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user error · Posted: Wed Jun 29, 2011 3:43 pm Post subject: Too much CFM?

Just joined the forum and need a stupid question answered (big shock, I know, right?).

I recently finished building my rig and the only thing left to do is hook up a vacumm source. I was thinking of using my dust collection system which pulls about 1,000 CFM!

So my question is what's the maximum CFM you can have on the Thurston James vacuformer? Confused

Thanks

crashmann · Guru Joined: 27 Sep 2005 Posts: 501

I don't know if you can have too many CFM's, except if you are fighting webbing while pulling multiple parts. Then you might not have enough time to jam down the web before it seals together and ruins the pull.

Shop vacs usually only pull a maximum vacuum of 4 to 5 inches of mercury, but have lots of CFM. I would imagine your dust collection system would have similar performance. Depending on the shapes your pulling and the level of intricate detail you're looking for, the dust collection system should work fine to get started with vacuum forming. Once you move into more advanced designs, you may need to upgrade to a vacuum pump and tank which will pull up to 29" of mercury.

Charlie

RRK4 · Novice Joined: 17 May 2011 Posts: 58

Also, isn't that the CFM at the source? If you constrict it to connect to the vacuum former I don't think it will be pulling anywhere near 1000 CFM.

jdougn · Posted: Thu Jun 30, 2011 7:37 am Post subject:

What type & thickness of plastic do you plan on using? That will determine whether the vacuum will work or if you need the vacuum pump.
DougN
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Fredo · Posted: Thu Jun 30, 2011 9:09 am Post subject:

It's not how much air a vacuum cleaner sucks, it's how hard. A little hand held vac. can suck as hard as a floor model, it just doesn't move as much air.. Put you hand over the end, and it stops moving air, even if the hole is 3 ins. in diameter. Try covering that same hole with your hand when a 3/4 hp Gast is on the other end.. It will probably double your heart rate in an instant...It keeps sucking till there's no air left in the plumbing. Vacuum Cleaner--Vacuum Pump = Apple --- Orange... If vacuum forming is to be more than a hobby or a lark to you, forget about vacuum cleaners already. The only reason they were used in the beginning is because they will work, and they're cheap and at hand. Another reason is that most platens built here leak. I know , some don't, but most do. With easily formed plastic a vacuum cleaner can still do the job because of the volume of air they move, unless the leak is to big.. The items this site was vacuum forming at it's inception was SW Armour... HIPS in the thicknesses used for armour is easily formed with vacuum cleaners. If the plastic is heated perfectly, thinner abs can be formed with a low-vac system...The problem is, the ovens shown on this site don't heat the plastic evenly. A hivac pump can overcome, somewhat, unevenly heated plastic. If you plan on getting off the porch and running with the big dogs, you're going to need that vacuum pump. I can ride a 100 miles on a scooter, but I'd rather drive a car. It doesn't matter what it looks like or costs, as long as it's a car...... Pardon my metaphors............Fredo
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user error · Posted: Fri Jul 01, 2011 1:25 am Post subject:

Hmmm... I see what you guys are saying and I think crashman is correct about how much hg my dust collector actually pulls. I have a CV 1800 Cyclone made by Clear Vue and the specs on their site are as follows:

Static Pressure (water gague inches) = 4.19
Velocity Pressure (water gague inches) = 3.36
Velocity (fpm) = 7341
Volume (cfm) = 1442

So if I'm reading that right, it only pulls around 4 hg, maybe less. Sad

Not that I'll be trying to form anything crazy with the table, just .060 and .080 HIPS, but I'm pretty sure my shopvac gets at least 5 hg. Oh well, I was hoping to get more mileage out of the $1,500 cyclone, but it looks like that would only be a waste of time.

I appreciate all of the replies, at least I now know that a vacuum pump is really the only way to go and I'll just have to keep saving up for a decent one.

Thanks again everyone. Very Happy

jdougn · Posted: Fri Jul 01, 2011 6:54 am Post subject:

Yeah, the vacuum pump is the way to go with thicker or harder to form plastic. However, seems like a lot of guys function fine using a shop vac to form HIPS. Post up picts of your project/s if you get the chance!
dn
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user error · Posted: Fri Jul 01, 2011 7:36 pm Post subject:

Will do, but it might be a while. I just finished planning my dream shop and only constructed the oven while shopping around for a contractor to help me build it. Once that's all done, I'll get started on some long awaited projects I've been sitting on.

RRK4 · Novice Joined: 17 May 2011 Posts: 58

You can get a pretty nice rebuilt pump on eBay for about $50. I bought a dud and rebuilt it myself but it ended up costing me about as much as a professionally rebuilt one would. The guy that sold me the rebuild kit said as long as you don't get an ancient pump they can be rebuilt to almost 100%.