Arc wobble during cut

[Chillertech]

I am a newbe to the cnc world. I have been setting up
My table and now I am down to the fine tuning portion.
I have a precision plasma setup DIY. I have c and cnc controls
And a hypertherm 45. I have made several cuts and the last
Project was with 16 ga mild steel with new consumables
And got a poor cut and I noticed the arc wobbled as it cut. I got the
Same results with 30 amp consumables and 45. Profiles are
Correct according to hypertherm. Could this be caused by contaminated
Air? I have new filters installed (2). I also tried to speed up and
Again by slowing the speed. I am at a loss on why this is happening.
If someone has had experience with this type of issue I would greatly
Appreciate what you found to correct it.

[jimcolt]

Two things to check first:

-Make a holder for a fine tip pen to be held in place of your plasma torch, tape a clean sheet of paper to a clean piece of steel and go through a complex part program in trial (no plasma) mode at the same speed that you plan to cut at. Look carefully at the tracing done by the pen. If there are any wobbles at all....these will show up in an amplified form in the cut. This test checks for the machines ability to follow the path.....but does not check for speed induced fluctuations. If you see overshooting in sharp corners it may be mechanical backlash or flex, if you see it on diagonals more than tru x or y....it often is machine acceleration and gains that need adjustment.

-Do the same as above, with the torch installed but in trial mode (don't fire the plasma) and rest your hand on the torch body while it is cutting at the plasma speed and on a complex part. Do you feel vibrations, speed changes, dwelling, jerky motion? This indicates that your part file may be segmentized....and the cnc is trying to accelerate and de-accelerate for each segment. When speed changes....(the plasma arc power remains constant)....you will see a wider kerf when it is slowing, a narrower kerf when accelerating....and the actual arc will fluctuate.

-Put your hand on the material while it is cutting. No one believes me on this until they see it themselves.....often the cutting bed slates get into a directional movement or vibration. You should be able to feel it by touching the plate while cutting. If this is happening reconfigure your slat bed.....often running thin slats in a serpentine fashion will solve the issue.

-If you are cutting with a water table, water causes a rough cut edge on steel. To determine if this is the issue, lower the water enough so it won't splash on the edge and do a test cut.

-If you are using an arc voltage height control.....do a test cut with the height control in manual, if the edge roughness goes away....maybe the z axis is oscilating. Some z axis speed and tuning may be in order.

- If you are 100% sure that none of the above are at fault....check the consumables carefully per the consumable inspection section in your operators manual. Make sure you are using the lowest amperage level that the cut charts suggest for the material you are cutting. Some alloys need to cut slower than the book specs in order to get a smooth cut....maintain the suggested cut height and slow down on test cuts about 5% at a time....look at the edge for improvement

-You have two filters (usually that is one too many!) make sure you have a pressure gauge installed within 6" of the plasma air inlet, after the filters. With the amperage knob turned fully ccw (air flow test) read the inlet pressure gauge to ensure it is above 90 psi and below 125 psi. Then adjust (withthe air flowing) the onboard regulator until the pressure LED's are satisfied on the Powermax45. A rough edge caused by arc instability is usually a pressure related issue.

- With brand new consumables....moisture in your air line generally doesn't affect the cut. You have two filters, there is another filter in the Powermax45.....and I assume you drain your compressor tank daily. There likely is not enough moisture to cause an issue with new consumables. moisture in the air will cause consumables (electrodes especially) to wear much more rapidly....so cut quality will be affected after some time is put on new consumables.


Hopefully the above will help you troubleshoot. I usually cut a test sample that has true x and y direction cuts (rectangle) as well as a right hand 45 degree diagonal as well as a left hand one. Often if it is tuning issues in the machine the diagaonals will be really rough, the true x and y directions will be smoother. The hand on the torch while cutting is usually a quick indicator of mechanical or tuning, and keep in mind that tuning issues will make the plasma arc physically wobble....as the torch movement is rough of jerky, one end of the plasma arc is attached to the torch, the other to the plate.

Jim Colt Hypertherm

[Chillertech]

Thanks Jim.
It's help like yours that keep hypertherm customers coming back.
I will start the process of elimination later today. Thanks
Again

[plain ol Bill]

Jim Colt to the rescue again - it is hard to believe the high level of customer service provided by Jim.

[beefy]

Hi Chillertech,

when you say the "arc wobbles", do you mean the torch is dead steady but the arc wobbles, or is it the torch that is wobbling.

My torch was once acting like a jack hammer (up and down motion) and this was caused by the THC RATE setting. I had to put it down to 15% before my torch became steady. When the THC Rate is too high the torch height control is always overshooting, but because the system reacts quite fast this turns into a fast up and down motion.

My table also has shake but that is simple due to a design lacking rigidity in several ways. It's OK at low speeds but at higher speeds its always there.

Keith.

[Chillertech]

It's appeared as the torch was steady. I have had shaking
Issues with the constant velocity; it acted like me when I've
Had too much coffee... I do have the THC rate at 40. I was going
To try slowly adjusting that down in small amounts. As I was watching
The arc it appeared like a wobble or as I call it when tig welding
As arc wander. However I was wearing cutting goggles and was just
Focusing on the arc. I have a lot of good information and a lot of things
To try and narrow it down. Lots of great people here. Thanks for the info.

[urbnsr]

I copy and print things like this from Jim Colt. That's when I think that there should be a Jim Colt Notebook. Thanks Mr. Colt.

Paul

[beefy]

Sorry if this has already been suggested (have to dash so can't check), but while the cut is in progress and this arc wobble is present, just switch off the THC. If the wobble stops then it seems like it was coming from the THC side of things.

Keith.