Problems with shifting in my taller prints

I am still getting comfortable with the RoBo and its plethora of tweakable settings, and as such I've been printing mostly small parts less than four inches tall. I've tried printing taller parts twice so far and both times I've run into the same issue: for some reason, at some point during the print (always when I decide to leave the printer unattended-- go figure), the printer shifts a few millimeters. I'm pretty sure the shift is only along the Y-axis, but I have not checked closely enough to be 100%. I've read on these forums and elsewhere that it could be a loose belt, but the Y belt feels tight enough to me (my X belt, on the other hand, is much looser). I'm attaching an example of exactly what my shift looks like. As always, thanks for any advice you can offer.

 

Ack, the photo is rotated 90 degrees counter-clockwise.

 

Supplemental info in case it helps:

Printer: RoBo 3D (duh )
Layer height: .2mm
Material: PLA
Software: MatterControl, Slic3r

 

If your x-belt feels loose you need to tighten it. I've seen a variety of different methods. I currently use the method as described in the build video:


Around 10 minutes

 

Thanks! Any tips on how I can judge whether or not I am at the correct tightness? I haven't had enough experience with printers to know on my own. I want to say that the belts are the same tightness as they were when the printer arrived, but I guess it wouldn't be impossible that they loosened for some reason. I've never messed with them myself.

 

And if the shift is along the Y axis, would tightening the X belt solve the problem?

 

if the shift is along the y then you need to tighten your y.

Basically a tight belt should have a "twang" when you pluck it. It needs to be tight enough so that it can't skip on the pulley, but not so tight it "Pulls" the pulley and bearing inward creating a moment on the driveshaft of the nema motor causing torque issues. You want it about as tight as you can get without inducing added torque on the motor. You can tell this by feel, if it's difficult to move by hand, it'll be hard for the motor to move as well.

 

It could also be your stepper missing a step due to drag on the slides, or trying to move to quickly, the Y axis is most prone to this due to the mass of the bed. trying slowing down your infill speeds and accelerations.

 

That reminds me, I have no idea what the acceleration settings do. Is there a one-size-fits-all optimal setting for the Robo?

 

the acceleration setting sets how fast the axis will go from stopped to full speed or from one direction to the opposite. So when it's rapidly changing directions like during an infill, it doesn't jar as much.
easiest way to grasp it is set them very low to say 200mm/s2, run a simple test print and watch what happens.
I'm running my infill at 4000mm/s2, it's helped in my Y axis shifting problems.

 

Barnacules Nergasm on youtube has a great video called Best Robo 3D Printer Fixes.....

There he describes a mod he did for stabilizers for the vertical rods. Helps when doing taller prints. Short cut for the stabilizer in thingyverse in the description under the video, link: about


Sent from my iPhone using Tapatalk

 

I stumbled across that video yesterday, Peter, and I'll definitely be printing those stabilizers (http://www.thingiverse.com/thing:126873) at some point.

There's been an interesting development in my quest to upgrade the Y-axis rails that could fix my problems once and for all.