Vacuum Table Question

[Ben Mitchell]

Howdy!

I'm in the process of refurbishing a Precix router table that I acquired for nearly nothing. The electronics / controls were all beyond salvaging so I just gutted everything from the control box except the power supply and built it up with a BOB, a SmoothStepper, some Gecko servo controllers, etc. and am going to run it from Mach3. So far that's all progressing nicely.

What I'm a bit perplexed by is the table bed on this machine. It's an aluminum t-slot system, but there are three vacuum zones and the flat portions of the extrusions are perforated with small holes every 3-4" that are clearly for the vacuum to be pulled through.

I've never used a vacuum table with out a spoil board, but I'm not sure how well that will work in this case. For one thing, it feels like I won't get enough flow through the LDF if all the air has to go through that grid of tiny holes. For another, the underside of the spoil board would leak air like crazy because of the T-Slots.

So what's the protocol here? How is one intended to use a "hybrid" table like this?

Thanks!
-Ben

[Gary Campbell]

Ben...
How about a couple pictures, so we don't have to guess?

[Mick Simon]

Is there any material adhered to the top of the aluminum, like sintra, with small recessed pockets around the ports? Generally that type of table is used for signmaking applications cutting a lot of thin materials like aluminum without any spoilboard. It's designed to be used with a high volume / low pressure blower.

[Ben Mitchell]

Gary: Sorry. I'll take a pic next time I'm in the shop. I'm out of town for a couple of days. Stand by. In the meantime, here's a rough SolidWorks sketch of what I have. (I just modeled a small section. Each of the "flats" is about 4" wide and the length of the table. There are about a dozen of those strips across the full-sheet width of the table.)

Screen Shot 2018-02-26 at 12.16.25 PM.jpg

Mick: No. It's just straight up aluminum with holes (maybe 1/16" diameter) in a pretty widely distributed pattern per the above.

[Mick Simon]

"Mick: No. It's just straight up aluminum with holes (maybe 1/16" diameter) in a pretty widely distributed pattern per the above."

Normally that type table would have ~1/4" Sintra PVC strips glued with contact cement to the tops of the aluminum channels, leaving the t-slots open. After table milling it flat, you'd then cut a small pocket around each access hole about 1/8" deep and 1" in diameter. The holes combined with the Sintra form the vacuum seal. Not ideal, but they do work.

http://www.skylinepictures.com/Route...-R122_full.htm

[Ben Mitchell]

Ah. Interesting. Definitely not what I'm used to. Perhaps the answer here is to remove that table and replace with something I'm more familiar with. IE: A lower plenum with a sheet of sacrificial Trupan glued to it as a spoil board. Or maybe building that as something that gets clamped to the existing bed via the t-slots. The problem with that is that the machine has a pretty low gantry already and I'm a bit loathe to use up 1.5" or so of my Z-height with something that sits on top of the existing bed. Hrm.....

[Jim Becker]

If you're not dying to use the vacuum, you can put a traditional spoil board on top of the aluminum and use the tee-track facility to fasten it down securely. For additional safety, you can use nylon bolts rather than metal ones if you prefer so that as you eventually mill down the spoil board through repeated true-up/clean-up, there will no danger to a cutter. When it gets thin enough, just glue another 1/2" layer on top, surface it and keep going.

[Ben Mitchell]

Heh. I'm pretty much dying to use the vacuum. That's pretty much the only way I ever hold things down for the kind of work I do.

[Jim Becker]

That's understandable. When my machine arrives, I don't believe I'll be jumping in the deep end with a major vacuum setup, but I do intend to leverage the small Gast pump I have for a smaller setup to do, well...small work where using clamps might be cumbersome.

[Ben Mitchell]

It can be done pretty simply. For the quarter-sheet machine I have now I just use a 220V central vacuum motor. Works very well. That obviously isn't enough to power a full-sheet setup, but I'm planning to just manifold together three or four of them. It's a lot cheaper than a 10-15HP centrifugal blower system and can be powered with single phase. Unfortunately I didn't size my phase converter to run the DC, the spindle VFD, and a big blower motor simultaneously so I need to make the holddown system work on 1PH power. In this case the big challenge is simply getting the vacuum to the zones on the table, but I may just bore holes through the extruded table for that. Given I didn't pay much for this machine and I have no real use for the system as it stands, that might be the best option...

[Mike Heidrick]

I do it with a FPZ regenerative blower vacuum pump, relief valve, and solberg right angle filter and PVC manifold I built that also uses PVC ball valves. Mine is 2" NPT plumbed. It was built from parts from Ebay except the relief valve that I ordered new from FPZ.

The tiny Gast pumps will work with pucks but you are not cutting through much less pulling vacuum through LDF/MDF.

One day I will try this roots blower vac pump. It will up the game (or blast me out of the shop). Its 4" NPT!

Someday I will buy a Becker TFTL series bad boy!

[Mike Heidrick]

Ben, Try cutting the LDF to the strip width for each section area between the T slots (4 strips in your picture). Seal all the edges of the four strips of LDF (you could use tape on them for now but a glue water mix will work or latex paint the edges, great use for the $1 cans of offmix paint at the BORG). If you work does not need the full area (all 4 strips) block the un needed areas off with plastic or vinyl. Just use the strips that are needed for your work size and seal off the parts of the LDF strips you dont need. Seal off the areas you dont use. If you are not cutting through do not use the LDF.

[Ben Mitchell]

Out of curiosity, does anyone have a recommendation for tape for bonding phenolic to the aluminum extrusions if I decide to go that route? A lot of the stronger tapes I've worked with are foam-based which seems like the wrong answer for something you want to have a consistent / stable z-height.

[Jerome Stanek]

I would look at the tape they use for automotive trim.

[Gary Campbell]

Jerry is right on. Google 3M VHB