Bed_Hoist_for_a_3D_Printer_ (D-Bot, Core_XY)

by printingSome Apr 1, 2018
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Have you ever though about replacing 2040 for 2020 extrusion in X axis ? I think i2040 is too heavy for speeds >100 mm\s


X-Carriage, Linear, Modular, 20x20 V-Slot
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Now and then. And decided to stay with the 2040, for now at least. The plates, as they are now, see https://www.thingiverse.com/thing:2206664, where this question belongs anyway, can use the stiffness in the Y direction 2040 offers in combination with them, I feel. And I like the universality those plates offer for now.
Anyway, at the time I am not so much interested in speed as I am in quality, which is not what I would like, as it is. Can't wait for those pulleys to arrive...

Edit: had another look at a 20x20 solution and saw that I probably can do it without losing/changing the several modules (hot ends, fan mounts) ànd, even more important perhaps, get those hot ends closer to the linear rail. Shouldn't take too long (weeks?) when I don't stumble on something unexpected.

3-wheeled or Linear Railed Modular X-carriage (D-Bot Core_XY 3D Printer)

Have you ever tried to use a SINGLE belt ?

No, not yet. I think it could very well done with those linear shafts, but, coming from the wheely world I immediately thought 2 belts would be better.
I would go for a 10mm belt if I would go that way, just te be on the safe side, though it could very well be that 6mm would be enough.
And don't forget: in the Russian printer the bed assembly is a lot lighter then here.
And I began to wonder whether it wouldn't be better for similar reasons I preferred 3 wheels above 4 wheels.

Edit: I am beginning to make up my mind. Because I cannot yet find an affordable worm gear which would fit in the same room, for instance 40:1, M0.5 with 2x 5mm bores, I'll have to redesign the motor+wormgear support, so I could have a go at the same time at redesigning the whole bunch.
If I succeed at least the upper and middle parts will be much simpler, including a single 10mm belt, but probably one could use a 6mm belt too, if one would wish so.
And in the meantime I'll let the printer work on a single 6mm belt, just too see how that goes. ;-)
Then we both will know.

Edited a couple of times and placed it after the right question, though it looks like the order of comments has changed which makes it very confusing. ;-(

Its the general rule: if it's possible to make it simplier - do it. Should be quite obvious - the less complex construction is, the easier to trobleshoot, easier to build and, above all easier to make it work properly. Maybe the idea to use a wormgear was wrong. Of course, you solve the backmouving issue. But added an additional position error which both of us did witness and do suffer of it. I did a tiny investigation on reprap.org and found that a two shafts (even better a single rail), single motor and single belt is a key to sucess. As well as solid and rather light table frame. But there are other simplier options. I'm also thinking about mouwing to plywood. There are plenty of open builds, FRIBOT for instance, and all I need is to lasercut some plywood and transfer almost all my parts to another, plywood body. Rigid case with all necessary holes, fully enclosed.

Pls. keep me in touch. I'm wery interested in results of your upcoming pulley replacement.

Haven't got it yet. If it doesn't make a difference, I am going to try it with 10mm belts, pulleys etc. Not for the greater strength of 10mm belts but for greater grip surface.

Edit: well, got it today after all. Slightly different profile, not better. but if anything a bit worse. Still amazed about this error.
So it's going to be plan B -> 10mm. Wondering, though...
So it's going a long wait again, I'll let you know whether it works.

I've already ordered belt and pulleys - 6mm. Somehow I feel that you're looking at wrong direction. 2x 6 mm belts should be more than enought. There are some corexy desighns with a bed suspended on a single 6mm belt and perfect prints. But anyway, I'm now rebuilding gantry. 2020 extrusion and no wheels at all. And also planning to replace linear bearings with backlash for 3d printed.

I have said several times that 2x6mm belts are enough, but, as I said in the earlier message, I am going for more grip.
Do you know anything else in this printer that has an absolute regular 2mm recurrence?
Much success!

