JohnFox

Looks like under extrusion to me. Wonder if that 0.25mm nozzle is too fine to be of real use, it's going to be difficult to extrude out of such a small hole. Maybe everything must be slowed down.

What speed does the Dremel run at? Do you get problems with heat build up at all? On my belt sander I have to take great care not to get the parts warm, it's very easy to melt them.

Suspect it is the dreaded Z axis bearing problem that quite a few of us have hit. In my case the bearings would periodically lock up, causing the missing layer. I eventually replaced the bearings but I think the underlying cause is lubrication on the Z pillars. Any oil on the pillars makes the balls slide, rather than roll and this causes the lock up. Some time ago I tested this by oiling the pillars and the fault occurred. When I removed all trace of the oil the fault cleared and hasn't returned ( yet ). Use kleenex to remove all lubrication from the pillars, move the bed up and down a few times and repeat the wiping.

I assume you have done some Atomic cleans? Can you see through the hole in the nozzle after a clean? Just wondering if you have a large bit of junk floating around somewhere.

A set of needle files. Wet and dry emery paper, grades from 120 to 400 mesh size. I also use a woodworkers belt and disc sander. Runs rather too fast but with care it can smooth the surfaces quickly. ( the items I am making tend to be regular solids with flat sides ). I like the waste paper basket suggested by |Robert|

Could also be a problem with the PTFE coupler, simply worn out.

I have a UM2, so it may not be exactly the same but try moving the cables in the area of the head to see if anything happens during a test print. If you get an error when you move them, you have found the problem. this is something on nozzle changing

After a print, the head is free and can be moved around by hand. Occasionally it parks and it still under control then you can't move it, it simply feels solid.

The first layer being wider is called 'elephants foot'. This is caused by the nozzle being a bit too close to the bed and the material is over extruded beyond the correct area. Lower the bed by about 1/4 of a turn on the screws and try again. I have just been doing some tests of this problem and the main cause of 1st layer problems is the bed height. I use the Cura default of 0.3mm 1st layer thickness, I suspect with 0.4mm it is trying to extrude too much material. Do you use PVA glue on the bed? I use a small amount of PritStick, then a tiny sponge with a few drops of water to spread it around, ( goes milky then dries). Never had PLA coming off the bed with this.

Yes, I now think curling was the main problem. Trying to spread the material too wide.

Sounds like a suspect connector on the temperature sensor cable. I had a bad sensor wire, only fixed by changing the whole thing.

Just done some tests, no dramatic results. I modified the first two layers of a test square, then went back to defaults afterwards. Printing PLA. No visible difference between 20mm/sec and 30mm/sec Possible change between 220C and 210C, (default) No obvious improvement between 100%(default) and 110% extrusion rate No obvious change between 60C bed( default) and 70C bed. A minor improvement when using 225C nozzle AND 70C bed. Similar result with 225C nozzle, 70C bed and 110% extrusion rate. The biggest effect on the print quality was any alteration to bed height, with less than 1/4 turn of the screws making an obvious difference. How does the UM2 zero the Z axis? Any minor fluctuation here would alter the quality of the first layer.

Just in the throes of doing some controlled tests on the bottom layer. I'll try the 65C idea, makes some sense. Not bothered about the elephants foot effect, it's the grooving that is the trouble.

I use a 0.3mm first layer as well. Would it help to have a slower print speed for the first layer? This problem on the bottom layer is my biggest problem at the moment. It takes quite a bit of work to sand away the grooves. The top layer is fine.

Any suggestions for improving the first layer, ( the object is shown upside down)? I watched the perimeter being printed and that looked OK but didn't see the rest of it. Also what could be causing the oddities at the two corners? I think the PLA is being squished down OK judging by the amount that is being pushed beyond the layer. PLA, 210C, 0.12mm layer, bottom layer speed 30mm/sec

That's rather impressive. Were the windows glued into place? What glue did you use?

Have you tried changing the material, taking it out and putting it back again? It's possible that the tip of the filament has got stuck in the PTFE coupler. At some point, you may have to remove the end of the Bowden tube to see what state the tip of the filament is in.

That all makes sense, those *&%@$£! Z bearings are causing a lot of problems recently. I suspect that their tolerances aren't compatible with the pillars.

I would NOT advise lubricating the Z guide columns. That can cause problems.

Not sure where the software people have got to, they usually reply pretty quickly. I think it's a conflict between nozzle and wall size. Probably trying to make two 0.4mm walls in a 0.5mm space. A thought! In Cura, (Advanced settings), try setting the nozzle size to 0.5mm. It may then just do the one pass over the circles.

That is very interesting indeed. Looks like something out of alignment, most probably the stepper drive. I think the two pillars are quite tight fitting.

It looks like you have the layer skipping problem, where the build plate drops down too much. My theory is that the bearings on the Z axis are sticking. Clean the two Z axis rods so there is no oil on them. Keep them oil free.

That looks like a lot of play on the print bed. Can you raise the print bed and check the 4 bolts holding the Z nut. Wonder if they are slack.

I noted that you didn't comment on the divorce option. Apart from the fans, I get a lot of noise when it does a retraction AND moves on the Y axis. It's a sort of grinding sound, never been able to find out where it comes from, the retraction itself is quiet but the motion is noisy. Does't happen during normal printing.

Have a look at the comments in the Thingiverse page. It says that the objects should be scaled by a factor of 10, they made a mistake. It's not you - it's them!