Building a vacuum table

[henrik_o]

Right, hooray, yet another vacuum thread. This one is pretty basic, though. All of what I’m asking is probably well covered in existing threads, but then uncertainty kicks in and I’m fearful I’m reading the ‘wrong’ threads (outdated or not for my situation). Sorry about bugging you guys about really simple stuff like this, but I want to get it right.

Between jobs, we are currently beginning to build our vacuum system. We have the pvc kit from shopbot. We will use a Siemens ELMO pump (which will probably be updated to a Dresser in the future).

Right now, we’ve bolted the support board to the table, filled in the holes with contact cement (I think that’s the name in English), and glued the plenum to the support board using liberal amounts of extra-filler wood glue, then clamping on the edges and applying pressure in the middle. (The official docs said to use screws, but Brady said glue, so glue it is. We figured the extra-filler type would give an excellent seal.)

Both the support board and the plenum consist of 19mm Karlit MDF. This is a high-density type of mdf somewhere in between regular mdf and hdf.

So, I think we’ve done it right up until this point. As the glue sets tonight, I’m beginning to realize I’m not sure what our next steps should be.

My thought was to follow the official instructions and use the 4-zone plenum cut file in the Sbparts folder. However, since the BradyVac and the variations of that, and then the BradyVac 2, seem really nice I don’t want to get locked into (or have to discard what we have) something else by cutting the wrong file.

Could someone point me to a thread where this is covered in detail, or if the answer is easy enough, help me out?

What files should I be cutting tomorrow?

[Brady Watson]

Henrik,
You're still on the right track
You can mill a grid into your top sheet, but leave the bleeder board (the layer that goes on top of the grid) relatively loose so that you can take it off if you want. I just foil-tape mine around the perimeter of the table and that's enough to seal it and keep it from sliding when I plop material onto it. You can use this as a universal type bleeder as is. If you want to do the BradyVac II setup, just remove the bleeder, and use thinner material (like .25" or 6mm) as a vacuum 'mask' that sits on the grid that you machined into table. As long as you can remove that bleeder layer from the machine, you have all possibilites at your disposal.

-B

[henrik_o]

Brady, gotcha. Thanks.

We encountered some problems the good folks at Shopbot tracked down to non-standard/wrong wiring by our electrician, so I'm not quite through this, but since we are hopefully good to go after the electrician comes by tomorrow morning I hope to still be on the right track...

Dust collection is set up and works. I was surprised how well it works, actually, having read some comments on the dust foot design, but our smallish portable 2500m3/h dedicated system soaked up well over 90% of the dust, it cleans out almost all dust stacked into the routed path (the raster pattern certainly helped on that one though), and standing right next to the table you couldn't detect any dust escaping into the ambient air of the room. I figure if we hook this up to our central dual-motor DC system, results would be even better, but as of now I see no need.

One question I have though, regarding the spindle (a 5hp Colombo), how hot to the touch is normal after say 30 min of cutting? I think we had it right speed/chipload-wise, the 1/2" bit was almost cool after we powered down, but the spindle housing was quite hot. Not so hot that it felt uncomfortable touching or holding it, but definetly quite hot. Is this normal?

The motors were cool to the touch, btw.

We stripped down the ELMO and gave it some bearing-changing and greasing love, it was whining quite proudly back at us when we powered it up. It's a small but quite wicked unit, I think it'll work well until the Dresser or similar arrives.

[Brady Watson]

Henrik,
Make absolutely sure that the electric fan on top of the Colombo is spinning ANY time that there is power going to the VFD. Is it? On warm days running at 15,000+ RPM, the case does get hot. I've designed a waterjacket for the 5HP Colombo, but haven't had the time to finish building it & testing it.

-B

[henrik_o]

Brady,

Yes, it's always on.

Regarding the problems mentioned above, the fan was the culprit afaict. The int'l version of the 5hp Colombo has a EMB 3314 fan drawing 24V DC: we had this wired into the 24V unit in the control box. Problems abounded. After we re-wired the fan to its own separate power supply, things are back to normal. I don't understand why this caused such problems, but it did.

A waterjacket? My, that sounds interesting. I trust you'll roll it out in full regalia once you're there.