Another issue occured.
When tried to print tall object, 35cm rocket.
It was printed in PLA with 2 perimeters and in upper part it looks terrible. Lower is ok for me.
It is much worse in X direction then Y.

Edited 1 time(s). Last edit at 01/29/2018 06:57AM by aceranic.

How sturdy is the printer's frame, and specifically, how stable is the bed? If the bed can flex or wobble at all, the higher you get the larger the wobble will be.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Hi digital dentist,

Well the frame is sturdy. It has all corners additionally supported with L and T brackets.

Z axis has 4 10mm rails with 2 Tr8 screws belted together. If I try it is posible to rock the bed a bit but it is stable.

I have chevked Tr8 screws and one was a bit bent. I managed to make it quite straight using lathe. I'll chech the other one as well and fix. Then print single wall tall cylinder.

The print quality is degrading int he X axis, so the bed is wobbling about the Y axis and/or the frame is wobbling in X. The amount is deflection only has to be very small and may be hard to see.

Put a tall object on the bed, put the extruder nozzle near the object, and try pushing on the printer's frame and on the bed. You should be able to see the extruder nozzle move relative to the tall object on the bed.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Some people generate problems by using the leadscrews as additional guides in XY direction. The best way to connect a lead screw nut to the bed frame, is to allow XY-movement and only fix it in Z-direction.

Using 4 guide rails in Z may be the problem. Guide rails are there to provide vertical guidance and restrict lateral movement. Two is enough. Using 4 may lead to the bed "walking" up and down if there is any slight misalignment, and with 4 guide rails that are supposed to be parallel, there's very likely some misalignment. It doesn't show up when the bed is near the extruder, but as it gets farther away, the height of the print amplifies the tiny tilting of the bed.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Ok, checked both screws and they are very straight.
Checked bedplate movement in Z and it is nice and free moving.
It can be cantilevered when nuts are not there but with nuts it is sturdy.
Still issue exists with printing.

Tried with just loose nuts to allow movement as per o_lampe instructions.
Still the same.

GOING CRAZY

My CoreXY has two linear rails and three ball screws. The three screws define a plane, so any racking or wobbling is "impossible".
I made some single wall airfoils for a H-windmill with it. I could hear the nozzle scratch a bit,when the part got taller, but never missed a perimeter.

*seems like embedding pics is disabled? Probably due to the sluggish server lately?

Edited 1 time(s). Last edit at 01/31/2018 03:20AM by o_lampe.

That looks awesome.

I have 2 Tr screws in the middle and it might be a reason.

[openbuilds.com]

There are lately chinese printers with same principle as mine but they seem to be working fine.
I have removed both screws and will check them again to see what might be a issue.

Two leadscrews in the middle are good for least friction, but if there is any play in the bearings the table can tip over anytime. Put them slightly offcenter, that way the bearings are preloaded.

Hm. Good idea.
Perhaps I could try and preload aft side a bit and see what will happen.

Preloading didn't really work.

I have installed 2 bearings on each corner instead of one and print improved a lot. Almost perfect. Really happy now.

Thanks to all on ideas and help.

Quote
aceranic
Preloading didn't really work.

I have installed 2 bearings on each corner instead of one and print improved a lot. Almost perfect. Really happy now.

Thanks to all on ideas and help.

Bearings on what ?

Edited 1 time(s). Last edit at 02/05/2018 02:32AM by MKSA.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Ok, on bed plate carrier.
2 instead of 1.
Leadacrews are free ended on upper side. I have 2 bearings on bottom.