Why not to increase a driving pulleys' diameter, say 30 tooth instead of 20 ? Would be cheaper and less desighn to be redone. I have an example: ZAV-L http://3dtoday.ru/blogs/mister-magomedov80-yandex-ru/friendly-and-approachable-zavl/

I can't find "pulley" on the page. Perhaps your link is old?
But: what a lot of beautiful prints and nice to see a printer which uses a bed hoist system. When I was trying out older prototypes of my bed hoist I saw a commercial printer which seems to use belts too in stead of the lead screw, so I knew that I wasn't the first/only one, but here it was clear what these people had done (complete with sketch). Do you know other designs with belts?

I had not gotten an e-mail from thingiverse but found your message when I came here to tell I had found another "absolute regular 2mm recurrence" which is the worm gear, of course.
Each turn of the motor translates into 2mm bed transport. So before I go "10mm belts" I have to think/whatever about that first.
I do have enough teeth in contact with the pulley, I thought, so in that respect the 30 teeth pulley wouldn't help much, but I don't like the coincidence of the 20T pulley and the 20:1 worm gear now, which means that I can't see what is causing what. ;-(

I've been thinking about wormgear too. And the simpliest way to test is to print a worm gear with a different ratio. Or to try some sort of gearbox.

Indeed, all of that. Or replace the worm with another one of the same seller... ;-)
I remembered that I had ordered 2 sets, exchanged the worms and the waving is almost gone, almost to the point of let's forget it.
But that is still unsatisfactory, and not only because I want it completely gone. What to say in the parts list? Just order this worm gear and hope for the best?
Still, both worms look good, but the quality seems to have to be too critical to be practical. And I wonder whether printed worms would have that quality. Much higher ratio could be a solution. I'll see.
For now I am relieved that I know where the problem is.
Edit: added picture. From left to right: before, after with 0.15, after with 0.2. Indeed, not ideal, but the difference is enough to have a look for other and higher ratio worm gear.

Thanks god ! Now at least I know a cause. Well, this wormgers are quite expensive and shipping takes a month at least. Too risky to gamble again. I'm going to finish gantry rebuild and maybe'll try to print another wormgear.

And did I understood correctly that to switch from conterweight to closed loop bed hoist design I need 4x idler pulleys with 3mm bore without teeth and 2х 20 teeth idler pulleys with 3mm bore and 2x1250mm 6mm GT2 belt ?

What can I say? Of course you are welcome to try it without those. ;-) But I understand what you are saying and no, I didn't think it would be helpful to mention all that separately, the texts are very lengthy already as they are and I hoped the images speak for themselves.

I'm asking only because you've mentioned in your notes v3b the following:
2x GT2 pulleys 20 with 20 teeth, ø5mm bore, belt width 6mm.
6x GT2 idler pulleys 20 without teeth, ø3mm bore, belt width 6mm
2x GT2 idler pulleys 20 with 20 teeth, ø3mm bore, belt width 6mm

But according to drawings and my common sence it should be:
8x GT2 idler pulleys 20 without teeth, ø3mm bore, belt width 6mm

So this little discrepancy should be clarified.

You are absolutely right. Apologies and thanks. It's done.

Do you have photos of before and after prints. I've bought a 5mm rod already, as well as arduino due + RURAMPS4D 1.3 and TMC 2130 drivers for all motors and extruder. But still dont have a time to install all this stuff. How did you manage to fasten belt and whormgear to the rod. Its quite hard, so the locking nuts in the wheels may just slip.

