www.TK560.com

TK 109 · Guru Joined: 11 May 2007 Posts: 712 Location: Galena, Ohio

well

it has all this weird vacuum-stuff on it, like "ari watts" CFM (i'm familiar with that...), and "sealed pressure" descibed as "sealed pressure representes how far up a glass tube a vacuum-motor will lift a column of water, measured in inches." kinda sounds like inches/Hg, but i dunno.....

also the amps on these things are INSANE (i guess):

12W, 12W, 11.5W, 11.7W, 7.9W, 11.5W, 9.6W, 8.2W, 7.5W.....

i guess i should have picked up a shop-vac instead of a RIGID wet/dry vac, eh.....?

oh well....

i'll get a pic of it soon...
_________________
-Alex

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TK 109 · Guru Joined: 11 May 2007 Posts: 712 Location: Galena, Ohio

here's that info sheet, thingy:

these numbers are WAY higher than RIGID wet/dry vacs!

just a visual!
_________________
-Alex

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TK 109 · Guru Joined: 11 May 2007 Posts: 712 Location: Galena, Ohio

jim,

i BELIEVE you have the "Easy Mobility" vac, correct?
_________________
-Alex

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drcrash

An inch of water is only 0.07343 inches of mercury, because mercury is way heavier than water.

The BEST of those Shop*Vac brand machines pulls 4.4 inches of mercury.

That's:

0. only a little more than 2 PSI.

1. Less than my little Shark hand vac pulls (4.5 in Hg.)

2. Less than half what (somebody else here's) awesome Philips canister vacuum pulls, with its 18-amp motor and 3-stage pump, and

3. Less than a fifth the pull I get from my converted bike pump, or my converted electric tire inflator, much less my Thomas vacuum pumps (like Doug sells).

The bottom line, as I've said over and over again is:

Shop vacs are not especially good for vacuum forming. They're just vacuum cleaners that suck air through a bucket. They are no more powerful than a good canister vacuum with similar watts/amps that you can get for $5 at a Goodwill Outlet Store----and *worse* than some.

Shop vacuums are optimized to suck a lot of air against very little resistance. That doesn't help much when it comes down to sucking HARD to get good detail.

DON'T BUY A SHOP VAC FOR VACUUM FORMING. It's a big waste of money. Put the money toward a vacuum pump, or a compressor that you can convert to a vacuum pump.
_________________
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com

jegner · Posted: Thu Aug 30, 2007 9:09 pm Post subject:

I use a Shop-Vac 6.5hp. But use it for more than just vacuum forming. I also have a Robinsair pump I got from Stomper. Finding a tank I like is the only thing keeping me from switching over, but I get accectable results from the shop-vac for the type of stuff I make a shop vac pulls fine. Double duty, as it helps keep my shop clean!

Jim

kayaker43 · Expert Joined: 13 Jun 2007 Posts: 175

Paul is right,.. no matter how much HP, or amps it pulls, No matter how much it dims the lights and hurts your ears, no matter how many stages they say it has, you won't get much over 5 inches of mercury. The biggest $300, 220 volt 3 stage motor may hit 6 in. Even the cheapest, smallest 1 gallon vacs flow more air then we can benefit from, but none of them suck hard enough. Don't spend much on your shop vac....

Despite this I still get arguments from people who swear their electrolux can suck the chrome off a bumper.

Not trying to sound arrogant but anyone who thinks their vac powered machine works good,.. just hasn't seen good yet! The difference really shows when you use thicker or difficult plastics. Thankfully many people can get the job done with thin gauge styrene or ABS parts.

drcrash · Last edited by drcrash on Fri Aug 31, 2007 6:49 am; edited 2 times in total

kayaker43 · Expert Joined: 13 Jun 2007 Posts: 175

Hmm,.. my last post still sounded a bit arrogant. I don't mean to belittle anyones efforts at vacuum forming. Costume armor is one of the best uses for vac powered machines, and for many that's all they need.

I'm just trying to communicate that there is much more forming power available if you need it. Unfortunately its hard to start with a shop vac system and try to soup it up later. Shop Vac's offer high flow and tolerate all kinds of sins when it comes to platen design. Once you start moving up the vacuum scale, you have to get more anal about leakage and excess volume.

