problem with angled cut

[da_Rayman]

i just finished my cnc-plasma and made my first cut 2 days ago. i borrowed a a budget plasma-machine and hooked it up. i managed to get a descent surface finish on 2mm mild steel that was coated with something grey. i got quite alot of dross on the backside but my problem is that the cut is angeld alot, atleast 20-30 degrees. i tried diffrent amps on the plasma-machine, diffrent feedrates and torch-height. i also changed the nozzle. if you look at the picture, the edge closest to the camera is angled more but has almost no dross on the backside. the edge away from the camera got rougher surface, more dross but the angle is better.





i also cut some 5mm stainless, probably 2333 but this was to much for the machine. you can still see the angle here more clearly.



same thing with the thicker piece. the side with the dross got rougher surface but less angle.

anyone got an idea why this is happening?

[jimcolt]

The varying angularity and dross levels on the steel part can be caused by:

1. Older technology/design plasma system
2. Damaged nozzle (tip) orifice from drag cutting or piercing too close.
3. Inadequate torch height control.


The stainless cut that you show just indicates that your plasma likely is under-powered for the thickness.

All plasma systems are not created equal......expect better cut quality with better plasma technology. Torch height control for pierce height and real time cut height is critical as well.

Here are some pics from one of my cnc machines with a Hypertherm 45 amp plasma with a good height control system.

1st pic is 3/8" steel, second is 1/4" steel, third is 3/16" stainless, last is 3/16" aluminum

Jim Colt

[da_Rayman]

ok thanx. what settings did you use for the 3/16" stainless? feedrate? amps? torch height? pierce height?

what are the signs if i got the torch to close or to far off the workpiece?

is there a standard torch height or is it diffrent between material and thickness?

[jimcolt]

All of the parts in the pictures were cut with a Hypertherm Powermax45 on a PlasmaCam DHC2 cutting machine.

The 3/16" stainless cuts were exactly as listed in the detailed cut parameter charts listed in the Hypertherm operators manual.

Amperage: 45
Pierce height: .15"
Pierce delay time: .5 seconds
Cut Height: .06"
Cut speed: 70 inches per minute.

Remember though....unless you use the same plasma you will not get the same results! There are a lot of technology differences...model to model and brand to brand.


Jim Colt Hypertherm

ok thanx. what settings did you use for the 3/16" stainless? feedrate? amps? torch height? pierce height?

what are the signs if i got the torch to close or to far off the workpiece?

is there a standard torch height or does it differ between material and thickness?

[da_Rayman]

ok. there got to be something wrong with my plasma machine. it was set to 40 amps but i couldnt go faster then 450mm/min (17 ipm) to even penetrate the 5mm stainless.

[da_Rayman]

i used a better machine when i tried today, but still the same problem. 5mm stainless cut with 60A and maybe 1200 mm/min. not much dross but still the damn angle... anyone got an idea?

[jimcolt]

You have not mentioned the brand and model of the plasma. Plasma cutters are not all the same.....some have better control of the arc energy desity, and can provide very square clean cuts.

I would recommend a Hypertherm plasma.

Jim

[da_Rayman]

i dont know the brand or model since i rented it from a company that sells welding equipment and machines. the arc seems to be stable considering that the cut is very even.

the cut is not conical but is a parallellogram. this is a section view with the yellow bit ofc being the arc...

[jimcolt]

I could see that in your cut pictures. Usually that indicates that the nozzle orifice is damaged....which can happen on the first pierce if you are not piercing at the proper pierce height. ule of thumb....pierce height should be 2 times the cut height.

Jim

[da_Rayman]

ok. how about the cut height? is it the same on all materials and thicknesses? i used the same on the 5mm stainless as you did, 1,5-1,6mm but i got other materials to cut.

[jimcolt]

Cut height and pierce height is dependant on the torch design. Most of the Hypertherm air plasma systems use .06" as the cut height from 30 amps up through 85 amps.....pierce height varies depending on materials thickness. Thermal Dynamics air plasma systems are designed generally to run at much higher cut heights.

Your pictures show cut angularity wildly varying around the perimeter of the part...that indicates a damaged nozzle....or a seriously bad gas (air) flow problem in your torch....could be a worn or damaged retaining cap, swirl ring, shield, or a restriction in a flow passage in the torch. Likely it is a damaged nozzle.

Jim

[da_Rayman]

no all the parts in the torch handle was fresh when i rented the machine. the gas-flow regulator on the back of the machine is set to 5 bar (72 PSI) wich is max according to the warning-label.