My problem was that the X axis and the Y axis were not square to one another.  While the method mentioned above of moving the carriage to the extremes and eyeballing the gaps between the carriage and the gantries did provide a small amount of improvement, I found a simple construction square to work the best.

All I did was loosen the spring loaded bearing holders so that I could move the bar and loosen the belts.  I used a triangle square from Home Depot.  I held it tight against the X axis bar in the back [the one you can't adjust] and brought it up against the Y axis bars, one at a time.  Gently, but firmly, you can rotate the X-axis carriage rods by pulling on one side or the other and you will hear it "pop" as the belt jumps teeth.  That's what you want.  It only took 3 minutes or so to adjust, but once it was adjusted, I was printing perfect consistent circles.

worked for me, but your milage may vary.

mpoffo wrote:

Also make sure both of the belts that control the y access up top are aligned.  Mine was slightly off on one side and I had similar issues.

Yep I forgot that.

You need to pull by hand your y carriage completely forward till it stops. The y carriage is the one that the head moves from left to right  on. Once you pull it forward look up where it make contact with the two white pullies. it should just touch or come very close to them. If one side is further away you have to use force to get the belt on that side to slip past the number of teeth it need to make it. All I did on mine was pulled the one did forward with a little more force and it jumped the teeth on the gear and was even with the other side.

You could use force but you can also take off the side and loosen the front holder and adjust the belt without much force.

See these videos I posted on another thread here:

https://www.youtube.com/watch?v=IoPpszi7HUU

https://www.youtube.com/watch?v=Y8H6lmYDs-I

Also make sure both of the belts that control the y access up top are aligned.  Mine was slightly off on one side and I had similar issues.

Yep I forgot that.

You need to pull by hand your y carriage completely forward till it stops. The y carriage is the one that the head moves from left to right  on. Once you pull it forward look up where it make contact with the two white pullies. it should just touch or come very close to them. If one side is further away you have to use force to get the belt on that side to slip past the number of teeth it need to make it. All I did on mine was pulled the one did forward with a little more force and it jumped the teeth on the gear and was even with the other side.

One does not print circles round, as seen in the images compared to the good one. Belts seem OK.

What could be the issue ?

Good one:

Bad one:

Thoughts ?

Thanks !