CTC - fixed my Y axis backlash- circles not round problem

[adrianq]

Ray,

Thanks for the info!

I have been looking to replace the plastic gears. The belt tensioner will also come in useful.

I am getting ready to put in my Drylin bearings so will probably change the gear while I have it open.

[slippyr4]

I am getting ready to put in my Drylin bearings so will probably change the gear while I have it open.

BE CAREFUL!

On my printer the right hand Y carriage block (the one that holds the X motor) cracked so I had to replace it.

Whilst I had it apart, I changed a whole bunch of other parts, including changing all linear bearings to drylin bushes. And when I put it back together, I had the dreaded non-round circle problem. The issue is the circles are flattened top and bottom. The usual cause is slop in the Y axis - when the Y changes direction, the print head doesn't move for a moment whilst slack in the belt is taken up.

It took me weeks to figure out the problem; I aligned and realigned the X/Y axes thinking they were out of square, but to no avail.

In the end, I figured it out - the drylin bushes on the Y axis had too much friction (static friction - "stiction"). What happens is the when the Y changes direction, even though there was no slack, the bushes stick until the tension on the belt has increased enough to suddenly unstick the bush. The result is identical to the one you get with slack, but it was not caused by the slack.

I put linear bearings back in the Y axis and the problem disappeared immediately.

You might get away with it, but if you end up with the same issue as me then at least you'll be able to solve it quicker than me, I hope. I think the problem is that where the bushes press in to the plastic mouldings, the clips deform the bushes slightly which increases the pressure on them.

The bushes in the X and Z axes are fine though, and I still have those in place.

Good luck.

[adrianq]

Slippy,

Thanks you for the info. I will definitely keep that in mind!

*crossing fingers*