No good comparison pictures. I haven't even got test prints yet from after, just printed new parts (soon in this theatre) etc. etc. I always dump test prints, shortly after I see what I need to see.
I also am not really confident about how the one screw in the wormwheel will keep up, even considered making a second thread in it, but in the end was too lazy. (I am at least happy to know what I have to do when that goes wrong... ;-) ) The pulleys do have 2 and I have no reason to doubt those. If your rod is really hard I wouldn't know, but why would it be? It doesn't have to do that much.
Specs of my rod: High carbon chromed bearing steel: Gcr15, Hardness: HRC602, Surface hard thickness: 0.8u~3mm,
Accuracy: G6. Not that I understand all that...
I also did find that those shaft collars, together with the brass gaskets (shims), gave those combinations a nice tight fit.
Once I had the right rod the mounting got really much easier and faster then before with the M5 rod etc.

It seems you're not a fan of making photos :) So, I've finally managed to replace threaded rod with polished. Somehow it turend out that gap between rod and bearings (I found that flanged bearings has much more precise inner diameter) is extremely small, 0.01mm or around I think. Absolutely no freeplay.
Whormwheel's inner diameter was slightly less than rod's outer. Simple 5mm drill and pair of hands fixed a problem. Absolutely no freeplay also. And a result: defenitely it worth it. Almost perfect vertical layers.

Thanks for your great message. My experiences with the parts were exactly the same. ;-)
After that first print I wrestled with other things, so I couldn't even make a decent test print to show for (and indeed making photos is the last/least of my concerns ;-) )

Still those 2mm waves (length, not depth of course. Compare them with the 0.2mm layering). And sometimes very ugly ones (same periodicity), but that would have to have a different cause.

Something went reallt wrong, I've never had anything like it ! BTW, Is your printer's frame really rigid ? Does it wobble in general ? I'd recommend you diagonal struts. For example: https://www.thingiverse.com/thing:2239970 I've installed this addition with a good results.

2020 Diagonal Frame Brace
by butchja

Not good indeed, but check again: I made the lighting so it highlighted the waves and you can compare the waves with the layering. I don't think it is much worse than on your "without_wheels.jpg", where the waves seem rather strong, but I can't see the layering, or the "belt_driven.jpg", where the waves are superposed by all those irregularities.

But still, I am not satisfied at all. The constant appearance of those 2mm waves during all the variations in the system I made bugs me.
My frame needs some overhaul. Can't say that it wobbles or anything like that, but I discovered some time ago some cracks in the corner-pieces at the top and will reprint them, but I don't think these are the cause (remember, those 2mm's all the time, very regular).

In the time of the lead screws and wheels everywhere, I put diagonal strips (strong on pull, not on push, but they help each other on that) on all sides, but that made no difference whatsoever, so I removed them again.
Where/how did those good results show with you?

But first things first. I am busy with the publishing of my new cooling on the X-carriage page, https://www.thingiverse.com/thing:2206664, still struggle with too much stringing, despite good advice everywhere on the net, etc. etc.

Edit: I get more and more the feeling that it has to do with the linear (in)accuracy of the belt-pulley combination, i.e. what happens at each point within the 2mm pitch of the belt, repeated every 2mm. Or something thing like that ;-)

3-wheeled or Linear Railed Modular X-carriage (D-Bot Core_XY 3D Printer)

Haven't been here for a long time, and you're already managed to improve the design. I have the same "~2mm vertical irregularities". Maybe you right and the problem in XY motor's pulleys. However, they are not that simple. For instance printed cube has 1 perfect face, 2 slightny affected and the one with notiseble 2mm effect.
PS: why did you decide to make design without counterweight ?

I never liked it much. A bit sloppy etc. though it worked. I didn't think of another way until I did. ;-) And secretly I hoped that varying the tension would influence the wave, but it clearly didn't change it fundamentally, so I didn't even bother to try the varying.

Going to bild this one. Having the same problem - leadscrevs seriously decreases build space as well as constant problems with 2 Z-axis motors syncronizing. But why you didn't consider 10mm belt instead of 6mm ?

I did, but in the end I didn't see a reason why I wouldn't do it with the usual belt. Should be strong enough, also in the long run.

I've installed your mod into my printer. It gave me much noticable Z-wobbling compare to lead screws.

