Is 25" Hg enough vacuum...you decide!

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MesquiteMan

MesquiteMan

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I see this question frequently..."Is 25" Hg enough vacuum for good stabilizing?". I always answer that it will work fair but will not give optimal results and best penetration. To prove this point, I decided to take some pictures during a recent stabilizing cycle.

These pics are taken using an acrylic stabilizing chamber and Cactus Juice. The juice is a little pink because I forgot to clean off my weight from the red I did right before this. It is normally clear!

This was taken in Central Texas at an elevation of about 940' above sea level. Remember, the maximum theoretical vacuum is 29.92" Hg at sea level and you loose 1" Hg for every 1,000' above sea level. Here, my maximum theoretical vacuum is around 28,92" give or take. In other words, if you are at 4,000' above sea level, your maximum theoretical vacuum is 25.92" Hg so 25" is a really good vacuum. I know, it is confusing!

Anyway, here is a set of black walnut blanks that are vacuumed down to 25" Hg by controlling the amount of vacuum through a vacuum bleed system on my chamber. I held it at 25" until the bubbles stopped.

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Here is the same set of blanks with the vacuum increased to 27" Hg.

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And finally, the same set of blanks at 28.5" Hg, close to my theoretical maximum vacuum at my elevation above sea level.

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So, as you can see, the more vacuum you can generate, the more the air is removed from the blanks. The more air you remove, the more the resin can penetrate and saturate the wood. So, in my opinion and from experience, 25" Hg when your elevation allows a higher vacuum is not going to give you the best results.

Hope the pics helped visualize this better for some!
 

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Interesting experiment. I can't argue that higher vacuum isn't better, but only question whether or not the bubbles are coming from air dissolved in the solution or are really from the wood. I do think the pores of the wood expand more in higher vacuum, but would be equally curious if you ran the same experiment without any wood. Just a curiosity.
 
No, the air is coming directly from the wood itself. You can see it streaming from the wood and it will eventually stop. These were taken at the very beginning of the higher vacuum. I have tested straight Cactus Juice with nothing in it and it will not start to bubble (boil) until it reaches just below 29" Hg on my gauge (the highest I can get) in an 80° F shop.

Also, it is not about the pores expanding. it is about the low pressure causing the AIR in the wood to expand. Same reason pressure does not do a lot for stabilizing. With pressure, you compress any air in the wood which will get the resin in there, but as soon as you release the pressure, the compressed air expands and pushed most of the resin right back out of the blank. Now, if you could cure the resin under pressure, that would be a different story.
 
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Here is a close up of the air coming out of the WOOD at 27" Hg

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And the same area at 28.5" Hg

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Curtis,

Thank you for this excellent post, just amazing. I don't think that I have seen as good a demonstration as this in a VERY LONG time. This makes your point clearer than a crystal lake on a bright sunny day! Very informative and helpful.

Linda
 
EarlD said:
What kind of vacuum pump is required to generate this much vacuum?
Earl
Click to expand...

Earl, you can actually get pretty deep vacuum with the $20 HF Venturi style pump. When I tested it, I was getting 28" Hg or so. However, the Venturi style requires a pretty good size compressor to keep up so I usually do not recommend it. The most cost effective deep vacuum pumps are going to be rotary vane pumps. HF has a 2 stage pump for $150+/- . Of course I m no fan of HF stuff so I have a JB Eliminator made in the US that I picked up for $115 used but like new. If you look at rotary vane pumps, they usually show the vacuum in microns which is a more precise measurement of vac. Look for something that will pull 75 microns or less
 
Actually, the higher vacuum might pull more cactus juice inside the blank... I won't disagree with you there.

Warning! Physics mode: ON!! :eek:

But what you are likely seeing is not that more air is being drawn out of the blank... instead by lowering the pressure inside the your stabilization chamber you are lowering the boiling point of the solvent (eg acetone, or whatever is in your "juice"). Thus you lowered the boiling point of below room temperature, and as you increased the vacuum further the mixture boils even more. This is the same reason why water boils at lower temperatures at higher elevations where there is less atmospheric pressure.

To test this out for sure, repeat the "experiment" without the porous blanks. I bet you'll see bubbles nucleating/originating from slight imperfections in the sides/bottom of the chamber. Try it out, inquiring minds want to know!!

​
Physics mode: OFF (whew!) :)

Andy
 
atsowers said:
Actually, the higher vacuum might pull more cactus juice inside the blank... I won't disagree with you there.

Warning! Physics mode: ON!! :eek:

But what you are likely seeing is not that more air is being drawn out of the blank... instead by lowering the pressure inside the your stabilization chamber you are lowering the boiling point of the solvent (eg acetone, or whatever is in your "juice"). Thus you lowered the boiling point of below room temperature, and as you increased the vacuum further the mixture boils even more. This is the same reason why water boils at lower temperatures at higher elevations where there is less atmospheric pressure.

To test this out for sure, repeat the "experiment" without the porous blanks. I bet you'll see bubbles nucleating/originating from slight imperfections in the sides/bottom of the chamber. Try it out, inquiring minds want to know!!

Physics mode: OFF (whew!) :)

Andy
Click to expand...

Andy, please see my reply above. I have done the test you suggest and it does not boil until real close to 29". Also, I have a very good friend who is a retired chemical engineer. He was the vp of processes for Exxon Mobile plastics while working. I have had him run the chemical calcs or whatever they are called on the chemical composition of Cactus Juice and he says it will not boil until it reaches close to a perfect vacuum at 85 F. And I am very familiar with the physics behind vacuum. Have studied it quite a bit.
 
atsowers said:
Actually, the higher vacuum might pull more cactus juice inside the blank... I won't disagree with you there.

