Cut Quality Question - Saw tooth edge

[lelyea]

Any input will be appreciated. Hypertherm PM-65 on CNC plasma table. I am getting an edge as pictured in the attached image - almost as if the plasma arc is pulsing . . .

Any ideas?

Thanks in advance

Len

plasma-edge-cut.jpg

[acourtjester]

Do you have a THC on the table?? Is the only vertical?

[lelyea]

Hi -
Yes, table has THC.

I am starting to wonder if there is a problem with the servo motor for the side to side action along the gantry. Possibly a loose set screw on a gear?

Is there anything I should watch for when R & R the servo motor? (I know to have the power off.)

Thanks,

Len

[weldguy]

Hey Len, it could be a number of things but THC can often be the issue or something too tight or too loose on the machine. I would do the same cut with THC off and if the cut smooths out you need to tune your THC a little better if possible. If the problem still exists than it is time to go over all of your drive system in search of a mechanical binding or loose issue.

[lelyea]

Hi -
Thanks for the replies. Did a cut with the THC off and still the same result.

Created an oval donut in CAD and cut it. Cut problem almost goes away on the bottom cut (cutting right to left) but is persistent on top cut when machine is cutting left to right. When creating cut files in sheetcam the reverse cut direction is selected.

Len

[acourtjester]

It may be better if you attach an image of the oval, marked with a sharpie as to you problem areas.
The direction of the cut should be cutting the outside of a shape you go CW and the inside cuts are CCW
Do you see this problem only no circular cutting.

[weldguy]

Hi -
Thanks for the replies. Did a cut with the THC off and still the same result.

Created an oval donut in CAD and cut it. Cut problem almost goes away on the bottom cut (cutting right to left) but is persistent on top cut when machine is cutting left to right. When creating cut files in sheetcam the reverse cut direction is selected.

Len

Ok so definitely a mechanical issue, sounds like something binding up a little when going left to right. Not sure what type of table you have but it could be that a follower bearing is too tight. For example if you have a tight follower bearing on one side of your torch carriage it could be smooth when moving right to left because your pulling the tight bearing along however when you are moving the other way your pushing the bearing making the tight bearing bind more. Not saying this is your issue but this a scenario that could be happening so definately check the tension of your bearings, you don't want clearance but you don't want them pinching the rails tight either.

[lelyea]

Thank you for your input. FIXED!

Not sure exactly what did it.
Removed the bearing blocks for the Z axis and cleaned everything - bearings, surfaces and put it back together. Removed the X axis motor and cleaned the belt and pulleys, cleaned the gear track and bearing surfaces and put it back together.
Something in there fixed it.

Thanks again. Len

[acourtjester]

Good feedback it helps other members when they search for info on a similar problem

[adbuch]

Len - sounds like maybe something was binding up. Glad to hear you've got it fixed.
David

[fridayrack]

Thanks for sharing information