Vacuum Pump Specs

[Wrenchman]

Hi guys,
I've been here as a guest for some time but I've finally decided to register and say hello and get some advice.

I've been vacuum forming for a few months now, using a vacuum forming table and shop vac. - mainly small rc models ect. but I'm looking to upgrade the vacuum because I want to try my hand at prop making and I want to get the pulls as sharp as possible on some detailed large moulds for scifi wearable armour pieces.

I've contacted some local pump shops and they've recommended some pumps ranging from around $400 up to $2500.
I was hoping to get some advice because I know many of you have been doing this for years and have used a range of tables/vacs.

Do you think a vacuum pump with the following specs would get a nicely detailed pull on my table with the forming area dimensions approx 18"x18" and the max mould height 8":

Two stage 12 CFM rotary vane vaccum pump Pumping speed: 12 CFM

Ultimate vacuum: 3 Pa

Rotating speed: 3500 Rpm
Power: 1 HP


Thanks for your help, guys.

Wrenchman

 

[Knowone251]

Well, how thick of plastic are you planning on forming? I have a 24x24 former I just finished with a workable space of 21x21 and it pulls .060 HIPS just fine with my 6.5hp shopvac. Same with .060 ABS. But my experience with thermoplastics is limited to those two materials, and that thickness.

 

[Wrenchman]

Hi Knowone,
Thanks for the reply. I'd be using .090 ABS. Have you tried this gauge with your setup?

Wrenchman

 

[Kubla Kraus]

don't know a tremendous amount abot it myself, but for big pulls on a budget, you might set up a vacuum tank. you would pump down the tank and pull with that. I think you can still do big pulls, but using a smaller pump and a bit more time between pulls to vacuum the tank down. put a valve between the table and the tank. you just drop the plastic and pop open the valve.

 

[Duncanator]

I second the vacuum tank recommendation! Then your pump size only matters for how long it takes to empty the tank. I particularly like having a valve between the tank and the platen that you can open gradually, because that can help reduce webbing on tall or complex parts. It allows the plastic to stretch down instead of folding into itself and creating webs.

 

[laellee]

Definitely a vacuum tank, you can use a 30 gallon hot-water tank, that'd work for an platen your size. As for the pump, like Duncanator said, it's all about how fast you want to get the air evacuated. (for perspective, a 10cfm pump would evacuate a 30 gallon tank in a couple of minutes).
I would also use a stopcock instead of an electronic valve so you can control the pulls, it gives you a lot more flexibility. Good luck!

 

[Loess]

Assuming you're in the USA, Harbor Freight sells a 2 cfm vac pump for under $100. That can operate a vac former if you use it with a pressure tank.

 

[Fizbin]

For the thickness of ABS you're wanting to pull, you'll need a better understanding of the equipment and setup required to do so. I suggest popping over to www.TK560.com :: Index and asking the gang over there. They have more advanced knowledge than what you're likely to find on this board.

FWIW, my machine is similar to Knowone251's (except mine is 24x24) and I've done a lot of .060 PETG and .080 HIPS pulls in the past, but .090 ABS is a completely different animal.

Hope that helps.