Hope nick got his vacuum pump sorted out.
Now I got a little question, someone might be able to help with.
Want to Vacuum form some 1mm thick ABS sheet as a little private job,
and have been watching some forming machines go for crazy money on ebay
the last week. Both the machine I watched would of needed some
modification to work with the sheet size I need anyway.
Not really seen a vacuum former up close enough to take a look at what
type of pumps they generally use.
But it can't be rocket science. The job I have would involve forming
over a mold 10" diameter at it's base but basically tiered just under 4"
diameter at the top.
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.
Not yet. I'll get a perfect one from Bob in the next few days.
I had a look at Wikipedia and found some usefull links:
At the bottom, there's this one:
Don't know about the vacuum a shop vac can do. But as they say that a shop
vac is good enough and if you pick one that is suitable for water, you
should at least get -0.1bar or more (1m of water column to suck upwards
into the vac).
If you want to make it cheap (and inefficient) you could build an
ejector-pump (needs a compressor). It is very good at making volume and
the -0.85 bar are **certainly** good enough.
No, I didn't do any vacuum-forming because it doesn't work with metal. :-))
That much I can at least tell you because I use an ordinary Wickes (rebadged
Goblin made in Ireland jobbie) wet n dry vac bought about 20 years ago to
operate my cylinder head development flow bench. The pressure readings
across the head and comparison orifice are taken with water filled U tubes
and the vac can easily pull over 1 metre of water across the cylinder head
when the inlet valve is closed. Without connecting it all back up (not used
it for a while) I can't say the ultimate figure against a tight seal but
looking through my file of test results it's pulling 1 metre even with the
inlet valve open to the first datum point of 50 thou and obviously quite a
lot of flow is already taking place by then and the pressure difference has
dropped a lot. I know I had to make the U tube about 6 feet long to ensure
it didn't just suck the water right out of it. I'd say close to 1.5 metres
of water against a seal.
But as they say that a shop
Job sorted then.
There's a book, 'Do it yourself Vacuum Forming' by Douglas E Walsh,
obtainable from Camden
various mould formers and vacuum pump methods. He particulary likes a
pair of vacuum cleaner motors in series, but has several other
suggestions including storage tanks, compressors and tyre pumps.
Peter. Not tried anything yet, but thats one thing I had thought about.
I was rather hoping something almost ready to roll would comeup on ebay,
but the last machine I spotted on ebay went for daft money.
Might just have to do some experiments once I have machined up the mold.
Good vacuum cleaners generally pull about 4-6 inches of Mercury or 2 o
3 PSI. That's generally enough for undemanding applications lik
typical cowlings and canopies made of thin (1/16" or less) easy-to-for
(HIPS or PETG or ABS) plastic. For thicker and harder-to-form plasti
(like Lexan-type polycarbonates) it's nice to have more forming power.
Shop vacs DON'T pull any harder than regular household vacuums, and
big expensive vacuum cleaner likely does NOT pull any harder than
medium-sized vacuum cleaner. The extra motor wattage usuall
translates mostly into a higher volume of air flow against littl
resistance, rather than a harder pull for vacuum forming when i
counts. (For example, if you look at the Shop*Vac brand shop vacuum
that Lowe's sells, the "6 HP" model only pulls 10 percent harder tha
the "3 HP" model, and costs a whole lot more. Neither pulls any harde
than my 1000-watt Shark hand vac, which is a fraction of the size. Th
horsepower ratings are completely bogus; you can't get six runnin
horsepower out of a standard 15-amp outlet.)
A used 8-12 amp canister vacuum from a thrift store generally pull
about as hard as a brand-new expensive high end shop vac from a hom
improvement store, at a small fraction of the price (and size).
A bigger vacuum cleaner may pull air faster against low resistance, bu
any decent vacuum cleaner can pull air fast enough for home vacuu
forming of anything that will fit in your kitchen oven.)
If you want a lot more forming power, you need a vacuum pump of som
sort---a commercial vacuum pump, or a compressor converted for use as
vacuum pump, or a kitchen vacuum sealer, or a converted bike pump, o
You can convert a typical cheap oilless piston compressor by replacin
the intake fitting (if it's a screw-on) or enclosing it and adding
fitting (if it's not), and using that as your vacuum intake. You'l
need an inline filter if you take the intake filter off rather tha
enclosing its intake to use as a vacuum intake.
(Unfortunately, I don't understand the issues in convertin
oil-lubricated compressors. I don't know how to tell whether vacuum o
the input side will interfere with lubrication scheme. Som
"compressors" are actually rated for pulling vacuum as well, but it ma
be hard to find that out... in some cases you can find the info from th
manufacturer of the actual pump, which is likely not the same as th
brand of "compressor" with a tank and everything.)
A compressor will usually pull something like 24 inches of mercury whe
used as a vacuum pump---about 4 or 5 times what a shop or canister va
can do, and about 80 percent of what the best vacuum pump can do.
Check out my
web site for more information.
Here's an "Instructible" on converting a $10 bike pump into a vacuu
pump you can use for small stuff:
and another one on converting a little 12V tire inflator compressor:
(The same basic strategy works for much bigger pumps, like the 5 HP, 1
CFM compressor I was given recently.)
The two-stage scheme (thanks to Doug Walsh) lets you use a vacuu
cleaner to suck the plastic down fast, then use a cheap low-volume bu
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 vacuu
sealer with a cheap air carry tank from Wal-Mart:
(I've simplified the construction of that setup a bit, using a regula
white PVC check valve from Home Depot and a tee, instead of a modifie
sump pump valve drilled for a barb.)
I've used the same basic setup with various small pumps. With a fas
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.)
I'm not sure what you're talking about here.
There are two ways to use a compressor as a vacuum pump. One is t
reverse the check valves (or equivalent) so that the exhaust become
the intake and vice versa... that makes sense for bike pumps, but no
usually for other kinds of compressors.
The other way is just to use the intake of the pump as the vacuu
intake, with the pump pumping in the same direction. That's usuall
easier and safer. (You don't have to take the pump apart and figur
out how to reverse the flow.) A lot of air pumps that are sold a
compressors are suitable for use as vacuum pumps as well. (They ma
not be optimized to pull a really high vacuum level, but they're prett
good for vacuum forming anyway---80 percent of a perfect vacuum gets yo
most of the possible benefit for vacuum forming.)
When you do it that way, nothing much changes on the output side of th
pump. (Just leave the compressor output open so that it never build
up much pressure. In itself that shouldn't be a problem unless you'r
running the pump continuously for too long and exceeding its dut
Oops... I forgot to adjust the amps for the forum. What really matter
for motor power is the watts (volts * amps). 8-12 amps here (US) mean
about 1000-1600 watts. At 2x the voltage you need half the amps to ge
(Either, way, that's only a measure of motor power, not vacuum level.
If your vacuum cleaner isn't simply underpowered, more motor power doe
not usually translate into much higher vacuum---you likely get mor
"throw" but not much more "leverage."