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3/4" SS kicking my butt

Posted: Tue Jul 25, 2017 1:46 pm
by motoguy
I've got a 3/4" ss job I'm working on. I cannot seem to get this to cut right. I'm practicing with a straight 2.5" cut. The actual cut is to be 6' (72in) long. :/ Here are a couple of the biggest issues:

1) about 1/2 way through the cut, my angularity goes all to shit. I've swapped consumables, o-rings, feed speed (from book of 20 down to 10), went from book voltage of 137 (20ipm) up to 147 (at 10ipm), adjusted air pressure from 75psi to 85psi...NOTHING seems to change this issue. 1st half of the cut is consistent, then big shift in angularity. Any ideas what would cause it to change mid cut? THC has a 1 second delay in the tool settings, and "min cut length for DTHC" is .2", so THC should be kicking on quickly. Indeed, watching the screen, THC is holding the voltage to the end of the cut.

Which brings me to issue #2...

2) I CANNOT get severance on this piece. I played with overcut settings, until I realized they don't matter. The machine is stopping between 2.6" and 2.7" of cut (I set overcut as high as .5", which should have the machine cut to the 3" mark). I see my arc voltage is running high at the end (up to 200v), due to the tremendous arc lag I'm experiencing (part of why I went as low as 10ipm). No matter what, the torch is stopping at 2.6" - 2.7", with .2" of matrial uncut (meaning tail of the arc is still at ~2.3" position).

I've also got an overall angularity issue to deal with, but I don't see any reason to fight that until I get the other issues corrected. Here are some photos. Any input would be most appreciated. If I can't get this dialed in shortly, I'm going to contact them and tell them I can't do the job. It's a rush job, and I want to give them notice as quickly as possible to look elsewhere. In addition, these parts are already machined, so...yeah...there's that.


Yeah...forgot to change voltage after changing feedrate on those two cuts.


Overall angularity issue, will deal with that later.


Lack of severance.


Looking at the two cuts with light showing through, you can see how the angularity goes wonky about 1/2 way through. There should be the same amount of light showing through those cuts, all the way across.


The most extreme example. THC wasn't set to kick on for 1.5" on this one, so I chalked this up to the settings issue. However, the issue still exists (in a milder form) on the other cuts.

Re: 3/4" SS kicking my butt

Posted: Tue Jul 25, 2017 3:51 pm
by Econdron
What are the specs of your air compressor?

Re: 3/4" SS kicking my butt

Posted: Wed Jul 26, 2017 3:38 am
by motoguy
Econdron wrote:What are the specs of your air compressor?

15.x CFM at 90psi.

I took care of the angularity (new O ring, 65a process instead of 85a process), but never did get rid of the lack of cut-through at the end of the cut. Even more weird, the same thing showed up (in what appeared to be the exact same distance before the end of the material) when I tested 1/2" mild steel, and 3/4" mild steel. I cut 1/2" all day long without issue, so this really surprised me.

I also tried several different lengths (up to 13"), and again...same issue in (what appears to be) the same spot on each cut. So it's not material related after all. It's control related. I wonder if it's something to do with being an open line?