Re: [CAD_CAM_EDM_DRO] Re: In need of a vacuum system for router with a lot of...

JanRwl@... wrote:
(snip)

>But I fail to see how this PVC-film "bag" over a surface with vacuum could
>"work" with a ROUTER eating-up the PVC film! Perhaps someone can explain in
>"1,2,3" sentences for us dummies???
>

I'd be happy to ! First off, the technique you are speaking of is
commonly referred to as "Vacuum Bagging". It is very popular when
applying veneers to wood or metal. That situation is a "closed" system,
where for example, you stick in a block of wood with a piece of glued
up veneer into a Plasic Bag, seal the bag, turn on the pump, and let the
bag suck flat, effectively "clamping" the veneer to the wood. 25" of
vacuum will have more clamping pressure on that part than you can
imagine. You would not want your hand in that bag! With very flexible
veneer, you can "bag" parts with multiple contours, apply it to wood,
plastics and metals. The process has become very popular in Marine and
Aviation, where hulls and fuselages can be "laid up" just like the old
Fiberglass way, but, be done in such way that the final product is
thinner and stronger because all air bubbles have been removed. Yes,
they put WHOLE Boats in Bags !

The aspect of Vacuum Clamping is different in that one uses a "cavity"
of evacuation to suck or hold a part to it. Its simple really. Take this
example. Cut a piece of 1/4" plexiglass 12" square. Drill a 1/8" hole in
the middle of the plastic. Now, take some "closed cell" 1/4" foam tape,
like they sell for weatherstriping your home. It has to be a closed
cell, and most packages clearly tell you if it is. It usually has a
liner and sticky tape on one side. Take the tape and make a 6" square
box in the middle of that Plexi. Set that piece of plastic on top of a
board or any flat surface. Find a way to apply vacuum to the center hole
from a pump that will deliver 20-28" of vacuum. Usually, you can just
run some clear reinforced vinyl/pcv tubing to that hole.

I bet you can't pull the rascal apart ! In fact, you could probably
pull a car out of the ditch of ropes were attached to each part! The
force or "pull" is directly related to the exposed surface area of the
vacuum "cavity". It has little or nothing to do with the cavity depth,
as long as there is a cavity. Bigger is better.

How does this apply to a CNC machine ? Well, with the right "vacuum
fixtures", you can effectively hold down most any part as long as the
machining necessary does not overcome the surface areas ability to hold
an item. Advantages are clear, NO clamps in the way, and if it is
something that gets done repeatedly, set up is a simple as turning on a
valve. Many Production shops have purchased premade vacuum fixtures with
long grooves cut into it, where you place a small rubber O-ring
material. That o-ring is your seal, creating a cavity.

I've used vacuum for a billion things in my life. A vacuum pump on a
tank in my Shop is every bit as important as my Air compressor. My CNC
router has a few strategically placed holes thru the top where I can
apply vacuum. A simple plastic sheet with a hole in the middle, and Foam
tape on each side, can hold down just about whatever I need to do, and
you can remove or replace the top foam as necessary to fit the part. You
should see what you can do by using slices of large diameter Acrylic
tubing !!

Vacuum..... Gotta Love it !

Long over my 2-3 sentence limit,
Chris L