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Y-axis belt drift

Posted by thanos 
Y-axis belt drift
January 31, 2013 06:13PM
Hi all,

I am having an issue where I cannot get the y-axis belt to not drift left and right (RepRapPro Mendel). I've lined up the bearings as precisely as I can, made sure everything is nice and square, but it still continues to drift several mm and hits the ends as I move the frog back and forth.

I can reposition the front bearing and somewhat improve it, but then the back one starts to drift, and then if I adjust the back one, the front one drifts.

Any tips?


Re: Y-axis belt drift
February 01, 2013 12:12AM
u need bearings with flanges ... im guessing
Re: Y-axis belt drift
February 01, 2013 01:33AM
You can download some pulley thingy to give you what you want..


Re: Y-axis belt drift
February 01, 2013 09:12AM
I can understand there are a number of ways to overcome the problem, but is it a general issue?
Most designs I've seen have the same type of bearings ... surely they don't all have a problem?

Re: Y-axis belt drift
February 01, 2013 09:14AM
That's kind of what I was wondering, since I have lined up everything very carefully to within less than mm tolerances, and I cannot even get this to be remotely stable on the bearings. Hmmm....
Re: Y-axis belt drift
February 01, 2013 09:17AM
thanos Wrote:
> That's kind of what I was wondering, since I have
> lined up everything very carefully to within less
> than mm tolerances, and I cannot even get this to
> be remotely stable on the bearings. Hmmm....

I've not even started to commission my machine yet and I'm already worried about it LOL
Re: Y-axis belt drift
February 01, 2013 12:06PM
I have an RRP Mendel as well. I was tweaking the Y Axis bearings for two weeks after I 'comissioned' before I got it to be stable. My problem was that the printed gear on the stepper motor kept drifting in towards the motor, even when I used super glue. It didn't seem to matter where the stepper was in realtion to the rest of the machine, the gear always pushed towards the motor. It kept throwing my tweaks off. I reprinted the gear three times until I got one with an extremely snug fit on the shaft that wouldn't move. I'v finally gotten it to have zero drift, but I've only been printing for three days on the new gear.
Re: Y-axis belt drift
February 01, 2013 12:08PM
Thanks Pete. My gear does not drift much and I have not added super-glue yet. Did you do anything else to stop the belt from drifting?
Re: Y-axis belt drift
February 01, 2013 12:14PM
I just tried to get the alignment between the bed and the stepper motor as close to perfect as I could and simply moved the front bearing in whatever direction was requied to stop the drift. I didn't worry as much about keeping it aligned to the other points.
Re: Y-axis belt drift
February 01, 2013 12:16PM
I did that, but no joy. How fine adjustments did you have to make with the front bearing?
Re: Y-axis belt drift
February 01, 2013 12:39PM
I found that as little at a 1/8 turn on the nuts made a difference.
Re: Y-axis belt drift
February 01, 2013 12:45PM
OK, I will give that another shot. I was doing the same 1/8 turn adjustments. Any other pointers you can think of would be hugely appreciated!
Re: Y-axis belt drift
February 01, 2013 02:16PM
slightly loosening your belt clips/mounts and turning them one way or the other---slightly--- can help with belt drift as well.

Edited 1 time(s). Last edit at 02/01/2013 02:16PM by xclusive585.
Re: Y-axis belt drift
February 05, 2013 11:13AM
Hi guys,

I'm in the process of buiding my ReprapPro Mendel too, and I face the very same issue.
Thanks for the advices, I'll try some of them further and let you know.
Thanos, if you find the trick I'd be very interested to know it smiling smiley

Re: Y-axis belt drift
February 05, 2013 12:57PM
I just added the x-axis last night and sheesh... belt drift again.

I think my plan is to tune it as best I can, and then print me one of these (http://www.thingiverse.com/thing:38753) as suggested by an earlier poster...

Re: Y-axis belt drift
February 10, 2013 05:56PM
Hi there,
Do you have large washers (fender washers) on the outside of you idler bearings? Is your problem that the belt is drifting too much and rubbing against your washers, or is it just running off the bearing because there's no washers?

I would advise against the printed Idler unless you have extremely good print quality, as a printed idler will just introduce print quality issues. There is another post here from someone that was having print quality issues due to printed idlers. You might take a read through that.


Re: Y-axis belt drift
February 10, 2013 05:58PM
It's drifting against the fender washers. BTW, I'm having very similar issues on the X-axis.
Re: Y-axis belt drift
February 10, 2013 06:32PM
A certain amount of drift towards the washers isn't an issue, provided the belt isn't gripping or dragging against the washer in a way that might cause the motor to skip. You'll have to judge that your self. In the other post I liked to above I posted photos of my current arrangement, where I fitted double bearings, and removed the fender washers completely.

The motor bracket can sometimes have the motor axle out of parallel to the threaded rod and cause the belt to ride left or right. You might have to move the lower clamping point of the motor mount to change the angle of the motor axle.

Re: Y-axis belt drift
February 11, 2013 09:41AM
Do you have the design for the motor mount from your post? That looks like a good idea, and then the extra bearing can go on the other side.
Re: Y-axis belt drift
February 11, 2013 10:26AM
Re: Y-axis belt drift
February 11, 2013 04:56PM
I was having some problems with x axis drift. It ended up being a problem with my idler pulley not being tight enough. When I tightened the belt fully it pulled the idler so that it was no longer perpendicular to the belt, causing the belt to drift to the outside regardless of how I adjusted my x-carriage.
Re: Y-axis belt drift
February 12, 2013 06:36PM
I too experienced the same sort of problems and wondered whether it would ever be correctly set.

