Solved Axis drift ONLY when printing multiple parts

So for the last two evenings I've been trying to batch up some of my parts to print concurrently. I setup for the print, watch the first few layers, and plod of to bed. I'll find THIS as the result tho. If o print the parts individually, no problems occur. WTH? Confused! Wouldn't I get axis drift with the individual parts too of I had to tighten them?

 

If appears to be drifting on the Y and X axis for the overnight prints. They are staying stick to the bed fine and the bed is down solid too. Perplexed!

 

So in an attempt to try and fix the belt being too loose, but not being able to tighten it any more by hand, I printed off two of these belt tighteners: http://www.thingiverse.com/thing:81991

WOW what a difference!!! That X axis is tight as a drum, or guitar string, now!!! Will do the Y axis later this evening and see how the overnight prints work out!

 

Belt tension shouldn't cause drift. Try turning down your travel feedrate. You may be losing counts or shifting the bed during high speed moves.

 

Sure it does! There have been PLENTY of folks who have had drift which has been caused by loose belts.

 

The only way you can get belt related drift is if the belt slips teeth and that would have to be *really* loose for that to happen. I will agree that you would see sloppier prints because backlash would be increased. You'd see that as a slight misalignment of layers.

I've seen your exact symptoms by not having enough current to my stepper motors. Basically, the motor couldn't meet the speeds I was trying to run.

 

I've seen cases of it slipping being far looser than "really loose"... I don't KNOW it's a loose belt that's causing the issue, but that's the most likely spot of me to check given I've already verified the bed is tight and the axis stepper pulley's two locknuts are tight. {shrug}

It might be the stepper is loosing steps, but I honestly have my movement turned down pretty low. Not saying that isn't it, I just can't think of any other causes. I'm using the stock speeds from Repetier and other than turning the first layer speed down to 20%, the rest have remained untouched.

 

When you verified the y axis pulley's locknuts did you also verify they were seated on the 2 flat faces of the stepper motor drive shaft? I noticed on mine that they were not aligned with the flat faces so I had to adjust them myself. Since then my slipping is almost non-existent.

 

I tightened the Y axis without that printed part. For one it wouldn't have fit, but for the other I was able to tighten it without the need of it by just unbolting it, loosening the belt from the holder, tighten, and reattached it. I was able to tighten it about 3 teeth and it too sounds like a guitar string when plucked so I think I'm good there.

Last nights batch print of 3 parts failed due to a clogged hotend. Bah! I'd watched about 2/3rds of the first layer, things were looking good, so I finally plodded off to bed around 1am. I woke up at 4:45am, checked, and there was the 1 layer complete, and the second layer totally boogered up with a glob in the upper left corner and the Z axis about 8mm above the print surface happily churning away but no filament feeding correctly... So, I tore the hotend apart this AM and am starting in on my batches of smaller individual prints... tho I am trying one print now which has two parts, the LED holder which has two parts to illuminate the print area and clips onto the print head - http://www.thingiverse.com/thing:176238 and so far that's going well. I was having issues with stringing and my Z axis as well. My temp was too high by about 8c or so, and I needed to reduce my first layer height. I think I've got those issues resolved, so with the improvements in the belt tightness and the filament extrusion adjustments, I'm hopeful things are on the right track. I'm still not able to get anything like Jeff does on his amazing rig, but I'm getting there I think. I just need more time and more configuration / test prints.

I wouldn't have thought that there would be much of any difference between printing just one part, and printing 2 or 3, but clearly there is. Being able to successfully print one part is by no means a guarantee your setup is good for multiples!

 

Heyya Mike... Sorta. I verified on the X axisthe retaining bolts and shaft were aligned. That was the first thing I checked, then the tightness. Both were good. My belt just couldn't tighten enough on the X axis by loosening it by cutting the zip tie, pulling it tight by hand, and then fastening with a new zip tie. The teeth just wouldn't slide around the plastic to allow for me to get that last tooth around and I was having problems with getting everything held and fastened as well. I've got some big assed paws of hands and working on small parts like that has never been the easiest of tasks for me. {shrug} Anyway, that belt tightener took up ALL the extra slack and it's GREAT now. The bottom half of the belt sounds like a guitar string, and the top sounds like a Bass. LOL

 

How much of a shift are you getting? When my pulley was loose I was getting a 1" or so shift. Lately my worst shifts are about a mm.

 

That 1" realm as well. Seemed like the belt was tight, just like yours was... but certainly had lots of room for improvement. I wasn't getting the issue with single part prints, but when I would print multiples the rapid traverse seemed to have been killing me. I've attached a photo of the failure from a few evenings ago. Last night I couldn't get my initial layer to work, so finally threw in the towel and went to sleep and tried again this AM. I've got about 75 minutes left for a 5 hour print that's finally worked. I'll try kicking off a large 9-11 hour print tonight with multiple parts and see how that goes again. I think with my current belt tightness I'm good tho! That belt tightener on the X axis is awesome... the Y axis is a PITA. I think I might have even tightened it too much even. The build platform glass initially had a small thin line on it. When I received it I noticed it, but thought it was just a scratch on paint or something so dismissed it. Now it appears to actually be a crack, probably created when the hole was drilled... it has since started to spread with the additional load of the tight belt. Not sure what to do about that. Might have to design a different clip for that side of the bed which distributes the load better along the glass by clipping around the whole edge or something.

 

So far I've been successful with multi-object prints with the tightened X and Y axis. All of the timing pulley grub screws were tight. I haven't put loctite on 'em... yet, tho I'm sure next time I'm in there I will just as a precaution. I did verify they were all on the shaft flats as well. I think the slightly loose belts were tight enough to allow a single part to print successfully, but the rapids between one part to the next was just too much so yeah, teeth were being skipped.