Warning! Physics mode: ON!! :eek:
But what you are likely seeing is not that more air is being drawn out of the blank... instead by lowering the pressure inside the your stabilization chamber you are lowering the boiling point of the solvent (eg acetone, or whatever is in your "juice"). Thus you lowered the boiling point of below room temperature, and as you increased the vacuum further the mixture boils even more. This is the same reason why water boils at lower temperatures at higher elevations where there is less atmospheric pressure.

To test this out for sure, repeat the "experiment" without the porous blanks. I bet you'll see bubbles nucleating/originating from slight imperfections in the sides/bottom of the chamber. Try it out, inquiring minds want to know!!

​
Physics mode: OFF (whew!) :)

Andy
Click to expand...
MesquiteMan said:
No, the air is coming directly from the wood itself. You can see it streaming from the wood and it will eventually stop. These were taken at the very beginning of the higher vacuum. I have tested straight Cactus Juice with nothing in it and it will not start to bubble (boil) until it reaches just below 29" Hg on my gauge (the highest I can get) in an 80° F shop.

Also, it is not about the pores expanding. it is about the low pressure causing the AIR in the wood to expand. Same reason pressure does not do a lot for stabilizing. With pressure, you compress any air in the wood which will get the resin in there, but as soon as you release the pressure, the compressed air expands and pushed most of the resin right back out of the blank. Now, if you could cure the resin under pressure, that would be a different story.
Click to expand...
Andy,
Curtis' quote from his post, #3.
 
Fair enough... I stand corrected.

If the bubbles stop, it either means that:

1) air IS being drawn out.

OR

2) you've boiled off all that particular solvent, which under the circumstances is not likely to me now that I've read your MSDS...

My reply was based on the premise that you were using a solvent with a lower boliing point like acetone which boils at only 133F at atm pressure...
 
theories and physics lessons are great.. but I think a very simple test
would answer the question definitively.

You can tint the juice and vacuum each one to it's respective mark,
and then cut the blanks in half. That will show how far into the wood
the juice goes at each level of vacuum.
 
NewLondon88 said:
theories and physics lessons are great.. but I think a very simple test
would answer the question definitively.

You can tint the juice and vacuum each one to it's respective mark,
and then cut the blanks in half. That will show how far into the wood
the juice goes at each level of vacuum.
Click to expand...

Already done that, I got 100% penetration with burgundy dyed resin on a 7.25x7.25x3.5" bowl blank at 28.5" Hg. Uniform color throughout. On pen blanks, you can get 100% color through the blank at 25" Hg but the color is darker or more intense at higher vac. Just because you get complete penetration, that does not mean as much of the air is displaced with resin as it is with higher vac. I have also done similar weight blanks with lower and higher vac and the higher vac blanks weigh more once cured. Pretty definitive proof if you ask me.

Also, this was not meant to be any kind of discussion about Cactus Juice but rather a discussion about stabilizing in general. The same principles should apply regardless of what solution you are using. Higher vacuum will remove more of the air molecules than lower vacuum, thus leaving more room for higher concentrations of stabilizing solution.
 
I had been wondering how a vacuum would force the resin INTO the blank. Now I know.

Sorta.

Once the bubbles stop, do you then kill the vacuum? At that point is the resin "sucked" into the wood?
 
jbswearingen said:
I had been wondering how a vacuum would force the resin INTO the blank. Now I know.

Sorta.

Once the bubbles stop, do you then kill the vacuum? At that point is the resin "sucked" into the wood?
Click to expand...

To be totally accurate, the resin is "pushed" into the wood by the much higher atmospheric pressure outside of the chamber...but you seem to have the gist of it.
 
I was able to see Curtis perform a demonstration at the Centray TX meeting last month. It makes a lot more sence how it works if you have seen it done. I ended up buying a chamber with some of his Cactus Juice and them got a new vacuum pump from Harbor Freight. Have used it twice since then and it makes a big differance. I have some very soft 50 + year old white oak that I stabelized twice and now it turns like a very solid piece of wood and the pen looks fantastic.

It took nearly 2.5 to 3 hrs for the bubbles to stop almost completely but they did finally all but stop and they were coming from the wood. Very interesting to watch and see how much air really is in the wood.

Thanks again Curtis for the demo, was worth it to see it in action.
 
HeartofaPen said:
It took nearly 2.5 to 3 hrs for the bubbles to stop almost completely but they did finally all but stop and they were coming from the wood.
Click to expand...

How did the pump hold up after that long? I have the two stage HF and was wondering how long it might take and if it over heats. What for some more juice to try out the chamber.

Jorge
 
Back before all the new regs about fridg, many small shope used old fridge pumps to evacuate small systems. Once since the ozone hole thing and the new regs, environmental regs require different style pumps. The old fridge pumps still will pull a great vacuum.
Charles
 
Jorge, The pump did very well I figure. It was a little warm when it was finished but appeared to hold the vacuum without any issues and no other problems noted. I will need to make sure I add oil when I run the next batch or even change it out. Will have to see how it looks. It was only the second time I had used it.

For anyone who may be looking, HF has the 3cfm vacuum pump on sale with a coupon for $129.99. It came in an e-mail I received yesterday. The sale only last until Aug 14th.
 
HF had a 20% off coupon good through last night. I was getting ready to order it when the new coupon came through. Saved me an extra $7 with tax and all. Now lets hope it lasts. I never have been much of a HF person, but I was not going to drop $300 on a vacuum.
 
Great experiments, may I ask if you've tried one based on mass? Basically, if the best stabilization comes from the incorporation of the most "juice" into the blank, then take 5 blanks, weight them, stabilize at -max Hg allowing to dry and then determine how much was Incorporated by weighing them again. Repeat at other pressures and compare. Could also try other woods to see how it varies.

All very interesting.
Jim
 
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