I am very sorry to hear that, but also very surprised. I wouldn't know where to look for a reason. I suppose both belts are under somewhat the same tension?

Do you have any Z-wobbele issues in your construction ? Because bed becomes less stiff without leadscrews. But thanks for answer anyway. Maybe some adjustment is required or something wrong with wormgear. Because the bed somehow tremble while lowering. And almost not while rising.

Less stiff? Aren't you using you those linear Z-guides? Those are essential to this thing, I think. And anyway, those lead screws were never intended to keep the bed in place, only to provide up and down movement. The wheels should take care of that and they certainly did not do that as well as the linear Z-guides.
I have no trembling whatsoever. Smooth is the operative word here. ;-)
Let's go over some checkpoints, which you have done, of course, but just to be sure.

  • with the belts decoupled check that the bed assembly goes smoothly up and down (manually), so you are certain that those rods are well placed.
  • check that the ballast weight glides smoothly up and down, so it doesn't interfere with the next point:
  • it is important that that weight is really less than that of the bed assembly. That way the play in the wormgear (or even some stick-slip in the guides, if there is any, which I doubt with those rolling balls) has no influence any more. It should be substantial though.
  • aren't the worm and wormwheel so close together that they press upon each other vertically and so produce extra friction? The construction should prevent that, but please check. A bit of grease should help with the normal friction, though I thought that the bronze helps with that too.
    I don't have any other ideas, at the moment, but please tell how it goes.

I've made some modifications and have some results.
First, I decided to combat bed heavy wobble by adding two addition supporting points. I had some V-slot wheels, prints and extrusion from original J-bot desighn. And yes, It helped alot ! Vertical fuzzines completely dissapeared. Yet, I still have some imperfections in vertical or layer-to layer arrangement.
Got some ideas about what caused and what-to-do.
First, I suspect incorrect between whormgear pair axies' distanse. I think it's too big and contact surface is insufficient. This may cause uneven rotation of the driven gear
Second - my threaded rod have a diameter of only 4.75mm, so all geared belt pulleys are slightly off-centered.

Thanks for the update. :-)
I am happy that you found improvement.
Where/how those wheels? Picture(s) would help.
Can't imagine how you did it, but be careful: more support points could work against each other, as those 2 linear Z-guides already do when the rods aren't properly aligned.

Distance between wormgear pair axes could wobble a bit (with the threaded rod less than ø5mm, as is the case with me too), but I don't see how that could make a perceptible difference.
Ditto with the pulleys.
Both causes would give a repetition rate of 2.5mm (1600 steps/mm -> 8 motor-revolutions/mm -> 0.4 whormwheel-revolutions/mm).
Do you have that?

I still can't get why prints still have this Z-wobble pattern. Maybe wormgear isn't that precise, maybe 12mm rods is not enought or something else. But in general, after swithing from leadscrews to belts prints didnt became noticebly or maybe even somehow better. Hope swithing to precise 5mm rod will help.
Here is some pics

  1. general overview
  2. test print (belt driven Z), bellow boat is a part printed with leadscrew
  3. hollow test cube (belt driven)

Thanks for the pictures. But now I really am confused. Is that Z-wobble?
I see irregularity in the XY-direction and I am struggling with that too, but what does that have to do with irregularity/wobble in the Z-direction, i.e. in the vertical displacement, which is what this thing is about.
And I don't expect a precise ø5mm rod is going to change a bit with your irregularity.
Let's try and get some points straight:

