# Backlash



## hockeyguy (Apr 17, 2020)

Hi Forum 

I am having trouble correcting backlash on my cnc. I am using mach 3 currently and the machine has ran well for several years. I am starting to notice my circles are not circles anymore. I have tried adjusting my backlash in setting but that has not helped. This is only happening on my Y axis. I have made sure that everything is tight on my gantry. I have re zeroed my machine a couple times. I have tried a radius into the cut in my cut and nothing has seemed to help. 

I did have a slight crash a few weeks ago when my machine lost it position on the table and it hit the hard stop. it was very small. I didn't notice anything after this. I have been looking at videos about setting steps per inch on my motors. I did this along time ago and I don't think I need to play with this again. 

1 other thing I have a large gantry of about 5 feet in length and use a two motors 1 is a slave. I have the machine set so when I zero my gantry to the machine I have 2 limit switches to make sure that it is square. 

Any suggestions would be great. 

thanks.


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## Cherryville Chuck (Sep 28, 2010)

Hi hockeyguy and welcome.


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## ger21 (Feb 10, 2019)

That doesn't look like backlash. 
If it were backlash, you'd see it either at the top and bottom of the large "S", or the left and right edges of the small "S".
Backlash will show up at every direction change, and not just in one place.

My guess would be a mechanical issue, where something moved for a moment, then moved back. A slightly loose set screw can cause what you are seeing, as can numerous other things.


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## difalkner (Jan 3, 2012)

Welcome to the forum! Add your first name to your profile to clear the N/a in the side panel and so we'll know what to call you. Add your location, as well.

Are you seeing this in the same place if you cut the same project again? Even though you say everything is tight I'm with Gerry in that it looks mechanical to me. What design software are you using to generate the G-code?

David


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## sreilly (May 22, 2018)

Welcome aboard. You'll find some great help on this forum.

Also if you get a minute please fill in the user profile info with name and location. Location can make a difference in answers especially on where to buy and or electrical issue/questions.


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## roxanne562001 (Feb 5, 2012)

Welcome to the forum


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## hockeyguy (Apr 17, 2020)

Thanks Ger 

I remember you from years ago you were a lot of help to me when I set my machine up around 2011. I believe I am using your screen on my mach 3. Blue I think the name of it is but I could be wrong. I am glad that you responded as after I get this sorted out I want to ask you a few questions in regards to that skin for mach3. 

So going back to your suggestion. I have done some more investigation into my problem and I may have an issue I just wanted your thoughts and maybe guidance. 

I will have attached a few picture of my machine with this note. (If I can) 

So I do have a large gantry as I said earlier nearly 5-6 feet. I am using two steppers and they are slaved together. As you said something maybe wrong mechanically I took them off and noticed something different between the two steppers. When the machine is turned off I can turn both sprockets as normail. When I turn the machine on and it engages the one stepper can still be turned by hand. the other side of the machine stepper can not be turned. Is this an issue? I would suspect the one that I can turn has an issue. When I say it can be turned it is tight but still able to turn with a little force. These are nemia 380 oz steppers. The picture of the machine that shows the left side of my gantry is the one that can be moved.


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## difalkner (Jan 3, 2012)

If it can be turned by hand while the machine is under power then I would say that that stepper is not getting power. I don't think it's possible to turn these by hand if they're under power. I would trace that down and verify it's getting power. Can you switch cables to see if the opposite is true, that you can now turn the other one while the machine is powered up? 

David


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## hockeyguy (Apr 17, 2020)

Update 

thanks for the suggestions on this matter. After a few hours of changing cables and trying the suspected motor with another cable I thought I found the issue with the motor and on my last check that I was going to do I found the actual problem a set screw was lose and the pully was slipping. I tightened it and put everything back together and reset the backlash as I was playing with it earlier. It is back to .0035. I will cut a circle tomorrow to see if I got it. I cant turn that motor by hand after it engages. 

Thanks again.


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## Stick486 (Jan 4, 2013)

put some fingernail polish on the screw... use gel type polish...
it will be a big help to you...


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## Rusty Nesmith (Feb 1, 2020)

Sounds like you might have found it. Sometimes the simplest thing can be the hardest to find. Hope it is good now.


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## hockeyguy (Apr 17, 2020)

does that work like lock tight ?


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## Stick486 (Jan 4, 2013)

hockeyguy said:


> does that work like lock tight ?


yes..
but more forgiving if you need to disassemble later...


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## ger21 (Feb 10, 2019)

It won't hold nearly as well as loctite.
Try Blue Loctite, which is removable.
Setscrews on R&P pulleys come loose for a LOT of people.


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