Experimental vacuum plate

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Jose Rivera
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Experimental vacuum plate

Post by Jose Rivera » Fri Apr 11, 2008 12:02 am

I machine a lot of thin, flat pieces of plastic and aluminum with my home made CNC mill.

For years I have been using a piece of aluminum tooling plate as my working table (not shown on pictures), and on top of this plate I use a piece of 1/8 white polished finish polypropylene attached with Scotch industrial type double sided tape.

I would use also double sided tape to attach the working piece to the polypropylene and program to cut some .005" deeper than the material and into the polypropylene to complete the cut-outs.

After experimenting with crazy glue I have been so happy of the results holding down parts or materials that are hard to hold, either by shape or thickness (very thin stuff).

So I bought a piece of Acrylic plastic and made myself this experimental vacuum plate that is divided in three sections.
A 4" X 4", a 8" x 8", an an area where I can use the whole 19" X 17" capacity of the machine using all three ports at once

If this works for me, then I will be using pieces of plastic to crazy glue the parts to and then I will be holding them with this vacuum plate.

If successful then I will be saving money and time not having to double sided tape everything. It can be a pain removing the tape from the parts.
Attachments
Cutting.JPG
Areas Close-up.JPG
Almost complete.JPG

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millman5
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Post by millman5 » Fri Apr 11, 2008 12:18 am

Are the black lines some sort of seal to help hold the vacuum?

I would think your idea will work great as long as you can hold the vacuum.
If it works Don't fix it....

Jose Rivera
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Location: Vallejo California

Black traces

Post by Jose Rivera » Fri Apr 11, 2008 12:25 am

The black traces are buna .135" diameter "O" ring cord bought by the foot.

Once the ends are cut square with a new sharp razor blade, then they can by crazy glued to form one continuous O ring.

I have a dry-running vacuum pump that will be on during the time that the machine will be cutting.

I will be testing it tomorrow and will update this thread with maybe more pictures.

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millman5
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Post by millman5 » Fri Apr 11, 2008 12:49 am

If the buna N doesn't compress enough to allow your part to pull down flat. I seem to remember seeing closed cell foam cord somewhere in one of my publications.

When I was in the automotive machine shop business, I had a vacuum crack detection bench that used a piece of closed cell foam to sit the head gasket surface of a cylinder head to. With 20 in. Hg pulled on that you couldn't have knocked one loose with a sledge hammer.
If it works Don't fix it....

HotGuns
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Post by HotGuns » Fri Apr 11, 2008 6:35 am

Interesting post. I have been considering fabricating some sort of vacuum chuck at work to do very thing pieces in the mill.

This post could be educational.
Bob

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JHenriksen
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Post by JHenriksen » Fri Apr 11, 2008 7:50 am

I made one for my engraver out of 2 pieces of .500 acrylic. Milled grooves .200 deep on both pieces so they lay at right angles to each other when assembled. Drilled .062 holes on a 1/2 inch pattern. Held the two together with small screws. Its all one section. To hold small parts, I just lay a piece of plastic on the area I'm not using. I use a pump that started life in the refrige service industry.

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tmcd
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Post by tmcd » Fri Apr 11, 2008 9:57 am

How much vacuum do you have to pull so the parts stay in place? Perhaps that is yet to be determined.

Tim

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mechanicalmagic
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Post by mechanicalmagic » Fri Apr 11, 2008 9:59 am

Jose,
In my former life I used a Hurco bed mill, with (tool changer) to make Printed Circuit type boards. (We needed instant turnaround, and acid etching required a new SAFETY PROCEEDURE.) I used flood coolant to keep the dust down. The vac pump was a dry vane Gast, with a catch tank for the coolant.

The voids were treated as pockets, and it took less than an hour per board, including holes. These were very high speed photo detector amplifier boards that had to be hand designed. We only needed two, but getting the right configuration demanded quick prototyping, assembly, and testing.

In another building, we had a board router. The SAFETY folks were so paranoid about Fiber Glass dust, (in an office facility), I don't think it was ever used. The machine shop people wouldn't take and use it, because it was a "toy". The real e-fab shop wouldn't use it, bacause it wasn't "the right way to make boards".

I wonder why I retired?
Dave
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.

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tmcd
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Post by tmcd » Fri Apr 11, 2008 10:05 am

mechanicalmagic wrote:In another building, we had a board router. The SAFETY folks were so paranoid about Fiber Glass dust, (in an office facility), I don't think it was ever used. The machine shop people wouldn't take and use it, because it was a "toy". The real e-fab shop wouldn't use it, bacause it wasn't "the right way to make boards".
One place I worked we had one of those small routers. No one liked it because it made such an outrageous amount of high pitched noise when it ran. For what it cost it was rather poorly made as well.

Tim

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mechanicalmagic
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Post by mechanicalmagic » Fri Apr 11, 2008 10:10 am

tmcd wrote:How much vacuum do you have to pull so the parts stay in place? Perhaps that is yet to be determined.

Tim
Tim,
For light work, it doesn't need to be that good a vacuum. If Jose has a 5" x 5" surface, and the pressure is 4.7 psiabsulute, that's 10 psi on 25 square inches, for 250# of overall force.

Quite adequate for light milling and engraving.

This level of vacuum can be easily done with a mechanical vacuum pump, either a dry vane, or a lubricated pume (that's what I have now). Also, can be done with a simple venturi, IF you have the compressor to drive it.
http://www.harborfreight.com/cpi/ctaf/d ... mber=96677

In all cases, a vacuum gauge is needed to insure you truely have a good seal. Otherwise.....

Dave
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.

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SteveM
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Post by SteveM » Fri Apr 11, 2008 10:28 am

mechanicalmagic wrote: For light work, it doesn't need to be that good a vacuum. If Jose has a 5" x 5" surface, and the pressure is 4.7 psiabsulute, that's 10 psi on 25 square inches, for 250# of overall force.
A friend arranged a leaf blower motor to suck the air out from under his race car (LeGrand MK25) and added a rubber skirt around it to seal it.

It only generated a couple pounds of vacuum, but with the number of square inches, it generated so much downforce, you couldn't push the car when it was on.

Would it help to have a block on the side in the direction of the cutting force to help make sure it didn't creep?

Steve

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mechanicalmagic
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Post by mechanicalmagic » Fri Apr 11, 2008 11:02 am

SteveM wrote: A friend arranged a leaf blower motor to suck the air out from under his race car (LeGrand MK25) and added a rubber skirt around it to seal it.

It only generated a couple pounds of vacuum, but with the number of square inches, it generated so much downforce, you couldn't push the car when it was on.

Would it help to have a block on the side in the direction of the cutting force to help make sure it didn't creep?

Steve
Steve,

I was at Laguna Seca in 1970 when the Chaparral 2J "sucker car" was running. ABSULUTELY amazing cornering. He could go into the corners with the others, and while they were drifting to the outside he'd just stay on the inside and pass underneath. There was NO competition, would have won by MANY laps, but they only ran practice, broke it.

http://www.photoessayist.com/canam/chap ... parral.htm

Side blocks might help, I never bothered.
Dave
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.

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