What's a good inexpensive Vacuum Pump?

It's difficult to find equipment for vacuum pressure casting that can be considered "inexpensive". I was a bench jeweler (goldsmith) and I got lucky. I picked up my set up from a former employer who was selling out his shop for retirement.

This is pretty much identical to my set up, but mine has a digital controller -

https://www.riogrande.com/Product/rio-vacuum-table-with-3cfm-pump-for-mold-making-investing-and-casting/705013

It was a good price, but after a few months, there were problems and I needed to replace the bell dome because of a hairline crack. The dome alone set me back close to $350 with shipping. Then the seals on the table then wore out, followed by a leak in the oil reservoir and a bad valve. By the time I had it running properly, I could have spent enough to purchase a new rig from a jewelers supply store.

With Mrosko's set up, please bear in mind that it was a business investment for him because of his association with Warriors Scale Models and Verlinden/VLS. Resin casting and mold making paid the bills, so the machine earns its keep pumping out a lot of castings. Mine degasses more casting investment for spinning jewelry than resin in an attempt to recoupe my losses on bringing it back to work. It's nice to have around for tinkering with my hobbies, but it has a day job. It's nowhere near what Chris uses and it can still be considered "overkill".

Your specs will be determined by your requirements.How large do you need it to be to fit your molds? The larger the molds, the larger the dome/pot, and this determines how large a pump you'll need to sustain the vacuum. Mine fits an 8x8x8.5 cubic mold, but I tend to use flasks because most of the stuff I pour is small in size and I can fit more in the dome while being more efficient with RTV.

Check jeweler supply houses, companies that carry equipment for dentists, and scientific supply houses as potential sources. Also, consider shopping around for parts to build your own rig as a way to possibly save on the investment. 

If you are careful with your mold design, you can get pretty good resin castings without a vacuum pump.  Use gravity to help get air bubbles out of the mold during casting.  When you design the mold, think like an air bubble.  If you were trapped in your mold, how would you get out?  This means increasing the vertical extent of your mold, to increase hydrostatic pressure.  Make the incoming pour sprue J-shaped, so resin enters from the bottom, and make sure there is a vent tube leading up from each local high spot in the cavity.  The incoming resin pushes the air out the vent tube, and there should be no unvented region in the cavity to trap air.

My big desire for a vacuum pump is for vacu-forming.  I have the same question.  I am thinking of trying to convert one of my old two-stroke model airplane engines into a vacuum pump, driving it with an electric motor, and putting a one-way valve in the glow plug hole.

STOVK, Don - I think I have good news for you. Don - for vacuforming you can get pretty good results if you just use a vacuum cleaner. It's not called that for nuthin'! While the mm/Hg reading of it isn't that great, the pressure difference bends heated plastic sheet just fine - and that's something I have tried many times, personally.

As for de-bubblin' resin castings, I can think of two solutions. I didn't try them myself, but I would bet a little money that they would work. First - a refrigerator compressor. You can get it for free if someone you know is throwing out his old fridge, that is still working. Refrigerator repair shops also sell those babies cheap, as long as you don't have a very special model in mind. A fridge compressor can be a good source of compressed air for airbrushing (I use one more than 20 years now), but I have also heard they can create a pretty good vacuum on the other end. Plus it's easy to fit a rubber hose to both ends.

The other solution would be to use an automotive part - an electrically driven vacuum pump. I don't know how popular those are in the USA, but in Europe almost every Diesel-powered car has one of those. A diesel engine doesn't create as much intake vacuum as the gas engine does, and vacuum is still needed for power brakes. You add 12V power source ant there you go - your own vacuum pump. When I was repairing my car some time ago, the mechanic demonstrated to me that such a pump creates an underpressure that makes it hard to take your finger away once you plug the open air line with it.

Hope it helps - good luck with your builds and have a nice day

Paweł

An interesting read Pawel.... 

Hello!

Well, I'm glad this is picking up - I try to get people to build rigs like that for years now, but they mostly prefer to buy cheap Chinese stuff instead.

Here's a rig that I have built for my pops like five years ago:

More on this build here:

http://cs.finescale.com/fsm/tools_techniques_and_reference_materials/f/18/p/151920/1628509.aspx

As for the youtube video - it's nice, but it might scare some people - like that moment with soldering with a torch. That isn't always necessary - you might as well use some well fitted rubber hose, clamped over the pipes and get a good connection. Or use a powerful electric soldering iron, or use epoxy glue instead. A power on/off switch would also be nice. So there's potential for fine-tuning, but the starting design is sound, and with little luck could be built very cheap.

Good luck with your compressors and have a nice day

Paweł