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Old 11-01-2017, 04:34 PM   #1 (permalink)
 
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Default Pressure Pot Suggestion Please

It seems that more and more of our members are learning to cast blanks.

At some point I would like to join in that activity.

I have not looked around seriously for a pressure pot, just asking for suggestions as to what other people use.

One or two of the hardware/tool stores that I frequent sell "paint pots" with a gauge on top, a lid seal, and sturdy clamps. . Is this a pressure pot ?

Another question I have relates to the use of pressure for casting as opposed to vacuum.

My intuition seems to be telling me that vacuum is what you need for casting as opposed to pressure. . Isn't vacuum the way to get bubbles out ?

I do understand the difference between pressure and vacuum and worked with both for many years in my career as an experimental physicist.

In spite of that, as I consider doing my own casting I would intuitively go for vacuum.

Happy to hear what others think.
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Old 11-01-2017, 06:09 PM   #2 (permalink)
 
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I've never done any casting myself, my experience with resin is solely based on aircraft composite structure.

If I understand what I have read properly the biggest factor that rules out vacuum is the pot life of the resins. Since they cure much more quickly than common resins used in other industries there simply isn't enough workable time for the vacuum to eliminate bubbles.

Pressure can quickly shrink bubbles small enough that they aren't an issue.

I'm sure people with experience doing this have a better explanation but that is my understanding of the reason people use pressure as opposed to vacuum.

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Old 11-01-2017, 06:26 PM   #3 (permalink)
 
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Thank you, Doug.

So it seems that under vacuum, there is not enough time for the (probably even enlarged) bubbles to migrate to the resin surface and burst before the curing process prevents complete migration. . Probably the resin is extremely viscous and becomes moreso as curing progresses. . I had not thought of this.
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Old 11-01-2017, 06:43 PM   #4 (permalink)
 
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Well drat... Now I'll never retire in the proceeds from selling you blanks. ;)

You could probably get away with vacuum with a slow set but it's certainly very reliable to crush the air into not being a problem.

The tcp global style pot is about where I'd start. Same one is marketed by Grizzly and a few others. I've not found a need to go above 50psi personally so that one suits my needs well without being too expensive. The lid style is much more secure than the slightly less expensive harbor freight model. Switching it to pressure casting purposes is very very easy.
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Old 11-01-2017, 07:11 PM   #5 (permalink)
 
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Thanks, Tim ....

You don't have to worry any time soon about losing a pen blank customer !! . I like yours !!

I think that I am an incurable collector of tools ..... and blanks
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Old 11-01-2017, 07:16 PM   #6 (permalink)
 
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I have the California Air Tools 5 gallon pressure pot which is rated to 90 psi and has worked great. I never considered by the harbor freight similar sized one due to the lack of quality of much of their stuff.
For me, pressure casting absolutely eliminates all the bubbles and helps to force resin into areas where it normally may not flow. Vacuuming the resin to remove bubbles works also but with quick setting resins it can be a challenge to get everything set up in time plus adding colorants and pouring can add more bubbles. I mainly use my vacuum chamber to stabilize wood and to degas Weld-On 40 which is used in acrylic fabrication.

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Old 11-01-2017, 08:16 PM   #7 (permalink)
 
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I look at it as insurance. The cost of resin and time make a pressure pot necessary. Especially if your going to do any hybrids or pine cones etc. I went with the HF and its fine for my use. Like any tool use it carefully and double check it before pressurizing.
Before long you will have boxes full of blanks to add to your collection.
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Old 11-01-2017, 08:24 PM   #8 (permalink)
 
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Great timing for me on the conversation, thanks guys.
Question, is there anything that would preclude using a 5 gallon pressure pot on its side with a support to cast larger pours than just pen blanks?


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Old 11-01-2017, 09:43 PM   #9 (permalink)
 
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I've cast PR using both vacuum and pressure. Vacuum doesn't come close IMO, even when I was sure the resin was thoroughly degassed sometimes I would still get an air pocket. As mentioned, you don't have enough time to use vacuum with Alumilite and if it's hot out, even PR can start to set while degassing.

I just use the regular HF pot and replaced all the fittings with ones I ordered from Amazon, there's a thread here on how to do it. The pot has functioned flawlessly for me, and I have a couple friends that have one and they've never had issues either. I wouldn't mind getting 1 or 2 more - and probably will - so I can have several batches of blanks going at a time. For the price it's a great toy to have if you plan on casting, and absolutely necessary if you'll be using Alumilite.
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Old 11-01-2017, 09:44 PM   #10 (permalink)
 
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Quote:
Originally Posted by MRDucks2 View Post
Great timing for me on the conversation, thanks guys.
Question, is there anything that would preclude using a 5 gallon pressure pot on its side with a support to cast larger pours than just pen blanks?


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I've seen it done so it shouldn't be a problem. The pot has no idea what way it's facing
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