Thread: Vacuum Chamber for Punky Timber

The set-up looks Ok. I was always worried about glass jars coping with the vacuum and imploding.

The Cactus Juice stablized ones look Ok as expected. The white glue ones don't look stabilized, but could be just the photo, so how are they really?

Ps I have ordered some of MesquiteMan's cactus juice and his chamber for my new set-up. I already have a new vacuum pump too similar to yours

Originally Posted by dai sensei

The set-up looks Ok. I was always worried about glass jars coping with the vacuum and imploding.

I don't think it's an issue really. I can tell you that the lid of the jar was compressed a lot tighter when new and filled with pickles than my vacuum pump pulls.

The Cactus Juice stablized ones look Ok as expected. The white glue ones don't look stabilized, but could be just the photo, so how are they really?

They are stabilized ... when they came out of the mixture they were solid white and after drying they turned clear.

But this is a different type of stabilizing. This doesn't give you a 'finished' shiny end product.

I use the 50/50 mixture on the punky woods to simply stabilize the timber while turning and not having to use excessive amounts of CA as I turn.

Ps I have ordered some of MesquiteMan's cactus juice and his chamber for my new set-up. I already have a new vacuum pump too similar to yours

Hope you have better luck with your pump than I did with mine ... the juice works well. Just be sure to test your temps of your toaster oven or whatever you use.

I have two and neither were remotely accurate (both low) and one off by 25ºF ...

Neat set-up there Ron. I've been toying with such an idea myself.

How much vacuum do you pull?

Originally Posted by dai sensei

The set-up looks Ok. I was always worried about glass jars coping with the vacuum and imploding.

If by -22 mm Hg Ron means 22/760 th of an atmosphere, then the pressure on the jar is only ~0.5 lb/cm^2 and it should be no problem. If he means 728/760 th of an atmosphere then there would definitely be a problem. I doubt its the latter since it is unlikely that can be obtained by a simple venturi effect.

For those that try this and wish to go to to higher vacuums, BEWARE, comparisons to the pickle jar lid dimpling are very misleading. Sealing food in full glass jars under vacuum is considerably safer because the jar is virtually full so the free space volume under vacuum is small so the implosion potential energy is negligible. ln a full pickle jar like that the free volume might be say 70 cm^3 whereas the entire pickle jar might be say 3000 cm^3 or 40+ time greater. Also in food jars the vacuum is usually in the region of the neck where the glass is thicker and the lid usually made of metal.

The implosion potential energy is related to the free distance over which the shattered glass particles can be accelerated. In the situation where the jar is full, in the small volume of vacuum remaining there is stuff all distance before the glass hits food or the lid so there is no implosion. In an empty vessel with a much larger volume the potential energy scales by volume so this is something to be wary of. Even at moderate vacuum, glass vacuum chambers are totally smooth, accurately hemispherical or cylindrical so they compress evenly on all sides, and the glass is nominally about 7 mm thick and they have a 1/2 mm thick steel safety mesh screen placed around them at all times. The problem with the pickle jar is the bottom is semi flat and it is not smooth. Flat glass surfaces of that area under vacuum have to be a minimum of about 2 cm thick or made out of laminated glass

If the pickle jar was to fail under a high vacuum the most likely thing to happen is that the glass would just crack but if it happened to be hit in the right place it could implode. I would then suggest making a simple safety screen screen for the jar and wearing safety glasses if one needed to remove the screen while it was under vacuum. I have never seen a glass chamber implode but have seen what it did to the steel safety cage and it looked like someone had taken to it with a 2 kg hammer.

Oh yeah, very neat set Ron! I like it.

My venturi vacuum pump pulls 22"Hg no problems, 26"Hg max if you leave it long enough, so I imagine Ron is referring to 22". I have no idea what vacuum results from process you normally use pickle jars for. I have noted a lot of people are using the them and I have not heard of any issues, but like yourself it worries the hell out of me, especially when you think about good pumps and that they can pull full vacuum.

My new electric 4.2cfm pump is supposed to pull the full 29.9" I'm told, although tests to date only show 26", but the manufacturer tells me there is something wrong with my gauge . The new chamber I have ordered is coming with another gauge, so I can double check. I also only want 24", to avoid the resins separating, so only a problem if it is pulling higher than the gauge is reading.

Originally Posted by rhossack

They are stabilized ... when they came out of the mixture they were solid white and after drying they turned clear.

But this is a different type of stabilizing. This doesn't give you a 'finished' shiny end product.

I use the 50/50 mixture on the punky woods to simply stabilize the timber while turning and not having to use excessive amounts of CA as I turn.

