Vacuum Table questions

[Nick12]

Hello all,

I could not find a forum on here for Vacuum table questions so I am posting here. I own a 5 x 10 Laguna Smart Shop II with a vacuum table powered by a 10 HP Becker pump. 169 CFM, 24 HG. I bought it used and know that this table is not the best on the market. I am not impressed at all but its all I got right now. I have the Becker pump dedicated to a 22" x 96" zone. I have a piece of 1" MDF planed down on both sides and the zone is gasket-ed off. I cut 3/4" thick x 5 -1/2" wide x 8' long HDPE. I put 4 boards on the table to cover up the complete zone. My questions are:

1: Is my pump big enough because my boards are still moving pretty good?
2: I noticed the piping and hoses under the table are 1" Should it be 2" or bigger? Could this result in Vacuum Loss
3: Should I purchase a Busch, Becker or Decker pump. I am looking for something that pulls 25-29HG and 400-500+ CFM?

Thanks

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[ger21]

1) Hard to say? How fast are you cutting, and are you cutting in one pass? Have you tried onion skinning?

2) Our morbidelli has a 5x12 table, and two 10HP Becker pumps. Each pump has two 3" hoses going to the table.
So I'd say that your hoses are too small. But it also depends on the design of the plenum.

I don't cut plastic, but similar sized melamine parts would move on our machine if cutting in one pass, which would be in the 800-1000ipm range.

I'd try using 3/4" MDF for the spoilboard. Seal all the edges, and remove .01" from each side. That's what we do.

[Nick12]

I do a total of 3 passes. I do 2 passes at ~.35 on all my pieces first and then run a 3rd pass at .05 "Onion Skin". I cut at 100 IPM which is considered pretty slow compared to what I have heard other people are cutting at. I cut that slow because any faster and I get chatter on the edges of my material. I use a 1/4" upcut 2 flute spiral bit. I use 1" MDF because I have been told by other people that the thicker the MDF the better. I have used both 3/4" and 1" now and dont know if it is making a difference. I have the edges completely sealed off using a thick paint. On the grid plenum I have it gasket-ed off on only the area I am cutting. You said your running 3" hose to the table so do you have 3" ports coming through your plenum or does it transfer to a smaller port? I run a 2" hose to my tables manifold and then from there it has 6 zone valves that have 1" hose running to all the different zones. Also I hear of people like yourself who are cutting plastic at 300-800 IPM. I have tried 300 IPM many times and it produces crappy finishes for me. It appears that the bit deflects or wobbles way to much at that speed for me. Is there a secret I dont know about. I am just debating on buying a bigger vaccum pump but wanted to check on here to see if there are other things I should change first before I spend $15,000 - $25,000 on a new pump. I am considering 20-40 HP Decker VMAX pump or Busch claw Vacuum (Mink) But not sure if that would be overkill for me. At this point having pieces jump off the table is costing me just as much.

[gfacer2]

If I were doing that job (and i do work in HDPEs and acrylics/abs etc) I'd do maybe 4 passes at 200ipm (on my machine) - maybe with an offset on the toolpath of .01" and the onion skin pass at 0 offset and .01' depth if the table is flat enough. At almost 3/8" a pass on a 1/4" bit, it is a little much and so I could see deflection and chatter (and premature tool wear) as issues. You could probably go faster and less depth. HDPE can be cut pretty aggressively (but nothing like mdf) but its low surface friction makes the final pass an issue.

If I was really having issues, I'd just hand deburr or flush router the remaining while the machine was cutting. I am guess the cycle time is small enough that the operator is not doing anything else while its going. I have a regular 1/2" hdpe job that I don't cut through at all - I just let the customer trim the last .01-.005 or less off.

With that size of table and only 4 parts, you should have plenty of vacuum. Sometime the problem is more that the excess material moves and it then pushes the part, which I could see happening if you have 4 boards side by side. Another approach would be (if you can increase the zone) to make a jig for the boards to separate them a bit. The jig would help each board stay in place even if the vacuum is loose. The hoses are a bit small - especially if you aren't using them all but that typically would only matter when you are already starting to get issues.

