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Incomplete steps
« on: April 13, 2012, 05:12:22 AM »
I've been using my CNC router for a few years successfully now and have just replaced chains driving X and Y with ballscrews. I now have A Slaved to X with 2 motors & 2 ballscrews driving the X axis and another ballscrew driving Y.
It seems to function reasonably OK
EXCEPT
that when I crank the feed speed up rather than completing one line of G code before starting the next line it commences the following line early.
So for instance - where previously 3 lines of code gave me a straight cut in the Y direction followed by a CCW quarter arc and a straight cut in the X direction - but now before the first straight cut is completed the CCW arc starts (early) before the second cut in the X direction commences. I end up with an ugly big eliptical curve where there should be a neat little arc in the corner.
What's going on ? ???

Offline BR549

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Re: Incomplete steps
« Reply #1 on: April 13, 2012, 08:09:45 PM »
The acceleration is too slow for the velocity you are running. Mach3 is having to BLEND the curve due to the slow accelleration/deaccelleration.

Just a thought, (;-) TP
Re: Incomplete steps
« Reply #2 on: April 15, 2012, 06:04:56 AM »
Does that explain it starting a step before the previous step finishes ?

Offline BR549

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Re: Incomplete steps
« Reply #3 on: April 15, 2012, 11:38:15 AM »
Yes it does. Try running it in G61 mode(exact stop mode).

(;-) TP
Re: Incomplete steps
« Reply #4 on: August 22, 2012, 11:34:47 PM »
Thank you BR. You were exactly right. Both solutions solved this problem.
You're a wealth of information. If you're any good at machine design then can you please make a suggestion to help me with my posting on CNC Zone ;
http://www.cnczone.com/forums/showthread.php?p=1157938#post1157938
I sincerely hope I haven't broken any Forum rules by mentioning that forum. These guys don't get jealous do they ? lol

Offline RICH

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Re: Incomplete steps
« Reply #5 on: August 23, 2012, 06:26:31 AM »
plasticbakly,
If you want assistance with a particular problem suggest you post it here along with the complete info.
It keeps the thread from becoming fragmented. No problem on mentioning the other forum.
Said another way, don't want to read multiple threads on different forums to understand the context of it all.

RICH