small irregularities on the surface of prints
 
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Chris
(@chris-64)
New Member
small irregularities on the surface of prints

Hello guys,

im printing on my Prusa i3 for half a year and multiple kilometers of fillament went by with great quality prints. So im still very pleased with the printer.
After breaking some parts whilem perfoming the mk2s update, and rebuilding most of the printer, there is a problem i havent seen before. Im quite used troubleshooting, as my old prusa mendel was doing problems all the time, but i really dont know what cause this problem.

The pictures show the small lines, they are not caused by layers, but it seems like the layers themselfes are not properly alligend.

I have two things in my mind, but im not sure about them:
Maybe the belt tension is wrong. Right now they are tensioned like a guitar string and i heard this might me to tight. (Also the belt is tilting on the bearing-side when the direction is changing, but this was never a problem before)
Maybe the linear bearings are broken. The new mk2s bearings are grooving the new rails some mikrometers where the balls are. As im working as an engineer, at work i would throw them away but it seems like they are doing their job.

Do you have an idea what can cause this?
Greetings
Chris

Respondido : 17/09/2017 7:04 pm
henrik.w
(@henrik-w)
Estimable Member
Re: small irregularities on the surface of prints

Hello Christian!

(I am using the original linear bearings and rods from the MK1 era).
I have the same kind of problem - that is - layers on one side of the bed is not so well aligned as at on the other side of the bed. When I assembled the x-axis, one of the linear bearings was not so smooth - rather jerky - when moved by hand from one side of the rod the other. Well, it even performed worse when the weight of the extruder was attached to the x-axis. One could feel the hesitations of movements, when the extruder was pushed/pulled on place on the machine. So I believe these jerky linear bearings are the culprit of the problem. I even measured straightness of the rods by placing them on a straight ruler of good make and watching light seep through the column between the rods and the ruler. The light looked like a wavy road where at some areas the light didn't seep through and on other areas there was more light seeping through. To compare if the ruler or the rods were in charge of slipping through light, the ruler was placed on a flat glass plate - and pretty much no light seeped through at all. So one can even, on an assembled machine , feel the x-axis is somewhat jerky when pushed/pulled gently - so there is no need to disassemble the machine to try the motion of the axis. The y-axis on the other hand is very robust and smooth - the original linear bearings on.
I plan to exchange both the rods in the near future - maybe before Christmas - and the linear bearings on at least the x-axis with a good make to see if the quality of the prints will get better. The price range for good quality will be in the range of 20€ / rod and 26€ / linear bearing, totalling 120€ / axis. That is what I believe in at least. Well expensive bearings may not perform better when there are numerous other things that can go havoc, but I want to get really smooth linear movement on the x-axis.
If you think about it for a second - when the stepper motor steps one step and the linear bearing hesitates by refusing to move smooth, then that hesitation should show up in the print somehow - don't you think?

/Henrik

Respondido : 19/09/2017 7:10 pm
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