Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: alex850 on March 01, 2009, 07:07:31 PM
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i have a vertcal cnc mill and i have .015 backlash in x,and 10 or .011 in y. i have looked at the old post on backlash and tried everything.so far this is what i have done. backlash ,put amounts in and hit ok and restart. that did not work so i went to configure ,shuttle accel and matched that wiith same amounts. i have been on this for about 3 hours. i have never checked backlash in this machine since i had it ,seemed to always cut at decent tolorences it is a bridgeport series one 30 years old with a new contoller. thanks for the help in advance
alex
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Alex, try this. Set you backlash amounts to what you are showing you have and set the speed to 200% and enable backlash comp. Then go to general config. and set the shuttel accel to .01, restart Mach and see how it does.
Brett
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thanks ! i did everything you said and i could not get it out,so i lowered the speed to 50 percent and it seems to have done the trick.i just picked 50 and it worked could you tell me why it worked at 50? i left the shuttle speed at .01 like you said at 50 percent also .does it need to be changed?
thanks alex
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Alex, are you running steppers or servos?
Brett
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steppers.
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I think what is probably happening at 200% is it was trying to move that fast but would skip steps. Ususally you can get away with this because while takeing up backlash the only load it should be trying to move is very small but depending on where the backlash is comeing from, I can see where it may cause a problem. Those suggestions are only the ones I have seen a lot of sucess with and they are only a strating point I suggest. All set ups are different so lots of times the settings will vary.
Brett
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You may need to play some with the shuttle accel. It determines how fast the backlash will be done.
If too fast you may skip steps. Just don't remember as it's been some time ago.
Brett can correct me if wrong. I can change % frorm 50% but never had it over 100%.
RICH
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Your right RICH. Both the speed setting and shuttel accel effect the speed it takes up backlash. I'm not exactly sure how each relates but are both related to it. I wonder if the shuttel accel sets the ramp or time it will take to get to the speed set in the backlash config box? Art or Brian suggested the shuttle accel setting once I'm pretty sure and it was one of those things that stuck. LOL
Brett
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Haven't the foggiest idea Brett. But I remember I just started gradually changing the shuttle speed till i was happy it wasn't "crawling along" or seemed fast enough.
BTW, Think that was one that Brian mentioned at the seminar, they didn't know where to put the settiing and it just ended up being thrown there.
RICH
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You can also temporarily set the backlash distance to a large value so you can more easily see the effects of the shuttle and speed settings.
rc
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Good point RC,
Never thought of that, so you can check it out similar to doing a motor tuning.
Hmmmmm.........
Just do backlash moves in a coded loop and see what happens by changing settings. By indicating
along with say a number of dfferent cycles you'll see how repeatable or good your settings are.
RICH
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Yes Rich,
I saw that in the CV notes. It really helps you to see whats going on.
My first lathe had .007" backlash in both ballscrews. The cheapest Thomson's from MSC.
I set the backlash to .500 and by watching the results of each adjustment, optimizing the settings became much easier.
I like the loop idea, I just programmed a full circle in the X-Z plane with an M47 at the end.
RC
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i had to uncheck the backlash setting to make the stepers quit missing steps. i hope my backlash did not come back but it was the only wat to make it run right.i have not put the indicator back on it yet.
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ALEX850,
If you have backlash you have it and it dosn't go away unless you do something other than using the sofware to
change the amount. Backlash compensation just adjusts for the amount of non-movement if it's activated.
RICH
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I have the same backlash problem. without the backlash enabled the setup works great with a wide range of acceleration and shuttle travel speeds. When I enable the backlash compensation the motor skip and or hang. I tried backlash speed settings from 3% to at least 50%. Same results with all.