  • the belts take care of how much the bed moves vertically. If that system does not work well, one should see variations in vertical displacement.
  • the linear Z-guides guide this movement. If these rods are bent you could expect some horizontal movement of the bed assembly, but that would look very different. Suppose one vertical rod would be bent in the middle in the y-direction over 1mm than the bed assy would move steadily sideways less than that over half of the height of the printer. So that's not what is going on. Room in the ball bearings could give some jitter, I suppose, do you have that? Then you should be better off with other guides, but don't decide that too early.
  • one of the probably several causes is/was obviously sideways movement of the bed assy, because of your success with the wheels. The only function of those wheels would be to limit this sideways movement. Nothing to do with the hoist. I wonder, though, why that was so successful. Should not be necessary, so have a look again at the bed assembly.
  • I can't find any sideways movement in the first V-slot rail between the rods. That seems to be very solid. It should be with you too.
  • the movement could come from looseness of the rails under the bed, because those wheels keep those better in check.
  • what those wheels don't do is check the movement, i.e. wobble, of the bed on those rails. How is that with you? Can you move the bed against its rails? I made an effort to diminish that movement (see https://www.thingiverse.com/thing:2094263), it is better than before, but I feel there is room for improvement still.
    I still feel there is some risk in having all those wheels again, in that they could work against the linear Z-guides. You know, similar to what could happen in the old days ( ;-) ) with the lead screws when clamping the vertical rods above and below. When that happens the resistance in the vertical movement would get out of hand very soon and than you are in real trouble. Especially because there is so little sideways room in those linear Z-guides, when they work right. They really don't want sideways pressure from the wheels.
    Just some thoughts.
D-Bot Core_XY gone Linear (was: in Threes)

When said Z-wobble, I meant some irregularities in Z axis i.e. some layers are slightly offset from another in some pattern. Maybe I'm wrong and Z is OK. As to wheels - I used them involuntarily, because without them the bed swings really hard. Maybe I'm out of luck with chineese linear bearings - they have some freeplay. Yep, looks like jitter .Maybe bigger rods (16 ?) and precise bearings may help. Do you have some pics of your prints closeup ? Just to compare.
Here is a print made without front wheels.

I too have the same sort of regular irregularities as in this and in the the other pictures, and I had them too with the lead screws.
By the way, I like the last picture "without wheels.jpg" better than the "belt_driven.jpg", less sharp jitter in the first one and the softer regular 'wave' appears to be in both pictures, only superimposed by the jitter in the others. And there is also something like that in the "leadscrew below", only not regular, which should give you food for thought, as it does with me.
Again, a swinging bed has nothing to do with the hoist, or even the linear Z-guide, as far as I am concerned, and the thickness of the rods has nothing to do with play in the bearings. As I said: if the rods were not straight that would only show over a great distance, decimeters instead of millimeters
And you can see for yourself that that soft regular wave could not be caused by those bearings: how could such a regular aberration occur each few mm whilst it takes much more displacement in mm for the balls to go round in those blocks. Would a single or a couple of crazy balls give such a soft wave, time and again? And again: I have no reason to doubt my chinese blocks, can't feel any room, and I have and had also that same variation. And I am still looking elsewhere...

I came home after work and made some test prints again and... Found that prints without wheels are smoother when scratching it with nail along Z axis. So, it seems that you was right and I decided to remouve bed's front support. Because prints made without wheels seems less noizy while scratching along Z. But I found noticeble regular irregularities (as you said) along Z axis, seems like nozzle slightly, but periodicly trembles every 2,5mm. The same thing with wheels, but it seems its not that noticable, or so clear. Or the peaks are somehow deaden. Yet the period is same.

Mine are about every 2mm. Thought of irregularities in the delivery of the filament to the nozzle, but I use Nimble and you don't, so...
Forget also about trembling or jitter, it is too regular and "nice" and wavy for that.
I am out of ideas for this problem, but there should be some solution, so I keep trying to find it and as soon as I find something I'll mention it here, though I still think that it has nothing to do with the hoist. Hope to hear from you if you find something.

Yes, I'm using MK8 bowden clone.
I think I was complaining the hoist in vain. You made a good mechanism. But I still going to replace threaded rod with something more precise.

