Re: [CAD_CAM_EDM_DRO] Clamping Fixture

Victor, if t'wer me, I'd mill a fixture with a recess of the precise size
and near full depth of the plate in aluminum or steel, and mill vacuum
channels underneath the plate recess, connected to the vacuum source. This
fixture would securely bolt to the mill table.

If the plates have small variations in size, i'd arrange a bolt that
tightened a tapered wedge to hold the plates, in addition to the vacuum,
using at least one clamp on each of two non-opposing sides.

I would not try this with a flycutter (well, yes, I might try it, if I was
able to convince myself that it was safe, which isn't likely).

If it isn't worth making a fixture, then you don't have enough of them to do
to justify a vacuum device. In that case, you clamp down one half, mill the
other half, then reverse the clamps and mill the remaining half; or you
get/build a different workholding device.

People I know personally have been known to bolt an oversize vise to a plate
that was previously bolted and surfaced to the mill table. You could use
the Might Mite clamps on such an oversize plate too.

You could mill a recess with a 90 degree inside corner, then mill angled
sides and matching wedges for the opposing sides of the workpiece to clamp
against the work, using less than a 5 degree taper so the wedge would be
less likely to "self release". Hmmm, that's a strange sentence...

rexarino

On 3/7/07, Victor A. Estes <vestes@...> wrote:
>
> Jon,
>
> Very good point about the vise, unfortunately I do not have a milling
> vise that opens to 2 1/2". I have the Sherline vise and it just does not
> open wide enough. 127 lbs does not sound like a lot of holding power, and
> that is what I was concerned about.
>
> I'm going to use a 3/8" dia end mill. I've tried the fly cutter and I
> just don't like that thing swinging around, it scares me.
>
> Thanks,
>
> Victor A.
> ----- Original Message -----
> From: Jon Elson
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Sent: Wednesday, March 07, 2007 11:33 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Clamping Fixture
>
>
> Victor A. Estes wrote:
>
> >Hi, has anyone built a vacuum table for a CNC mill? I need to clamp
> some aluminum plates (2 1/2" wide x 3 1/2" long x 1/2" and 1/4" thick) flat
> to the milling table so that I can surface the top of the plates. This is
> not a one time operation, but rather something that I will need to do all of
> the time. I was thinking that a vacuum table might do the trick, what do you
> think? Any suggestions. This will need to fit a Sherline metric CNC mill. I
> figure I can scale something up or down to fit.
> >
> >
> >
> Assuming a rectangle, that is 8.75 in squared, and the holding power of
> a hard vacuum will be
> 127 Lbs. That may work for light milling, but it is a bit iffy. If the
> vacuum is much weaker
> than 28 In Hg, I don't think it has a chance of working. Why not just
> put it in a vise with
> parallels under the object? That's what I do. No way is the piece
> going to fly off the vise
> jaws. If you use a flycutter with your vacuum table, there is a good
> possibility it could fling
> a full pound "bullet" at you!
>
> Jon
>
>
>
>
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