Vacuum vs Pressure - When to use?

[Rich Aldrich]

I am new to stablizing and casting, so I will ask an obvious question. Is vacuum used for stablizing and pressure used for casting? Or is it that too easy?

I make a lot of bowls and have some really good burl scraps that I can recover for pen blanks. They would need to be dry and stablized to use. Also, I have been buying some buckeye blanks on Ebay some of which will require stablizing.

Thank you for your help.

 

[Monty]

I am new to stablizing and casting, so I will ask an obvious question. Is vacuum used for stablizing and pressure used for casting? Or is it that too easy?...

That's the general consensus. Most have found it necessary to use pressure when casting with Alumilite, but not always needed with PR.
The closer you can get to 30mmHg vacuum, depending on how high above sea level you are, the better the stabilizing results.
Oh, and welcome to IAP.

 

[robutacion]

I am new to stablizing and casting, so I will ask an obvious question. Is vacuum used for stablizing and pressure used for casting? Or is it that too easy?

I make a lot of bowls and have some really good burl scraps that I can recover for pen blanks. They would need to be dry and stablized to use. Also, I have been buying some buckeye blanks on Ebay some of which will require stablizing.

Thank you for your help.

Yes, generally speaking, that's what those 2 systems are use more frequently, for...!

A pressure pot is an ideal basis for a stabilizing system, you will need a clear thick Perspex lid, a flat seal, a vacuum pump some hose and fittings (including vacuum gauge). The only disadvantage I see, is that you will not able to use both system at the same time, something that may not be a problem for you and many others, but worth to be mentioned...!

Probably the rule #1 with wood stabilization is that, Cactus Juice (or any other resin for this propose) and moisture, DO NOT work well so, the wood has to be dry and moisture free, this is easily achieved but putting the wood in a toaster over for a couple of ours or so, just before stabilizing.

The oven temp. shouldn't exceed 90° Celsius to dry the wood, and the wood has to cool down considerably before the Juice (resin) is added, as the Juice sets/harden by heat...!

I just though, you should know...!

Cheers
George

 

[gketell]

The only time you NEED vacuum is if you are trying to get resin into deep, thin cracks or porous wood. And then you need a thin resin with a long cure time. Put the item into a bath of the resin and pull as strong a vacuum as you can and hold it for quiet a while to pull all the air out of the blank. Then release the vacuum and apply pressure to collapse any bubbles the vacuum couldn't get out. Let the resin cure under pressure for the best cast you can get.

If you are casting solid blanks, or big pieces of scrap wood (like making a worthless wood blank) then you don't need vacuum and may not need pressure I'd you stir carefully so you don't "whip" air into the resin. But pressure never hurts.

Vacuum can hurt. It works be expanding the trapped air until it bubbles and the bubbles pop. But there are always bubbles that don't pop, and if the resin begins to set while still under vacuum you have just maximized you pits in the final product.

Gk

 

[edstreet]

Why use vacuum when you can use 4,000+ psi?

 

[Monty]

Why use vacuum when you can use 4,000+ psi?

Because my compressor won't do 4,000 PSI.:biggrin:

 

[edstreet]

Why use vacuum when you can use 4,000+ psi?

Because my compressor won't do 4,000 PSI.:biggrin:

Sorry I do not know what type of equipment you have. It's a simple question really and I was dead serious.

 

[Indiana_Parrothead]

4,000 psi are you serious? What kind if equipment do you have, your pressure pot must have 1" thick walls and be hard plumbed. I have never seen a rubber hose that can handle that kind of pressure.

 

[edstreet]

4,000 psi are you serious? What kind if equipment do you have, your pressure pot must have 1" thick walls and be hard plumbed. I have never seen a rubber hose that can handle that kind of pressure.

Dead serious about 4,000 psi. Nor does it matter what equipment I have but the question does still stand. What advantage does vacuum give you when you compare it with 4,000+ pounds of pressure.

 

[Monty]

4,000 psi are you serious? What kind if equipment do you have, your pressure pot must have 1" thick walls and be hard plumbed. I have never seen a rubber hose that can handle that kind of pressure.