While we're bashing vacuum cleaners, here's some trivia:

750 watts is 1HP. so a 15 amp 120 volt circuit won't support much over 2 HP,.. someone explain to me how you can buy a 6.5 HP vac?? That "peak" thing is just the spike you see on startup.

The reason they use inches of water instead of mercury is because it makes big impressive numbers.

The big 2 inch hoses make the vacuum seem more powerful on your hand because its grabbing more surface area and they usually build a little compressability into the hoses to give the impression of awsome power.

And finally,... that ear splitting howl you hear when the hose is plugged is not the motor struggling for all its worth. Its actually unloading because the impeller is stalled. The highest load that motor sees is when sucking free air.

drcrash · Posted: Thu Aug 30, 2007 10:50 pm Post subject:

An interesting thing in that table is that the lower-powered Shop*Vac(TM)'s pull nearly as hard as the higher-powered ones. The 7.5 amp ("2.5 HP") machine only pulls 10 percent less hard than the 12.0 amp ("6.5 HP") machine.

That suggests to me that

1. the HP ratings are as meaningless as Doug says they are

2. the higher-powered machines, which SHOULD pull substantially harder than the lower-powered machines, are optimized for higher CFM, not higher vacuum, and only pull a little bit harder. They can pull substantially more air, which you don't need, but they can't pull a small amount of air significantly harder.

If that's true of shop vacuums in general, it would explain why Jim didn't notice a difference between a 3.5 and a 6.5 (for vacuum forming)---basically, there just isn't much difference. The cheapest Shop Vac in that pamphlet is about as good for vacuum forming as the most expensive one. (And they're all comparable to a typical canister vacuum.)

A 10 percent difference in forming pressure doesn't generally give you noticeably different results. A factor of two or four does.

On the other hand, the higher CFM shop vac may be better for cleaning up your shop, making a wider swath of air moving fast enough to pick up sawdust and stuff. If you need more CFMS, it's got them.
_________________
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com

drcrash · Posted: Fri Aug 31, 2007 7:01 am Post subject: self-doubt & a question

I'm not confident of what I said in my second-to-last post, so I edited a meta-comment in at the beginning, and now I'd like to ask: is it true? Do you get less webbing with high vacuum because you can use less sag?

Or was I just bad at using low vacuum, and not using the "right" amount of sag in the first place?

(Doug, I'd be especially interested in your opinion on that, since you probably have the most experience with both high and low vacuum systems, and have obviously thought about this sort of issue a lot.)
_________________
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com

kayaker43 · Expert Joined: 13 Jun 2007 Posts: 175

Yes,.. I think the only effect higher vacuum has on webbing, is that it allows you to use less sag. which helps to some small extent. Shop vacs force you to overheat the plastic to compensate for less suction.

The other debate is whether applying vacuum fast or slow has any effect on webbing. I'm thinking no, or negligible just based on observations. I can however make a weak argument why it might, but don't have time to set up controlled tests.

Webbing is complex, yet understandable. It could be the topic of a very boring book Shocked

Fredo · Posted: Fri Aug 31, 2007 6:22 pm Post subject:

If you open up your shop vac you'll find a vacuum motor much like the ones listed here. www.grainger.com #2m195 The best vacuum this design will deliver is about 6in hg. no matter how many stages it has.

drcrash · Posted: Fri Aug 31, 2007 7:55 pm Post subject:

Plasticman · Expert Joined: 08 Jul 2006 Posts: 109

I have often wondered how a central vac woulf do for vac forming. You know, one of those vacs that is located in a basement or garage and has pipe running throughout the house. I bet if it were just hooked up to table it would pull pretty good.

TK 109 · Guru Joined: 11 May 2007 Posts: 712 Location: Galena, Ohio

woa!

lotsa input!

well, so far i pull fine with armor, i mean i can put risers on the molds, and get a decent pull. that's my humble little vac-machine for ya!

but you're right doug.

i completely understand what you are saying.

now, i've heard (from some other thread) that you can get better performance with shop-vacs not by connecting the hoses in sequece, but by making a box and sealing it, and cutting out lage holes for the shop-vac heads to fit through, then adding weather stripping to that, and having a single hose coming out of that box unit thingy.

has anyone tried this, does it REALLY make a difference, and is it REALLY worth it? i'm just trying to come up with some ideas in case i can't get the tight pull i need in a tight situation.

i'm thinking too hard again... Laughing

_________________
-Alex

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