Help on custom bot, bad cylinder, calibration issue or what?

Hi, i need help becouse i cant get rid of the problem i have with my custom bot.
My bot is 500x500x500 custom made,
frame is laser cutted (all 4mm steel plate) and then assembled. Firmware is sailfish (makerbot style electronic)

Z axis is runned by3 leadscrews TR10x2, a GT2 2MGT drive all the three leadscrews. A nema 23, 1Nm motor drive the z axis. Number 3 20mm linear shaft with bronze bushing keep z axis from moving on the xy plane during movement. Z screws are free to move on the top side (no ball bearings) and i have 2 oblique bearing (X configuration) on the bottom that take all the wheight.
XY is corexy with 2 nema 23 motor. a 9mm GT2 2MGT belt drive the corexy and i use CPC linear rails for the gatry. All motors run 24v with external digital driver.

I had, with ABS and PLA, the same problem: when in a print i have a "cylindrical" feature, i have dots and zip on all the wall if it is bigger (about 30mm in diameter), and a very bad cylindrical shape if it is small (below 10mm in diameter). I've tried to use or not use random starting point, lowering the acceleration, the speeds, increasing the motors current, decreasing them.

On a big print the problem is less pronounced but is there, especially on the corners (90 degrees corner or also big radius ones)

I use the latest simplify 3d. The print in the photos are all 0.2mm layer height.

I cant go on with this problem. I've checked and z axis move smooth if i move it by hand pulling the belt. i've all lubrificated well. I've print a 300mm radius circla and its out 5/100 of mm in one axis.

I know that its seems a z wobble problem, but the frame is very sturdy and i cant think that 3 10mm leadscrews, free at one end, can bend 3 20mm linear shaft.


I hope someone can help me!

You may find more help if you post in the CoreXY Specific section of the Forum

I am building a CoreXY similar to yours and also with 3 tr 10x2 leadscrews but when you consider that they will only turn on Z layer changes I can't see how that would cause your Problems.

sorry can't help any more than that at this point in time.

Doug

thank you for your kind respond, i'll try!