I discovered the same thing. Be warned the PVA never goes completely hard and can keep moving, so if the blanks are left for a long time before turning down, they often bend like bananas The epoxy stabilizer can have a similar result

Originally Posted by rhossack

Hope you have better luck with your pump than I did with mine ... the juice works well. Just be sure to test your temps of your toaster oven or whatever you use.

I have two and neither were remotely accurate (both low) and one off by 25ºF ...

My oven is not a toaster oven, although relatively small, it is a propper oven made for camping set-ups. Mind you, I still use a temperature gauge in the over, to make sure .

Originally Posted by artme

Neat set-up there Ron. I've been toying with such an idea myself.

How much vacuum do you pull?

Thanks ... I got -29hg according to the gauge.

Originally Posted by BobL

If by -22 mm Hg Ron means 22/760 th of an atmosphere, then the pressure on the jar is only ~0.5 lb/cm^2 and it should be no problem. If he means 728/760 th of an atmosphere then there would definitely be a problem. I doubt its the latter since it is unlikely that can be obtained by a simple venturi effect.

For those that try this and wish to go to to higher vacuums, BEWARE, comparisons to the pickle jar lid dimpling are very misleading. Sealing food in full glass jars under vacuum is considerably safer because the jar is virtually full so the free space volume under vacuum is small so the implosion potential energy is negligible. ln a full pickle jar like that the free volume might be say 70 cm^3 whereas the entire pickle jar might be say 3000 cm^3 or 40+ time greater. Also in food jars the vacuum is usually in the region of the neck where the glass is thicker and the lid usually made of metal.

The implosion potential energy is related to the free distance over which the shattered glass particles can be accelerated. In the situation where the jar is full, in the small volume of vacuum remaining there is stuff all distance before the glass hits food or the lid so there is no implosion. In an empty vessel with a much larger volume the potential energy scales by volume so this is something to be wary of. Even at moderate vacuum, glass vacuum chambers are totally smooth, accurately hemispherical or cylindrical so they compress evenly on all sides, and the glass is nominally about 7 mm thick and they have a 1/2 mm thick steel safety mesh screen placed around them at all times. The problem with the pickle jar is the bottom is semi flat and it is not smooth. Flat glass surfaces of that area under vacuum have to be a minimum of about 2 cm thick or made out of laminated glass

If the pickle jar was to fail under a high vacuum the most likely thing to happen is that the glass would just crack but if it happened to be hit in the right place it could implode. I would then suggest making a simple safety screen screen for the jar and wearing safety glasses if one needed to remove the screen while it was under vacuum. I have never seen a glass chamber implode but have seen what it did to the steel safety cage and it looked like someone had taken to it with a 2 kg hammer.

Oh yeah, very neat set Ron! I like it.

Well thanks and that's a lot of interesting data.

The Pickle Jar is thick and the jar inside the pickle jar that contains the fluid is thick too.

Originally Posted by dai sensei

I discovered the same thing. Be warned the PVA never goes completely hard and can keep moving, so if the blanks are left for a long time before turning down, they often bend like bananas The epoxy stabilizer can have a similar result .

Wasn't aware of this Neil ...

Was mildly surprised at how much the amboyna twisted from the time it went into the jar to coming out of the oven.

Did some Russian Olive and it twisted like crazy in the PVA and when drying under the forced air furnace.

Some folks think stabilizing means a totally shinny finished product when turned. That was the intent of me using the PVA and maybe I'm using the wrong word to describe what I'm doing.

My oven is not a toaster oven, although relatively small, it is a propper oven made for campig set-ups. Mind you, I still use a temperature gauge in the over, to make sure .

Good to check with a gauge ... I was using a Digital Gauge she got for Christmas from ne of the boys and I'm beginning to suspect it may not be totally accurate.

I bought a $5.00 toaster oven from the junk store my wife spends hours in looking for hidden treasures and the other oven is an Oster Convection Oven that sits on the kitchen counter top that I used while she wasn't home in case there might be ownership/permission issues to avoid

...the danger of implosions is covered in the video game Portal 2...but it does get rid of the deadly neurotoxin gas...
.

Originally Posted by dai sensei

I discovered the same thing. Be warned the PVA never goes completely hard and can keep moving, so if the blanks are left for a long time before turning down, they often bend like bananas The epoxy stabilizer can have a similar result

AHHHHHHH!!!!! That explains what happened when I tried to turn a piece of wormy spalted X-Cut Spalted Russian Olive wood this week.

Started drilling it and it was soft ... didn't even sound good when it hit the 'junk wood metal container'.