Why does my machine torch cut crooked as nozzles wear?

[I Lean]

I've noticed that as my consumables get more and more use, my cuts get more and more angled--beveled one direction, and always the same direction too. (the sides of a cut piece will look like this: /---/) What causes that to happen, and why is it always the same way? New consumables make nice square cuts, so I know my torch is mounted vertically....just wondering if something's off a bit, that I could change to get more usable life out of my tips. Everything still cuts nice and clean, just angled.

[keebler303]

This thread is ironic given your username. Plasma has a swirl to it. Generally it will cut more straight on one side than the other. As the consumables wear, obviously the angle will increase. I'm sure Jim Colt will chime in soon with some recommendations but consumables have a limited life so once you start geting unacceptable cuts, you switch to new consumables.

Matt

[I Lean]

I understand the plasma stream swirls, but it doesn't compute in my head why it would start shooting more sideways as it wears, that's all--especially why it always goes the same way.

Just for the sake of more info for Jim assuming he'll chime in:

Powermax 45, T45M torch
45A Hypertherm consumables
Last job cutting (which triggered this thread) 1/4" steel, 45A, 50IPM, .15 pierce .06 cut height. I'm REALLY happy with the cut quality, but as it starts angling the parts don't fit together properly without dressing with a grinder in the slotted parts. It starts to have a noticeable edge angle with somewhere between 1000 and 1500 inches cut, give or take.

[Tensaiteki]

Originally Posted by I Lean it always goes the same way.

Is it always the same direction relative to the torch or to the table? If you rotate the torch after changing consumables will the angle form in the same direction or will it have rotated? If it has then the problem is probably in the torch, if not it might be a problem with the table.

[4R8]

You mention slotted parts, Is the majority of the cutting straight line stuff? For instance is the majority of cutting done in the X axis? You may have 200 inches to cut in X and only 50 of cut in Y. This may cause uneven wear?
If the parts could be nested in a way which evened out the cuts each direction you may find an improvement, but wouldn't be anything large.
Just a theory which works in my head.

[I Lean]

Originally Posted by Tensaiteki Is it always the same direction relative to the torch or to the table? If you rotate the torch after changing consumables will the angle form in the same direction or will it have rotated? If it has then the problem is probably in the torch, if not it might be a problem with the table.

Good point, I'll rotate the torch next time I change tips, to see what it does.

Originally Posted by 4R8 You mention slotted parts, Is the majority of the cutting straight line stuff? For instance is the majority of cutting done in the X axis? You may have 200 inches to cut in X and only 50 of cut in Y. This may cause uneven wear? If the parts could be nested in a way which evened out the cuts each direction you may find an improvement, but wouldn't be anything large. Just a theory which works in my head.

No, the parts have round and straight parts. The way I have them nested, the straights are always angled to some degree, not lined up with either axis exactly.

That brings up a question though: Does the torch "care" what direction it's moving? Does the arc "pull" enough that it makes a difference in nozzle wear?

[jimcolt]

Sorry I have not responded sooner....i am on vacation until the 28th....and have limited internet access!

I don't see much information regarding your machine, height control method, or information about the materials you are cutting.

Since the nozzle orifice shapes the arc....if any wear or damage occurs on the nozzle orifice...then you can expect the cut edge angularity to change. If it seems to always start to lean in the same direction...which I have noticed in a few (but not all) applications over the years...it can be related to the direction that the majority of your cut paths are lined up in. If 80% of the cuts were in the x plus and minus directions...then expect the nozzle orifice to wear more in those directions.

If you are piercing often and the machine starts moving before the pierce is complete....then expect damage from spatter back on the nozzle orifice.

If you are getting a poor work ground connection (dirty slats in the area that you most often cut....may be forcing the work ground current flow to be directional....from the cleanest slats)...this can be an issue as well.

You also don't mention how many starts you are getting. I typically see about 400 to 600 starts with my Powermax45 (clean dry air) when cutting 3/16" through about 3/8"thick steel before cut angularity starts to change. On thinner materials I experience 800 to 1400 starts often with the same machine.

Even after over 33 years in the plasma business...it is still amazing to me the the nozzles....especially on our air plasma torches....last as long as they do. The arc can be as hot as about 25,000 F., and copper melts at about 1000 F.!

Best regards, Jim

[I Lean]

Originally Posted by jimcolt Sorry I have not responded sooner....i am on vacation until the 28th....and have limited internet access! I don't see much information regarding your machine, height control method, or information about the materials you are cutting.

1/4" mild steel, cut on a homebuilt machine using CandCNC controls, including the DTHC II.

Since the nozzle orifice shapes the arc....if any wear or damage occurs on the nozzle orifice...then you can expect the cut edge angularity to change. If it seems to always start to lean in the same direction...which I have noticed in a few (but not all) applications over the years...it can be related to the direction that the majority of your cut paths are lined up in. If 80% of the cuts were in the x plus and minus directions...then expect the nozzle orifice to wear more in those directions. If you are piercing often and the machine starts moving before the pierce is complete....then expect damage from spatter back on the nozzle orifice.

Today I increased the pierce delay just a little bit (from .3 to .35)...I don't know that it was moving before the pierce was complete or not. Does it damage the nozzle or electrode to sit in one spot at the pierce for longer, or does it just create a larger hole and not hurt the consumables at all?

If you are getting a poor work ground connection (dirty slats in the area that you most often cut....may be forcing the work ground current flow to be directional....from the cleanest slats)...this can be an issue as well.

Work ground is clamped directly on the steel sheet.

You also don't mention how many starts you are getting. I typically see about 400 to 600 starts with my Powermax45 (clean dry air) when cutting 3/16" through about 3/8"thick steel before cut angularity starts to change. On thinner materials I experience 800 to 1400 starts often with the same machine.

I notice a change after a couple hundred pierces, give or take. It's still completely acceptable, just noticeable. I did do 550 pierces and about 3000 inches of cut from 1/8" aluminum before I noticed any change.

Even after over 33 years in the plasma business...it is still amazing to me the the nozzles....especially on our air plasma torches....last as long as they do. The arc can be as hot as about 25,000 F., and copper melts at about 1000 F.! Best regards, Jim

That is crazy, and amazing. Just to be clear, I am NOT complaining about how this thing's working--it's fantastic. I just want more.