cut beveling in wierd way

[twicecustom]

I have a new table I'm just finishing up on. When I cut this test square I have 2 sides beveling and 2 sides square. I have changed speeds and direction and still same result. I would understand to have two sides across from each other being beveled but not like this. I have an L-tec PCM-750i, commercial Refrigerated air dryer, running right at 70lbs air, The material is 3/16" and I am cutting with 50amp tips. I have tried as slow as 20ipm and as fast as 40ipm. My standoff height has varied from .075 all the way to about .2 with no change. I'm confused.

test square.JPG (20.79 KiB) Viewed 1580 times

[jimcolt]

Varying bevel around the perimeter of the cut is most often caused by either a defective or damaged nozzle orifice. If you inspect the orifice under a magnifier or an eye loupe, often you will see a small defect suuch as a nick or an out of roundness. The nozzle shapes the arc, and if the nozzle orifice is not a perfect circle, then the arc will be out of concentricity, and the cut will be affected. Nozzles most often are damaged by piercing too close to the plate, or with inadequate pierce delay time. One bad pierce can damage a nozzle, more consistent piercing is done with a good quality torch height control that is properly set up for the power level and material thickness being cut.

Gas flow issues can also affect the concentricity of the arc......while I am not very familiar with the Esab torch you are using....make sure that 1. you have the correct mix of parts in your torch, and 2. that the swirl ring and retaining cap are in good condition....if you are not sure replace with new. A damaged, worn or incorrect part number swirl ring will affect the gas swirl rate in the torch which is critical in controlling cut edge angularity and concentricity.

Also.....and this probably should go without saying....check the squareness of your torch to the plate. The fact that you have 2 square sides indicates that the torch may be leaning.....as you cannot get true 90 degree edges with any air plasma, in reality, you should see a bevel that is consistent around all 4 sides when all of the above is working correctly, and the torch is truly square to the plate. On 3/16" steel with your Esab system, I would expect 3 to 7 degrees of taper under ideal conditions around the part perimeter. If you had a high definition class industrial plasma, you could expect about 2 degrees of taper, and a laser would produce about 1 to 2 degrees taper on this thickness of material.

Jim Colt Hypertherm

[twicecustom]

I will measure the bevel angle tomorrow at work. I replaced all the consumables and it cut exactly the same, and I will double check the squareness of the torch. This torch normally produces very good quality cuts, that is why it baffled me so much. I got my LCTHC from CandCNC in the mail today, but am still working on a new torch holder to get it all together 100%. Thanks for the reply!

[jimcolt]

Check torch squareness with a square from torch body to plate, don't use a level. Also, if you are cutting without a height control.....that alone could account for the out of squareness! If the torch is .010" too high, you will produce more bevel.....a good height control is the only way to control that. Further, if you are piercing and cutting at the same height.....I'm quite sure that either you are damaging the nozzle orifice on the first pierce (piercing should be done at twice the manufacturers recommended cut height), or you are cutting at the pierce height, which is far too high and will cause abnormal bevels.

Jim

[minnfatz]

I vote torch squareness. It has gotten me a couple of times. Luckily it is an easy fix!