Need Vacuum table help....

[jzarski1]

This is a question regarding a new iron CNC I purchased. Hoping all the vac table experts can help me.

The machine came with a vac table and Becker vac pump. (picture below)The pump says on the tag that it is 5.5kw which is about 7hp. It is a three phase unit. I can't seem to pull a good vac on the table. Pump turns on, it has suction, feels like alot but if I open more then two zones the bleeder board gets loose.The table is broken up into 4 zones. Each zone consists of three 7.375 wide by 48 long grid that has a one inch hole in the middle. So each zone has three one inch holes for vac. That's a total of 12 holes for the entire table. So my question is, well I have a few.

Is 7hp enough to pull vac on a 4x8 surface?
Does the table have way to may zone sections causing a CFM issue?
Would I maybe be better off making a vac table with MDF like a shopbot and use it that way?

Video of vac table surface. You can see what I am saying about all the holes.
http://youtu.be/SOVGVAzRKG8

Hope someone has an idea.

John

[bleeth]

John:
I have been using a 7.5 HP regen blower with 8 zones on a 4 x 8 table for a long time now. It has done very well for me and the only "toolpath quirks" I need to use is if I am cutting a large number of smaller parts from a full sheet. When you say the bleeder board gets loose I presume you are using a brady-vac method in which the bottom is cut with your channels and the top is the spoilboard on the same piece which is not glued down.
The main thing in both methods is to make sure that all areas where vacuum may be lost is well sealed. If your bleeder board is not held down when turning on your vacuum I can only assume that you are trying to suck the entire bleeder down with nothing on top of it to actually receive the vacuum. You won't have that work. If you have a full size bleeder on it then you need your full size part on it in order for it to work. When only cutting a smaller piece you need to either have a smaller bleeder or cover the rest of the bleeder with filler pieces that will prevent air loss.

[jzarski1]

Hey Dave, thanks for the reply.

My vac table is part of the machine. The vac grid is cut into the machine table. I put a .75" ULMDF bleeder down on top of that. I can't even get the bleeder to stay so I can surface it. Each zone has a gasket around it for sealing. They are all in good condition.I have checked for leaks in the system, there are none. I had the electricians come back and make sure all three legs of power where ok, they where.

Dave, can you hold your palm over the pump inlet or will it suck your skin off? on my pump I can put my palm on it but I will say this, it's scary. It won't suck the skin off but it's got some pull.

John:confused:

[bleeth]

When I put a new bleeder down and am getting ready to skin what will be the bottom side after I flip it I screw it down with a bit of counter sinking before hitting the switch on the vac and then surfacing it. Even before skinning, ultralight or Trupan is porous enough that the vac won't hold it well enough for me, and I know darn well it will start to lift as one side is skinned.
I don't stick my hand or anything else in the inlet side of the blower!!!

[jzarski1]

ok, that is making some sense. Few more questions.

Do you seal those counter sunk holes after you skim both sides or do you keep the screws in there for a precaution?

John

[bleeth]

When I flip it I glue it down, pile a bunch of weight on it, go home, come back, and then skin the other side in the morning. I don't worry about the 4-6 little screw holes. I only screw it on the first skinning.

[jzarski1]

Gluing will be an issue for me as my vac table is a thick hard rubber. Not sure if you looked at the video. what I am cutting is the rubber vac table. Any suggestions on how I could hold it down?

John

[bleeth]

OK-watched the video.
Why using hard rubber for plenum?

[jzarski1]

OK-watched the video.
Why using hard rubber for plenum?

I have no clue. That is how it came from the factory over seas. I guess I could take the rubber off and make a MDF table.. Just kinda of stinks to. To be able to use the factory table.

John

[don_roy]

I think Dave is trying to say that what ever portion of the table you are not using should be masked off with dummy material that you will not be cutting.
Don

[bleeth]

Yep. All parts of a vac zone in use should be covered either by the part being cut or other non-porous material.
You said 4 zones with 3 one inch lines each. This is a bit different than most SB setups. Typically we will use 1 line per zone but use larger pipe. I think the design intent of your factory rubber was either that it is a combination plenum/spoilboard or, as some do, use a piece of 1/4" mdf as the spoilboard.
Is the rubber porous? Maybe someone over on cnc zone is more familiar with what the manufacturer of your machine had in mind. Or you can try asking their customer service center direct.

[dana_swift]

Additional notes regarding the Becker pump(s):

I use almost the same model pump, which can achieve MUCH higher vacuum but lower flow than a regenerative blower at the same horsepower. It is critical that you cover unused areas.

The Becker pump is vastly better at cutting smaller parts, the regenerative blower is vastly better at cutting large sheets where you cut through a lot.

With my Becker I try to design my cuts so the "cut through parts" are the last thing cut, and then the cut through areas are cut as two toolpaths. The first one leaves a skin, but does most of the cutting depth. The last one goes back and re-cuts that last little bit of skin cutting the parts free. The vacuum will drop quickly during the final toolpath. Sometimes I run along behind the fresh cut-through area and add masking tape to re-seal the cuts if the cut-through area is too large. (Not a safe thing to do!)

