Vacuum chambers and use with wood

[hawkeyefxr]

I am not new to this site though it has been a few years since i was last here.
Anyhow down the the topic, i have been turning all the time but fancied getting into using a vacuum pot. I bought a pump and pot from FB but wanted to try this out. In my bowl turning i have come across many wild wood bits of wood that have split when i have left them to part dry, small cracks i used super glue but bigger ones thats not possible. It set me to thinking about vacuum pumps, i am an ex air con engineer and decided to give it a go.

I want to take it a stage further and part turn bowl, wait for the cracks to appear and fill them. This can't be done in a pot obviously, so i cam up with the idea of putting the wood into a bag pouring in resin and hardener, pull the vacuum and force the resin into the cracks so making it stable and look good.

I got my old gauges out and set about making this possible, i found the heaviest/thickest plastic bag i could find. I altered some of the fittings so i could easily change from the pot to the plastic bag setup.
I thought i would try infusing wood first so found an old pen blank, immersed pen blank in just resin and pulled a vacuum, after an hour (yes i know it will take longer) i removed the pen blank and placed it on foil, this is where thing went a bit wrong. it caught fire i forgot to wrap it up so starving it of oxygen. Back to the drawing board or a new piece of wood lol.
I ran a test on my vacuum bag idea, i put a bit of soft leather into the bag and pulled a vacuum on the bag and it work really good the leather in the bag i could hardly bend it.

As an aside to the above i was on a walk and found two pieces of wood that have grown and fused together, i though that it will make a fantastic bowl so dragged it home, go knows what the neighbours thought!! This i want to use the vacuum bag method on.

I have seen a couple of mentions on vacuum pumps but was wondering if anybody is into this.

 

[Dalboy]

I always thought that a vac system was for stabalising the wood with something like cactus juice the put it into a pressure pot for the resin process. Maybe I am wrong as I have only ever cast resin without any form of chamber system

 

[hawkeyefxr]

I am not by any means an authority on this by any means. I am just trying to make it do what i want.
You may have seen when they make body parts for F1 cars, they are carbon fibre i know but they still use a resin. If you can imagine a half turned bowl that develops a crack it pretty much makes it useless or just plain does not look good. If it was filled with a resin with colour it would look good.
My idea is that you have a sealable bag with the split bowl and coloured resin in the sealable bag that has a hose take off to the vacuum pump the air it pulled out. Once the air has gone the resin will migrate to spaces, ie. the split. The pressure in the bag will be many tons one the bowl and resin.
The bowl could then be finished turning, sanding and polishing which hopefully will look very good.
This is all in my thoughts as at the moment as the resin is to gloopy because of the temperature. I know i can warm it up but as it's cold it will soon return to gloop.

 

[21William]

Welcome back Ken. I have absolutely no idea but have you seen this?

https://youtu.be/bpqh3vNEsMs

Please let us know how you get on as I’ve often thought of using resin with wood for small turning projects.

 

[Phil Dart]

Nice to see you posting again Ken - welcome back.

I'm no caster I'm, afraid, but what little knowledge I do have suggests that, as Derek mentioned, maybe you should be pushing the resin in with pressure rather than pulling it in with a vacuum. I can't see how you'd fill a big hole under vacuum, but then maybe that's where the bag comes in. I'll be interested to see what people who know what they're talking about have to say, which I freely admit I don't when it comes to casting.

 

[Dalboy]

When they are producing body parts for cars they are not using the vac system to pull the air bubble out but as a clamp as the parts are all odd shapes the same as using the vac and bag to apply veneers it just pushes the veneer down onto the backing board.
If you try and use a vac on resin casting like pen blanks you can get a foaming effect and end up with more bubbles than what you started with. A pressure pot squeezes the bubble very small and once set stay that way

 

[21William]

As Derek mentioned they use a vacuum to pull cactus juice into wood to stabilise it. Why does this method not work with thin resins then, is it just the viscosity? I appreciate to work properly it needs to fully penetrate the wood.

 

[hawkeyefxr]

I know you get bubbles when you pull a vacuum on wood immersed in resin. I also understand that a pressure pot will force the resin into fissures under pressure, but with a vacuum you still have positive pressure on the outside of the bag but negative pressure inside the bag. Like i said above the test piece of leath was nice and supple in you hands but in a sealable bag it went rock hard. The bag seal is even better under vacuum as it is being pulled together.
If you had a steel, or plastic bottle pulling the air out will eventually crush the steel or plastic bottle. It would need a good vacuum pump for the steel bottle granted.
This intrigues me, i used a vacuum pump a lot in my job as an A/C engineer and never gave much thought to what was going on inside A/C pipes just got on with the job. Vac pumps we pulled doe to a torr but that last bit can take some time depending on the size of the system.

 

[Dalboy]

As Derek mentioned they use a vacuum to pull cactus juice into wood to stabilise it. Why does this method not work with thin resins then, is it just the viscosity? I appreciate to work properly it needs to fully penetrate the wood.

You place the wood into cactus juice making sure it is submerged you then put on the vac pump this draws the air out of the wood when you release the vac as the wood is submerged then only the cactus juice can be draw into what was the air pockets in the wood therefore it is only cactus juice which I believe need to be baked to harden it.
Because you add hardener to resin it can start to go off which will in effect cause the resin to foam and as it is going off as soon as the hardener is added can give you problems

 

[21William]

Just seen this. There are others I’ve not watched yet.

https://youtu.be/MsednHxoE_A