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Finally cut some steel, how to get plasma going in a void??



Mike94531
04-20-2009, 10:06 AM
Finally wired up my machine yesterday, cut a few pieces of 1/8" steel, decided to try some 1/2" steel.

Worked pretty good, however, if I didn't cut all the way thru, I had a hard time trying to get the arc started in the kerf area. I would have to move the torch over a bit and start cutting into new material so that I could finish getting all the material cut new the bottom (looked like I was about 1/8" shy or less)

I am in the planning stages of doing a CNC plasma cutter table. What if I make a pass and not cut all the way thru for some reason, how would I get the arc to start again since the material would be too far away due to me starting already?

Hope this makes sense.

vault
04-20-2009, 10:28 AM
When I was cutting 5/8 this would happen frequently if I got the angle slightly wrong or moved to fast. I think the problem you are having is once it doesn't go all the way through if you don't back up to where it has burnt through and move forward again and instead just sit in one place trying to get it to burn through you create a wide crater that you can't restart in. When I would do this I would just drill a small hole all the way through and restart on the edge of the crater. Hopefully with CNC the torch angle and speed it so controlled that you won't run into this problem.

KHK
04-20-2009, 11:10 AM
I have had the same problem and have found that the speed of cut is critical. With my 160P if i went slower the plasma would quit. I found that varing the arc force solved this quiting problem. I could go at a slower speed and maintaied the cutting arc. On my machine I am about 50% of the dial.

keith

bhardy501
04-20-2009, 12:35 PM
If you have to stop and restart move porward just enough to establish the arc and then back into the cut. That way you are still on the cut line instead of starting to the side where you dont want to cut into.

arandall
04-21-2009, 01:24 AM
Mike:
This is just a shot in the dark, but I thought of it in the shower. Are you getting tricked out by the Post Gas Flow"? On the Pilot Arc start cutters anyway, the arc won't re-ignite until the post gas timer expires and the air stops flowing. On my LS200-P, even with the "Post Flow" set to minimum, it still flows for about 4 seconds. Thus, the arc won't re-start till then. I don't know whether this is design intent, or design flaw, but that's apparently the way they work. I know this would have fooled me for awhile, but Simon forewarned me about it before my machine was sent. I know the older "contact start" machines didn't work this way.
Hopefully that is of some help.

Cheers,
Art R.

jbman45
04-21-2009, 07:12 AM
Yes, on the 200P the post gas flow continues to work so for settings I always have post flow at full left or zero; max on arc force and half to max on current depending on thickness of cut. The post flow air has to stop before the pilot arc will relight. Not a big issue when you get used to it, probably helps cool a bit after a cut. Thinner metals cut nicer at lower amperage and lower air flows, just a matter of testing your material for a clean cut.

Gadget
04-21-2009, 06:53 PM
For CNC cutting use the 60 amp torch if it will fit (contact start) Then make my ground wire mod to enable air start, the torch will start even if you have to retrace in an open cut. I absolutely do NOT recommend this for hand held operation though for safety reasons.
I will get my photos and video uploaded to the CNC section when I get my laptop fixed. It just died tonight.
Dan