Re: More Vacuum stuff


Wayne Weedon Wrote:

What kind of pump do these machine normally use? Some have said I
might
possibly get away with a powerful industrial vacuum cleaner.

Any other suggestions welcomed.


Good vacuum cleaners generally pull about 4-6 inches of Mercury or 2 or
3 PSI. That's generally enough for undemanding applications like
typical cowlings and canopies made of thin (1/16" or less) easy-to-form
(HIPS or PETG or ABS) plastic. For thicker and harder-to-form plastic
(like Lexan-type polycarbonates) it's nice to have more forming power.

Shop vacs DON'T pull any harder than regular household vacuums, and a
big expensive vacuum cleaner likely does NOT pull any harder than a
medium-sized vacuum cleaner. The extra motor wattage usually
translates mostly into a higher volume of air flow against little
resistance, rather than a harder pull for vacuum forming when it
counts. (For example, if you look at the Shop*Vac brand shop vacuums
that Lowe's sells, the "6 HP" model only pulls 10 percent harder than
the "3 HP" model, and costs a whole lot more. Neither pulls any harder
than my 1000-watt Shark hand vac, which is a fraction of the size. The
horsepower ratings are completely bogus; you can't get six running
horsepower out of a standard 15-amp outlet.)

A used 8-12 amp canister vacuum from a thrift store generally pulls
about as hard as a brand-new expensive high end shop vac from a home
improvement store, at a small fraction of the price (and size).

A bigger vacuum cleaner may pull air faster against low resistance, but
any decent vacuum cleaner can pull air fast enough for home vacuum
forming of anything that will fit in your kitchen oven.)

If you want a lot more forming power, you need a vacuum pump of some
sort---a commercial vacuum pump, or a compressor converted for use as a
vacuum pump, or a kitchen vacuum sealer, or a converted bike pump, or
something.

You can convert a typical cheap oilless piston compressor by replacing
the intake fitting (if it's a screw-on) or enclosing it and adding a
fitting (if it's not), and using that as your vacuum intake. You'll
need an inline filter if you take the intake filter off rather than
enclosing its intake to use as a vacuum intake.

(Unfortunately, I don't understand the issues in converting
oil-lubricated compressors. I don't know how to tell whether vacuum on
the input side will interfere with lubrication scheme. Some
"compressors" are actually rated for pulling vacuum as well, but it may
be hard to find that out... in some cases you can find the info from the
manufacturer of the actual pump, which is likely not the same as the
brand of "compressor" with a tank and everything.)

A compressor will usually pull something like 24 inches of mercury when
used as a vacuum pump---about 4 or 5 times what a shop or canister vac
can do, and about 80 percent of what the best vacuum pump can do.

Check out my www.VacuumFormerPlans.com web site for more information.

Here's an "Instructible" on converting a $10 bike pump into a vacuum
pump you can use for small stuff:

http://www.instructables.com/id/make-a-manual-vacuum-pump-for-under-%2420-by-convert/

and another one on converting a little 12V tire inflator compressor:

http://www.instructables.com/id/convert-a-tire-inflator-type-air-compressor-into-a/

(The same basic strategy works for much bigger pumps, like the 5 HP, 12
CFM compressor I was given recently.)


The two-stage scheme (thanks to Doug Walsh) lets you use a vacuum
cleaner to suck the plastic down fast, then use a cheap low-volume but
high-vacuum pump to pull the plastic down hard to get detail.


Here's an old thread on "two-stage" plumbing using a Food Saver vacuum
sealer with a cheap air carry tank from Wal-Mart:

http://www.tk560.com/phpBB2/viewtopic.php?t=424

(I've simplified the construction of that setup a bit, using a regular
white PVC check valve from Home Depot and a tee, instead of a modified
sump pump valve drilled for a barb.)

I've used the same basic setup with various small pumps. With a fast
enough pump, you don't need the tank to store up vacuum, or the manual
valves. With an even faster pump, you don't need the vacuum cleaner or
the big check valve. (For example, with a 12 x 18 platen, I could just
connect the intake of the big compressor straight to the platen, like a
simple vacuum-cleaner setup, with just a filter in between.)


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drcrash
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