Hole Cutting - Ok on top side, elliptical on underside?

[Chris-D]

Ajan 260 CNC plasma cutter, which is our first experience on CNC plasma cutting.
We're finding that regardless of the sheet thickness, speed, amps etc, we're suffering an issue (when cutting holes of various diameters (20mm-60mm) where the upper side of the material looks fine, almost perfectly round, but the underside is elliptical.
The mis-shaped area is on an axis approximately 2 o'clock to 8 o'clock.

Any ideas?

[adbuch]

Chris - Please post some close-up photos of both sides of some of the holes so we can see exactly what your are dealing with and better help you to try to resolve your problem.
David

[robertspark]

is the torch perfectly square? have you checked?

rotate the torch 90 degrees does the ellipse move 90 degrees?

carefully remove the consumables, when you get to the swirl ring, rotate it 90 degrees, and reassemble.... does the ellipse move 90 degrees? if it does move remove the swirl ring again and look at it carefully for any burrs on the air vents.

[mdwalker]

Damaged consumables, improper cut height, improper pierce height, improper cut speed, torch not square to material, can all cause hole quality issues. Make sure your torch is perfectly square to the material. Check actual cutting height and adjust if needed. Make sure you are piercing at the proper height and delay. One bad pierce can damage consumables. Start with new consumables. Cut speed for circles should be about 60% of normal cut speed. Once you have everything else dialed in you can do some test to find the optimal cut speed. Do a search for Jim Colt and read some of his post on hole quality. He has a wealth of information.

[Chris-D]

Thanks guys.

I'll try rotating the torch / swirl ring to see if it shifts the problem.

[weldguy]

For sure check that...

1-the orifice in the nozzle is good as new, not out of round or a crater in the end
2-cut direction is correct, counter clockwise for interior holes
3-an overall reduction in speed on all holes may be needed
4-be sure cut speed is reduced by approx. 50-60% for holes smaller than 1"
5-correct cutting height
6-THC turned off for holes where speed reduction is being used
7-clean dry air is being used (if you see carbon deposits in your nozzle and around electrode you need cleaner air)

Ensuring all these items above are addressed will without a doubt improve your performance and get you closer to where you want to be

[acourtjester]

another quick check is to see what the outside edges of the squares look like

[adbuch]

https://www.hypertherm.com/en-US/suppor ... e-quality/

[Chris-D]

That's really great advice guys. Thank you very much.

[robertspark]

also check if both your X and Y axis have the same step + acceleration settings......

I suspect that if 1 axis was set differently to the other it may slow down and cause something like that too.

However I suspect that as per my earlier post if you rotate the torch in the holder 90 degrees that it will probably move (indicating its a consumables issue / swirl ring).

If it doesn't move when you rotate the torch .... then the torch holder is not square to the table

(first thing I would do before anything else would be to rotate the torch in the holder if possible and re-run the gcode) This will shift where the problem may lay between squareness + motion and consumables / torch inner bits.

[weldguy]

If you found one of the suggestions has worked for you please post back which one it was. May be helpful for another member in the future.

[Chris-D]

If you found one of the suggestions has worked for you please post back which one it was. May be helpful for another member in the future.

Thanks, will do.

Rotating the torch did seem to somewhat shift the problem, as per robertsparks suggestion. Nothing noticeable in terms of burrs or anything, but regardless, all consumables in the torch have been replaced and we've reattempted but things but still no better.

The machine has done less than 1hrs work so far.
I'm on with the supplier for assistance but will report back the outcome for sure.

[weldguy]

If rotating the torch shifted the problem and your consumables are in perfect condition (new consumables doesn't mean they are perfect, a single pierce can destroy new consumables before they even cut 1 inch if your air supply is wet/dirty) then I would move on to operating conditions. I suggested 50-60 reduction in cut speed for holes, mentioned proper cut direction and cut height. Have you tested those yet? What plasma cutter are you using?

[robertspark]

when you replaced the consumables did that include the swirl ring?

did you inspect the swirl ring for any burrs?

what is the oring like? try a bit of silicone grease on it (don't use an petroleum oil based grease)

https://www.hypertherm.com/learn/spark- ... sma-torch/

[weldguy]

when you replaced the consumables did that include the swirl ring?

did you inspect the swirl ring for any burrs?

what is the oring like? try a bit of silicone grease on it (don't use an petroleum oil based grease)

https://www.hypertherm.com/learn/spark- ... sma-torch/

I am not sure that he is using a Hypertherm machine, had a quick look back through this topic and I didn't see that mentioned. Curious to know what plasma he has, that could very well be the problem.

[robertspark]

I am not sure that he is using a Hypertherm machine, had a quick look back through this topic and I didn't see that mentioned. Curious to know what plasma he has, that could very well be the problem.

oops. I just assumed..... quite right if it's of cheapo origin it may not even have a swirl ring and be blowing / cutting the kerf in any direction the wind blows..... you get what you pay for.... my mistake

[Chris-D]

Thanks guys. Its an Ajan 2004 260 (Turkish made). It does have a swirl ring.
The cutting speed reduces automatically with the software depending on hole size/sheet thickness, and defaults between 50%-90% speed. I've also tried overriding this to various speeds with no improvements. I've replaced every consumable inside the torch.

[Chris-D]

Forgot to mention - The air is through a refrigerant dryer, pre filtered, then goes through a triple stage carbon filter at the machine down to 0.01 micron, so I'm confident the air is clean and dry.

[weldguy]

I have never heard of Ajan, maybe its good, maybe its not. I would try a Hypertherm plasma out if you can borrow one or get a demo unit. You may find it cleans everything up for you. It sounds like you have exhausted all efforts on the Ajan.

[Chris-D]

Plasma now well within acceptable limits - Hole optimisation has had parameters tweaked by Ajan engineer, and the lead-in positions were made more central, and this seems to have resolved it 90%.

[weldguy]

That's great, glad to hear it. Just goes to show for others with similar issues that with some tweaking you can make a lot of improvements. Thanks for posting back.