Very very weird issue, looks like z wobble, but....

mrehorstdmd

@wyvern The lead screws are the only support for the bed. The guide rails don't support it- if you took out the lead screws the bed would happily slam to the bottom of the printer on the guide rails.

I think people buy skinny 8mm screws because they're the cheapest ones available.

Wyvern

@mrehorstdmd I meant support as in stability and alignment of the bed.

And a big fat lead screw is going to overcome the rods/rails alignment faster than a skinny pliable one.

You would need thicker leads for very heavy beds or whole gantry assemblies where a skinny leadscrew would actually deflect under the weight.

iamthebest22

Hmm so maybe it was a mistake for me to use 12mm lead screws? that's what I'm using at the moment, maybe I should switch to 8mm lead screws?

Wyvern

@iamthebest22

You can try, 8mm screws and nuts are cheap as dirt, I had to get 4 just to have two that were straight.

You have a tall platform, but you also have 3 leads so it should be fine.

Double check when you alter your machine to see if there is any binding in the axis without the leads installed, putting the machine on it's side and moving the bed is a great way to find out- it should slide with almost no resistance, a out of whack Z rod will usually cause the bed to have resistance or spring back- The way I set my FT-5 was to get one rod perfect by checking with a square, then for the other rods, loosen one rod clamp slightly and tighten back down with the bed as close to it as you can get and repeat on the opposite end. I do this usually twice on the other 3 rods until it's perfect.

It was a PITA to get it perfect, but it's super important- just make sure the reference rod is square. Next machine I build/design will have 3X linear rails and 2020,

iamthebest22

yeah I will probably try that at the end of the month, since I'm doing another big one that I'm working with in the HEVO pro modified group that is overkill in terms of rigidity (30 metal brackets and 6 T shaped metal ones with over 40 corner brackets used) so I'll order those along with that.

that's the first thing I always do, it was a PITA too, but it's very very smooth, absolutely no binding or spring back before I installed the lead screws.

iamthebest22

Oh wyvern, cause the z wobble only happens on the back side with only one motor, and we're talking about switching to 8mm lead screw, is it possible to maybe only switch the back motor lead screw to 8mm and keep the front two at 12mm lead screw, this is only cause I'm tight on budget until next month, so I'm wondering if that's an option, or no so I should just switch all three to 8mm lead screw? Thanks

Wyvern

The only problem could be the manufacture tolerances (like pitch is slightly more or less). But it's worth a shot.

iamthebest22

okay will try just switching out the back one to 8mm for now, see how that goes and report back.

grizewald

@iamthebest22 said in Very very weird issue, looks like z wobble, but....:

@grizewald thank you very much for the suggestions, damn.... I guess I went too big >.<

the lead screws are from Zyltech and they said it's ACME screws, so I hope they are as they said.

Unfortunately I'm on a tight budget for another month or so, is there any way I could make mines even more rigid then it is right now? I do have external brackets printed out and attached on the bottom, these ones:
https://www.dropbox.com/s/y17zvr8yb6z4gx9/2019-02-07 19.14.29.jpg?dl=0

should I do it also for the top?
damn had I realize this I would have stopped using L bracket as the stock design said and go metal corner brackets all the way

I'm doing a print right now without the belt, so I'll report back when it finishes.

So I guess the first thing I should do is to try the best I can right now to further brace the frame more with un more 3d printed brackets? or go for metal ones like these ones:

http://www.zyltech.com/3030-extrusion-90-plate-bracket/

Thanks!

It was hard to see from your photos if the lead screws were indeed lead screws or just simple threaded rods. It's good that you have the right kind of lead screw, but they aren't exactly what I'd call straight!

The first thing I did when I got the hardware for my printer was to roll the lead screws on a mirror to see if they were straight. If they weren't, they would have gone back to the supplier. When I run my bed from the lowest point back up to level, the lead screws don't wobble in the slightest.

The plate you link to is exactly what I have on every corner of my frame. They really do help a lot to ensure that the frame is rigid. Skip the plastic versions, you need metal here and they should be both on the top and the bottom of the frame.

