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Offline Davek0974

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Stop CV issues...
« on: September 12, 2015, 02:51:28 PM »
Been trying to improve my plasma cut quality on internal corners, using the "Stop CV on angles >89" appears to help but I seem to get a visible jerk in the cut upon each transition from a straight line to an arc or radius, is that normal??

Is there any improvement to be had or is it just the way it is?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline BR549

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Re: Stop CV issues...
« Reply #1 on: September 13, 2015, 01:15:26 AM »
What are you trying to improve about your cuts ?? Rounding ?? 

(;-) TP

Offline Davek0974

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Re: Stop CV issues...
« Reply #2 on: September 13, 2015, 03:26:22 AM »
Pretty much, yes, its a plasma PITA :)

With CV on i get a bit of a radius on the top of the cut, (the bottom is always rounded due the the flame lag) and with CV off the tops are much improved but there is this jerk when going from straight to curve every time, not much, just a judder in motion.

I'm just tuning up my new table so looking at ways to get the best, I have tried pushing acceleration into the shudder zone but the stop-CV is still the best for a sharp corner. Acceleration is currently around 0.3G and speeds are around 4000-5000mm/min on my test parts.

As i say, I'm just looking for improvements really, Mach is doing what it does best as usual :)
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Offline stirling

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Re: Stop CV issues...
« Reply #3 on: September 13, 2015, 06:21:17 AM »
Bit confused here Dave. TP asked if you were talking about (corner) rounding and you said yes but then described the problem as top edge bevelling. Which is it you're concerned about?

Offline Davek0974

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Re: Stop CV issues...
« Reply #4 on: September 13, 2015, 06:41:06 AM »
Its a confusing thing plasma, the bottom of an internal corner is always rounded because the bottom of the flame or arc lags the top by about 15degrees or so, so as the top has passed the corner the bottom has no option but to round it leaving a bevel..

I think the main crux of my question was is there way to stop the jerks when transitioning from a straight to an arc when using stop-cv???
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Offline stirling

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Re: Stop CV issues...
« Reply #5 on: September 13, 2015, 07:04:54 AM »
I think the main crux of my question was is there way to stop the jerks when transitioning from a straight to an arc when using stop-cv???

The problem here is that if you have a line tangentially joining an arc then it is essentially pointless using stop-cv on angles > because there IS NO angle.

The fact you've asked the question would suggest that you do indeed see a difference. That is baffling because it makes no sense.

Offline Davek0974

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Re: Stop CV issues...
« Reply #6 on: September 13, 2015, 07:39:27 AM »
Yes the line joins as you say - no angle.

Yes, It's pointless using stop cv on that part BUT lets say the part has internal corners AND arcs etc, the corners are improved BUT the arcs are degraded by the blip.

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Offline stirling

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Re: Stop CV issues...
« Reply #7 on: September 13, 2015, 08:39:11 AM »
but here should NEVER be a "blip" with CV - anywhere - period. If there is then CV would be pointless - and it isn't.

maybe time to post some code and a description that demonstrates your problem(s).

Offline ger21

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Re: Stop CV issues...
« Reply #8 on: September 13, 2015, 08:58:29 AM »
Quote
but here should NEVER be a "blip" with CV - anywhere - period.

I've cut parts on my router where CV would stop when it shouldn't.
An oval, two straight sections with tangent round ends. On one side it would stop before making the turn, and the other side it would transition smoothly.
Gerry

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Offline Davek0974

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Re: Stop CV issues...
« Reply #9 on: September 13, 2015, 09:16:24 AM »
Ok, g-code and a picture attached.

You can clearly see the hiccup in the cut on the last two parts in the picture, the only difference was turning stop-cv on angles>89 deg on for these two.

The reason for wanting the exact-stop is because there is a 3mm slot in the parts which i wanted as square as possible.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives