Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Davek0974 on February 17, 2014, 04:45:10 AM
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Having just got my hand jog wheel working nicely (thanks Hood) I have uncovered an issue that i need help with
The first cycle runs perfectly - jog to position, reset origin, run code.
this however leaves the z-axis at zero work co-ords but -50 machine co-ords.
the next time i issue a start cycle i get soft limit warning on Z axis as i am trying to probe to -65mm from machine zero but it obviously wont let me as that would be way beyond machine z limit max.
is there a way round this????
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You need to home the machine on startup and have the SoftLimits correct. The Z will likely be Zero as Max and the travel of your Z axis as the Min setting, but as a negative value.
You get the soft limits setup from Config menu then Homing and Limits.
Hood
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Yeah, thats all done and understood.
I just ran one part, it left the z axis at -95, when i went to repeat the run it faulted on z-axis soft limit.
Z soft is set at -75/0 as that is the physical limits.
I think i'm getting in a state with work offsets or something lingering at the end of each run that i need to reset??
dont forget i'm using G31 probing.
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soft limits are machine coords so as long as you are homing the correct direction and have the soft limits set to axis travels then it should be fine no matter what the work offsets are.
If however you are homing fully down then you will either need to set the Z Min as Zero and Max as travel as a positive value or better would be set a Home Off value to the Homing and Limits setting for the Z, that value would be the travel of your axis as a negative value.
So basically it all depends where your Z homes to and also make sure your Z is travelling the correct way, ie Z negative motion is down.
Hood
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Yes z home is at the top and works ok,
The part i run left z at 10 which is the park setting in the post processor.
I have mach set to issue a g92.1 reset at the end of each run.
the run left the z dro at -95 with a work offset.
When i go to run again i get z soft warning.
If i re-home, all is well but only for one run, i cant run more than one cycle without rehoming??????
something is not set right but i fail to see what.
Z max is zero and min is -75 as it homes at the top.
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Could someone have a scan of the simple .tap file attached please.
I am trying to learn why it throws a soft-Z limit upon cycle start.
Z max = 0
Z min = -75
Homed to top position.
I can run the part but not without acknowledging the warning first
thanks
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Not had a chance to look through the code but it is likely the G31 that is making Mach think the motion will go outwith the limits. Might want to try an older version of Mach if you are currently using 066 as that may also be an issue.
Hood
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Oh dear.
How do i get an older version and will it upset the work you did on the screen set???
Dave
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Is there really an issue with probing/offsets in v066??
How can i probe in another way that works??
I was finally hoping to get my machine cutting this week for the first time but I am having serious issues with z soft limits and my code.
Is it easy to downgrade and where do i find older versions? Google brings up nothing.
Will it upset the custom screenset & xml i have?
I'm losing the faith :(
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I dont know if 066 has issues with probing, I do know it has issues with homing if using an external controller and also issues with Lathes and I have heard of a few others.
You can get older versions from here ftp://anonymous@machsupport.com/ (ftp://anonymous@machsupport.com/)
As I said I have not had a chance to go through your code with your xml, bit busy at work today so will be tonight at the earliest before I can spend time.
Hood
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Ok thanks
I will not downgrade until i hear back from you as i really don't like downgrading stuff, it always seems to cause problems.
If there is a better way of doing things then would rather get it right now before it starts costing me metal wastage etc.
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I posted the same issue on Sheetcam forum and got this reply....
"I think the soft limit warning is due to the probing move. During simulation Mach does not know when the probing move will end so it uses the maximum possible move. Each time it probes it moves further down, eventually running into your soft limit.
There isn't really any good solution to this apart from turning off soft limits or disabling probing."
SO second question, is there a way to have the Z axis return to machine zero at the end of a run???
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Just noticed the error is on Z-Max which is the upper zero point so the code is sending the head above zero and not too far below.
Apart from disabling Z soft limits, is there a way round this?
All I want to do is have the machine probe Z height before every cut starts, sounds simple but seems not.
I really like the soft limits but if i have to kill the Z one then so be it i guess.
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An alternative way of looking at this is to ask why you're using soft limits at all. On a small light machine they really don't bring much to the party. If you DO want them for some reason then they're perhaps most useful to prevent jogging into a limit but personally I'd just turn the bloody things off (at least) when you're running code. Why would you reduce the size of an already small work area for no particular gain?
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I like being able to run the gantry around without slamming it into a stop, I guess the z limit is the least important so i could kill it i guess.
Its most useful while im still testing the machine i suppose.
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Fair enough. I just never really see the point of limits on a small stepper machine - never mind soft limits - but that's just me.
Thing is that if you hit a soft or hard limit when you're running you more than likely just screwed the job - so the best approach is not to do it. Plus limits of either kind in plasma do nothing to stop the machine when you get a tip-up and that's FAR more likely AND far more likely to cause damage.
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That's a pretty good point there Stirling, thanks.
I'll kill the Z soft limit at least for now.
My main goal is to protect the machine not the workpiece at present, this is hobby stuff and i've spent a fair bit on it so just want to protect my build that's all.
Dave
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Ok here's what I've done...
I have disabled the soft limits on the z axis, this makes the code run very nicely.
Secondly, I have modified the probe switch so that it now has two break contacts, one opens for the probe sense and further travel opens the second contact as a limit switch.
Now, when probing it works as normal, but during manual z axis movement if I ram the torch into the table the second switch acts as a normal limit switch. Works pretty sweetly too ;)
At least I know that it is the way the probing is initiated that was causing the issue now.
Thanks for the help on this one.