Wyvern's comments about making sure that everything is perfectly square are right on the mark. It took me ages to get my frame completely square and it's a royal pain to do with aluminium profiles.

iamthebest22

Thanks for the reply everyone, the lead screws will be bought at the end of the month (when my big paycheck comes xD) so I'll reply hopefully by March.

metal brackets are bought though and on their way, and yeah grizewald that's the first thing I did was to make my frame as square as possible, I only have one corner that's like 89.8 degrees, the rest are 89.9 or 90.0 according to my angle measurer

Question, I just bought some thrust bearings, but they are 10 x 24x 9 which is just a bit too wide that they don't go on the motor itself, but sort just a bit on the motor mount itself, is that okay or they must be on the motor itself? I just bought some 9 x 20 x 7 and they are on the way, but wondering if the bigger ones can be used or not? I do need to make spacers of course. Thanks

EDIT: here's a pic to show what I mean, it might look like it's on the motor, it's actually touching the white part mount instead, so is that okay or should I use the smaller ones that will definitely fit instead? Thanks.

Forgot the pic xD:
https://www.dropbox.com/s/n5v42pb6ld066sj/2019-02-15 21.54.25.jpg?dl=0
https://www.dropbox.com/s/am4acj27sit960c/2019-02-15 21.54.18.jpg?dl=0

Stephen6309

@iamthebest22 The larger thrust bearing may slowly get pressed in further into the plastic mount. You could use a spacer under it.

iamthebest22

oh good idea, another spacer didn't think of that, thanks!

I do have the smaller 9 x 20 x 7 on the way, and that I know will not press into the plastic mount, should I use that instead? it's 20mm wide and the mount is 22.3mm so it won't press into the mount, should I use that?

iamthebest22

It's been almost a whole month, but Spring break yay! I finally have time to mod the machine to try and fix the z wobble issue. Here's what I've done so far:

metal brackets everywhere I can on the machine for rigidity
changed all three 12mm lead screws to 8mm ones
Changed to high quality jaw couplers from Zyltech.
Thrust bearing between the jaw coupler and stepper motor and spacers so the weight of the big bed isn't causing possible floating issues

Here's a pic of the print, it looks like there's no more z wobble, but I can't tell for sure because my head suffered a partial jam.

with that being said, is it suppose to pause before a layer change? it wasn't doing that at the lower layers.

video (ignore the partial jam): https://www.dropbox.com/s/ntekqxoq4obdfc0/2019-03-22 18.24.16.mp4?dl=0

Phaedrux

Pauses at the layer change during a Z move could mean you might have a too low Z speed, acceleration, or jerk in your config.g. Or if you have retract on layer change, it could be the extruder speed, accel, jerk, retraction settings.

It'll be hard to see any z wobble with such extruder issues.

iamthebest22

@Phaedrux yeah It just finished reprinting today, and... YES! no more z wobble for sure now. There are some slight layer inconsistencies, but that's due to the filament (3kg +-0.05mm tolerance). I dunno which 4 things I did fixed it, but I can print for sure up to 720mm with no problems (thing can print up to 750mm my print was only 720mm so haven't tested the last 30mm :P).

With that being said though, this circle was about 30% smaller than the other one (140mm diameter instead of 200mm). Should I maybe try a bigger one? Or no it doesn't matter.

was also printing at 0.4mm layer height (0.6mm nozzle), should I also try 0.3mm to see if it possible gets worse there?

By the way about the pausing, it was retraction, but now here I'm stuck, because it's in vase mode, so obviously no retractions, but it started doing it above this height as you can see in this pic near the top:
https://www.dropbox.com/s/jxl6ldozlbhdxs4/2019-03-23 09.50.39.jpg?dl=0

and I can't seem to find the setting in retractions in Slic3r PE that does that. Any ideas?

Phaedrux

Well vase mode still has Z movement and if the layer height is quite high (like 0.4) and the model isn't very big (like a 140mm cylinder) it may need to execute a large z move to keep up. I think if you reprint with lower layer height it might not do that.

iamthebest22

@Phaedrux oh okay so I should be good now with this printer? I'll do more testing, but if I understood your comment correctly, I'm good now in terms of the z wobble test?

Phaedrux

Well I merely offered an explanation for what could be happening. I'd still do some testing to confirm that your issues are actually fixed.

iamthebest22

@phaedrux Ah okay, what's a good test you can recommend me to do to see if there's still z wobble at very tall heights?

Phaedrux

I think you were doing the right type of test just try a larger cylinder and lower layer height.