The sides of all my prints have a wave pattern running around them. The pitch of the wave is the same as the M8 rod on the Z axis.
I have followed the advice on this forum and have made sure the M8 rod is as straight as possible and have securely clamped the bottom of the servo to the frame.
The print is now much better but not as good as I would like.
What other things can I do to improve the Z axis? I’ve been looking at the coupling on the servo, I don’t think it’s as true as it could be. I’m thinking of drilling a hole up the centre of the M8 rod to help centre it onto the servo. Anyone tried that?
Also, looking at the nut that lifts the assembly up and down, it’s housed in a plastic part but the hex of the nut is a very loose fit allowing it to move around a lot. Is there any reason for this? I’m thinking of some how packing around the nut to tighten its fit.
Anyone got some thought on this or any other ideas?
The loose fit of the nut on the z-rod is better to reduce the wobbling, is my guess. If this nut would be fixed in x- and y-direction then the movement of the z-rod will be transfered onto the extruder arm, thus create more wobbling. Following this idea it would make much more sense to allow the nut to move freely in the x-y-plane and keep it fixed in z-direction.
I don’t really understand the reason of the z-axis wobble… the M8 nut in the z-axis slider can move in x- and y-direction, so there is no way that a wobble of the M8 rod could be transferred to the z-axis slider. I can bend the M8 rod by hand for more than 1 mm in any direction without any effect on the z-axis slider.
But nevertheless i have this wave pattern on the sides of vertical sides, in x AND y direction. :-((
I also tried the z-axis holder mentioned some posts above, but this didn’t bring any improvement.
[quote=“skywatcher”]I don’t really understand the reason of the z-axis wobble… the M8 nut in the z-axis slider can move in x- and y-direction, so there is no way that a wobble of the M8 rod could be transferred to the z-axis slider. I can bend the M8 rod by hand for more than 1 mm in any direction without any effect on the z-axis slider.
But nevertheless i have this wave pattern on the sides of vertical sides, in x AND y direction. :-((
I also tried the z-axis holder mentioned some posts above, but this didn’t bring any improvement.[/quote]
The rod ist stable fixed at the motor and additional guided by the upper bearing. That’s the reason why the motor is wobbling when the rod is bent, not primarily because the nut. Additional, at least at by printer, the motor, nut and upper bearing was not in line what caused a permanent bending of the rod.
Did you straighten out the rod as good as possible?
Yes, the botton of the motor wobbles, about +/- 0.5 mm.
Now i have clamped some sheets of plastic material between the bottom of the motor and the frame, and now it doesn’t wobble any more.
The M8 rod also wobbles a little bit… but i think this is compensated by the shifting of the M8 nut…
Let’s see if the elimination of the motor wobbling will improve the results. I will print out a test cube and have a look.
Hi all,
i have exactly the same issues with the x-axis wobble on the outer side of the surface.
The wobble are matching the gradient of the M8 thread which are 1,25mm.
In this and also other forums i have read different ideas to reduce this issue.
I would like to summarize all the proposals i have found in relation to the z-axis wobble.
Replace original (fixed) coupling used for the z-axis with flexible coupling. viewtopic.php?f=53&t=9355#p37394
It is very visible that the original fixed coupling is not fully aligned centrally which causes the M8 threaded rod not to turn silent.
In addition the z-stepper is heavily moved by this coupling issue.
I have ordered a flexible coupling at ebay and will give it a try.
From my perspective one of the real root causes.
Self locking nut’s on the top of the M8 threaded rod should be not too tight.
Idea was to loose the self locking nut’s so that the rod can move a little bit up and down (because of coupling issue).
I tried this and i could realize very small improvements. Anyhow the coupling issue is to strong.
Stabilize the z-stepper based on self printable motor holder. viewtopic.php?f=53&t=9658#p38159
This looks really very professional and i will give it a try soon.
Based on the modified motor holder the stepper will be fixed with 4 screws and not only with 2.
Beside this also the z-axix home switch can be fixed very professional with 2 screws.
Wow … Really great modification for the K8200.
Stabilize the z-stepper with simple tension belt. viewtopic.php?f=53&t=9355#p37379
For me it looks not so promissing, but if it helps … why not.
Idea in this and also other forum was to replace metric rod with trapezoidal thread. viewtopic.php?f=53&t=9355#p38135
For sure trapezoidal thread is much better then metric thread.
The problem is that metric M8 has 1,25mm gradient and TR8 (TR8x1.5) has 1,50 mm gradient.
The replacement will require to change rod, coupling, nuts and may be also the nut-holder (fitting the nut).
In addition to this the firmware needs to be manually modified to compensate the different gradient.
I think it is good idea to replace metric with trapezoidal but it is also expensive and time consuming.
Oil the shafts and M8 threaded rod. viewtopic.php?f=53&t=9355#p37456
I can confirm that oiling the threaded rod is improving the situation.
Unfortunately not completely and still visible.
I hope this summary is also useful for other users.
Please feel free to add other ideas and solutions to remove the z-axis wobble.
I did a further improvement and replaced the nut with a own designed. The M8 insert inside the holder is made of PTFE (Teflon, and thus not printable), has nearly no more backslash (adjustable) and is running smooth over the whole range.
In my oppinion there is no need to replace the rod ones it is straight. I now get pretty smooth surfaces.
Fixing the z stepper motor so that it’s not able to wobble eliminated the problem almost completely.
Now i see only some slight ‘random’ roughness on the surface, but the regular patterns with 1.25 mm waves are not present any more.
I will probably go one setp further and will design a ball bearing nut based on thingiverse.com/thing:139596 suitable for the K8200’s M8 rod. Stay tuned.
Hi,
firstly I thank you all for this topic, because I’ve experienced the same problem…
I’ve partially solved, recalibrating the axis of z threaded rod , better I’ve dismounted all parts from the motor at bottom to the ballbearing at top (leave ballbearing holder mounted); dismount little screw in coupling nut, then I’ve centered the threaded rod moving gently the metallic stepper motor holder starting from the screws on frame (to centre the axis long the plane parallel rispect the frame) then made the same with two stepper screws (to adjust the plane perpendicular rispect the frame) in this last case could be usefull some piece of paper to insert between the holder and motor in order to change very slight the angle.
Repeat the procedure (unlock screw, move slight holder, lock firmly the screws, run the stepper motor) until the rod at the top turn in the centre of ballbearing holder with no contacts and no forces (little wobling is ammitted, but less wobling means more accurate finish);
fix the screws starting from bottom (screw into the coupling) with warning to keep the rod top always in centre of ballbearing holder for each screw you lock…Self locking nut’s on the top of the M8 threaded rod should be not too tight and ballbearing is better to leave slight raised from the plastic holder site (0,2-0,5 mm are good).
Since I’ve tested run of rod for each screw tight, little wobbling at half rod is normal (the rod is not rectified) but you can reduce some decimals of mm the bending forcing with hand…further the nut into the plastic holder at half rod shall have other decimal to move into, following the wobbling of rod and limiting it. (beautiful could be a spring bumper to absorbe the differences on the horizontal plane…)
OIL all the moving parts, and use.
My two cents to this forum.
I’ve improved my results at least 50% of final finish
The z axis movement in my opinion is the most critical part of project due to normal tollerances of parts holders…, but with some little tricks during mounting make difference between a good job or a bad print finish.
