Screwing into the surface of a vacuum table...

[jeffreymcgrew]

Hey all, we're thinking of putting in a vacuum table soon. However, we think we'll still need to screw some stuff down sometimes, like when we cut aluminum sheet and such.

If we go with the 'typical' vacuum table plans, will screwing into the table mess it up? Can you only use certain screws? Or is there a design that's more friendly to screws?

Thanks in advance...

[richards]

Why not use a pallet? That's what I do when I need to use screws. Basically what I do is to use a sheet of MDF (usually 24x48) that I screw the material that I'm going to cut on to. Then I just slide than piece of MDF and cutable material into place on the regular vacuum platen. I let the normal vacuum system hold that pallet in place. By doing that, I don't have to drill holes in my vacuum platen and I still get more hold down than I need.

[jeffreymcgrew]

Mike that's brilliant. Do you think it would hold even heavy aluminum sheets?

[richards]

That's the method that I used when I machined 1/2-inch aluminum for some motor mounts. Since the edge finish was almost perfect, I'll have to assume that there was excellent hold-down.

[byoc]

Mike,

What kind of aluminum were you cutting? What kind of bit were you using and what was your chip load?

[richards]

Keith,
I used 6061-T6 aluminum. The cutters were 1/4-inch, 3/8-inch and 1/2-inch spiral high-speed-steel end-mills made for cutting aluminum. Unfortunately, I can't find any other data that I used. I know that I posted a photo of a belt-driven gearbox that I made using aluminum for the side plates, but I can't seem to find it on the forum. You might look through the posts made in July and August, 2006, which was the time that I did that project.

What I do remember is that the job took forever (more than five hours) and that I was a nervous wreck before it was finished. Towards the end, I used aluminum cutting oil so that I could increase the feed speed and step-down to some practical level, but even then it seems that I was cutting at 0.4-ips with a step-down of 0.050 inch - but I really don't remember. I do remember that cleaning up the mess took a full day. The entire experience made me decide that, as good as the Shopbot is, using it to cut aluminum was one of my least practical ideas. (Right after running that experiment, I bought a vertical mill which was able to cut those same parts in well under 1/2 hour.)