Cutting 1/2" & thicker - pieces move?

[slvr98svt]

Hey guys I have a 5x10 Tracker table with a Powermax 1250 on it. Most of the work I do is 1/4" and below, however lately I have picked up a contract to cut a bunch of 1/2" - 5/8" plate along with an occasional piece of 7/8. They are all square or rectangle pieces in the vicinity of 10x14 and up to 14x14.

My problem lies in the fact that at the end of the run, it seems the heat or something "moves" the piece so it becomes out of square by anywhere from a 1/16" to an 1/8". The first 3 corners all measure out to be pretty much square, however when it is on the last leg of the cut, it "pivots" or turns as the material there is to hold it in place gets cut.

I have cut at 60A up to 80A with different speeds on the 5/8" plate which is what I am having trouble with at the moment. Seems the best ones I have gotten are at 80A @ 24IPM. Is there some way to combat this problem or is something I will have to live with?

Thanks,
-Matt

[jimcolt]

I don't generally have the parts move in the table....but have seen it before. Likely it is thermal input to the plate reacting to the particular shap of the part. Best suggestion would be to cut the part that is moving in a couple of separate cut paths....then trim it out of the sleleton after the temperature has stabilized....this can all be done with you part program....and is fairly common in both laer and plasma cutting to leave "stitches" to ensure the part won't move.

Jim Colt Hypertherm

[WSS]

Are you edge starting or letting the pierce run into another cut area? .0625" - .125" sounds like a "kerf width" problem. Sometimes you can have a screw driver or similar item (chisel ground thin or a thick putty knife) ready to stick/jam into the kerf at the far end or wherever you think the problem of moving is occurring to stop that shift. A water table helps a bunch too. If you are edge starting or somehow creating a opening in the web/profile, you may need to clamp either side of the slice to keep it from widening and shifting parts, I have watched that gap open as much as an inch before

I have seen guys weld a "U" shaped tab around the area of an edge start and pierce in between it to hold shape.

WSS

[slvr98svt]

With the part being a rectangle, I am starting off the edge of it and letting it come straight into the one side. So then when it finishes the cut it somewhat goes through the lead-in. I have tried the screwdriver trick and although it works, it doesn't combat it completely. I think I will try the couple different cut paths and see if that cleans it up any.

I should clear up that the piece that I have been cutting, 10x14, still measures 10x14 on a tape measure, but when you put a square on the last leg of the cut, it is about a 1/16 off by the time it reaches the end of the cut.

Thanks for the tips,
-Matt

[WSS]

Just to be sure, try zip tying a sharpie to the torch and do a dry run with the torch off and the marker touching to see if it is a out of square gantry or some other issue. Crossing over the leads should be OK as long as the web is held intact.

WSS

[slvr98svt]

I will give the sharpie trick a try tomw and see what I come up with.

Thanks,
-Matt