# The $100 Vacuum Table



## JAAune

No pictures yet but today I'd gone to the shop planning to mill panels for a kitchen out of 8 sheets of pre-finished ply. While programming the parts, I started thinking about how to clamp the stuff down and feeling too lazy to bother with complex solutions, decided to build a vacuum table instead of working on the kitchen.

I'll furnish the pictures later but briefly, the thing was built from one piece of 3/4" melamine and a 1/4" sheet of MDF. The power comes from a Shop Vac and a Festool dust extractor. Yes, I know that Festool is more than a hundred but the Shop Vac actually works better due to higher airflow and larger hose. We just didn't have a second Shop Vac on hand.

Basically all that's needed is to mill a 3/8" deep grid of grooves in the middle of the melamine. Two holes in the bottom allow the shop vacs to plug in. A 1/4" sheet of MDF goes on top, gets faced, then flipped and taped around the edges to the melamine plenum. One more facing to the top surface of the mdf completes the setup. Before going further, I used some pva glue to seal all the edges of the melamine and mdf.

I was able to test it today and it will definitely hold a 4'x8' down using onion skins while taking 3/16"x3/8" passes. I'll have to test heavier passes later and see if it's possible to remove the onion skin with a final cleanup pass.


----------



## klw

Very interested in seeing the pictures on this!


----------



## redSLED

Sounds interesting, looking forward to pics of your setup.


----------



## JAAune

Here are the promised pictures.



















There's not much to it. Just a couple vacuums, a 3/4" sheet of melamine, a 1/4" sheet of mdf and some carpet tape plus a little pva glue. I wish I could remember where on the web I got the inspiration for this but I never bookmarked the source.

The day was spent at the shop milling 8 sheets of plywood for the kitchen at an average of 30 minutes per sheet plus downtime switching sheets out. That's twice as long as it should be but my programs were done before I knew I'd have a vacuum table so the cuts were not as aggressive as they could have been. Also, now that I have this setup, I'll buy some bits that are designed for high speed milling of veneered plywood.

The cuts that were made today used a 3/8" diameter Onsrud down spiral at 300ipm and max cutting depth of 3/16". It was also possible to cut right down to the spoilboard for the larger parts but I never attempted it for the small components.


----------



## fge

JAAune,

That is cool. I will probably follow a lot of your threads since I am very new to all of this. We just got our CNC today and now I am on a huge learning curve since we have never had any CNC experience. I will be happy to just get the thing going. I still need to run a load of 2/0 wire for our RPC and then run home runs from the RPC to the spindle and vac pump.

My question I have for you, do you have an ATC? Our machine did not come with an ATC so I am hoping I can just run a 5 mm cutter and use that cutter for my shelf pegs, reduce my dado to 3/8 wide and just 3/16 deep and use it to cut the dados in 2 passes and then finally to cut out the parts. All with the 5 mm cutter. This way we would not have to change out cutters. I am hoping this works.

Anyway, I am looking forward to following all of the CNC community here at LJ.


----------



## JAAune

No ATC here. That always forces me to make some compromises.

For starters, I'd really like to run a down spiral to take out the rabbets then switch to a compression bit to do the rest but instead I end up using the down spiral for everything to eliminate changes. I tried an upcut starting with light skim passes then moving into the full cut but there was still too much lifting of the veneer (or the bit could be dull).

Since we're using down-cut bits, our dust collection needs to be upped to evacuate the chips. That flex hose is too flexible and cuts off some suction plus the 3Hp bag system isn't the most efficient.

I'm guessing you'll find it more efficient to switch out bits rather than use a 5mm to do everything. I don't know your machine specs but I'm assuming you have a lot more horsepower than I do (and a much better vacuum). That means you can probably cut a sheet of plywood in 1-2 passes if you have a beefier bit. That's a lot of time savings.

Changing bits is a minor hassle but you only have to reset the Z axis at the most. Perhaps your machine has a method of indexing tool height? Mine doesn't but a changeover only costs me about 2 minutes runtime so if it saves 10 minutes it's worth it.

Choosing cutting bits and feed rates is a big part of the learning curve. Early on my mistakes were not clamping parts down tight enough then compensating with slow feed rates. My RPM's were too high since I used the wrong bits and wanted to minimize chipping. Life is a lot easier if you use compression or down-cut bits on veneered material.

Rather than me instructing you in a field at which I'm still a novice, I'll just link you to the resource I've been studying.

Onsrude Production Routing Guide


----------



## klw

So the 1/4 " mdf is on top? Do you just pull through it? I don't understand how that would work?

But then there is a lot about CNC I don't understand yet! Pretty new at this whole thing.


----------



## JAAune

Yes, the vacuum pulls through the MDF. It helps distribute the vacuum more evenly and also provides a cheap, sacrificial surface to cut into. I can probably do 100 sheets before replacing it. I forget the cost but it's probably around $15 a sheet. That's 25 cents expense per piece of plywood I mill. I may in the future switch to 1/2" Trupan mdf which is supposed to be more porous.

Note however, that my instructions mention facing off both sides of the MDF with the CNC before using it. The outer surface of MDF is extra dense and doesn't let air flow through that well. You have to eliminate the outer .02" on both sides and work with just the porous inner portion.


----------



## dannelson

If you can get light weight mdf and seal the edges it will be much more efficient . We used to use 2 shop vacs and a 8 zone on our 5×10 and it worked pretty well. And yes surface both sides .


----------



## JAAune

Our supplier carries Trupan so I'll pick up a sheet with our next order and see how that works out.


----------



## DS

Holy Cow! When I saw your first pic showing how you routed your table, I immediately thought that it was a lot of area for your vacuum to pull. Then I saw the next pic and saw you had a shop vac attached to it.

The shop vac is low pressure, high volume - which might work with how you routed the table, but I kinda question it's holding power on a large sheet. Have you measured how many inches of mercury you're pulling with it? I would think you'd need at least 20 inches to be worthwhile. I wouldn't think a shop vac could get very much pressure. ( I could be wrong )

I have a small Venturi that I can pull 28 inches of mercury with, but it could never keep up with the volume that you routed into the table. There are cheap 10hp vacuums coming out of a China for about 2500 dollars that could easily make short work of your table. (I suppose that might not be cheap to many, but a really good vacuum setup around 40hp runs over 30k.)

Also, a quick note about MDF spoil boards. More porous is NOT necessarily more desirable. As you cut, the kerf exposes the spoil bd and causes vacuum leaks there. More porous equals higher leakage equals degraded holding power near the end of the cutting cycle. FYI. 
Once an MDF sheet gets below 1/2" thick it's value as a spoil board falls off rapidly.

P.S. A quick tip/trick: you can seal the edges of the MDF spoil bd with PVC edge banding, or, melamine glue to decrease the leakage.


----------



## JAAune

I don't have the tools to measure anything but it does work well enough to be effective. It's unlikely I can cut small parts in one pass without stuff shifting but the Porter Cable router doesn't have that much power anyway. 
A better vacuum system will have to wait. Extra cash is going elsewhere at the moment.

As the setup is now, I can either cut out sides for cabinets in four passes or cut small braces with onion skin. It's easy to pick sheets off the table while the vacuum is running but pushing the full sheet any direction takes a lot of force.

The edges are sealed with pva since there was an ancient bottle of it lying around.


----------

