Poor linear bearings on i3

[Ole Jensen]

Hello,

I have bought and assembled a i3 prusa, and have found that there is way too much play in the linear bearings. They are also running rough, and seems to be of a poor quality. That means that the extruder changes position when the axis changes direction, resulting in edges on each layer of print. Has anyone experienced the same, or has I just been unlucky?

Regards
Ole

[russellz]

I think it's more likely that the problem is with the "smooth rods". They should be hardened and to H6 tolerance, ie., between +0 and -0.01 mm. I measured mine and they were between 7.959 and 8.012 mm. I had to put the biggest one in the lathe and polish it down a bit with very fine abrasive paper to get the bearing to slide smoothly. I am using them as is for now but intend to replace them with the correct material at some point.

By the way, do make sure that the belts are sufficiently tensioned to stop backlash.

Russell.

[Ole Jensen]

Thanks Russell, you might have a point, but the extruder carriage can wiggle almost a millimeter up and down, and sideways! And the heatbed carriage sounds as if there are sand in the bearings - (the printer is less than a month old). Do anyone know where I can buy good quality bearings og the proper size?

Ole

[russellz]

If the extruder carriage can move a little sideways with with the stepper motors energised then I suspect that the belt is too loose.

Up and down freedom is normal. The weight of the extruder should keep it in the lowest position. If not perhaps the bearings are a little tight on the shafts? The design could be better as the weight of the extruder and x assembly is supported on the z motor shafts. I've seen somewhere that someone has fitted thrust bearings to the top of the threaded rods to take the load.

Russell.

[russellz]

P.S.
I don't know where you live but you should be able to buy good quality linear bearings (and shafting) at any reputable bearing suppliers.