Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: RICH on March 14, 2009, 09:53:23 AM
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Is there a known problem or has anybody else experienced backlash problems with MACH R3.042.020
current lockdown version?
In trying to help two guys out with their backlash on their lathes and here is the common problem.
All jogging and backlash is working fine, then after some time, and "all of a sudden", The backlash seems not
to be implemented on direction change, during a jog the Z axis will ramp up to speed and then ramp down say over
a long travel distance, say 3" , come to stop, pause, then a short burst ( think it now implements the backlash).
It will do this constantly once it starts this behavior. The only way to stop it is to set the Shuttle Accel to "0"
and all seems to work well. Now if you go out of MACH and come back in and again reset Shuttle Accel to some
more appropriate value , back comes the problem. In one case thought it was gone and it did this wierd axis
change while durng threading, of course the piece was ruined.
I need to try and narrow it down more, but anything that i could think just didn't seem to work.
Any experience on this one or thoughts on the matter?
RICH
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I haven't seen that myself RICH but that doesn't mean it isn't happening. Can you post their XMLs and code they were running with notes when it goes haywire? I don't have the lathe running on Mach yet so I can't do a good test but I will try to emulate.
Brett
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Thanks Brett,
Got my other pc hooked up here, so will be using the PP and will try to see if i can duplicate it at my place.
Will first try R.018 since it's still loaded on this PC and never had a problem wiith it. Then go to .020, it could be any number of things. Even a corrupted
XML or installation. I will fool on my end and also go back over the guys house maybe tomorrow.
I'll repost if i can duplicate it here.
Save ya some time for now.
RICH
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Thanks Rich. If you can get it to repeat you may want to try another version of Mach if you have time. This sounds like a really odd one to me and the more we know about it, the easier it will be for Brian to track down.
Thanks Rich, great group we have here!
Brett
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Hey Brett,
See if you can duplicate as this is what seems to cause the problem.
Backlash values / %, motor tuning, CV or exact stop, etc, etc. dosen't seem to be changed or if you change them won't help the problem. Now i was able to duplicate the problem in ver .18 and also .20 as follows:
Simply:
Put in a backlash and enable it / save and do the normal out back in etc.
Just jog the axis's. All should work as expected.
Now for the Shuttle Accel do the following:
Change value to "5" , save the settings, even go out and back in, but just check and see what value it saved.
It saved mine as "5.0073", and if you now jog the axis's back and forth you get the weird movement.
Now change the value to 4, and try, then 3, then 2, then 1 as all are saved for those values but the problem persists. Finaly change the value to "0" and the problem goes away .
Now change the value back to "5" and see if again you get a value of "5.0037".
Problem comes back.
RICH
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Well here is a liittle more Shuttle Value info:
MACH
Shuttle Value Saved value Jog Problem
------------------ ---------------- -----------------
.005 .005 no
.05 .05 no
.5 .5 yes
.6 .6 yes
.06 .06 no
.7 .7001 yes
.05 .05 no
5 5.0073 yes
Obviuosly it's number related and i always thought the number 13 was the unlucky one. >:D
RICH
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Rich, with the larger numbers, I can see where that would be a problem. Can you set the shuttle Accel to .005 and see how that works? If you want, you can leave all other settings the same and have a play with the shuttle accel value and see how it affects the backlash comp. I don't understand it fully yet but most often good results come out of setting the shuttle value to .005. I haven't tried to emulate yet but I'm going to play with the mill and see if I can explain it better in a bit.
Brett
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Brett,
I use .005 as the value for my lathe and personaly never had a problem. It was probabaly back a year ago that ya'all mentioned that it affected the speed at which the backlash will be implemented.
This problem came to light when two frends were having problems with the their backlash and described the axis
movement ( of course i said, what?, no way) but once we got playing with the settings the problem surfaced
then the nature of it was understood to some degree. So still curiuos i duplicated it today at home.
