Y Stepper Belt Slop (Page 1 of 2)

+1 neat idea, looks like it will be quite simple to implement too (which makes for a good mod!).

I did the same as accusedmonk, it looks messy (sticks out a lot!) but it works well (once aligned correctly... took a couple of goes!).
Currently not happy with the mounting, it's all a little cramped and needs to allow for a spider coupler (not the rigid one I've got in there) I think - not going to post it up until I've investigated that route more thoroughly.

is that motor mounted different on SD4 than SD2? mine just has a small belt to the shaft that drives the 2 sides

Nothing special, max 80mm/s print / 110mm/s travel.
Shakes a bit, but most of my wobble right now is E3D-in-mk5 movement... Lots to do haha!

Direct drive with a hard coupling did halve my measured y-backlash instantly (well, once I got rid of the new wobbles created by the added alignment problem) - that little belt is hard to get tight enough via linear tension alone, I think pirvan might be onto a (much simpler) winner here.

Y-drive for SD3 and SD4 appears identical except for the main y-belt tension adjustment being done at the idler pulleys on the SD4 (as opposed to at the carriages on the SD3). Small belt to the driveshaft you describe is the one we're trying to eliminate / tension better.

FINALLY, PERFECT CIRCLES!!!

Last night I finally got a chance to print a put together the belt tensioner I designed, and would you believe it, that was the solution to my flattened out circles.  I've been chasing this for the last 2 years, and tried everything under the sun, but ultimately it was the slop I noticed during small infills that provided the key and the solution

Happy, Happy, Joy, Joy !!

For those that want to try this as a possible solution for their problems, here are the STL's.  You will need some 3mm socket head screws, a 608ZZ bearing, and a 8mm O.D. (or less) spring.

Would you mind posting your results from this circle test STL? It is a little difficult to tell from your photos--I have my circle deviation greatly reduced, to the point that it's unnoticable in holes and the like, but if you have any remaining deviation, this print will bring it out.

Nice work. This is a very interesting solution.

Thank you kind sir, I will try this.

But can anyone explain me why there's a slop to begin with?

PS. I would also like a picture like jagowilson suggested. Kind of hard to tell from your pics if its gone completely.
Maybe you could even 2d scan the print?

EDIT: actually, what's a "belt slop"?

Just curious: Why is this better than loosening the motor, forcing it down harder, and tightening the screws?

deflection of the rod?

pillow bearings instead of the bushings will just reduce friction on the rod and allow to tighten the motor belt more without causing binding from not enough torque, right?
I'm guessing this mod has the same effect.

And wardjr has perfect circles without pillow bearings.
I actually havent seen a SD with a pillow bearing, and printing circles.

Really waiting for pirvan's reply.
The STL seems to be old version. There's no way to secure the bearing with a screw like in the photo.

I'm going to try to explain and answer some of the questions.

First of all, I do have pillow blocks on my rod, yet I still had the problem.  In fact it would be interesting to find out how many here that have done the pillow block mod, have solved their circle problems.

@ Claghorn: Just curious: Why is this better than loosening the motor, forcing it down harder, and tightening the screws?
I don't know exactly the physics behind this, but I don't think it has anything to do with rod deflection.  What I think is happening, is that as the motor pulls the belt, it stretches it imperceptibly, and when it changes direction it quickly releases that belt tension which momentarily accounts for some slop and looseness while the belt tries to go back to it's original shape.  That translates into the deviation we see.  So it's a belt stretch  problem, not a rod deflection problem.

The spring loaded tensioning device, applies "self-adjustable pressure" on the belt, taking up any slack as it happens.  This cannot be done with static tensioning such as when you simply adjust the motor to pull on the belt.

BTW, this also accounts for the small infills that don't touch the perimeters on on some areas of the model.  So this mod also seems to fix that problem.

@Redbarret:  The STL seems to be old version. There's no way to secure the bearing with a screw like in the photo.
The model I posted doesn't have the split bearing post as in the original drawing above.  It has a round shaft for the bearing, with a hole in it.  You need to use a washer and a 3mm socket head screw.  Here is an exploded view:

BTW, here is what my printer "Y" drive looks like right now.  Notice the pillow block I have (circled in green), which, although it provides nice support for the rod, it never fixed the circle problem.

They look pretty good to me! Nice work. How tight are you running the belt prior to applying this? As tight as you can get it, for the most part?

Nice work, pirvan!