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JohnFox

Z axis banding again

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I would like some more ideas on this Z axis banding issue

JFB_2611-18sl.thumb.jpg.53865ea6f7c443a49eb303c3e2398124.jpg

These bands cause total delamitation in ABS but are not fatal in PLA.

It isn't a feed issue, as the bands occur on both the arms of the object and there has been a retraction between each arm. I am also using the PLA on a coil, not a spool, so the filament is not tightly wound.

It really looks like a Z travel problem. I have re-lubricated the lead screw and when I pull the build plate up and down there are no obvious tight spots of high friction. However, the problem does tend to occur in the same region each time between 8mm and 20mm from the base, never below 8mm and rarely above 25mm. The position is random, I can build the same object with the same file and the bands can move about and vary in number. The Cura file X-ray is clean.

Other people seem to see the same or similar problem but I can't see any fix which has nailed the problem.

Any ideas would be greatly appreciated.

John Fox

JFB_2611-18sl.thumb.jpg.53865ea6f7c443a49eb303c3e2398124.jpg

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I have done a complete clean of the lead screw, wiped off all the grease from the threads and re-greased. Slides a treat, the build plate almost falls by itself under gravity.

However, around the area in question, 10-25mm down, there is some friction which appears periodically. At the same time, I can sometimes hear a faint grinding sound from around the bearing/slide area. The sound isn't from down below where the motor is. The lead screw looks perfect, no signs of any imperfections at all, so I am wondering if there is a problem with the slide bearings. The slide pillars look perfect, no marks on them and are lubricated OK.

Hope this isn't a duplicate, I posted it about 30 mins ago and it didn't appear.

John

 

I usually use a piece of cloth and a spray for de-greasing e.g. bicycle chains. Afterwards you should quickly put grease or oil on it (I use a special chain oil).

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Is that the bearing at the back on the build plate?

No obvious play on it. One of the four bearing mounting screws was loose, tightening it hasn't made any difference, ( the other 3 were tight ).

 

What about the nut? Does it have play on the thread?

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The bearings are left and right.

The nut is that cheap looking brass piece at the back of the build plate (center). The piece de resistance might be in there as the pattern occurs regularly. Take the whole build plate away and unscrew the nut and clean it thoroughly.

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I think the problem is the slide bearings though.

I have unscrewed them from the build plate and tried to slide them up and down the pillars. Really very difficult to do, they seize every few centimetres, then work for a while, then seize again. I was expecting very smooth motion on these, occasionally I started to think they had totally jammed. Both of them seem the same.

Is this correct?

 

The bearings are left and right.

The nut is that cheap looking brass piece at the back of the build plate (center). The piece de resistance might be in there as the pattern occurs regularly. Take the whole build plate away and unscrew the nut and clean it thoroughly.

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Sounds as if you're getting closer. It's possible that it's the bearings. Another possibility would be the rods. But the bearings are actually more likely to be the problem. Maybe your printer was hit during shipment? This might be a good point to contact support if you have not yet. Maybe they can send you new bearings.

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Thanks, I have already put a support ticket in.

Unscrewed the 4 bolts on the nut but the nut won't come off, daren't put any more pressure on it.

The rods look clean and true.

When I slid the bearings up and down it felt like loose bits inside them, really rough.

John

 

Sounds as if you're getting closer. It's possible that it's the bearings. Another possibility would be the rods. But the bearings are actually more likely to be the problem. Maybe your printer was hit during shipment? This might be a good point to contact support if you have not yet. Maybe they can send you new bearings.

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I think I have solved it!

The problem was due to the Z axis slider bearings. The pillars should have NO lubrication on them at all. I had put a spot of light oil on them along with the X & Y slides.

I eventually realised that the Z bearings are ball races and lubricating the pillars caused the balls to try and slide rather than rotate. Some slid, some rotated and that is what caused the jamming. After wiping the pillars dry, they began to slide really smoothly. Have done several prints since, all without any of the problem bands.

I eventually got the nut undone but that rotated very smoothly.

thanks

John

 

Sounds as if you're getting closer. It's possible that it's the bearings. Another possibility would be the rods. But the bearings are actually more likely to be the problem. Maybe your printer was hit during shipment? This might be a good point to contact support if you have not yet. Maybe they can send you new bearings.
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