The Beckers have a vacuum regulator. Its a black knob on the pump, which works like the regulator for a compressed air line. In your picture its the black knob at the top right. Turn that knob to increase or decrease the maximum vacuum you get. I set mine at 27" of mercury, the pump can go higher than that but pulling higher vacuums wears out the vanes sooner.

Also be sure to lubricate the pump according to the maint schedule. There are two grease ports under the six black thumbscrews, lubricate those with a Becker grease gun. (A chainsaw bar tip grease gun works great too!) That lubricates the bearings at each end of the vane pump. My recollection is they say every 3000 hours of run time per lube. I just do it every three months and so far I have had no problems.

One other note about my setup, I have the pump hooked to an old 100lb propane bottle which acts as a vacuum accumulator. Then I have a electronic vacuum switch which turns the pump off at 26"Hg and back on at 18"Hg. Then the pump can rest, saving my electric bill a bit. For most of my cuts the pump only runs about 2/3 of the time before that last cut-through happens, then it runs continuously. During the cut-through times the pump will hold around 15"Hg if I use the masking tape trick. The electronic controller prevents the mechanical one from getting to do anything other than protect the pump in case the electronic one fails.

Between the pump and the propane bottle, I have a dog-ball vacuum check valve I made from PVC pipe and a dog ball. (I got the design off the forum.) That seals really well, its cheap to make, and the dog ball lifts up off the seat when the pump is running allowing full flow.

Though I may be making smaller parts than most botters, but the Becker has been a great tool. The propane bottle really helps when I need to have high peak flow when initially sucking down parts onto the vacuum table.

I also have a very small Gast pump for dedicated fixtures where there is almost no leakage at all, saves putting hours on the bigger pump. It has no lube schedule. Also makes a great vacuum bag pump. Before I bought the Gast, I used the Becker for everything. It makes other kinds of hold-down possible.

One other note- I found trupan type bleeder boards allowed more bleed through the edges, even after sealing, than I wanted. I have gone to drilled-holes in a non-porous material for my bleeder which has worked really well with the Becker. Thats not what you will read about on the forum where higher flow systems are more typical.

For high flow backup when I do the final cut-throughs, I have considered having some lighthouse vacuum motors just to help with the really high flow part of the hold-down. So far I have just been mulling that idea.

Hope that helps- not many of us Becker users out here :)

D

[jTr]

Since nobody else has asked, I must. Not trying to be a wise guy, seriously - no offense intended, but someone's gotta ask this....

What do the people who took your money for the machine have to offer for assistance? Any? Don't like their answers?

Just curious why another brand (in another country?) gets the sale and the Shopbot community gets the tech support.

Sorry John - don't mean to be harsh - just a bit of curiosity with a dash of cynicism.:o

jeff

[jzarski1]

Since nobody else has asked, I must. Not trying to be a wise guy, seriously - no offense intended, but someone's gotta ask this....

What do the people who took your money for the machine have to offer for assistance? Any? Don't like their answers?

Just curious why another brand (in another country?) gets the sale and the Shopbot community gets the tech support.

Sorry John - don't mean to be harsh - just a bit of curiosity with a dash of cynicism.:o

jeff

Your not hurting my feeling. I have two Shopbots and I just purchased this Big Iron machine to help with production. Shopbots are amazing tools. They are the reason my business is where it is. Not only are the tools great but so is this community that is surrounded by it. I consider myself part of the community having two Bots in my shop, hence the reason why I ask here. The knowledge on this form is beyond what most folks can realize.

Now to answer the question about the company that "took my money". They have been very helpful. I skyped with then last night and let them see with a video what the issue was. Well the issue in my opinion is that everything they gave me works at 100% of what is is suppose to. The problem is my inexperience in vac tables. I have played around with a few, but nothing with a pump this size. That is why I asked here.

Hope that answered your curiosity.

John

[jTr]

John -
I was a bit confused, as I thought you owned a bot based on your history here on the forum, though I didn't mean to imply you are unwelcome if you are not a 'bot owner. Glad to hear things are going well enough to put you into a 3rd machine.
Thanks for understanding and clarifying - just had a sarcastic mood on this morning I guess!

Sorry to hijack the thread - I'll try to be more helpful instead of critical next time!

jeff

[jzarski1]

Dave and Dana,

I would like to thank you both for supplying me with the avenues in solving this problem. I am pleased to say that with both of your suggestions I was able to pull vac on a 4x8 sheet. I will now be able to skim the top and bottom of the bleeder and start cutting. Again thank you both and this community for helping me.

John

[bleeth]

You're welcome John. Glad to have been of assistance.

Dave

[donclifton]

Hi John, I think one of the problem you might have is that you cut MDF and the vacuum can sucks right thru it.
Don