[Joe Rodney]

Hey all,

For the past 15 years I've been machining primarily glass, and none of that has been over 9" square by .120" thick.
We are going to start making our own fixtures for our other departments and dedicate a machine (Haas MiniMill) to milling metals and plastics.
I have a standard 6" Kurt type vice and was wondering what the best to clamp a piece of plastic that is 12" square by 1" thick for flycutting without it vibrating too much, which is currently happening. The facemill seems to bury itself a bit on the areas that overhang the vice.
Like I said, I new to this type of machining and would appreciate any help.

Thanks in advance.

[.xXACEXx.]

one good way to machine plastics is to use what is commonly reffered to as double sided tape....it is sticky on both sides...clean your table with alchohol or acetone.or something of the like,then stick the tape down to the table,peel off the backing on the top side of the double stick tape and clean the surface you intend to stick down on the tape with alchohol as long as your table is flat and you dont get to wild with cutting you can do pretty well flycutting with sharp tools ,in case you didnt know cleaning with alchohol will remove all the oil that may be on you table or part...so the tape will stick well .
again be easy with it at first..till you see how well it will hold...some times you can reuse the tape...but in most cases its best to just roll out some more as its cheaper than a new part if the tape turns loose...hope this helps...

[tauntdesigns]

I'm not experienced in cutting plastic.
From your description, I guessing that you moved the movable jaws to the back (2 ends) jaw mounting surfaces and it's chattering.
Is it moving in the jaws? If the plastic bows a little in jaws from over-tightening it, it would chatter, But if it's not tight enough, it will come out of the jaws with a big boom.

I've used (what I called) Toe clamps on alum that size before. They clamp to the table next to the material. It has a movable Toe that moves out against the block. Put 2 on one side and 1-2 on the other. The Toes move on a downward angle holding the part without being on top.

Double back tape??? I not sure if tape would hold plastic..... if it did, I wouldn't want to take off more then a clean up cut.

Te-Co Double Action Edge Clamp
http://www.jlindustrial.com/CGI/JISR...727+4294966245

Gotta' go get Lotto,
Jack
Pic:
http://www.jlindustrial.com/CGI/JISR...TEM=TEC-33717L

[tauntdesigns]

Oh yea, I forgot to add this.

Would a vacuum fixture work?
If you're going to run a bunch of them you might invest in a vacuum pump and make a vac fixture.

Thinking out loud,
Jack
P.S. If your face mill has inserts, try removing every other one, or all but one insert (kinda like a flycutter)

[mark c]

double sided tape works great for plastic. We use it daily.
Use a high spindle speed and start with a relatively low feed rate and depth of cut and sneak up on it

Mark

[Joe Rodney]

Thanks guys.
I'll try all of the above. At this point I have nothing to lose, so I have some "trial and error" time afforded to me.

[Geof]

....I have a standard 6" Kurt type vice and was wondering what the best to clamp a piece of plastic that is 12" square by 1" thick for flycutting without it vibrating too much, which is currently happening. The facemill seems to bury itself a bit on the areas that overhang the vice.....

Make custom wide step jaws in aluminum to grip the full 12" with the step about just deep enough that the facing cutter clears the top of the jaws.

Put a relief in the bottom two thirds of the step depth so you have a ridge that does the gripping along the top of the jaws. Because the grip is above the centerline of the material any bowing induced by tightening the jaws goes downwards so if you place packing that is exactly level with the bottom of the step under the material it is held firmly in contact with this packing.