What's the rule of thumb for amount of vacuum/pressure required to hold
a flat part for milling operations?

I need to machine up aluminum and plastic plates.

Aluminum plate 4"x4" square
flat plastic puck 2.5" round

Can anybody point me to some links for low cost DIY alternatives to
buying a plate/pump set?

TIA, Mike

Mikester (in )
said:

| What's the rule of thumb for amount of vacuum/pressure required to
| hold a flat part for milling operations?
|
| I need to machine up aluminum and plastic plates.
|
| Aluminum plate 4"x4" square
| flat plastic puck 2.5" round
|
| Can anybody point me to some links for low cost DIY alternatives to
| buying a plate/pump set?

Mike...

There's a link in my sig to a DIY how-to for building 4"x4" vacuum
pucks.

These are intended for CNC wood routing applications; but you may be
able to use/adapt them for milling flat aluminum and plastic parts.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/assembly.html

Cool idea for the fridge pump, never thought of that. I was thinking
of butchering an old portable air compressor.

Mikester wrote:

What's the rule of thumb for amount of vacuum/pressure required to hold
a flat part for milling operations?

I need to machine up aluminum and plastic plates.

Aluminum plate 4"x4" square
flat plastic puck 2.5" round

Can anybody point me to some links for low cost DIY alternatives to
buying a plate/pump set?

TIA, Mike



This has been discussed extensively before. Google this group for
_vacuum, fixture, pump_ etc.

fred

On 25 Mar 2006 15:18:08 -0800, wrote:


Mikester wrote:
Cool idea for the fridge pump, never thought of that. I was thinking
of butchering an old portable air compressor.

Fridge Pump can work, but they are lubricated by oil that is supposed
to be circulating in the freon. Eventually, they will act up and sieze.
When they run, they will often SPIT oil out (and often it stinks), and
you can certainly feed some of it or new oil back in to add to
longevity.

I suggest you search ebay and buy a Gast or similar "rotary vane" pump.
This is NOT a piston pump, but carbon vanes that run in a smooth bore
cylinder, not much unlike a Wankle. No oil... continuous duty.... You
can put a checkvalve in the vac line, hang on a tank and cycle them
like a compressor.

I do not have the math in front of me, but you would have enough
surface area on both of the parts you speak of with 25-28" of vacuum
(easily provided by a Gast pump as mentioned), provided you do not get
overly wide with gasket material on that 2.5" puck. Then again, its
plastic, and you likely will not exert a lot of cutting pressure with
sharp tooling.

The 4x4 plate, depending on thickness could actually bow or bend with
even far less vacuum than I mentioned. So, you may need to provide
support in whatever jig you make.

When it comes to vacuum jigs, the DEPTH of the vacuum area is NOT
important. It is all about the SURFACE AREA you can provide the vacuum
access to. The bigger the surface area, the more you need to be
concerned about the vacuum pulling the part into a bow, IF you only
have a perimeter seal.

Vacuum is no weany way of holding stuff..... You can pull a hinder out
of a skunk with 29" of vacuum !

The next rule of thumb is you only need the amount of CFM that you are
LOSING via your gasketing. In other words, if you get a great seal, you
could suck it down once and it would effectively stay down until you
released the vacuum. So, this means you do NOT necessarily need a
monster pump. I only have a 1/3 horse unit, and as long as I have a
good seal, a 50 horse unit would NOT hold it any better.

For a seal, Use Soft Sheet rubber, Closed Cell foam (Volara, the stuff
under padded vinyl tops), or even closed cell weatherstripping tape if
necessary.

Vacuum jigs can be made from anything not pourous. Plastic, aluminum,
phenolics, corian, etc. If you know someone who can get you some short
lengths of various larger diameter acrylic tubing, these when flown off
parallel, Vac port in the side and a gasket top and bottom make a quick
vac jig.

Grummy
Greetings,
What Grummy says. Also, it's best to have the seal compress completely
so that the part does not warp. When making the vacuum chuck (the
plate you will have the vacuum passing through and which your part
sits on) think about how the vacuum will be applied to the part. If
you start with a very flat part, and a very flat chuck, when the part
is drawn tight against the chuck the vacuum will only be present at
the holes. I have found that cutting narrow grooves across the chuck
helps to keep the maximum surface areaexposed to vacuum.
Cheers,
Eric

On 25 Mar 2006 05:20:39 -0800, "Mikester" wrote:

What's the rule of thumb for amount of vacuum/pressure required to hold
a flat part for milling operations?

I need to machine up aluminum and plastic plates.

Aluminum plate 4"x4" square
flat plastic puck 2.5" round

Can anybody point me to some links for low cost DIY alternatives to
buying a plate/pump set?

TIA, Mike

Someone may wish to mention safety concerns if it comes loose ....
--
Cliff

On Sat, 25 Mar 2006 19:18:52 -0500, Cliff wrote:

On 25 Mar 2006 05:20:39 -0800, "Mikester" wrote:

What's the rule of thumb for amount of vacuum/pressure required to hold
a flat part for milling operations?

I need to machine up aluminum and plastic plates.

Aluminum plate 4"x4" square
flat plastic puck 2.5" round

Can anybody point me to some links for low cost DIY alternatives to
buying a plate/pump set?

TIA, Mike

Someone may wish to mention safety concerns if it comes loose ....
I had a job years ago that required removing .062" from a 20" long 1"
wide aluminum bar. Double sided tape was the method I chose. I did
think about the parts coming loose because all the material was being
removed in one pass. I made sure that when the parts came loose they
were thrown away from me. And out of a couple hundred parts 4 or 5 did
come loose.
ERS

Mikester wrote:
What's the rule of thumb for amount of vacuum/pressure required to hold
a flat part for milling operations?

I need to machine up aluminum and plastic plates.

Aluminum plate 4"x4" square
flat plastic puck 2.5" round

Can anybody point me to some links for low cost DIY alternatives to
buying a plate/pump set?

TIA, Mike


I've no experience with vacuum chucking, probably never will.

Just a thought, though - is there some reason that you would not use
solid stops, particularly in the direction of the cutting force? Seems
that would help a lot.

John Martin

Cliff wrote:
Snip

Can anybody point me to some links for low cost DIY alternatives to
buying a plate/pump set?

TIA, Mike

Someone may wish to mention safety concerns if it comes loose ....


I'm qualified- make sure there's something substantial between you and
the part. An unobstructed view can be more unobstructed than you care
to experience.

Later,

Charlie

On 27 Mar 2006 09:53:35 -0800, "John Martin"
wrote:


Mikester wrote:
What's the rule of thumb for amount of vacuum/pressure required to hold
a flat part for milling operations?

I need to machine up aluminum and plastic plates.

Aluminum plate 4"x4" square
flat plastic puck 2.5" round

Can anybody point me to some links for low cost DIY alternatives to
buying a plate/pump set?

TIA, Mike


I've no experience with vacuum chucking, probably never will.

Just a thought, though - is there some reason that you would not use
solid stops, particularly in the direction of the cutting force? Seems
that would help a lot.

John Martin
Solid stops are used. Or should be. At least for locating. But
sometimes the cutting forces lift the part from the chuck. Then the
part can fly out.
ERS