Hi,
I built a Prusa i3 printer using 30x30mm aluminium extrusion profile. After I calibrated the axis and the extruder, I was getting decent prints. However, now prints are not good when I changed the 5mm threaded rod to 8mm lead screw (pitch 2mm). I'm not getting straight edges (it looks arc edges) when printing the calibration box .
Can someone please give me a direction what could be wrong?
Thanks

Edited 1 time(s). Last edit at 11/12/2014 07:00PM by GOO2014.

Since you went from 5mm to 8mm rods, did you printed and assembled new parts? Did you checked the rod for wobbling? Thicker rods will have more force to move stuff around. It looks a simple case of z wobbling, but can also be some loosened belts or smooth rods sliding, when you move z axis at higher speeds can you see any wobbling or shaking? If you move fast your x carriage does your printer belts shake or your smooth rods slide inside their holders? .

Thank you ggherbaz for your response. Yes i did print new parts. I think it's the X axis (X-Idler Clamp) because i'm using the bearing without any plastic attach to it (bearing holder).
I have uploaded pictures showing that.

Edited 1 time(s). Last edit at 11/13/2014 04:17PM by GOO2014.

with the new picture you posted, and if the parts where printed the way I think, then yes your problem is in the x axis since z looks straight and the circles were properly made in the y axis.

Few more things, are you using bearings or bushings? also does the rods slide in the side carriages or it's a tight fit, check for any up and down play and if using zip ties tight them good

From the looks of the prints in your second post, you have a nasty case of z-wobble in either the X or Y axis, but not both. Any bend in the Z rods is going to push the axis out of alignment in a sinus wave just like you're seeing there. If you have a rigid clamp connecting the Z rods to the steppers and have the other end clamped as well, you're guaranteed Z-wobble if there's any bend in the rods. Can you give some more details about your setup and post pictures of the way your Z rods are set up?

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Hi guys,
I have replaced the X end motor, x idler and I added 2 lm8uu bearings on the Z-axis (Before i was using one on each side). Also I added bearing holder on the x tensioner ( before i was only using the bearing itself ).Therefore, after I made the changes, the print is coming out good with straight edges . @ggherbaz and 3dkarma, you guys are correct about the Z-wobble because the X-axis was dancing on Z rods when it had only 2 bearings on both side lol (2 lm8uu bearings got damaged when I was removing it ). Also when I was printing the X end motor for the 8mm lead screw, the part (printed on BFB-3000) was bad and I ended up using my friend Mr hammer to help me fitting the rods lol.
Most of the problem was my fault, but I have learnt not to use Mr hammer on any 3d printer and also I will take my time when fixing/replacing any part. I am very sorry guys.
Thank you very much

Edited 2 time(s). Last edit at 11/14/2014 08:28PM by GOO2014.