help choosing a vacuum for a table press

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sammer
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Location: Fernie B.C.
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Post by sammer »

Yup PU...

If that first pic is with your pump pulling full vacuum you have a weak pump or a leak somewhere.
I would hook up a vacuum gauge directly to your pump and see what it's pulling.
If your not getting below 23"hg I would look at getting another pump.

I would suspect though, if the pump worked just using vacuum bags, you probably have a leak.
Smaller vacuum pumps don't usually create less vacuum, but take a lot longer to pull down.

The other thing I wanted to mention is that if your epoxy is not rated for the heat you are applying you will get the voids shown in your pics. The epoxy just gets too thin and runny once the heat is applied and runs out of the layup before it has a chance to set up. this will also cause lumps and bumps as the epoxy is moving around then setting up where you don't want it to.

Check your pump with a gauge, I'm betting you have a leak!

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)
pmg
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Post by pmg »

silicon is more than stretchy enough! Made my hollow tips with a silicone sheet, the silicone membrane moves around every uneventy easily.
wdwyeriii
Posts: 9
Joined: Mon Dec 14, 2015 11:23 am

my vacuum

Post by wdwyeriii »

Thanks for all the help so far. I will certainly seal the frame... and I will play with the heat to see if it stretches the silicone.

I was curious if people on here could provide some advice on this.

Right now, I am using this vacuum to pull the silicone on my table:

http://www.jula.se/catalog/verktyg-och- ... mp-739003/

I don't think the little kicker is strong enough, but before I buy a new vacuum for this, I wanted to see if people thought this vacuum should be able to do the job. What are your thoughts?

Also, do you think I could just connect 2 vacuums like this one to the same table at opposite sides to get more strength? (Julia has these on sale, so I could get a deal here).

Thanks for the help.
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chrismp
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Location: Vienna, Austria

Post by chrismp »

It really all depends on the seal you are able to achieve. A well sealed vacuum system will be able to pull a good vacuum even with a small pump. If you have a lot of leaks, a larger pump will still be able to pull a good vacuum as it is has a bigger airflow.

Hence my recommendation to seal your press as good as you can.
sammer
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Joined: Wed Dec 19, 2007 10:37 pm
Location: Fernie B.C.
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Post by sammer »

You can buy a cheap vacuum gauge at any auto parts store. Back in the day mechanics would use them to troubleshoot carburetor/engine problems etc.
That's where I got mine. (Haven't had to use it on a car in years, just collecting dust in my tool box)
It doesn't have to be super accurate, but will let you know if it's your pump or a leak.
Something like this will work;



Your pump is really small, around 2 cubic ft/min. It won't be able to keep up with even a very small leak.
It should work fine if you can get your system sealed up.

Leaks can be very hard to find.
If you put some white absorbent paper (paper towel) around inside the edge of your press and spray a bit of water with food colouring while your pump is running you may find something.
It's a bit messy but can work.
Double check all of your fittings and connections. How is your line attached to your frame/bladder?
When your pump is pulling a full vacuum there should be no air coming out of the exhaust.
Depending on the design you can put your thumb over the outlet and feel the pressure building if you're still sucking in air.
Usually the pump will get quieter once it has achieved full vacuum.

I don't think 2 pumps is the answer. If you have a leak you may end up with uneven pressures from one end of your ski to the other.

If your pump is pulling a good vacuum and you absolutely don't have a leak then...
Are you using some sort of breather to give the air an exit to your pump?
Is your vacuum hose collapsing blocking air flow to your pump?

Lastly...
You can't thermoform silicone sheet, it's very temperature stable. You can damage it with enough heat, but it won't soften it up really.
Silicone is the best vacuum bagging material, it should easily conform to your mold and it's contents.

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)
sammer
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Joined: Wed Dec 19, 2007 10:37 pm
Location: Fernie B.C.
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Post by sammer »

Did you ever find your leak???

Pressed a ski last week and my press frame now has a pretty good leak it didn't have before the move out to the new shop.
I could hear it and tried to seal it up but ended up just going with it and pressing the skis.
5cfm vacuum pump was still reading 24inhg at the gauge and pulled the membrane down tight.

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)
wdwyeriii
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Joined: Mon Dec 14, 2015 11:23 am

Post by wdwyeriii »

Yes! Thanks Sam, I did a few things that really helped:

1. bought some silicone in a tube and put some beads around both sides of where the silicone sheet meets the frame and pushed it in with a glove, then turned on the vacuum so it sucked the wet silicone in. I repeated putting a bead around the frame and stacked up more in the corners (quite liberal with the silicone)

2. I painted the frame in a 2 to 1 wood glue to water mixture to seal off the micro-holes in the MDF.

3. I bought some vinyl (normally used on a floor of a bathroom or something) at the local paint supply store and covered the table with it attaching with the remaining silicone (photo attached: although it looks like a tile texture, it is flat and smooth).

Below are photos of the vinyl and then the vacuum I am getting now... looks pretty good, and I think I will run a couple tests, then try to press again.

Vinyl on table


With vacuum on, and vinyl table
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