Re: [CAD_CAM_EDM_DRO] Using Vacuum to hold down sheet metal.

>I was thinking of building a vacuum assembly to hold the metal down
>while milling. I've put in mechanical stops to prevent shifting but
>I was thinking if I built a box and connected the shop vac that I'd
>be able to use lots of little 1/8" holes through the MDF frame to
>suck down the metal.

Why? Masonite is available for cheap with the holes
pre-drilled. Build your MDF box, but route the grooves and drop in
the Masonite. If you feel really good, spot some 1/4" dowel pins so
the Masonite can't move.

>A bit of math tells me that the 7 square inches of a 3" diameter
>vacuum hose translates into about 575 holes 0.125" in diameter.

So? If they all are covered, it doesn't matter.

>But do I really need that many. I plan on only putting holes under
>the metal where the mill does not do any cutting so no leaks.

Ah, consider that something like shelving foam (often used by
woodworkers while routing wood) or just plain thin foam (like thin
stick-on insulation) will help hold things in place. Also, if you do
a cutout, either the slug needs a vacuum hold down or it will grow
wings, and the sharp edges will make it a great s

huriken

!

>Would this work?

Yes.

>Is it better to use a vane type vacuum pump instead?

Yes, shop vacs have notoriously short lived motors. Lots of volume,
less vacuum. Even the best ones will not get down to 30".

>The milling cycle for all the holes is about 00:05:45 so that would
>mean the shop vac would be straining for a fairly long time perhaps
>overheating.

How many pieces do you want to do? One is no big deal, 100 and you
may need a new shop vac.

>Suggestions?

Yes, look at
http://www.surpluscenter.com/item.asp?UID=2007042918090300&item=16-1139&catname=
for cheaper
or
http://www.surpluscenter.com/item.asp?UID=2007042918090300&item=4-1540&catname=
for more money if you have 220 VAC available. Add an exhaust
silencer/mufler and it can run thousands of parts safely.

A shop vacuum source is really handy (not the same as a shop vac or a
dust collector) for many things including holding parts, lamination
and fiberglassing.


David G. LeVine
Nashua, NH 03060