RE: vacuum hold down

Hi All

I'm always amazed that people want to drill lots of holes to make a vac
hold down fixture :-))

I do admit to doing this myself some years ago 'though :-))

It's a little known fact that MDF (and especially the lite version) is
porous.

Make your vac table top from MDF lite and use that as the sacrificial
top too (fairly cheap).
I find the 9mm material best with an eggcrate affair below - I use 20mm
squares of 9mm MDF as "pillars" to keep the top and
bottom apart (spaced about 75mm) - strips of 9mm MDF around the edges.
Machine the top flush using your router and a big bit.

Ensure that the rest of the vac "box" walls are well sealed using any
old paint/varnish/epoxy.

I've been using this system for some years to hold down balsa/ply etc
for routing (mine is [actually was, it got covered in Hydrochloric Acid
a few months ago] 500*300mm)

Various pieces of poly sheet (I tend to use Visqueen DPC, a bit thicker
and tougher) are used to "mask" off the unused areas
to increase the pull (I use a big vac pump for heavy stuff and my old
shop vac for balsa).

A nice way to achieve vacuum is to use a bernoulli/venturi valve
attached to your shop compressed air (or even mains water if you're not
metered!) - your local "pipe"
supplier should have one or failing that, go to Darren Kings site at ...

http://www.bagpress.com

This site has a lot of useful stuff that will interest CNC builders!

Cheers

Neil


________________________________________________________________________
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Neil D. Gillies Tel: +44
(0)1383-823489
iGull Technologies Mobile: +44
(0)771-4330793
11 River View
neil@...
Dalgety Bay, Fife
http://www.igull.co.uk
Scotland KY11 9YE
http://www.sea-gull.demon.co.uk