What can happen to the unknowing, is that if they use some random Shuttle Accel value, and gradualy work their way down to a faster speed, like 10 down to one and happen to hit a range of numbers that cause a problem,
then good grief, hours later they don't know what the heck is wrong. Just imagine coupling this with say the curent threading problem yet to be addressed and you would need to have a crystal ball to to even explain what
what's happening.
I quess until it gets addressed, folks should just make note of what is posted here, and don't use a value like 5, .5,.6, or some range around those and make sure that they are not skipping steps.
If your using the SS, since it dosen't have backlash implemented yet, all this would be transparent
/ you wouldn't even be aware of the problem.
Good that your trying on the mill since maybe it's only a problem with MachTurn. Don't know.
RICH
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Just to kick in..
>>Well here is a liittle more Shuttle Value info:
MACH
Shuttle Value Saved value Jog Problem
------------------ ---------------- -----------------
.005 .005 no
.05 .05 no
.5 .5 yes
.6 .6 yes
.06 .06 no
.7 .7001 yes
.05 .05 no
5 5.0073 yes
Shuttle Accel is the number of seconds to take to slow to zero to implement BL, so a setting of less than .1 is less than 1/10th of a second, pretty
much instant.. The larger numbers would like 5 is 5 seconds.. which means youd expect the 5 second slowdown. Keep it less than .05 and you shouldnt see
any rampdown..
So the question is.. if set to .05 does it stay at .05? Does it take several seconds to ramp down ever at that point?
Thx
Art
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ART,
"if set to .05 does it stay at .05?" YES
( BUT IF PRIOR TO INPUTTING .05 , IF YOU HAD INPUT .4, OR SOME RANGE OF VALUES
BL WILL BE BE SCREWED UP..... UNTIL..... "0" VALUE IS INPUT FOR THE SHUTTLE ACEL)
I remember something like this as a problem in the last year,
------maybe it was a problem in "saving" the setting. -----------
This is a odd one, 2 other Mach users brought it to my attention and it happens
for the mill and lathe.
RICH
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Rich:
Some days Im denser than others.. I still dont understand this one..
>>( BUT IF PRIOR TO INPUTTING .05 , IF YOU HAD INPUT .4, OR SOME RANGE OF VALUES
BL WILL BE BE SCREWED UP..... UNTIL..... "0" VALUE IS INPUT FOR THE SHUTTLE ACEL)
So, you mean you start up, and enter 5.0 for example. It then puts out a 5 second ramp until 0 is entered in the accel?
And is backlash screwed up, or just working with a 5 second ramp? Its normal, if set to 5 for example, to do exactly as you stated, during motion the axis will slow over 5 seconds, a burst of motion ( BL) very quickly.. followed by a ramp back up to speed. The speed the BL is put out is the BL % setting..
So Im not seeing anything screwed up, just using the extended time entered..?
Thx
Art
Art
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Art,
Thanks for the response and will get back to you in a day or so.
Both my computers need fresh Mach installs / cleaned-up.
Can't even get the SS to do threading at all!
RICH
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ART,
May the Bird of Paradise put white and yellow yoke on my face! :P
Backlash works just fine and as expected on my fresh install of Mach Ver: 3.042.20.
I do not see a problem with the program, after three hours of testing.
RICH
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Rich:
Good!! I hate backlash issues. :) LOL
Art
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Hello,
We are having a similar problem.
We have a CNC lather we are contolling with Mach3. We can move the steppers just fine. We can not finish the motor tuning because we have not been able to get backlash to work for either axis. We set the backlash screen. Save settings, restart, and it still does not work.
Any suggestions?
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BTW, we measure backlash this way:
We have a dial caliper that measures thousandths. We place the gauge against a solid part of the item that is moving, zero the gauge, move the axis by the hand dial until the guage starts to move, that is our backlash. We have the x-axis which is transverse to the spindle at 0.007 in. backlash and the z-axis at 0.005 in. backlash. We have set those in the backlash screen. Saved, rebooted Mach3. Then we move the axis by exactly the back lash to see if compensation occurred. None. We move more say 0.1 - 0.3 with gauge still in place, still off by backlash at least.