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Anet A8 - Anti Z Wobbel TNG (Set)

by OderWat, published

Anet A8 - Anti Z Wobbel TNG (Set) by OderWat Jan 27, 2017
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Fusion 360

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Summary

After printing the original anti-z wobble for the Anet A8 I found out that it is a bit to small to fit the original screws. It also is a combination of two other volumetric objects which does not slice really well with Simplify 3D.

Because I had no bearings at head I printed some dust caps for the z-axis hole in the top of the frame. To make them a guide for the z-axis I heavily scaled their original design.

Now as those stuff is working fine I thought I create a set for this modification which prints out of the box without any hassle. After more than 20 iterations I think I am done now!

I also included the raw fusion 360 files for anybody who wants to change the design.

My version does not use the original models but for reference. It was build from ground up and later even changed quite substantial. Many thanks for all people which experimented with that kind of mod!

Update: Fixed the model so it will be sliced by Slic3r, Cura and Simplify3D

Print Settings

Printer:

Anet A8

Rafts:

No

Supports:

No

Resolution:

0.2 mm

Infill:

40%


Notes:

It is meant to be printed it with 3 perimeters and 6 shells which is the same as printing with 1,2 mm wall and surface thickness. It is hard to design in a way that everybody can print it. I hope after about 20 iterations the models fit for most people out of the box!

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I really like the concept of this part. I was looking for a solution to allow the leadscrew nuts some play in the x carriage ends. My original plan was to increase the distance between the leadscrew and the straight rod to allow to fit the leadscrew nuts underneath, instead of fixing them on top. This would require a redesign of both z axis ends and would only work to compensate for a fairly small wobble.

Your solution, however, works with any amount of leadscrew wobble. What needs to be understood here is that with the leadscrew nut and linear bearings originally constrained, any wobble for is being applied to the linear bearings against the rod, and ultimately to the motor shaft. The amount of torque these motors are able to generate will bend a very straight leadscrew that has been constrained by any misalignment in part design or assembly.

Thanks for this great idea, I will apply it to my custom i3!

These are amazing, printed and installed. I can say that when jogging the z axis down i don't hear any screeching and scratching anymore. Probably because the lm8luu bearings aren't being pushed into the rod horizontally.

Thanks for design. The reason I made this one was because I had a really bad surface from z-wobble and tried before that some other so called "upgrades" and also reinstalling the t-shafts. For my printer (anet A8) it sadly doesnt work. The contrary of that it getting worser.
After hours of reading I finally solved my z-wobble problem by installing T-shafts correctly. Think I act a little bit clumsily the first time :-D.

Just got my printer back together after having it in pieces for a BLTouch and install of these brackets (it was a preventative install, not to specifically solve a problem with anything more than minor banding, was hoping it'd help make even smoother prints), but found on the very first print that the anti-wobble mounts actually induced horrible ringing/Z-banding. I removed them and the problem is completely gone.

I've about figured out that it seems to be because these brackets remove half of the support structure from the Z axis. This allows printing or rapids to upset the fine tuning in the X axis as the head moves back and forth because the guide rods can't soak up the additional movement that the Z lead screws helped with. It allows for some really bad resonation to build up because the Z axis isn't fully supported. I even slowed my printing speeds down to half of what they used to be and it still happens, but to a lesser degree.

YES, this is anecdotal evidence. I have no scientific equipment to test this beyond observation and theory.

This might be a great bandaid for you if you're waiting on new lead screws, but the fix is straight lead screws. They play a more important role here than just moving the gantry up and down.

P.S. I want to make it clear that I am using top caps to center my lead screws. I have made no mechanical or operational changes other than these brackets and a BLTouch install. Writing this comment isn't meant to be an attack on the print or the author (who did a great job with the design!!), it's just feedback on my own experience.

Stock (mostly, just a couple of support brackets here and there, BLTouch, LEDs for visibility) Anet/Alunar A8.

Well, there is not need to change your printer if there is no problem. Having a working original setup (space between the couplers, free movement at the top) there is probably no need for another setup. One can experiment though. For some people that is more fun then print something useful :-)

This design is just an alternative design for the Z axis which primarily lets you move the Z axis upwards freely at any time. I used it mainly because it did not harm my quality and let me check out a multitude of sensors and helped protecting my hardware while developing on the Skynet software.

