Planning a vacuum fixture and need help for vacuum source.

[gundog]

I plan to make a vacuum fixture for this part (see picture)I need a vacuum source either a pump or a venturi type source. Cycle times I expect to be around 5 minutes or less. I will probably make 20 to 50 at a time. Right now I have a fixture made that uses some corner shop made clamps allowing me to drill and tap the holes in the interior,I add hold down screws through those drilled holes and cut the profile. I would like to put the blank on held by vacuum and do the whole part to get the cycle time down.

I use vacuum on a router table but it is a high CFM low pressure system that allows a lot of air leakage. This fixture I plan to be a high hold down pressure no leakage or very low leakage system. Of course I want to get by as cheap as possible. I plan to machine the fixture specifically for this part. I have a couple Harvey "O" ring cutters and some "O" ring material. The part is cut from a 19.5" x 11.75" X .250" 5052 AL blank it has plenty of surface area for vacuum the part is bent after machining.

I have been looking on my local CL for a vacuum pump but I don't really know what type I need other than it needs to be continuous duty. I am not sure which type are designed for continuous duty. I have heard the venturi type vacuum source use a lot of air.



Would this work? GAST Vacuum Pump DOA-V720-AA Oil-less Diaphragm Pump Air Compressor with Vacuum | eBay (https://www.ebay.com/itm/GAST-Vacuum-Pump-DOA-V720-AA-Oil-less-Diaphragm-Pump-Air-Compressor-with-Vacuum/202609089865?hash=item2f2c715d49:g:wJ8AAOSwPvVcdaU F:rk:16:pf:0)

[Brian Harnett]

I made one from a lawnmower engine works great, trouble free for the last 6 years I pulled the camshaft put a soft spring on the intake valve Made a check valve on the spark plug hole and its good to go I have it hooked to a old 20 lb propane tank for a reservoir for good initial high volume suck down. Pulls good volume and 22-25 inches mercury.

Video of it working
https://vimeo.com/78819653

[jTr]

As an avid veneering enthusiast, I've got a venturi style, automated pump from vacupress that I've run for years. If interested in veneering as well, I'd highly recommend. Unless you're evacuating a 4'x8' press bag, they do not use much compressed air at all. Especially for your intended use - a quick shot will establish your vac hold down to 20-25 Hg in a second or less, air triggers off and silently holds your part til the next one.
However, I'm sure they're now going for $750 to a full grand now days.

AVOID: cheapo-vac pumps, or at least make sure it's oil free. Thought I pulled a bargain through HFT, until it completely fogged the shop with oil vapor while in use. Good grief!

Quick search on my favorite veneer supplier revealed this:

https://www.veneersupplies.com/products/Vacuum-Pump---Thomas-315-CFM-120-VAC.html

Doesn't get much better.
Also, check his veneer pressing supplies - awesome vac-seal tape you'll likely need around the jig, unless you mean the O-ring stuff you have is intended to be the vac seal point on your jig.

https://www.veneersupplies.com/products/Vacuum-Templating-Gasket-Tape-38-x-116-x-100.html

Okay- just meant to advise, but I guess I've done some shopping for you too...!;)

Jeff

[Burkhardt]

You can look for a refurbished oil-less double piston pump on eBay like the ones made by GAST or Thompson.
I have 2 of them and they cost about $150 each some 6 years ago. Usually I would use only one of them for a pod like you describe. Occasionally I also turn on the second pump when there is more leakage or to draw down vacuum faster.
I recommend a few gallons vacuum reservoir to evorcome the initial laekage before the blank settles down on the gaskets.

You may also want to look at this 1.2hp Harborfreight compressor: https://www.harborfreight.com/2-gallon-12-hp-135-psi-ultra-quiet-oil-free-professional-air-compressor-64596.html

It is the same oilless double piston design as the GAST pumps, inexpensive and higher power (mine have only 1/2 hp). I am pretty sure this compressor can be reconfigured as vacuum pump as well (swapping in and outlet and eliminating the pressure switch) and you get a reservoir for free.

As mentioned in the other post do not use the cheap air conditioner pumps the spew out a lot of oil.

[bobmoore]

I will put pictures up of a pump I will be selling tomorrow night.

[gundog]

Thanks for the info. Bob you can shoot me an email of what you have if you want to. mike@millermarineproducts.com

[bobmoore]

Mike are you planning to vacuum 20-50 and run them in one run or is 20-50 at each run but 1 at a time? It makes a big difference what vacuum pump is appropriate.

[gundog]

Mike are you planning to vacuum 20-50 and run them in one run or is 20-50 at each run but 1 at a time? It makes a big difference what vacuum pump is appropriate.

These parts are one at a time made in my VMC 50 part runs. I have been making them on my router table 20 at a time but edge finish is not great and my shop built vacuum system is not really up to the job I have probably made 200 with the router over the last year. I changed the design slightly and added taped holes. I was spending way too much time sanding the edges of the parts. The VMC cuts much nicer and faster.

Thanks Mike

[Burkhardt]

One more thing comes to mind. Depending on the bit, feed rate and depth, the forces on the blank will be substantial. While an o-ring cord in a groove can seal the vacuum well (given proper compression), it will not hold major horizontal forces and the slippery aluminum on e.g. a wood or plastic fixture will also tend to move. You could use a thin adhesive compressible gasket foam tape that will hold vacuum and horizontal force or add some other non-slip material to the fixture surface.

[jerry_stanek]

One more thing comes to mind. Depending on the bit, feed rate and depth, the forces on the blank will be substantial. While an o-ring cord in a groove can seal the vacuum well (given proper compression), it will not hold major horizontal forces and the slippery aluminum on e.g. a wood or plastic fixture will also tend to move. You could use a thin adhesive compressible gasket foam tape that will hold vacuum and horizontal force or add some other non-slip material to the fixture surface.

We use pods that are just a custom fixture to machine parts on our Pod and Rail cnc that has way more force then a shopbot.

[bobmoore]

A ridged flat fixture is ideal, aluminum or I use corian because I have it in stock. Use a compressible oring that will pull perfectly flat to the fixture with the vacuum on. If your oring stays proud even 1/4 aluminum can bow down in the center. An oilless vacuum pump in good condition with a good fixture will pull 25 inches of mercury give or take a little and should hold your part just fine. If the part does move line the bottom of your fixture with some adhesive backed 120 grit sand paper and that will hold it.

[bleeth]

Here's a couple links for the right type of pump:
https://www.veneersupplies.com/search.php?search_query=vacuum+pump.
https://www.vacupress.com/
Google vacuum pods and you will see tons of commercial examples of fixtures used. A great way to make your own is out of corian, although plenty have used hardwood.
I got a Vacupress many years ago that works in combination with my compressor and it still works fine. It has a choice between holding whatever pressure you set or constant on. Unlike the pumps used for full sheet holddown, you are pulling low volume of air but high pressure.

[gundog]

Thanks for the info guys Bob has offered to sell me a pump I think is going to work very good for this project I will follow up with some pictures and a video using the fixture when I get it built.