[BackyardDan]

We recently installed 2 Becker vacuum pumps on a 20' table. They combine at the pumps to a singe 1 1/2" line that runs to the table and is about 75' long. We seam to be having some trouble holding material down to the table through the MDF. The meters on each pump are reading around 16 oz of mercury which doesn't seem to low but was wondering if anyone had any solutions to help with hold down or with getting more pressure from the vacuum's. Also wondering if the air line is sufficient at 1 1/2".

[txcncman]

How many square inches is the part before and after cutting?

If you have 2 pumps, run them separate on 2 overlapping zones.

Add sealant to open edges of the MDF.

Switch to a pod type vacuum clamping system.

[ger21]

What are you cutting? How much of the spoilboard is exposed? Does your spoilboard have seams in it (multiple boards)?

We have two Becker pumps on a 5x12 table, and smaller parts will still move. The more table area you have exposed, the better the chances of your parts moving.

[BackyardDan]

The table is 4'x20' and we are routing a lot of different things. Since it is 20' long we have 3 pieces of mdf so there are 2 seams. The material we most frequently rout is 4'x12' or 4'x18' sheets that lay flat on the surface. We originally had a little trouble holding these down but it was not significant, for some reason this week we have had more trouble especially around the edges. I see we can seal the edges of the mdf so we will try that and I think that may help a lot on the larger items.

We also rout aluminum that is 3 1/2", 6", 8", and 10" wide and this has almost no hold down. Can you drill the mdf to make the air pull directly on the surface of the material we are routing?

[txcncman]

When you do any cuting to your MDF you are increasing surface area and vacuum leakage and defeating the purpose of MDF. We used to spray our MDF with sealer on the outside edges and on the top side and then fly cut pockets to fit the material size. But then we were usually setting up to run a couple thousand parts per run too. Then we would mark those MDF sheets for that job and store them for a few weeks until needed again.

[ger21]

If the entire surface of the spoilboard is not covered by the workpieces, then sealing the seams won't help a lot, as the vacuum will leak right through the adjacent face.

How are you sealing the seams. My guess is you'd lose a ton of vacuum at the seams, unless the sheets are glued together tightly.

If you want vacuum to hold down parts that small, you'll need to cover almost the entire spoilboard to block leakage.

[txcncman]

I have also used vinyl sheets to cover unused spoil board areas.

[dodger889]

I have some questions. What are you pulling in vacuum with nothing on the table?? Or maybe a better way of asking what are the gauges reading with an open circuit? This will tell you weather or not the pipe is too small. Ideally you should read all most nothing. If you have restriction from your hold down area to the pump you are kidding yourself to ever think that it will hold well.

Also do you have table setup in zones? So you can use one part of the table with vacuum and the area not being used with nothing.

You said you have two pumps are they on separate feed or are you using them in tandem?

Also something that help is blocking off the unused part of the table that has vacuum being applied to will greatly increase your holding power. This might you to make up some cutouts in the shape of the smaller pieces you are cutting or milling.

[fizzissist]

All the previous discussion aside, you're losing right off the get-go with a single 1 1/2" line, in both that small dia and the length, then the overall square footage. For what you're talking about, you should be at 3" min.

Assuming that 16oz is 16"gage? That's only about 350 torr... nothing to get excited about unless it's a Kirby.

Simply, you need more pumping power and bigger dia lines to reduce your losses. I wouldn't run them coupled together either.