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Author Topic: ONE of THOSE days (;-(  (Read 7900 times)

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Offline BR549

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ONE of THOSE days (;-(
« on: February 03, 2012, 08:38:34 PM »
Well it happened again. this is the 15th PLASMA part in the last 12 months that MACH just ATE. Look at the Gouge at the top of the outside cut. THAT is not in the Gcode. It just took a diversion  and then corrected itself and returns BACK to normal by the time it got back to the satrt of the cut at the 3 oclock position.

It has always acted the same each time it has happened.

Always started the cut at 3oclock position and by the time it gets to the top of the circle it goes crazy ,then corrects itself somehow and will always end up correct when it gets to the end of the cut.

ONLY happens with circle cuts LARGER than 24 diameter NEVER smaller so far.

YEs it has cut correctly I cut 3 today (only needed 2) THe first cut perfect. Mach3 ate the second one and the 3rd cut perfect. Nothing on the machine was changed between cuts. Move into 0,0 position zero xy and push the go button.


Anyone have any ideas or clues on this one.  Like I said this is #15 in 12 months

(;-( TP
« Last Edit: February 03, 2012, 08:40:22 PM by BR549 »
Re: ONE of THOSE days (;-(
« Reply #1 on: February 03, 2012, 09:37:18 PM »
Post the gcode.

Offline stirling

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Re: ONE of THOSE days (;-(
« Reply #2 on: February 04, 2012, 07:54:21 AM »
Hi Terry - first off I feel your pain - this sort of sh*t can be a real PITA. HOWEVER - one thing I've learned about plasma is that it's a house of cards that can be affected by a gazillion variables. This problem could be:

Mach is failing in some way. - you could be right.
Your electronics is being spooked. An alluminium welder starting up in the next shed used to throw mine off but nothing else bothered it. (now fixed!).
Your mechanics could be sticking. >24" job takes you to a bad area on your table where as a smaller job doesn't maybe?
Your air supply is loosing pressure momentarily. Someone else in your shop just happened to use it at the same time maybe? - Or perhaps long cuts hit the air tank more than short cuts?
Your THC is quirking. None of them are perfect!!!
and probably loads more...

Just trying the voice of reason before we try to nail this problem.

Ian
« Last Edit: February 04, 2012, 08:05:17 AM by stirling »
Re: ONE of THOSE days (;-(
« Reply #3 on: February 04, 2012, 08:29:41 AM »
One thing that I recommend is to replace the plasma head with a pen and draw instead of cutting.
Disconnect the plasma and other electronic tools around the machine. If it draws correctly, then the plasma cutting source (the plasma itself) can be messing with all the rest. You can take one hour changing everything, but at the end you will know what is happening.
I know because I already been there and in my case it was not Mach.
Re: ONE of THOSE days (;-(
« Reply #4 on: February 04, 2012, 09:12:14 AM »
If it's not in the code, and the control is open loop, how can it go nuts and not stay out of whack, then get back to normal ? (just wondering)
Is it an arc motion or short segments ?
Could it be accel/decell/CV related ? Similar to rrc's recent post ?
Curious one.

Offline stirling

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Re: ONE of THOSE days (;-(
« Reply #5 on: February 04, 2012, 09:19:44 AM »
If it's not in the code, and the control is open loop, how can it go nuts and not stay out of whack, then get back to normal ? (just wondering)
Good point Russ - I'm glad someone's awake already. The only way I can think that could happen is metal pop - you know - it get's hot and pop it suddenly kicks/expands up/down out - every which way - of course I could be talking complete bo**ox.  ;D

Ian

EDIT: Then again depending on the scale of this thing (which we don't yet know) if your arc expands you could get something like this and that could happen if your air supply falters as I suggested above as a possibility. Just a thought...
« Last Edit: February 04, 2012, 09:29:07 AM by stirling »

Offline BR549

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Re: ONE of THOSE days (;-(
« Reply #6 on: February 04, 2012, 11:07:23 AM »
It is always in a LARGE circle (arc code) that is MORE than 12" radius. It has never done it with segmented code. The process it does is it STARTS perfect and towards  the end of the first quadrant section 0-90 it takes a diversion to a smaller radius still going in a circle then it works it way BACK to the original radius and ALWAYS makes a perfect end at the starting point of the circle.

It has also NEVER done it with LESS than a 24"circle. (so far)

It is LARGE enough a diversion that it is NOT arc quality flicker, we are talking a .500-1.00" change at times .

ALso it is a random thing NOT readily repeatable.

I think I will create a large circle and just dry run it to see IF I can get it to fail IF I run it often enough??

Something HAS to be triggering it but what ?????  (;-) TP


Offline docltf

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Re: ONE of THOSE days (;-(
« Reply #7 on: February 04, 2012, 02:07:08 PM »
open the code with the editor and go to the lines of code for that area.
go to the end of each line of code and hit enter.
that way you know you have a carriage return at the end of the lines of code.
looks like you are skipping lines from reading the returns.
mach will sometimes read a line without a return and sometimes won't.

bill

Offline rcaffin

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Re: ONE of THOSE days (;-(
« Reply #8 on: February 04, 2012, 08:07:11 PM »
You know, looking at that pic with magnification, I reckon I can see several steps in the Y axis movement, as marked  below.
None in the X axis, and the circle returns to what it should be when Y gets smaller.
But the errors are small - possibly within the limits of the following error of the driver IF it is a servo system rather than a stepper.

If I didn't know any better, I would be looking at stiction at the limits of the Y axis. I would not be looking at Mach as the circle completes.

Yeah, a few dummy circles of about that diameter with a pen would be the trick.

Cheers

Offline BR549

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Re: ONE of THOSE days (;-(
« Reply #9 on: February 04, 2012, 08:57:01 PM »
The circle is 28.5" in diameter that is more than a few steps. IF it were lost or gains steps then the rest of the cut would be OFF as well and it woul dfinish as offset. But it does not it does correct itself somehow and by the time it is finished it is spot on with position compared to teh startpoint.

When I get timeI will setup a test program and just let it dry run to see IF it will show up in a controlled version and get it to repeat itself.

Note to self DOn't cut large circles with arcs use segmented code (;-)

(;-) TP