I discovered the same issue when I followed the video on adjusting the belts. Since the rod floats back and forth, the motor not being parallel to the rod is the culprit IMHO.

I stacked a thin washer between the motor and the frame on the top two bolts. My SD3 prints almost perfect circles now.

I would like to explore this. Can you post pictures of your fix?

1) Diagnose if your y-motor is level or not (parallel) with the y-axis or not. Here is how I do it: I look at the y-motor from the top of the printer and try to align the edges of the motor with the edges of the cage through my line of sight. If the y-motor is not level the edges won't align.

2) Diagnose if the cage sheet metal where the y-motor attachs has been bent (flexed). Take a ruler or any straight edge and put it on the sheet metal and see if the sheet metal is straight or not.

3) If the y-motor is not level, and the sheet metal has been bent, then put washers between the y-motor and the sheet metal to level the y-motor.

4) Don't push on the motor down too much when you are screwing it in; the belt needs to be in tension but it shouldn't flex the y-axis too much.

I hope this helps!

I think friction between the Y carriage bearings and the shafts has a huge effect on backlash since switching directions makes the carriage temporarily stop.  Even with tight belts, restarting motion means there is a static friction threshold to overcome.   While tensioning the belts helps overcome the carriage friction, it also creates more friction in the bearings on the rear rod as well as the idler pulleys which adds to the problem and creates misalignments.  I think the way to go is to replace all components with low friction components (LM8UU bearings for carriage, ball bearings to replace bearings in the back rod, maybe different idler pulleys...) thus requiring less tension in the belts to achieve the same drive reaction.  Thoughts?

I stacked a thin washer between the motor and the frame on the top two bolts. My SD3 prints almost perfect circles now.

Few feedback:

1) It looks like the gear was not sheared off! The gear is spool-like (it has a cap at the end). The cap came off so I was able to glue it back together.

2) I am having hard time with the y-motore:

a. Due to tension the y-axis dip down with the max flexing point being in the middle of the y-axis. So the belt takes the path of least resistance and start shifting away from the motor.

b. Due to tension the y-motor axis is not parallel (not level) but pointing upward a bit. Even the sheet metal part of the cage it is screws onto is not flat but flexing; when I put a ruler against the surface I can tell that the sheet metal is flexing because of the tension.

c. If I don't tense the belt then the belt starts to skip.

Any ideas how I should fix this? I know I am probably don't something wrong so please guide me to how to fix it.

That part# is for GT2 belts.  Unless they have changed them in the last 9 months or so, I believe they have been using MXL belts.

From Jerseydevil last feb-

If anyone needs the the MXL drive belt from the Y axis stepper is marked on my system.
It is an SDP-SI part number: SDP A6Z16 084 025/060
That should be actual part number: A6Z16M084060 (the M is implied, 84 is the number of teeth, the 025/060 are SAE/metric belt width).
This is just a fiberglass reinforced neoprene belt so a steel or Kevlar reinforced belt would be an improvement.

If you want to get the pulleys on your own, these will work - https://sdp-si.com/eStore/PartDetail.as … roupID=347
They are MXL pitch timing pulleys with 18 teeth, 6mm bore, 2 flanges and hub. about $5 each.

Whats the difference between an MXL and GT2? I just went by counting and measuring the teeth and measuring the gap between each tooth then measuring the width of the belt. The last time I printed something (3 months ago) it seemed to be printing the same as it was before the belt failed.

Edit: Nevermind... i googled.
Sorry for the wrong info folks... Honest mistake...

Looks like I'm gonna be changing my belts again... or changing to GT2 pulleys.

From Jerseydevil last feb-

If you want to get the pulleys on your own, these will work - https://sdp-si.com/eStore/PartDetail.as … roupID=347
They are MXL pitch timing pulleys with 18 teeth, 6mm bore, 2 flanges and hub. about $5 each.

fadilee wrote:

Thank you for the helpful reply. For whatever reason I can't seem to know how to search in their website! I don't know how to find the part number! :s

I am also thinking to switching to a V-belt since the supplied belt never stays in the centre of the spool for whatever reason.

It's pretty easy, just go to the tab that says "Buy Online" at the top blue and then copy and paste the part number...

http://store.solidoodle.com/index.php?r … uct_id=104

We also sell the belts directly.

Thank you for the helpful reply. For whatever reason I can't seem to know how to search in their website! I don't know how to find the part number! :s

I am also thinking to switching to a V-belt since the supplied belt never stays in the centre of the spool for whatever reason.

It's pretty easy, just go to the tab that says "Buy Online" at the top blue and then copy and paste the part number...

I am also thinking to switching to a V-belt since the supplied belt never stays in the centre of the spool for whatever reason.