Gantry Racking At Center-ish of Table

Hey Everyone,

I'm having a problem all of a sudden with racking. When I press go to zero, when the gantry gets close to the center of the table the Y & A axis motors seem to come out of sync and rack the gantry. When I sight across the T-slot table the gantry is misaligned about 1/2" with the slots. I use Mach 3 & the motors are tuned exactly the same.

Is it possible something is out of square? Does anyone have any advice or suggestions?

Thanks in advance, much appreciated!

Simon

The machine is a Velox VR-5050 with a travel of 53" x 53"

• Home Switches on All Axis - Home Zeroed Saves all Part(Fixture) Zeros
• Nema-34 960oz/in Stepper Motors on X, and Dual Drive Y-Axis (A-slaved)
• Nema-23 400oz/in Stepper Motor on Z-Axis

Possibly a mechanical issue causing binding on one side?

After looking up that machine I would suggest disconnecting the ballscrew flanges so that you can move the gantry by hand. If the liniar rail blocks need to be greased grease them and then check the ball screws for binding and lubrication. If everything is good, lubricated and moving smoothly then I would square up the gantry and bolt everything back up. If it happens again then I would think that one of the steppers is losing steps. If you are losing steps then you will have other things to look at. But as Gerry said start by looking at the mechanics first.

Thanks again Gerry! I'll take a thorough look tonight, hopefully it's something stands out....

Thanks for taking the time to do that Ntl, now I have a place to start! I'm still fairly new to cnc and each problem seems to be a completely new & unique one, so I appreciate the help!

I'll give it a look tonight and keep posted... thanks again!

Quote:

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Originally Posted by Ntl

After looking up that machine I would suggest disconnecting the ballscrew flanges so that you can move the gantry by hand. If the liniar rail blocks need to be greased grease them and then check the ball screws for binding and lubrication. If everything is good, lubricated and moving smoothly then I would square up the gantry and bolt everything back up. If it happens again then I would think that one of the steppers is losing steps. If you are losing steps then you will have other things to look at. But as Gerry said start by looking at the mechanics first.

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Hey guys,

So we disconnected the flanges, cleaned the hell out everything, re-lubricated, re-aligned the gantry (it moved very smoothly by hand) then jogged it at 80 & 60% along the y-axis and the same thing happened. It racks a bit and binds up at roughly 1/3 from the ends of the table & at the mid point.

Does it sound like it's losing steps then?

We quickly checked the table for square (not an in depth square check) but it looks like it could be out 1/4" or so. Which could mean it was bumped into by the other occupant while we were gone the past couple of weeks. It's on a welded base, so we are going to move it, re-square it, etc...

But if that doesn't do it, I guess we should look into the motors losing steps? That seems like a broad area of possible problems :)

Thanks again, we've learned a lot from this thread already. Much appreciated!

Simon

I may not be remembering correctly, but is this the Y with a Slaved axis? If so I believe I had to reverse the Slave direction.

My guess would be the nut is not aligned with the screw mounts, so the screw gets tighter as it gets closer to the ends. You can check by removing the motors and turn the screws by hand, to see if they get harder to turn near the ends.
I'd loosen the screw mounts, then move the gantry all the way to the end, and tighten them back up. Do this at both ends.
Hopefully there's some adjustment

Is it still binding in the middle of the machine?

Quote:

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Originally Posted by wmgeorge

I may not be remembering correctly, but is this the Y with a Slaved axis? If so I believe I had to reverse the Slave direction.

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Hey wmgeorge,

Yet the A is slaved to the Y axis. I will definitely try reversing the slave direction and see if that helps. I'll keep you posted...

Thanks for the reply!

Simon

Quote:

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Originally Posted by Ntl

Is it still binding in the middle of the machine?

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Yea it's still binding unfortunately, but now I know how to disconnect the anti-backlash nut and move manually! Gerry (ger21) has suggested that the nut is not aligned with the screw mounts and to check by removing the motors and turn the screws by hand, to see if they get harder to turn near the ends....
It's also been suggested to try reversing the direction of the slaved axis.

I can't get back up there til tomorrow evening though, this is still something I started on the side for now. I just got a project doing (12) 4' x 8' decorative window panels for a store and of course this happens :D That's still a month or so out though...

Thanks Ntl!

Simon

Quote:

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Originally Posted by ger21

My guess would be the nut is not aligned with the screw mounts, so the screw gets tighter as it gets closer to the ends. You can check by removing the motors and turn the screws by hand, to see if they get harder to turn near the ends.
I'd loosen the screw mounts, then move the gantry all the way to the end, and tighten them back up. Do this at both ends.
Hopefully there's some adjustment

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Hey Gerry thanks! I will give this a shot for sure. I do like to take things apart :D I won't be able to til tomorrow evening though. This is still on the side for me for now. I will keep you posted...

As always I appreciate your time & suggestions!

Simon

Quote:

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Originally Posted by ger21

My guess would be the nut is not aligned with the screw mounts, so the screw gets tighter as it gets closer to the ends. You can check by removing the motors and turn the screws by hand, to see if they get harder to turn near the ends.
I'd loosen the screw mounts, then move the gantry all the way to the end, and tighten them back up. Do this at both ends.
Hopefully there's some adjustment

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Hey Gerry,
Here's the update. I'm not sure if we did this correctly.
I've attached a diagram of what we did numbered below, which I hope helps visually & not make more confusing :D

1. we removed the motors
2. moved the gantry manually using wrenches to turn the nuts at the opposite end of table from the motors. Moved little by little, but seemed okay.
3. disconnected anti-backlash, cleaned thoroughly, there was some build-up. Gantry slid easily from end to end w/ one finger while disconnected.

Should we have taken the coupling part at the motors off & moved from that area?

Notes:
At 60% jog it seems to move fine from end to end, but if we set a zero, then move it from there a bit and press "go to zero" it binds up instantly.
At 80% jog it still racks starting at the +/- 1/3 point

I hope I'm explaining things correctly, I really appreciate your help so far!

Have a great weekend,

Simon