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Author Topic: Feed Hold bugs  (Read 2532 times)

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Feed Hold bugs
« on: January 09, 2012, 11:43:52 AM »
I've been trying to research Mach3 revision history/bugfixes, but the only thing I found so far was a large text file I saw as painful to search through...can anyone direct me to any bookmarks that may help? or, better yet, maybe someone has had this happen before, and can tell me what's going on?

Our problem with FeedHold pops its ugly head in one of two cases...1) any time we pause on an arc, and 2) any time we try to do anything in between pausing and resuming operation

1) it kind of seems to forget it was on a G2 or G3 line, and instead of resuming as it should, it goes straight to the end of the arc as if it defaults back to G1...this also applies if we pause in between cuts (on a G00, when the head is turned off) and instead of moving quickly, it moves at the current FeedRate

now that I post it, I wonder if it would go straight to the end of a second arc, since our CAM software doesn't include G codes on many lines...something for me to try, I guess (would it be important?)

2) we tend to get very erratic results when we try to shift the origin while its paused (namely, shifting upwards so it doesn't hit the material)

Offline Chaoticone

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Re: Feed Hold bugs
« Reply #1 on: January 09, 2012, 05:47:34 PM »
Feedhold in Arcs is a touchy situation. When you hit feedhold in a arc all of the math that has been done to accout for velocity and blending axis gets thrown out the window and the primary concern at that time is to bring Mach to a controlled stop ASAP.  The only way I know to over come this is to rewind the g code, ref the machine and start back on the line before the arc.  This is how we do it on fanucs as well.  We usually use the feedrate override and turn it 0 when setting up a machine. 

Shifting orgin in a pause state is a no no IMO.  Not that a prep move or similar cant be done to compensate but I personally would never do that.  All of the tool path planning is done either at rewind or run from here (I think).  If you pause and reset the orign where is the extra move going to come from to adjust the tool path?

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Re: Feed Hold bugs
« Reply #2 on: January 14, 2012, 07:51:46 PM »
yeah, we've found the same...hadn't really thought about the math that went into arcs though, so I'll forget about that

I don't see why I can't raise the Z axis though, and have it otherwise continue without problem...we don't TRY make any such changes any more, mind you! but we had to learn the hard way...I just don't see much of a use for Feed Hold beyond letting it come to a gradual stop, or pausing it to give ourselves time to make sure we want to continue...maybe that's all it's supposed to be for, though, idk

Offline Hood

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Re: Feed Hold bugs
« Reply #3 on: January 14, 2012, 08:00:34 PM »
You should be able to raise the Z and then press cycle start again as you should get a prep move box pop up. But if changing Z offset, or any other axis offset for that matter,  I personally would feedhold, stop then Run From Here. In fact I always do that when I feedhold anyway even if I dont change the offset, unless of course I have not moved anything.
Re: Feed Hold bugs
« Reply #4 on: January 14, 2012, 08:16:40 PM »
yeah, that's what we do...guess I always thought it a bug, now it seems I was trying to make it do something it wasn't intended for?