Corrugated X and Y axes

A place where discussions are about 3D printing.
Post Reply
User avatar
ge_rik
Administrator
Administrator
Posts: 6497
Joined: Sun Oct 25, 2009 10:20 pm
Location: Cheshire
Contact:

Corrugated X and Y axes

Post by ge_rik » Mon Aug 23, 2021 6:30 pm

I've had my (very) cheap Anet A8 clone for about 18 months now and upgraded almost every part of it. I've also strengthened and reinforced the structure to try and overcome a consistent problem I've had since I first got it - I get regular corrugations every 1mm or so on both the X and Y axes.
DSCF0981.JPG
DSCF0981.JPG (391.35 KiB) Viewed 1994 times

I've always assumed it was because the plywood structure is a bit rickety but I'm having doubts that it is the cause:
  • I've done my utmost to eliminate movement in the structure and it has made absolutely no difference
  • The corrugations seem too uniform at every 1mm or so which means the structure would have to flex one way and then the other after every 10 layers
  • The corrugations seem uniform on both X and Y axes
So, do you think there's some sort of bug in the firmware or am I barking up the wrong tree?

Rik
------------------------
Peckforton Light Railway - Blog Facebook Youtube

User avatar
ge_rik
Administrator
Administrator
Posts: 6497
Joined: Sun Oct 25, 2009 10:20 pm
Location: Cheshire
Contact:

Re: Corrugated X and Y axes

Post by ge_rik » Mon Aug 23, 2021 6:36 pm

PS - Until now I've fought shy of updating the firmware as I believe the Z axis screws are non-standard. They are actually M8 threaded rods (I told you it was a cheap clone)
------------------------
Peckforton Light Railway - Blog Facebook Youtube

metalmuncher
Cleaner
Cleaner
Posts: 95
Joined: Sat Oct 20, 2012 4:15 pm

Re: Corrugated X and Y axes

Post by metalmuncher » Mon Aug 23, 2021 7:11 pm

Looks like typical z-banding or z-wobble artefacts, if you look up those terms online you will see a wealth of information on this common issue.

You say its every "1mm or so." Coarse M8 is a 1.25mm pitch, if the banding lines up with the pitch of the leadscrew you know its something linked to the rotation of the leadscrews. Most likely bent leadscrews.

My machine originally came with threaded rod for the leadscrews, and I had similar issues, but not as pronounced. I ended up using a part similar to this: https://www.thingiverse.com/thing:141479, which allows the nut to slide around under the x axis ends following a bent rod, but not transferring that motion to the x axis. It helped a bit, but didn't fully eliminate the issue.

A bit later the threaded rod on one side wore out, and I replaced the z axis with proper trapezoid leadscrews which work much better than ordinary threaded rod.

User avatar
ge_rik
Administrator
Administrator
Posts: 6497
Joined: Sun Oct 25, 2009 10:20 pm
Location: Cheshire
Contact:

Re: Corrugated X and Y axes

Post by ge_rik » Mon Aug 23, 2021 8:44 pm

metalmuncher wrote: Mon Aug 23, 2021 7:11 pm Looks like typical z-banding or z-wobble artefacts, if you look up those terms online you will see a wealth of information on this common issue.

You say its every "1mm or so." Coarse M8 is a 1.25mm pitch, if the banding lines up with the pitch of the leadscrew you know its something linked to the rotation of the leadscrews. Most likely bent leadscrews.

My machine originally came with threaded rod for the leadscrews, and I had similar issues, but not as pronounced. I ended up using a part similar to this: https://www.thingiverse.com/thing:141479, which allows the nut to slide around under the x axis ends following a bent rod, but not transferring that motion to the x axis. It helped a bit, but didn't fully eliminate the issue.

A bit later the threaded rod on one side wore out, and I replaced the z axis with proper trapezoid leadscrews which work much better than ordinary threaded rod.
That makes perfect sense. Thanks.
Did you have to recalibrate the Z axis when you replaced the leadscrews?

Rik
------------------------
Peckforton Light Railway - Blog Facebook Youtube

metalmuncher
Cleaner
Cleaner
Posts: 95
Joined: Sat Oct 20, 2012 4:15 pm

Re: Corrugated X and Y axes

Post by metalmuncher » Mon Aug 23, 2021 9:43 pm

I moved from M5 rods (0.8mm/rev) to TR8x8 leadscrew (8mm/rev) which meant I had to change the steps per mm.

Steps per mm should not really be a calibration per se, the correct value can be calculated by knowing various physical aspects of the machine, including the steps per revolution of the stepper motor, any microstepping the controller board uses, and the leadscrew lead. The calculation for my machine is pretty simple:

(200 steps per rev motor) x (16x microstepping) / (8mm/rev leadscrew) = 400 steps per mm.

There is also a set of calculators that can help on the Prusa site: https://blog.prusaprinters.org/calculator_3416/

For replacing the leadscrew, as long as you know the old pitch, old steps per mm value, and new leadscrew pitch, you can work out what the new steps per mm value should be without knowing about the motor or microstepping setting. In my case, I went from 0.8mm to 8mm lead, so my steps per mm changed by a factor of 10.

If you have done an extruder calibration you may be familiar with the M92 command for setting steps per mm. The same can be done with any axis, not just the extruder, so if you do swap the leadscrew you can use the M92 command to alter the steps per mm for the Z axis without having to reflash the firmware.

Post Reply

Who is online

Users browsing this forum: No registered users and 4 guests