Unthreaded? Would be nice, but with what are you going to replace the nuts? To keep the ball bearings in place?
At the start I tried that with a sort of collar but that printed very badly. ;-(

Edit: thanks for having me sort of thinking again. ;-)
I am going for it: a ø5mm shaft and 5mm shaft collars. Even if it wouldn't improve things, it would work much more comfortably, without the risk of ruining the threads etc. It removes any wiggle and our doubts in this and just is much more elegant.
Thanks again!

Collars is a good idea, but I think all will work well even without them. For now I run without nuts, pulleys are well secured by its own bolts.

They are not meant for the pulleys but for the ball bearings, as were the nuts.

Mine bearings are still secure w\o any support from nuts.
Bearing seat should provide tightness.

May be, maybe not. I would not want to do it without, but if it works, it works. ;-)

Thank you very much! ;-)

And thanks also for your advice. I am sure that is great quality.
My thoughts on this were:

  • we don't need the best quality, there is no speed, there is hardly any weight etc.
  • we need constant length over time and of course here I am not absolutely certain. But I feel also confident in this, having seen the (pre)loads these GT2 timing belts are advised or willing to take respectively.
    As I warned: when the height of the print is really critical: check after a while whether there was stretching.
  • we need good flexibility so there is as much contact with the pulley-teeth as possible. And then I am not getting very happy when I look at http://mulco.de/sites/default/files/34184-3_0.pdf and I see (p.29) that the willingness to bend (Biegewilligkeit) stops at a minimal diameter of ø20mm. Thanks to the steel threads, I think, as I mentioned in my Notes.
    So that seems to be simply out of the question.

I can't have an opinion on the teeth forms, so there I remain stumm. I didn't see GT2 there, but I saw nice comments on the quality of the GT2 form for driving the X and Y axis, so why not stick with that. I would need to make a complete different design with very big pulleys etc. to achieve the same result. And for that I would need more convincing.

Great that you want to think with me. Thanks. :-)

Perhaps you will be happy with my new Bed_Hoist, Version 2, coming soon. There I only use 1 belt, but the diameter of the pulley will be a bit greater, so steel could come in at that point, though I don't feel the need for it myself.
I will be using a 10mm belt, but I feel rather confident that 6mm would do nice too, even with fiberglass. I am waiting for a part, but already threw away one hoist. I positioned the other one in the centre and am happily printing with it that way.

I've decided to implement ultimate solution : single rail\single drive cantilever bed. ZA Preloaded original Hiwin EG20 rail is already ordered. There will be no wormdrive. I gonna try single leadscrew and maybe single belt. No mechanical owerconstrain in bed kinematics at all. Printing area will be reduced to 200x300 to increase bed stifness.
PS did you win a battle against Z banding with a single belt design ?

Look forward to read your experiences with it. For now I do not understand the combination single leadscrew "and" single belt, or do you mean "or", but I suppose all will be clear when you show your results.
Still printing with the one hoist of this design and still got a bit of a 2mm wave, as one would expect with the same worm gear, though not very pronounced. Hope that will disappear when the new stuff has arrived.

Thanks for using my parts:)) Nice to see its redesign:) Is your rope from kevlar?
Moreover, I did not get how you are rising bed? what for belts if you have ropes?
Can you make video how it is working Sir?
https://s7.postimg.org/unnsnl3jf/cats.jpg here is the question.
Thanks in advance for additional explanations and show.

Yours was a great idea and thanks for that. :-)
The usual GT2 timing belt, no kevlar, rubber (neoprene) with fiberglass.
Just going up and down: motor turns the worm, wormwheel turns 20 times as slowly (see Wikipedia and my Notes.pdf), so does the axis and the rest, very straightforward.
I don't think a video would add anything.

Grate idea and implementation!
Thank you!

I added a picture of the counterweight system and some of the original content of this response to the Notes -> Notes-V1a.pdf, thanks to your comments.

Thank you dear for nice tech explanations at PDF, Grate job my friend, just grate job!