CTC DIY Printer Z-axis wobble repairs

First, an example of the wobble: https://drive.google.com/open?id=1sz34dHOgt0r1nmJpUiQsRUgLw2h_Svmb

Now a solution suggested on Thingiverse, found from a youtube video:
https://www.thingiverse.com/thing:2135784   I printed this, and it was necessary to file out the groove on it due to the effect of the Z-axis wobble. The side of the piece shows the effect of the wobble ( see picture)

This is the mechanism that has to be modified: [Picture 2]

and this shows where the piece fits, [picture 3]

with the metal piece screwed into the white piece and the rest of the mechanism resting on it.

How to do it.
1.  Undo threaded bar from coupling and remove it.
2.  Remove slider rod.
3.  Undo metal threaded part.
4.  find appropriate screws and mount  this threaded part on to white piece.
5.  Replace slider rod, and clip white piece in to it.
6  Replace threaded rod, through mechanism and through added piece.
7.  Align x-axis mechanism  for correct vertical positioning.
8  Test
9.  If successful, repeat  1-8 on other side.

This works, much less wobble. Here is the final picture. As the rod wobbles so does the white piece, but the frame doesn't. I had to do both sides. One of the main difficulties was finding small screws that would go through the metal, screw into the plastic, but not protrudre into the dome of the white plastic where it would affect the sliding motion.  It was necessary to reset the nozzle height afterwards.

All of this thanks to jpnurro the designer who put it on thingiverse.


I am quite pleased with the results, but will still work on how I can stop the threaded rod from wobbling, which is the cause of the problem.

11 May 2020
The problem seems to have got worse again, I don't know why, except that the Z-axis spindle does seem to wobble around a lot.  I have tried putting shims into the coupler where I think I can centre the spindle, but that doesn't seem to help.

This morning I put the X-axis machinery up on trestles and have removed the Zaxis threaded spindle.  The Coupler wobbles. THIS IS BAD NEWS.

In effect, back to square one. Does this mean that the axle of the stepper is bent? I have  seen that mentioned in a YouTube video.  Or is it that the stepper motor is mis-aligned? One of the screws bolting it on to the frame was looser than the others.  No. The way that the axle turns indicates that this last is not the problem.

12 May 20202 Have replaced coupler with plastic tubing and wobble is so much reduced. No signs of wobble in the stepper motor  axle.

CTC DIY Printer improvements

This blog to document what I have done with the printer to try and improve it.

The current state is that I have been printing face masks and they are not very good because the sides are rippled.

I tried to adjust the baseplate height but on one side the adjustment screws were completely tight and on the other side almost completely undone. At this point I measured the height of the horizontal guide bar (X-axis) and discovered that it was 6mm higher at one end than at the other, so I adusted that by turning one z-axis screw until both sides were the same height from the base. I then adjusted the z-axis  position of the nozzle so that it was with the plate about half-way done up on the adjustment screws. A business card  worked well to get the nozzle-baseplate seperation correct.

One of the problems that I have not been able to resolve is that the threaded z-axis rods are not straight but have a bow in them. Each level of deposition of the print is 1/8th of a turn of this screw.  I have removed and tried to straighten this rod, but have not been successful. The results are obvious in the picture below as you can see on the white knight . The black knight  was the very first thing printed on the printer.

What can be noticed is that the ripple up the sides of the white knight is very close to the pitch of the thread of the rod. One implication could be that as the rod turns  it moves the nozzle head from it's perfect position and  gives a bit of an offset to each layer.

In the next picture you will see that at the top of the threaded rod where is is held by the top board I have added a bushing to hold the top of the z-rod more firmly. This means that the bowing of the rod will push against the other vertical guide rod and force the print head mechanism out of position.   If I remove this bushing that I have added, then the bowed rod would have room for play in the top mounting, and hopefully will not affect the print.








Picture one - Closeup of Knights.

Picture 2 = Left hand frame showing guide rod and threaded z-rod (bowed) with blue bushing.

Removing the bushing sort of goes against good engineering practice, but if it allows the z-rod to flop around and not affect the print nozzle, it may have to be that way. There is also a bushing on the rod on the right side of the machine, but we will see if this sorts the problem to some degree.