It is important that you bear in mind that once set up correctly the belt will run true, it can be done.

My X-Axis worked fine .. I conclude that i was lucky.

My Y-Axis has been bad, then great then bad again. My approach was to move the stepper motor mount backwards and forwards by a minute amount in order to get it running true and then make adjustments on the other side very carefully until ir runs within the limits set by the big washers.

In the end I just started printing a 80mm x 80mm bracelet and adjusted as I went along. This messed up the print but I was able to move the non motor side until it started to run true.
Re: Y-axis belt drift
February 13, 2013 06:06AM
I was also concerned about this but in practice it's not been a problem at all.

For the X axis, the small adjusters that bear against the end of the smooth rods can be used to adjust the bracket so the bearing is at the correct angle.

For the Y axis you must first accurately line the bearings up with the clamp (which should sort the front bearing) and then the motor bracket can be adjusted by moving one side along the same axis as the belt to make it perpendicular to the belt.

Tension in the belts should be moderate - they should twang a bit when plucked but at a fairly low frequency (double bass rather than violin).

The weakness of this design is the need to align lots of parts but if you take your time and get everything as square as possible it will work well.
Re: Y-axis belt drift
February 17, 2013 04:06AM
I have the same issue with my RRP Mendel. For the X-Axis I put in an extra washer to alter the angle of the stepper which helped stabilize the belt somewhat. With the Y-Axis all that I could do was to make sure the belt wanders over the center of the bearings.
Re: Y-axis belt drift
February 17, 2013 08:03AM
You could try a self-centering crowned pulley as well.
It needs to be printed with precision to get the crown even, and if you have a serious underlying problem it might not help that much.

I've tried it on my X-axis, and even though my print wasn't perfect, the belt has yet to slip off with no washers (fingers crossed).


Edited 1 time(s). Last edit at 02/17/2013 08:06AM by anwe79.
Re: Y-axis belt drift
February 20, 2013 08:52PM
I'm also having the same issue on my RepRapPro Mendel, it's driving me to despair. I'm trying to make the Y-axis on my belt run true and stay on bearings for almost a week now - measuring and remeasuring, making sure all is as exact as I can make it and as paralell or square where it needs to be, then fiddling with tilt, tension, alignment, clamps - nothing seems ever to work. Now I took the motor and it's support off to see if I can make it run somewhat decent just on bearings - I tought maybe I can isolate where the problem is - nope, same thing, it just slides off to one side, whatever I do. I really don't know what else ...
Re: Y-axis belt drift
February 20, 2013 10:46PM
Another thing: The belt in this picture, note the darker dots between the teeth that go laterally from one side to the other - on my belt they don't go all the way to one side as do from the other - in other words, it's not simmetrical. So I tried to reverse the belt and I got some improvement - now, different from before, my belt drifts more one the side of the motor, and stays somewhat ok on the other bearing. Then I rotated the pulley, so that it's wider part is away from the motor. This way it can constraints more gently the belt to stay straight. The belt still drifts on the motor-side bearing a good 2 mm, but after much frustration I decided to consider this a modest success.
Re: Y-axis belt drift
February 20, 2013 11:01PM
i think, when the belts get tensioned up, and if the bearings that acts as idlers are not perpendicular for some reason even if very slight, as the belt rolls, it will start to drift. even gravity pulls them, dont forget that. and the belt needs to be really setup straight so if you give it a free roll by hand, the belt should move in a straight line and not be ajar slightly in any direction, i am contemplating to super glue the bearings in certain places so that the tensioning forces will not force the bearing to give way and that slight millisecond it does it will cause the belt to start running away.

Well at least thats what i did to my Z-axis, i am using XL belts over a distance and to prevent sagging, it has to be really tight, and aligning everything into straight and perpendiculars really takes some time, and i have to use flanged idlers to keep gravity from pulling them off rollers on the long run.

i also try to pull the belt in weird ways to see what will happen if there are any way the mechanisms will allow it to move into weird corners. poke, pull, roll it manually etc. imagine a belt it is not like a flat string, but the left edge is 1 rubber string and the right is another, both MUST have equal setting else they will just twirl all over.

the pic is the Z-axis frame i am fiddling with, and how 1 stepper will drive 2 threaded rods. its not very good btw lol my steppers are WEAK ! lol
open | download - IMG_2981.jpg (201.2 KB)
open | download - IMG_2982.jpg (239.2 KB)
Re: Y-axis belt drift
February 22, 2013 06:44AM
I have finally decided to un-mount everything and measure the space between the rods rather than the space between the (unperfect) plastic parts while re-mounting.
That improved the situation a lot as my whole metal structure is now perfectly square/parallel (even though the plastic feet do no seem aligned, but this is not important if the metal is ok, as it is what support the whole stuff)
I have also bought 2 more LM8UU bearings to enlarge the area where the belts goes and allow more variance while avoiding it to touch any border.
I bought GT2 belts and associated GT2 alluminium pulleys as well from there (France):
Now my Y axis is just fine. Let's start the X axis corrections now smiling smiley
See some pictures on the result of this part in this message.
open | download - WP_000377.jpg (406.1 KB)
open | download - WP_000379.jpg (407.8 KB)
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