DIY Vacuum Pump for 4x6 vacuum bed

I finished my CNC router build a few months ago and decided to make a vacuum bed for it. I made it a hybrid type with T slots and 6 vacuum zones. At the time I was building it I didn't know what I was going to use for a vacuum source. Others had used a shop vac and I had that available so my plan was to use that, learn about it's capabilities and decide what I truly needed for vacuum. I had never used vacuum hold down before and I quickly learned that I really liked it. There's nothing easier than throwing a sheet of material on the router bed and flipping a switch to anchor it flat! And not having to use tabs and avoid clamps. Fantastic!

The shop vac worked fine for larger parts but not the small stuff. I needed a source that pulled deep and had decent CFM for flow. The shop vac info I found indicated they flowed around 77 cfm and only pulled a couple psi vacuum. I quickly realized that a capable, used vacuum pump was going to run at least two to five thousand dollars (eBay). Way over my budget. After a lot of looking at various vacuum solutions, I figured out a way to do it that wouldn't break the bank and should out perform a 5hp Becker unit by a substantial amount. It's a combination of two pumps: a Roots vacuum pump paired with a common rotary vane vacuum pump. The roots pump is high flow and is called a roughing pump. It doesn't pull a deep vacuum but flows really fast and is used for evacuation of large volumes rapidly. The roughing pump feeds a rotary vane pump, called a backing pump in this configuration. The backing pump doesn't flow very fast but pulls a very deep vacuum. This is a video of this type of setup: https://youtu.be/tdOKjr4Jylk

The roughing pump generally increases the performance of the backing pump by a factor of 7 to 10x.

So after a lot of browsing on eBay I found a roots pump in great shape and within driving distance. The backing pump is just a common rotary vane pump available in all different sizes and capabilities. I found an oiless version that flows at 22cfm and pulls vacuum to 28" Mercury. I've got it put on a stand and wired up. Still need to do some piping but here's some pics. I'll update this thread as I get it running. https://uploads.tapatalk-cdn.com/201...ae49dc3e85.jpghttps://uploads.tapatalk-cdn.com/201...3b3a1a0146.jpghttps://uploads.tapatalk-cdn.com/201...b22e055dbb.jpg

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You are trying to use brute force and ignorance - and it is not working.
Get some builders plastic and cover the entire vacuum table except for the area of the job. That way your pump won't be sucking cusecs of air pointlessly.

Cheers
Roger

Hmm, how about I just valve out the zones that I'm not using... [emoji849]

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Is that thing really loud?

I haven't run it yet for any appreciable length of time but the little I have shows it's quieter than the shop vac. Not by much but some. Apparently from what I've read, under high vacuum when the flow is low they are pretty quiet.

To be sure, if you can isolate some sections there is no need to suck air through them!

I use a quite small vacuum pump - maybe 200 W. I seal all air leaks so I get a good vacuum.
Attachment 388360
This is a small PCB but it is still held quite securely because the vacuum is good.

Cheers
Roger

If that was all the surface area I wanted to pull vacuum on then yes, my set up is overkill. But my goal is to pull sufficient vacuum through a low density MDF board on a 24 ft² work area to anchor even relatively small (~1 sq foot) pieces of material. Our requirements are quite different.

I would say that you don't want to use low density MDF, as too much air leaks through it.

Small pieces will always be problematic. What helps is to block them in with some scrap, so they can't slide around.

On our 5x12 table, we have two 10HP Becker pumps. I onion skin any parts smaller than 2.5 square feet. Using smaller tools can reduce the cutting forces, and can help with smaller parts.

Thanks Gerry, that's good to know. Probably just use a sheet of regular 1/2" MDF surfaced on both sides?

We use 3/4, as it's more stable than 1/2" and allows you to surface it as it gets worn.
We remove .01 from each side, and then .01 at a time until it gets down to 1/2", and then we replace it.

my goal is to pull sufficient vacuum through a low density MDF board on a 24 ft² work area to anchor even relatively small (~1 sq foot) pieces of material. Our requirements are quite different.
I disagree. The difference in scale is minor. What works on my small vacuum table can work on your much larger one - IF you go about it the right way. Incidentally, what I describe below is well-known to other users.

Step 1: seal the underside somehow - that will depend on the details of your system.
Step 2: epoxy coat around the sides of the MDF to eliminate any leakage at the sides. Seal maybe 1/4" around the edges on top as well.
Step 3: Cover the top surface with builders plastic or something similar - and weight it down all around.

Now run your vac pump and see what vacuum you get now that you have blocked off the air flow. It will be a good.

Then take a 1' square of whatever you want to engrave and cut a matching hole in the builders plastic. Align job with hole. Run vac pump and check pressure.

This is nothing new; it is well-known. It is not especially dependent on the area of your vac table, only on how well you seal the unused part of the surface. Try it and see.

Cheers
Roger

Time for an update. I've had it operational for about a month now. I got some 3/4 MDF and surfaced about ~.020" off each side, then I sealed around all the edges with epoxy and this is now my router bed. I also added a vac guage to the manifold so I had some idea of how it was working. For a baseline I hooked up the shopvac, Craftsman 20 gal, and closed all the manifold valves and turned it on. It barely moved the needle, guage is scaled in mm/Hg. To reiterate, I had good results with the shop vac on large sheets of plywood but found it inadequate on smaller pieces less than a couple square feet. With all valves closed running just the backing pump i get about 20mm/hg vacvuum, turn on the booster pump and it pulls down another 5mm. And it pulls down pretty fast, full vacuum on the closed manifold in about 5-7 seconds. Start opening vacuum valves to the bed and I start losing vac pressure. With half the valves open I run at about 13mm/hg. With all valves open and nothing sealing the open areas of the bed, like plastic sheeting, it still holds about 7mm/Hg. But if I close off valves to focus the vacuum on just the sections of the bed I'm using I get close to 15mm/Hg. And this will hold down a non-porous, 1 square foot piece of material.

I could do some things to improve it I think. Even though the main bed is made of Expanded PVC board and should be non porous I think it leaks a little. So I could seal that up which is easy and not much to it. I could also modify the bypass valve on the booster pump so it stays closed longer and forces more air into the backing pump but I dont know if this will increase max vacuum or, just how fast it pulls down?

ANyway, I'm happy with it. For what I spent I got a capable vacuum pump at a bargain price. Its much quieter than a shop vac but its not "quiet". It definitely improves the convenience of using the router.

ANyway, I'm happy with it.
And that is all that matters.

Cheers
Roger

LOL I thought from the title 4x6 was in inches. Obviously after seeing the photos Its feet.