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



  • gah so close those holders you linked, they're 23mm away from the extrusions, the stock HEVO plastic parts are 22mm, are you kidding me >.<

    EDIT: Should I also try these oldham couplings? Heard great things about them
    https://www.aliexpress.com/item/-/32867555428.html?spm=a2g0s.13010208.99999999.260.67893c00yB3LTK

    I would be buying the 5mm to 12mm ones.

    EDIT 2: I just saw your edit on having an Ft-2, I have one too! Might get their Ft-6 in the future, but hmm okay I am using Precision Piezo as auto bed leveling, so many the belt isn't really needed after all. I shall try without belt and report back, so yeah I have ABL



  • Your lead screws look like threaded rods to me. If that is the case, you might like to re-consider as I doubt you'll ever get good accuracy and stability with threaded rods; particularly ones that long and that bent!

    I'd totally agree with running the motors from separate drivers and dumping the belt. The Duet and RRF is perfect for bed levelling via the Z axis motors and a piezo Z sensor is the ideal sensor for this.

    Looking at your machine overall, I'd say the frame is way too big for the motion components and frame itself is not mechanically rigid enough for the size. My CoreXY printer has a 500mm square frame built in a similar way to yours but with double (2040) extrusions at the top and bottom edges. Also, all the extrusions are bolted together with metal corner plates. It looks like a tank. Even though my frame is more rigid than yours, it's close to the limits when it comes to rigidity. Your frame is huge by comparison and seems to be made entirely of 2020 or 3030 extrusions. I don't see any bracing on the frame to help deal with how tall it is. With the twisting forces that a CoreXY exerts on the frame, I doubt it is rigid enough to provide accurate and repeatable results.

    Personally, if I was going to build something this size, I'd use doubled (2040 or 3060) extrusions everywhere and cross-braces on two or even three vertical faces. I would dump the threaded rods or lead screws and move the bed with belts. I'd also double the size of the Z axis smooth rods or maybe consider using linear rails instead. Certainly, at this size, all the motion components, including motors, idlers etc. would be mounted to the frame with metal parts, not plastic.

    Also, if you can't accurately verify how well aligned the output shafts of your Z steppers are with the drive screws, it's quite likely that the misalignment is beyond what a semi-rigid coupler can cope with. You may be able to improve the wobble somewhat by using flexible couplers. In the end though, they won't solve the underlying problems and you'll keep discovering new weaknesses as you print different things.

    In short: The frame is too big for the way it is constructed and the Z-motion components are not up to the job. You're just saving up lots of pain here with the current design. Going really big requires exceptional mechanical components.



  • @iamthebest22
    You can always sand the bottom down to fit!

    And yes, you are asking a lot from the frame, even on the FT-5 I had to brace it to the max and go to 12mm z rods to get rid of ossilations. My FT-5 looks more like a aluminium ladder now.



  • @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!



  • hmm I know this is really frowned upon, but would 4 motors help the rigidity, or no just gonna cause more binding/walking/ syncing issues?



  • Leads should not be used for anything but bed movement, using them as the primary support for the bed is asking for issues because no two lead screws are perfect or identical.

    That is why people get massive linear rods/rails and skinny 8mm leads.

    You could solve most your issues by getting new 8mm lead screws, replace the Z rod brackets with metal, and chop your Z axis down to size.



  • okay gotcha, lesson learned, thank you very much!



  • Good luck on your build!



  • Thanks! I'll still be reporting back here, first thing I'm going to do is like buy 20 of those 3030 plate brackets and attach them to the printer, then try again and see if it improves. do I need 2020 plate brackets also for the bed or no? I can buy them too just wondering if that's needed.

    Update on removing the belts, doesn't seem to help much, though there is slight improvement, but still there.



  • @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.



  • @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.



  • 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?



  • @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,



  • 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.



  • 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



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



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



  • @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.



  • 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



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


 

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