For the OP: If your lead rods are lose and your print head can move for/back/left/right you can't expect it to fix that. If your printer creates so much vibrations that this adds up and disturbs your prints, you need to find the reason for that. It simply will be worse with this design installed.

And maybe you should replace these crooked couplers with something like this:
https://www.dold-mechatronik.de/Wellenkupplung-RB-flexibel-D20L25-500-800mm

Since my rods are straight I am thinking about using two elastomeric couplings like these:
https://www.dold-mechatronik.de/Spielfreie-Elastomerkupplung-JM16C-D16L22-500-800mm-64SH-gruen

They have the advantage that they divide when the nozzle runs into the heat bed. ;)

Yes, that YouTube video shows the correct way to mount the Z rods.
No need for fancy mods. Everything you need to do is, follow the instructions when assembling the printer.

Thank you for this... it all makes so much sense now...

This made no difference to my z wobble problem. Any advice? I put the caps at the top and made sure nothing else was the culprit. Could it be my couplings?

Uncoupling the X axis idlers from the threaded rod works to remove wobble due to non straight threaded rods. This design should work (haven't tried it) but the threaded rod must move through the X axis idlers freely and not be constrained at the top either, that will make matters worse instead of improving them. Decoupling should rely only one the flex couplers between stepper motor shaft and threaded rod and X idlers that are constrained only by the smooth rods.

Please stop commenting with theoretical insights when you did not even tried it yourself. Your assumptions are wrong for this setup. There is no flexible part left at the lower end and the top just hold the rods in place. If your rods are so bend that they don't work you may try it without them but there is no negative effect from them for the average bend rod. Anyway. This is an alternative concept for the x-axis and not the holy grail or "better" solution per se.

EDIT: To make it more clear to you: When you don't haven the rod "locked" into the X axis and the rods are bend they are not anymore constrained and will move much more out of position. Holding them in place at the top end will make them stay much more in the center of movement and the "bend" part will be filtered by the decoupling.

Erm, well not wanting to get into any discussion, I actually thought I was being encouraging as the main part of the design that carries the X idlers is perfectly sound and I do recommend that as an upgrade, especially if your threaded rods are quite bent. That is not a theoretical insight as I'm using a similar decoupler on the X idlers of another i3 variant I have. I also have an Anet A8 which does come with flex couplers on the steppers (and a quick look on eBay shows they all appear to do). Constraining the threaded rod at both ends, stepper and top side, will, without a doubt, make things worse if the threaded rods are not especially straight. If the coupler at the bottom is a rigid coupler it'll be even worse. Note that the Prusa i3, which is still the best design out there, also does not constrain the threaded rod at the top.

Some people have commented that this upgrade does not work for them or negatively affects print quality and I would encourage to try without the top constraints, which is without a doubt the reason for their issues. Only trying to be helpful. As always, thanks for designing this and sharing your design and I've changed "could work" to "should work" in my comment to better reflect what I'm thinking.

Prusa i3 don't uses the decoupling. The flex couplers are supposed to be locked by pushing the rods onto the motor axis. This also removes the Z freedom problem. Fixing the rod on the top is good for what I described.

People which have problems with this design as it was meant to be can of course try alternate designs but I would not be surprised if some of them did not fix the rods on the top ;-)

About the "discussion":

You said "the top holders are to be avoided at all costs." .. this is wrong in my opinion and I already explained why I think so. Your counter examples all mention cases which are no valid for the correct usage of this design. You also said that you did not tried it but know you are using something something similar. Guess what? I use this exact design on exact the printer it is meant for and would not if it would degrade quality for me. Thats all I promise here :)

BTW: The Prusa i3 for example does not use a type of "flex coupler" like the A8 does but a version which allows no vertical movement. Comparing the Prusa i3 against the Anet also does not make much sense as this design is a try to get around the cheap quality of the Anet hardware in addition to the fact that this type of rods are hard to be perfectly straight.

Well yes, you're absolutely right in that if your rods are perfectly straight and well aligned with the stepper and X idlers you won't have any issues constraining the threaded rod or leadscrew on top :). And of course you are also right in that the Prusa i3s are in a different league, but the basics of the design apply - if you can't use steppers with integrated and straight leadscrews, use a flex coupler at the bottom and leave enough space between the stepper shaft and the threaded rod so the flex coupler can actually flex. If the threaded rods are not further constrained that will already eliminate quite a bit of Z artifacts stemming from a bent rod.