But end result is you should be OK for vacuum with the right strategy especially if this machine is doing that job all day. Even moving from an open spoilboard to a dedicated gasketed fixture would work (even better really) and cost a whole heap less. In fact - you could probably do that and then set up 10 parts rather than 4 and then you'd really be humming along.

[Nick12]

Thanks for the advice. I have tried 6 passes at 200 and 300 ipm and still get pretty bad finish. Thats why I think the machine itself might be the issue. As for the vacuum, I just hooked up a pressure gauge and at the vacuum itself I am getting 23 HG. The Vac is rated at 24 so that is pretty good. Once I hook up the table I get 17 HG. The weird thing to me is that when I have the 4 boards covering up the spoil board (Complete Seal) I am getting 17 HG when I take the 4 boards off I am still getting 17 HG. Shouldn't I be experiencing a vacuum loss? Why am I loosing 6 HG in between the table and pump? The pump is literally sitting right next to the table.

[gfacer2]

If you aren't getting vacuum loss the MDF is the issue. Its got too much glue in it. This is a relatively common issue and why I use ultralight MDF even though it has its own issues with dimensional stability. I tried regular MDF and had the same issue.

Graham

[Nick12]

Disregard

[Nick12]

What about loosing 6 HG from the pump to the table? Why might this be happening?

[ger21]

Leakage through the spoilboard.

[gfacer2]

Leaks probably. Not super familiar with Becker style. Distance too maybe but probably just leaks. Vacuum on the inside is pressure on the outside and high vacuum means the air is really trying to push itself into the void. By the spec chart that would be about 50cfm of leaks. You can easily verify this if the vacuum output feels like a decent amount of air. If it feels the same at 24hg and 17hg at the outflow, then I don't know what it might be but my guess is it will feel like more air at 17hg and then its leaks.

[Nick12]

My Spoilboard is completly sealed off on all edges. and the Gasket under is zoned off to just where I am cutting. What is normal size piping for under the table. I am wondering if I am loosing some vac because the pipe are 1" and not 2".

[gfacer2]

So if it's just 1 x 1" pipe, then probably not enough. But that's more an issue once you start to lose vacuum and have air flow. If you 17hg with table covered and 17hg with table open, you aren't drawing anything through it. That means it's the mdf mostly.

Don't worry as much about the 6hg drop, anything over 8hg (maybe as low as 6) at the table shouldn't cause any issues. I use a regen blower and it tops out at under 10hg but is much more tolerant of leaks.

Sent from my LG-D852 using Tapatalk

[Nick12]

I bought some normal MDF. I think the density on it is 45-50. I am trying to find Trupan Ultralight right now. Finding out that is it quite hard to get a hold of. If I cant find it what should I use?

[gfacer2]

Any light/ultralight. I can't get trupan where I am either. I was pretty annoyed when my attempt at an MDF table had no flow though (and so I went back to ultralight).

[Nick12]

So I spoke with some distributors of MDF and they told me the density for regular MDF is 45-50. Light is 40-45 and ultra light is 35-40. (Trupan Ultra Light is 32, Best on the market) I cant even really find ultra light over here. So as of right now I am stuck with just Light. Do you really see a major difference in flow from regular MDF to Light? I want to hold out until I can get some Trupan but I will settle for light if it works that well.

[gfacer2]

Hmm - just get the lightest you can I guess. You ideally don't want too much flow (ie ultralight is sometime too light as the kerf holes pull too much air through) but you want more than you have.

[Nick12]

How much Vac loss should I be experiencing from boards on and boards off. Are we talking like 1 or 2 HG or 5+?

[gfacer2]

If your hoses are big enough and the board flows enough - it should go to 0hg or close to it. But its really the difference you need. In other words - even if its 7hg wide open and 17 covered you have 10hg holding and should be fine. But if you have 17 closed and 0 when fully open on the table - then you have 17 hg of holding.

[Nick12]

Just so I am reading that correct. If I have good flow through my spoilboard with nothing on it I should be experiencing very little vacuum (somewhere between 0 and 10?) When I put the boards on it I should be experiencing the 17 HG or higher that I am right now. So The fact that I am 17 HG with boards on and off means that I am not getting enough flow through the spoilboard? Is this correct so far?

[gfacer2]

Yes, exactly. You essentially have 0hg holding right now the way you describe it.