Help with ESAB plasma cutter

[camobob]

I need some advice on plasma cutting.
I picked up a used PCM-875 that cuts great but when using the torch standoff i get about a 30deg angle. As far as I can tell, the standoff is flat (90deg to the work) so I'm confused why the cut isn't straight. Also, I can't find any instructions on setting the amperage. Could I be using too much current??

[jimcolt]

A couple of questions:

1. Is the cut edge bevel uniform......say if you cut a 3" rectangle....is it the same on all four sides?

2. What thickness and type of material?

3. What set of consumables and power level?

4. How are you maintaining the torch to work distance?

Jim colt

[camobob]

Thanks for the response Jim,
I'm using the standoff that came with the torch consumables kit - it's just a ring that fits around the head so the torch is kept slightly off the material. When cutting 1/4 aluminum I get a bevel to the edge that is perfectly uniform and yes, it always bevels in the same direction. Dry air pressure is 110psi to the ESAB's regulator which is set to 80 psi per the directions. I'm going to play with it a bit more in a few minutes.
I saw the pics you posted earlier and there is definitely a skill issue on my end. I would think the machine should still cut straight tho.
How do you determine the amperage settings??

Bob

[camobob]

Oh...I had the amperage cranked all the way up when it was bevelling.

[jimcolt]

If your bevel is uniform around the perimeter of the part.....and you said it was around 30 degrees (I'm not sure I could make my Hypertherm bevel that much....no matter what I did!)....then your torch to work distance is way too high. I would suggest removing...or modifying the standoff device for the Esab torch, and moving closer to the plate.

Are you cutting by hand or by machine?

Jim

[Boostinjdm]

Is the tip new? When my tips get worn they don't cut straight.

[camobob]

It turned out to be the tip alright - the new tip was bad
I switched to an old one it cut straight.
Do you get many bad tips?

[1awert1]

I also have a esab 875 and it also cuts at a angle, the manual i have (came with the cutter) says this is NORMAL. something about the nature of plasma cutting, it said to compensate by turning the torch slightly...... The thicker the material is the more noticeable angle you will get...

[jimcolt]

Angularity on the cut edge varies from brand to brand and model to model. Speaking for Hypertherm systems, I have seen cut edge angularity improve dramatically over the years. My Powermax 45 that I use on a PlasmaCam cnc table cuts with very little, if any angularity on most materials. The thicker I cut, the less angualarity. It is fairly normal for most plasma systems to produce a taper in holes, however this is minimized with systems with better technology. If I need to cut a 1/2" hole in 1/2" plate, I expect the hole to be approximately .025" smaller on the bottom as compared to the top.....so I eather increase the hole size, or I run a drill or reamer through the hole after cutting to straighten it up.

The key to good cut edge angularity? 1. A good quality plasma and torch (Hypertherm has the best quality) 2. Good torch height control. Torch standoff, and pierce height dramatically affect edge angularity......a variation of .005" in standoff can change angularity drastically.

Attached are some pictures of a rectangle cut from 1/4" steel, this is cut with a Hypertherm Powermax 45, and the edge angularity is measured and marked on each side.....this is the deviation angle from 90 degrees. This is done with proper height, with the best air plasma......all bets are off with other brands! The last two pics are of a piece of 1/4" steel with some holes......you can see it has pretty square edges as it is standing up on one of them. Hypertherm works hard to provide the best cut quality and consumable life with its systems.

Also, I must add....there is another whole world of plasma when you talk about industrial high definition quality plasma. Hypertherm produces HPRxd series plasma systems that cut with close to 0 angularity and can make holes with virtually no taper. These systems are not cheap....but are production workhorses in industry.

[duaneb55]

I don't mean to hijack but what's with the external yellow wire in the torch head Jim? Material sensing circuit? Just curious.


BTW, nice cuts as usual.

[jimcolt]

Yes, it is the "Ohmic contact" plate sensor. It locates the exact surface of the plate before every cut, thenthe torch retracts to the exact pierce height, as soon as the pierce is complete, the torch then indexes down to the cut height. Essential for best cut quality/best consumable life, in fact all industrial mechanized Hypertherm systems use this feature, but the only a couple of the entry level cnc machine builders have this capability, PlasmaCam and Dynatorch. The rest use limit switches or z axis motor current sensing.....which have a higher chance of innacurate pierce height. One bad pierce, and the accurately machined nozzle orifice is junk, and cut quality suffers in terms of poor angularity.

Jim

Originally Posted by duaneb55

I don't mean to hijack but what's with the external yellow wire in the torch head Jim? Material sensing circuit? Just curious.


BTW, nice cuts as usual.

[wintermute]

Also, you may want to check if you have the old style seat for the PT-27 torch that comes with the PCM-875. If you do have the old style seat, I noticed a difference in cutting cleanliness and straightness when I upgraded to the new style seat.

Or you can just make the jump to the Thermal Dynamics One Torch which is compatible with the PCM-875...huge improvement over the PT-27 and the consumables cost a heck of a lot less.

--Wintermute