Bevel on holes - Mild Steel, thicker materials

CrossFire ® PRO Troubleshooting
1

Hi there, I am getting a consistent bevel issue on holes when I cut 10 and 12mm steel plate (3/8 and 1/2" approx in freedom units). I have a Pro and XP45, clean dry air with refrigerated dryer, Im pretty much using the Hypertherm Cut charts. My edge quality is great, and no taper on the cut on the rest of the cutting, it only appears very prominently on holes. On the 12mm plate Im cutting 18mm holes for instance, the top side is cutting 18mm bang on, the bottom is closer to 16.5mm, so a 0.75mm taper over 12mm - so approx 4 deg of taper. I have tried running at half speed and even lower, Ive tried reducing the cut height which improved it a little (1mm vs book spec of 1.5mm). Im not really sure what else to try, or if I am indeed being too fussy. I would have thought a 1.5mm reduction in diameter over 12mm was significant. Id be happy with 0.5mm.

Appreciate any help, cheers

2

You can try slowing down more. It’s the nature of Plasma and cutting curves.

12mm and 45a is maxing out that unit.

If your holes are for slip fit, design for oversize hole. If it needs to be precision, then drill.

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3

Thanks Very much, Ill try slowing it down a heap more and see what happens. Agreed its at its maximum. I have been drilling out the12mm holes Ive been cutting in 10mm plate as the taper was also unacceptable. I wish I had a bigger plasma unit now as have been requested to cut up to 16mm! Might have to make this one pay for itself and go up a size.

Appreciate the reply.

4

I have a 100a Hypertherm, and for a .625 pass through the best I could get was a .715 opening and a 75% cut speed reduction in 1/2" plate

5

If you are using Fusion, you should try FEED OPTIMISATION at the bottom of the 2D passes tab on just the holes. Then, make a new cut profile for the remainder of the part. This slows down the cutting in the holes. It works well.
passes tab

images

I use 5 ipm reduced feed rate.

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6

Thanks, Im using Sheetcam. I think I can set up rules though…

7

Have you verified cut height with a feeler Guage? If not, you will need to.

8

Thanks, I have attempted to. I am using THC and when using smart voltage it definitely doesnt stay within the target range but when I stopped it part way through a cut and measured it looked pretty good. Without using smart voltage it was horrible and the torch was constantly hunting up and down.

9

Measure by using feeler gauges. .02" (.5mm) can be the difference between a good cut, and a bad cut + ruined consumables.

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10

Sounds like EMI. Get with Langmuir about it.
Or purchase a EMI filter. But, only after you check the cut height manually like @Sticks said.
Also make sure your table passes the Ohms test.

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11

Are you saying that it was hunting up and down while you’re using the nominal voltage setting?
If so what nominal voltage were you using?

Or are you saying that the THC was completely turned off? If so there should be no movement in the z axis during the torch on time.

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12

Yes hunting up and down while using Nominal voatage. Was using the book setting.

13

I did check with feeler gauges and it looked to be within spec but will double check.

14

Can you tell me more about the Ohms test? And where do you propose to put the EMI Filter?

15

ground-test
ground-test1000×816 186 KB

This test should read zero or almost zero. Test from the plasma table frame to the outside of the printer-style USB plug outside shield.

(upload://5D8fjn4zHInuHAvK9wlce94kCLK.jpeg)
Check out CNC USB Isolator 1Kv -(Bullet Proof USB) UC-100 USB, USB Ground Loop Eliminator on eBay!

The ground loop isolator goes between the computer USB and the control box USB input.

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16

So Im getting 3.7k ohms… What is the course of action and will this be having some effect on the bevel? thanks for your help

17

Email Langmuir to see if they consider that acceptable. I think it should be Zero. Make sure that the control box bushings are installed correctly, and ensure that the USB port on the control box is not touching the housing. This will create a ground loop. It will send stray voltage to the THC and play havoc with it.

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18

Also I have just been doing some cuts this morning on 8mm steel - Im cutting a circular spacer. I have now noticed I have a bevel in just one quadrant of the circle on both the inside and outside profile. the bevel is showing up in the y direction of travel when travelling in the negative y direction on the inside loop and when travelling on the positive y direction on the outside of the loop. On all other quadrants I am achieving near parallel cuts

19

The control box is isolated from the frame with the large plastic spacer

20

Well, it sounds like EMI is not the issue if you are completing cuts. I can’t help you with SheetCam.
In Fusion, you can compensate for circle and bolt holes. Some of our SheetCam rocket scientists may chime in.

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