Saturday, July 7, 2007

Instructable/Hack of The Day: Under-$20 manual vacuum pump (converted bike pump)

I wrote an Instructable on converting an old-school "floor pump" (bike pump) to a manual vacuum pump, for a total cost of about $18. (You could actually do it for around $13 with a little more effort.)

The Instructable got picked up as the Hack of the Day on www.hackaday.com a few days later, and got several thousand extra views because of it.

Here's a little video of using the vacuum pump on peeps in a mason jar:



A manual vacuum pump can be used with a small vacuum former for the occasional item formed from thick plastic. You wouldn't want to do it a bunch of times a day, though, unless you want to build up your biceps.

It can also be useful for vacuum pressing wood laminates or vacuum bagging composites. (A similar but smaller pump is used for vacuum bagging small things like skateboards.)

Check out the Instructuable here.

9 comments:

Garrett said...

Hey I read your instructable on vacuforming. I have a few questions about the different kinds of plastic.

Okay, basically I'm creating a custom water reservoir for my computer. I'm looking for a plastic with the following properties:

1. Can be heated in kitchen oven. (I've read acrylic explodes)

2. Can be drilled and bolted, i.e. will not pressure crack.

3. Not too difficult to vacuform. (I was thinking of using polycarbonate, but seems problematic)

4. Transparent.

5. Can be used with a bonding adhesive to form a water-tight and preferably transparent seal.

I've been looking into PETG, but can't find too much info on it. Do you know anything about using adhesives to seal two sheets of plastic together?

vacuumformer said...

I do heat acrylic in my kitchen oven, but I can't say for sure that's really safe. My impression is that the fumes are only explosive when they're very dense, and that's only when the oven is entirely closed for a long time.

My kitchen oven is a gas one that doesn't have a window, so I have to open it a bit about every 45 seconds to peek and check the sag. That lets some of the fumes (and hot air) out so that they don't get really dense.

You can use polycarbonate, but it is harder to form. You may want high vacuum for that, depending on the shape and the thickness you need.

Will your water reservoir be under pressure or vacuum? How hot will the water be? What kind of shape do you have in mind?

For adhesives, I'd check the manufacturers' machining and fabrication guides. For most plastics you can go to a manufacturer's web site and find a guide that tells you how to machine, form, and bond each plastic they sell.


I haven't tried to bond PETG, but if you look up a brand of PETG (such as Vivak or Spectar) and find the fabrication guide, it'll give you tips.

IPS makes a "Weld-On" line of solvent-welding solvents for various plastics and combinations of plastics and metals etc. Here's their selection guide, which has a chart saying which ones work for which combinations of plastics:

http://www.ipscorp.com/industrial/selectionguide.html

You can probably get the one you want from your local plastics supply place.

The advice is generally applicable to other plastics of the same type, but different brands.

(So, for example, advice about Plexiglas or Acrylite will generallly apply to other PMMA acrylics, and advice about Lexan will generally apply to other polycarbonates.)

Either polycarbonate or acrylic may require pre-drying. (Both can absorb moisture from the air, which can cause little bubbles when you heat the plastic.) Baking it in a 200-degree oven for something like 20 minutes per millimeter will generally fix that. The manufacturer's fabrication guides will give specific recommendations for each kind of plastic.

Garrett said...
This comment has been removed by the author.
Garrett said...

The shape will be complex and I'm planning on having bends of 3/8'' radius, if possible for the pipes leading into the reservoir. The reservoir itself will be 3-4'' in radius. (Think of a sphere with arms).

I'm planning on fabricating the whole thing with two sheets if possible to minimize leaks (each sheet will be a negative of the other, so if each has a hemisphere it becomes a full sphere when put together).

The water will be ~40C and under a little pressure created by a pump which pushes the water.

I'm leaning towards either acrylic or PETG right now. I'm not sure how to decide what thickness of sheet to use. My two choices for watertight adhesion seem to be a chemical solvent or using a rubber sheet bolted to the back.

If the transparency of using an adhesive between two plastic sheets is bad, then I'll go with the rubber backing most likely.

And thanks for the advice!

Mike said...

Hello Garret
This is Mike from NSW Systems LLC we are a vacuum forming company,
PETG clear might be your best choice for this project Polycarb(LEXAN) needs to be dried first then you can form it but you need 325 -375 depending on gauge (PETG) is formable at 150 deg and dose not need dried plus it is more forgiving if you mess up you can he heat and try again.
as for glue find a materal called resin bond it is used on polycarb to acrylic it is a clear liquid but you need a hypo type bottle we use a #125 hypo to apply you can assemble your parts together and glue them in place and clear parts you can watch the glue as you apply it to give a crystal clear bond..

good luck
Mike
NSW Systems LLC
nswsystems@gmail.com

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Rich Gunderson said...

Wow. Well thought out for under $20.

Vacuum Forming Mold | Thermoforming Mold

heins kellis said...

Vacuum pump will be use with the small vacuum formers and occasional formed with thick plastics.In this video show about vacuum pump on peeps jar.

Machine sous vid epas cher





wil70 said...

Hello, how much Hg or bar can I expect from such a vacuum pump?
thanks