Dead serious about 4,000 psi. Nor does it matter what equipment I have but the question does still stand. What advantage does vacuum give you when you compare it with 4,000+ pounds of pressure.

It's the advantage that you can use your shop equipment. I personally don't know of anyone that is capable of producing 4000PSI using a standard run of the mill compressor.
Now bear in mind that I'm not saying that what one can do in a home shop with vacuum will be as good as a commercially prepared blank from someone that uses 4000 PSI pressure stabilization, but it can come darn close.

 

[Rich Aldrich]

The only time you NEED vacuum is if you are trying to get resin into deep, thin cracks or porous wood. And then you need a thin resin with a long cure time. Put the item into a bath of the resin and pull as strong a vacuum as you can and hold it for quiet a while to pull all the air out of the blank. Then release the vacuum and apply pressure to collapse any bubbles the vacuum couldn't get out. Let the resin cure under pressure for the best cast you can get.

If you are casting solid blanks, or big pieces of scrap wood (like making a worthless wood blank) then you don't need vacuum and may not need pressure I'd you stir carefully so you don't "whip" air into the resin. But pressure never hurts.

Vacuum can hurt. It works be expanding the trapped air until it bubbles and the bubbles pop. But there are always bubbles that don't pop, and if the resin begins to set while still under vacuum you have just maximized you pits in the final product.

Gk

This makes sense. Seems like if you use vacuum, you definitely should use pressure, but using pressure seems to be the most beneficial option.

 

[Jim Burr]

Just to add to Greg's always good ideas, I've found that pressure works well on WW blanks to help force the PR into those little nooks and crannies providing a strong bond and fewer failures.
I use vacuum for stabilizing only...just MHO.

 

[gketell]

Why use vacuum when you can use 4,000+ psi?

If you can use 4,000+psi, then vacuum won't really add any benefit that I could think of. But the "when you can use" is the key. Which "home shop" users can achieve 4,000+ psi? And how much would it cost and how much room would it take to achieve that?

But I can get a 29" Hg vacuum followed by 60 psi pressure for about $400 and it takes up less than 2'x2'x4' area of my shop.

And I bet we would get "equivalent" results (at least as "equivalent" as makes no difference for pen blanks, etc).

GK

 

[MesquiteMan]

Ahaa, the old pressure thing. High pressure of 4,000 psi will do a good job for stabilizing, no doubt. However, you still need to use vacuum to remove the air. If you simply compress the air in the wood with 4,000 psi, as soon as you release the pressure, the air inside the wood will expand and push the resin back out somewhat. Every "professional" stabilizer I know who uses high pressure, uses vacuum first.

It MAY provide some benefit using very high pressure in the home shop. Mostly, it just speeds things up and reduces the cycle times which is important for production needs. Nature will do it just fine for you if you use vacuum and are patient.

I have a design for a very high pressure system capable of 5,000+ psi. I decided I did not want the liability of producing such a system. The tiniest leak could send out a stream of resin with such force it could severely hurt you. Then, of course, the cost would be an issue for the average home user.

 

[Jim Burr]

Ahaa, the old pressure thing. High pressure of 4,000 psi will do a good job for stabilizing, no doubt. However, you still need to use vacuum to remove the air. If you simply compress the air in the wood with 4,000 psi, as soon as you release the pressure, the air inside the wood will expand and push the resin back out somewhat. Every "professional" stabilizer I know who uses high pressure, uses vacuum first.

It MAY provide some benefit using very high pressure in the home shop. Mostly, it just speeds things up and reduces the cycle times which is important for production needs. Nature will do it just fine for you if you use vacuum and are patient.

I have a design for a very high pressure system capable of 5,000+ psi. I decided I did not want the liability of producing such a system. The tiniest leak could send out a stream of resin with such force it could severely hurt you. Then, of course, the cost would be an issue for the average home user.

And this is the reason we refer to your knowledge and expertise. Glad there are a few here that can built 4k PSI systems...your feedback will be anticipated Ed.