CNC Plasma problems

[Hood]

Finally got enough done to the CNC table to test out the plasma and I have had quite a few problems.
One however is more worrying than the rest as it is the one I am not sure how to fix.
What the problem is, the torch is at pierce height, the pilot starts and immediately it transitions to the cutting arc but then sometimes it kind of softens for a bit then comes back to life.
I have looked around and I am thinking it may be what is termed "Double Arcing" but I am not 100% sure of that.
I have tried quite a few things, increasing and decreasing the air pressure, increasing,decreasing the pierce height, increasing/decreasing the pierce time but none have made much difference.

I have a couple of other things to try when I next get time, I am going to reduce the current slightly and the other thing I will try is have a slow move whilst piercing.

Anyway here is a video of the issue, hopefully you can see what I am meaning.

 

[AdrianH]

I can not really help, but could it be possible that the work piece is getting a bad contact with the grill and hence eart?

Do you have any clamps on the metal to the grill?

what height are you running at?

Adrian

 

[Hood]

I did think it may be a bad return lead connection but having it connected direct to a cleaned section didn't help.
Have tried all sorts of heights for piercing from about 10mm down to 3mm and all are the same. it will be fine one cut and not the next, sad thing is it only takes one bad run to screw the nozzle

 

[AdrianH]

What is the plasma cutter, if I guess hypertherm

Then I assume 1.5 times for piece height, so just perhaps you ae still to high?

As I say all guess work as I do not have such a set-up and I am just starting to play with the idea of THC.

Adrian

 

[gaz1]

for bad earth it destroys the inner piece as it did with mine it also damaged the earth strap as well

ive got a few nozzles damaged by the user when dragging the tip along the metal sometimes it spits back at the nozzle

from your pics it looks like spit back against your plasma cutter end



a bad ended cutter end with hole in it

 

[Hood]

What is the plasma cutter, if I guess hypertherm

Then I assume 1.5 times for piece height, so just perhaps you ae still to high?

As I say all guess work as I do not have such a set-up and I am just starting to play with the idea of THC.

Adrian

It is a TecArc Opticut 65.
Only used it manually up until now and it has been excellent.
The material I was cutting was 5 or 6mm in that vid, was going far too slow but just trying things out and trying to keep things constant and changing one thing at a time.
Here is a vid of it going more like the correct speed but I don't have one of it at that speed doing a bad cut. When it did do the bad cut at that speed it would be half way round before the arc came good again and it started cutting properly.

 

[Hood]

for bad earth it destroys the inner piece as it did with mine it also damaged the earth strap as well

ive got a few nozzles damaged by the user when dragging the tip along the metal sometimes it spits back at the nozzle

from your pics it looks like spit back against your plasma cutter end

View attachment 95582 View attachment 95583

a bad ended cutter end with hole in it

View attachment 95584

Yes, seems to be what they call double arcing, the nozzle itself arcs to the material. Esab and Hypertherm both have info about this but I have tried most things and no joy yet. Lower current and slow move whilst piercing is the next things to try.

 

[AdrianH]

Well I am at a loss, I have read all sorts about cutting speed and that too slow takes more metal out and causes the arc to wander as the gap gets wider, then the THC shoves the tip down to the metal etc, but, I think you of all people would have that sorted out with Mach3.

Please post your findings when you sort out the problem

Adrian

 

[Hood]

THC is not on as that is another issue I am having

 

[gerrymoore]

On my CNC the plasma torch starts at pierce height and then comes down to cut height 5mm/2mm is yours doing that? Also your cutting speed seems slow...I use 1200mm/min for 2mm steel. Must say I had nightmares for weeks before I got my CNC running properly so it is a learning curve...you'll get there in the end

 

[Hood]

Yes, have altered the pierce height whilst trying to chase this problem and nothing seems to make a difference, after the pierce delay, which I have varied as well, the torch rapids down to cut height, again which I have varied. Nothing seems to make a difference. Cuts fine sometimes, others not.

Regarding the speed, yes was way too slow but wanted to try and keep things the same whilst I was changing other things and that is the reason I didnt alter the feed.
If you look at the second video I posted I am going at more like the speed I should be, think it was 3m/min but don't recall exactly.

Saw something interesting on the CNC Zone in the early hours. Jim Colt saying Alu causes that problem and that is why Hypertherm use shielded torches as it makes double arcing almost impossible.
My hand torch has a drag tip on it so basically it is shielded and that may explain why I have never seen that problem with the hand torch.
I am going to fit the electrode, nozzle and drag tip to the machine torch and see if it makes any difference.

 

[Hood]

Well I tried with the long consumables and the drag tip on the machine torch and if anything it was worse.
Made up a quick bracket to hold the hand torch onto the axis and what a difference.
I could see right away it was different, cut 1/4" alu and 12mm steel, pics of the steel below and videos of both attached.

 

[awemawson]

So is the implication that something is wrong with the guts of the machine torch?

 

[AdrianH]

wow! What is that little gismo that sets zero height, like it.

Adrian

 

[Hood]

So is the implication that something is wrong with the guts of the machine torch?

Definitely something wrong with the torch, may be something I have done when fitting the extension cable and central adapter although I can't think what, or something wrong with the torch head itself. It is a new torch but I had to extend it as it was only 6m and I needed about 9 or 10.
Will inspect the torch and cable and connections at some point but at least the plasma is cutting like it should now.

wow! What is that little gismo that sets zero height, like it.

Adrian

It is basically an air cylinder with a limit switch fitted to it, DaveK on the Mach forum did it on his plasma and I thought it was a good idea so did it for mine.

 

[Jim Davey]

What is your earth point on the plate like?

 

[Hood]

What is your earth point on the plate like?

As in the lead from the plasma? If yes then it was connected directly to the plate in most of the tests.

 

[Hood]

THC working exactly as it should thanks to info received from a guy called Ian who knows one or two things about Plasma

THC Speed % was the answer, turning it down to 50% seemed the best for my servo.
Here is a vid of it cutting 10mm steel plate, 200mm x 10mm at a rate of 800mm/min.

Here is it doing the same but with the plate raised at about 3 degress so that it raises 10mm over the 200mm cut length.

So big thanks to Ian

Now I just have to get the better of the M31 macro issue.

 

[AdrianH]

Not jealous much.

Adrian

 

[Hood]

No reason to be whatsoever, yours is coming along great and looks to be working fine and £10 as opposed to £200.