Odd bevel issue...

[davek0974]

I've been fighting an odd bevel issue with my PM45 for some time now, if i cut a square it is good on the verticals (Y axis) but tapered the same way on the horizontals (X axis) as if the torch was leaning over (it's not).

I have tried rotating the nozzle 90deg - no change, tried a new nozzle - no change, checked torch alignment - ok, checked cut height - ok.

Now, i'm building a new table so I won't be wasting too much time on this but thats just hoping the fault does not follow to the new table.

I have not tried a new shield yet but the orifice is good and clean as are the small jets around it.

One thing that did pop into my head yesterday was that the angle matches the airflow on my downdraught - back side to front side. But its not a very strong flow so i am doubtful if that is connected, I could do a small test with the air off next time I am cutting.

Are there any other causes for this odd angularity???????

[Brand X]

Change the electrode? Just to take that out of the mix. Rare, but I have seen that one before..

[davek0974]

Will try that, just looked at the last jobs and the bevel is not the same as the air flow, its opposite so i think thats a non-starter.

Will do the electrode.

[SeanP]

I seem to have been fighting that issue as well since I started, I can't pinpoint why it happens as well, sometimes can put a new electrode and nozzle in and still get that happening, damage to the nozzle seems to cause most bevel probs, I still need to get a new shield to rule that out though, it's amazing how long they last with a bit of care.
Had a big job the last few days cutting base plates from 8mm & 10mm, cut 4 sheets of 8mm up this afternoon all with the same nozzle and electrode, they had done a bit before that and would do more, that's using the consumables from plasmatech as well Dave so nowt wrong with those.

[davek0974]

Excellent thanks

Its an odd issue for sure, seems totally variable and quite concerning, on 3mm ally it can range from nice to scrap between jobs, the bevel can go almost 45deg on a bad one.

Baffling, will try a new electrode, shield and swirl ring to be sure.

[jimcolt]

A consistent bevel all the way around a part indicates incorrect height. A bevel that varies....especially if two opposing sides of a rectangle are a parallelogram type bevel.....then it is a consumable issue. It will be one or more of these...listed from most common to least common:

- Damaged nozzle orifice. Your operators manual has a section on inspecting this. The nozzle shapes the arc....of the orifice is not perfect the arc is not perfect. Most commonly...nozzles are damaged from piercing too close, they also wear over time. You can ruin a nozzle orifice with one bad pierce.

- Damaged shield orifice or bleed hole orifices. The shield on Powermax 45 as well as Duramax torches uses its inside shape in conjunction with the design of the nozzle to create a "conical" secondary gas flow that impinges (squeezes) the arc to increase energy density. Like with the nozzle... if this flow is not concentric it will change the shape of the arc.

- Electrode. A worn out electrode affects cut angularity....there is a section in the manual that suggests inspection.

- Swirl ring. Yes, these wear out! The gas swirl will change as the swirl ring wears.....the symptoms are misfiring, changing cut angularity and dross.

- Retaining cap. These too will wear over time. There are internal air passages that direct air flow to the critical shield....if these get plugged, melted or blocked in any way...they will alter the angularity of the cut.

My suggestion? Start with the above and change one part at a time, starting with the nozzle. Cut a rectangle after each change, mark the 4 sides (NSEW), and compare. One other thing.....a bad torch body or torch lead (leaks, restrictions, cracks, collision damage) can also cause angularity.

Best regards, Jim Colt Hypertherm

[davek0974]

Thanks Jim,

I have tried a new nozzle - that was my first suspicion, no change though.

The torch is practically new so i doubt there is an issue there yet.

I will try a new electrode next, followed by the shield then the swirl ring.

See what happens.

[davek0974]

Did a couple of tests tonight, also tried to improve my divots.

This is 3mm aluminium, the settings for sheet cam were as listed here, no lead-out was set on any cut. Holes are small, 6x6mm and 8x16mm.

1=no overburn, torch off at end
2=0.5mm overburn, torch off 0.5mm before end
3=1mm overburn, torch off 1mm before end
4=1.5mm overburn, torch off 1.5mm before end

front

back

Not a massive change but 4 is better than 1, much less divot. I then cut the job i had to do which has these small holes as well as larger ones on it, the small holes came out just as the test but on the longer, faster runs, the cuts did not complete at the ends and left a half cut tab at the end of cut, presumably the half-cut depth was caused by the torch being extinguished and the cut being made on the shrinking arc, BUT why did it leave a tab of about 4mm when it was set for 1.5mm of overburn???

Clearly a lot to learn here, but so many options

As for the original topic, I fitted a new electrode and new nozzle and I think can just be seen here, the bottom edge only of each hole is badly bevelled but not the other three sides - this makes no sense to me.

[davek0974]

Had to cut a few more of my aluminium parts tonight, I tried the test holes again, this time at full 45A (previous was 40A) and increased feedrate by 10% to allow for the higher current.

The result was surprising - practically zero dross and sharper corners (i have mach3 set to stop CV on angles >89deg) but the downside was a larger divot at the end of the cuts, this was still set for the 1.5mm overburn & 1.5mm torch off rule.

Two other points caught my eye -

The odd bevel on the lower edges only is still there, no change at the higher current.

There seems to be an issue with my THC, the top dross seemed bad and variable but followed a pattern I noticed...

The small details were cut with THC off and showed no top dross at all.

As soon as the larger cuts were made, the THC kicked in and the pattern seemed to be that they would start off clean (pierce height is good) but then either stay good until the first corner whereby the top dross would appear after or they would start showing top dross as the cut progressed.

I'm running at 5000mm/min and 106v whereas the "book" shows about 121v, my little machine is not happy at this speed but it was made necessary to run it faster when i got the PM45.

The voltages always seem low on this setup, I generally set the voltage so that the height does not plunge or raise as soon as the THC kicks in. Next I tried lowering the THC rate in Mach from 10% to 8% and different results were seen, still with top dross but the THC height reading was different, higher.

I have no idea how this is going to play on the new machine, I am hoping things will be more as expected but the THC seems very odd as does the top dross.