the paint pot you can get from Harbor Freight. Pretty cheap and large enough for all my projects. POTMy experience though is that if you did not make the mold using vac and pressure then when you cast the resin and place it in the pot to cure you will be very disappointed. What happens is that the mold will have lots of imperfections that you are not aware of until you place that mold in a pressure pot. The problem is that once under pressure all the tiny pores and bubbles will have resin forced into them. Once I made the mold using vac on the RTV first and then letting it cure in the pot under pressure my casts looked great. i was like you at first and just made a small mold and pored in the resin and it looked pretty good. Pressure improves the overall cast but shines a bright light on any flaws. Do a quick search for resin in this form as this comes up from time to time. Be warned though that in the end you will save money by just buying the parts if they are available. Resin, mold rubber, Vac and pressure all add up quick. As a side note I think I can easily convert the pot to also do vac. I just need to get a pump and some fittings. Smooth-on products work very well BTW.

[JasonW]

I use the paint pot you can get from Harbor Freight. Pretty cheap and large enough for all my projects. POTMy experience though is that if you did not make the mold using vac and pressure then when you cast the resin and place it in the pot to cure you will be very disappointed. What happens is that the mold will have lots of imperfections that you are not aware of until you place that mold in a pressure pot. The problem is that once under pressure all the tiny pores and bubbles will have resin forced into them. Once I made the mold using vac on the RTV first and then letting it cure in the pot under pressure my casts looked great. i was like you at first and just made a small mold and pored in the resin and it looked pretty good. Pressure improves the overall cast but shines a bright light on any flaws. Do a quick search for resin in this form as this comes up from time to time. Be warned though that in the end you will save money by just buying the parts if they are available. Resin, mold rubber, Vac and pressure all add up quick. As a side note I think I can easily convert the pot to also do vac. I just need to get a pump and some fittings. Smooth-on products work very well BTW.

Thanks for the reply!

I understand the cost involved, I buy the resin and mold rubber fairly often. I use the Smooth On stuff now. I mostly cast stuff I am unable to find readily or (since I do a fair amount of what-if ships) stuff that I have come up with. I recently made a four gun turret for 16" guns on a USS Montana variation and cast several of them.

About how big (length and width) is that Harbor Freight pot?

[salvine]

Give or take 11" by 11". Have to measure when I get home.

[J.C. Bahr]

I think I can easily convert the pot to also do vac. I just need to get a pump and some fittings.

Yeah, building it for dual role pressure/vac is not difficult at all... but if I was doing it over again, I wouldn't even bother with the vac side and would've saved the money. All of my pressure cast RTV moulds have been perfect with no failures and I've had several old ones that I've sliced through and not been able to find any air-bubbles in them.

[Aaronw]

I also have a Harbor freight pot but I haven't used it a whole lot. Like you I simply found the majority of my parts were acceptable without the added bother of pressure casting.

I have been told the Harbor freight is a poor quality pot that can fail explosively under pressure, although I have a feeling any truth to this has been under very high pressure. I found 30 psi to do a good job of getting rid of bubbles and that is within the specified manufacturers recommendations. There are many casters I've talked with who use ordinary kitchen pressure cookers which is something I am not comfortable with, since I don't think they are intended for even 20-30 psi like the paint pots. Apparently some casters use 50-100 psi which I could see being a problem for a low grade paint pot and well out of the capability of a pressure cooker.

Binks is a brand I have seen recommended by several commercial casters. Unfortunately paint pots are not the best shape for us, most being as tall as they are wide. I'd really prefer a low fat pot of 18-24" diameter, but haven't found one like that yet. The 2 gallon pots are affordable but kind of small (maybe 12" diameter), the larger pots get expensive very quickly.

I have seen the parts made by several casters who use pressure on both sides (while making the mold and when casting). It has the same effect as the vaccuum but is less difficult to perform, although it does tie up your pot until cured.

I have some radial engines JC sent me last year and they are as nice as any commercial resin engine I have purchased, so he obviously has a practice that works well.

[Spectre711]

I've been playing around with the small Harbor Freight pressure pot and Smoothon products wit h good results for a while. I haven't used vacuum yet but I'm thinking of it just to see if there is a difference.

[salvine]

My vac chamber is just a small mason jar that I attach my automotive snap on vac tester too. I pull vac by hand but it really is underpowered to do the job right. In a perfect world the vac chamber should be clear so you can see the bubbles burp out of the resin or silicon. My hunch is that if you are very careful mixing the silicon and keep bubbles to a min and then make the mold in the pressure pot you can do pretty well. The best way of course is to pull a real vac in the range of 28-29 inches of mercury which should be possible with one of the inexpensive vac pumps you can get from HF. When I get to a spot where I have more room to set all this up I'll prob spring for one and hook it up to the pot. Like others have mentioned, The HF pot is a little sketchy for this but I keep the press within the working range. You can also put the pot into some type of container or cage to keep the lid from becoming a missile.

[Charlie D.]

I found some 5 gallon, and 10 gallon binks pots at salvage/surplus yards for very reasonable prices. They needed a little cleaning, and some fittings, but they work very well. You'll also see them pop on craigs list, and ebay from time to time.

The 10 gallon I got from HGR surplus a few years back for less than $200 shipped. A bit bigger than what most users here would use it for, but we use it for larger industrial castings.

[Aaronw]

Charlie, nice to know they are out there for less than an arm and a leg. I have an 18x18" polyethelyne cutting board I cast on. Ideally I'd like a pot I could fit that into. Guess I'll just keep watching ebay and Craigslist.

Salvine, using pressure in molding essentially does the same as the vacuum, just from the other side. Instead of degassing the silicone, it crushes the air bubbles which are then trapped at a very small size by the cured silicone.