[diyengineer]

I'm slowly approaching the point of where i need to start thinking of hold down solutions for my table. The table is already fully outfitted for a vacuum hold down system.there is EXACTLY 300 3/8" holes in the top in patterns (which comes out to a whopping 33 cubic inches THEN milled plastic panels go ontop that contain thousands of small holes that i assume add up to 33 cubic inches of flow, i would have to remake these because my old panels were gross and warped, so i tossed them) underneath it already has 40 1" fittings and even has (2) electric valves to control different sections of the table.

The only problem is...

I dont own a vacuum pump!


I can only imagine how much a vacuum pump/s would cost for a table this size. I mainly need to hold down 4'x12' .063" sheets of aluminum, but would love flexibility. I'm limited to a maximum height of 1.5" for my Z axis. I dont want to simply bolt a panel in every time. This would take forever.

I was thinking about using 8-10 small pneumatic pistons that would push on individual cams. The cam could hold a piece 0-1" in diameter against the table with a great amount of force. All the pneumatic pistons would be linked together VIA 2 electric solenoids. 1 solenoid would be the fill, 1 would be the dump and would release the cams (each might need a small spring to retract the cam.)

Mach 3 could control solid state relays that would lock the piece in place, and release the part when the cutting is fully done. then i would just have to Slide a piece in hit go, slide the piece out when its done. No bolting, leaning over the table, and unbolting a million bolts, losing hardware, etc. Very fast and efficient. More automated the better.

For pictures of the machine and specs look below, check bottom link for current pics of machine in huge build log.
Thank You to anyone who contributes!

Machine specs below:
Machine max dimensional footprint:
Width: 89.5" wide (2273.3mm)
Length: 178" long (4521.2mm)
Height to table: 38.75" (984.25mm)
Height to gantry: 46.5" (1181.1mm)
Height to top of Z axis: 62.5" (1587.5mm)

Overall MAX table dimensions:
X axis: 82.75" (2101.85mm)
Y axis:178" (4521.2mm)

Actual "Usable" MAX dimensions:
X axis: 67.25" (1708.15mm)
Y axis: 139.5" (3543.3mm)
Z axis: 1.5" (38.1mm)



full build thread here:
http://www.cnczone.com/forums/showthread.php?t=103291

[Bill C]

Clean both surfaces to a water break then with precision, bond the parts to a substantial sub base with the glassy hard curing polymer of your choice. Clamp conventionally, mill, inspect, and demount with heat and/or with judicious encouragement, the part is released. This method is not new nor is it such a secret that some will wish it to be. In a jam, the use of JB weld for heavier parts with no clamp surfaces will do - no problem with proper cure. JB will go to 500f or so to soften to a release and is not glassy hard as is desirable for this type of fixturing adhesive. A sharp blow in a vulnerable spot will release most parts, and the remains can be ground, scraped, polished or aerosol spray paint removal - removed. Polyester resin works but the parts must be CLEAN

Bill

[mcphill]

You may not need as large a pump as you think. Once you have created a vacuum, keeping it there does not require much flow. Even an ordinary shopvac may be enough (have you tried it?) as long as the holes are mostly covered and there are not big leaks.

Uncovered holes will require vacuum flow or should be covered (a sheet of paper works!). If you are cutting wide slots, you will uncover more and more of the "thousands" of tiny holes, and flow will increase. If you don't cut too wide of slots, though, you don't need much flow.

I picked up a very large vacuum pump on eBay for about $150. Shipping on it was $100, because it is so damn big! I didn't find one right off, took a few weeks of diligent searching.

[4R8]

depending on the holding force needed, a simple vaccuum cleaner pump (or two) may suffice. You'd be surprised at how much suction those things actually give on close fitting parts