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nepenthes
01-15-2007, 02:51 PM
We just got our ShopBot up and running two weeks ago with a new vacuum pump. I started out cutting .060 aluminum with it and I have had no problems. Last week I switched to cutting diamond plate and all hell broke loose.

After much trail and error, I have determined that the problem has to do with the vacuum hold down system. There is too much irregularity on the bottom side of the diamond plate to get a good hold of the material.

I have been able to use carpet tape as a hold down and have gotten good cuts, but carpet tape just isn't going to cut it for production runs like I am shooting for.

As examples, when I put a new sheet of .060 on the table, the pump is pulling -10.5 bars and finishes pulling -5.5 bars. When I put a sheet of diamond plate on it starts at -5.5 bars and drops from there.

I would love any pointers you guys can offer me with this!


Michael Waltz

paco
01-15-2007, 03:20 PM
With valves at zones you could concentrate the vacuum in more restricted area.

Depending on your production, you could consider some sort of dedicate vacuum grid where the vacuum would be concentrate under each of the parts rather than where the cuts are made.

If the problem is the finish then you might need something else...

If the problem is hold down, you may consider tabs (one or two is generally enough)... still you need flat material for the tabs to survive.

nepenthes
01-15-2007, 04:32 PM
Since I am able to get a good cut using carpet tape, I assume that I am getting some sort of vibration in the diamond plate when I am using the vacuum.

Using the vacuum, I get a good cut for a few inches and then I get huge chunks of aluminum along the cuts and really jagged edges. Plus aluminum builds up on the bit.

paco
01-15-2007, 04:46 PM
What's the tooling? What are your feed and RPM?

You need (that's my belief) O-flute; either up or down, mostly with small CED.

If you have problem with hold down, you may consider spiral down. I personally don't have much experience with down cut but I've heard some good comments...

Utility grade aluminum tends to stick more to the edge (burring) and tooling (building up in the flutes). You may check for another grade (I can imagine your face now) or try air jet cooling or lube mist at the tool tip/kerf.

davidallen
01-15-2007, 09:08 PM
Michael,

You might try a 'soft' surface. A layer of 1/16" foam will help seal the metal and accomodate small irregularities.

The diamond plate may be of a different grade than you've cut previously. Check the specs then a machinests handbook for cutting speeds and rates.

da

Brady Watson
01-15-2007, 11:00 PM
It sounds like you are having trouble with vibration & in turn, the cut. If your parts have holes in them, you can help keep the vacuum seal by running some screws in those holes, right into the bleeder board.

You also might want to experiment with foam tape around the edges of the bleeder to help get good suck down. It's pretty tough to get warped AL to pull down with vacuum, so after you eat up your current stock, inspect future batches for warpage.

One other thing that you can do (watch the PW video for details) is bridge the parts with small tabs to keep the whole sheet together. That way nothing breaks free. Sounds nutty, but a few trash bags cut up the sides placed over open kerfs, eliminate the leakage that you are getting after you cut for a few min. Carefully planned cuts (ordered cuts) are needed to do this so that you don't wind up running over the bag...

I think you have the right bit and that you are in the ballpark on speeds, it's just getting that vacuum to work for you with warped material. Since it is only diamond on one side, you don't get to choose which way the crown goes...but you knew that already!

Hope that helps!
-B

nepenthes
01-17-2007, 12:25 PM
After examining the diamond plate that I have, I have noticed that it has been knocked around quite a bit and improperly stored plus the crown goes in the wrong direction. I will be using the carpet tape until our new batch arrives. Once I have the new diamond plate, I will let you know how it goes.

Thanks for the help.