Problem- HOLES LOOK LIKE SQUARES

[Pure-Powder]

Well got my machine up and going, did some not bad looking cuts but my holes are crap! I an not sure why? Hypertherm 1000 with fine cut consumables, Hypertherm PHC.

1/8 plate , Plasma set at 40 amps, arc voltage 78 , Speed 90 ipm also tried 60 ipm same result, Torch delay 2.5 sec.

Do these settings look reasonable... Sure would like my circles to be round.. Could it be a calibration problem. Thanks Dennis

[vladdy]

not sure what you have for a table, but might be worth a bit of time to tie a ink marker [fine tip] to the Z and see if the 'drawn' circle looks like it should,,
at least if that looks good then you can check your tips, or travel speed next..

just my 0.03 cents worth [inflation]

enoy..

[Pure-Powder]

Think I will try the marker, see what that gets me! Thanks for the Tip.

[vladdy]

If straight lines 'marker' ok, but the circles do not, may possibly be backlash, if so grab a dial indicator, measure, and pop it into the backlash setting on your software, and then try again...
wound up with 3 thous on my x and 2 thou on my y axis on my plasma table..[which I figured was pretty good, considering],just using 3/4-10 threaded rod so far, but not enough speed for anything thinner than 1/8" plate, may have to replace them with acme 3/4-6 and speed it up some, steppers don't want to go more than about 40ipm reliably with the threaded rod setup..

.enjoy..

[Torchhead]

A lot of it depends on the mechanics (backlash). Typically those (backlash) problems show up on all circles. If it's smaller circles only, then you may have to look at the control software. It may not be processing the circles fast enough.

MACH software has a feature called CV (constant velocity) that averages multiple arc/line segments and smooths out the move. I don't know what controller software your table uses so it's hard to say more. Also you artwork needs to support arcs and curves into the DXF and the import fo the control software (not turning circles into hundreds of line segments ESPECIALLY if your control software does not have CV.

If the holes are small (less then 1/2" dia) you will need to drop the feedrate to less than half of the normal rate. You will never get perfect small circles with conventional plasma.
We have several customers that are mouning a separate Z head with a punch (air operated) if precision hole location is needed then just punching, and then cutting the shape with plasma and taking it to a punch press or drill to complete is a lot more accurate.