The mistake that I've seen more than a few times is having the threaded rod and stepper shaft touching in the flex coupler. With a properly installed flex coupler and additional decoupling of the X axis using your design one should be able to eliminate most or all Z wobble artifacts. Constraining the rods on top is this case counterproductive, that's all. The original A8 design specifically warns against this for a reason.

Again, thanks for sharing your design, the decouplers on which the X idlers rest are quite elegant and a definite upgrade for A8 owners with bent threaded rods.

Well the problem that people don't set up the rod correctly in the flex coupler has nothing to do with this design which actually takes the opposite approach. Fixing them on the top for this design is as mandatory, as it is for the original design to have them free on the top.

Well no not really, it's really basic mechanics. Think of an archer's bow as an extreme example of a bent rod, held with one end in each hand... rotate the bow and the motion described by any given point of the bow in a plane perpendicular to rotation axis will be a circle.

Replace the archer's bow with the threaded rods or leadscrew (I'll stick to leadscrew for the rest) and you get the idea - the X axis assembly without the smooth rod will move in a similar circle around the Z axis. If one end of the leadscrew is left free, the smooth rods will constrain the X axis assembly along a linear path and the flex couplers will take up the unwanted forces exerted due to the leadscrew not being straight. Your design minus the top holders provides additional angular "slop" which is a good thing if the leadscrews are really bent. The free ends of the bent leadscrew will move in circles, which is a perfectly normal and desirable thing.

If the leadscrews are constrained at both ends, unless the leadscrews are perfectly straight (in which case, yes you can constrain both ends, but providing they are not misaligned with the stepper shafts and parallel to the smooth rods you wouldn't have this type of Z wobble in the first place), the result of the force applied by the bent leadscrew on the smooth rods and vice versa results the X axis assembly being displaced again leading to Z artifacts in the print.

Your design doesn't make any basic changes to the way the Z axis is constructed - leadscrew parallel to smooth rod and mounted to the stepper shaft using a flexing coupler. Rather it mitigates the net forces exerted on the smooth rods by the leadscrew and the other way around, as long as the top of the leadscrew is unconstrained. It's in no way mandatory to constrain both ends and (due to above) counterproductive. But hey, let's just agree to disagree. :)

This will be my last answer... it is already a waste of my time!

It does not use a flex coupler... and is a major change in how the X and Z axis are constructed. It is about X artifacts not about z artifacts. z artifacts are my worry for this construction. I also don't see how any force can be applied to the smooth rod? They are decoupled, that the main feature. I start to think that you didn't understand how it works in the first place.

Last answer here as well...Like I said, let's agree to disagree. Maybe there's a vocabulary issue at play here, a flex coupler is the cylindrical grey thing between the stepper and the leadscrew and your photos show that you have one mounted. You have a stepper at the bottom, a flex coupler, a leadscrew and a smooth rod in parallel to each other. Same basic design as every i3 clone in existence that uses two bottom mounted steppers on Z in parallel or series. The smooth rods are there to guide the movement, the leadscrews are there for linear motion and not for guiding or stabilizing and as such there is no need for them to be constrained top and bottom, unlike the smooth rods. Your modification is intended to remove the unwanted forces exerted due to bad materials (bent leadscrews) but the basic configuration of the Z axis is the same.

Again, your basic idea is sound and the way the X axis assembly is decoupled will work well, the point is that if the leadscrews are bent and the leadscrew is constrained at both sides, the smooth rods and leadscews will still work against each other to some degree because even with your design there is not enough angular freedom of movement (and if there were the X axis assembly would be unstable, you can't have both).

I stand by my suggestion to use your design which will have a positive effect on this type of Z wobble, minus the top constraints which are at best useless (because the leadscrews are meant for motion only, not for stabilizing) and at worst counterproductive, The ends of the leadscrews can and should move all they want.

I loved your description using the bow analogy and until I actually looked at his design properly I was right on your side reading this. But....it looks like he has entirely decoupled the X-carriage from the Z lead screw thread assembly and the X-carriage just rests on the new Z ("block"?) by the force of gravity alone, you could just lift it up to the top of its travel at any time if you tried. To this end, when he counters your, usually correct (in any other standard circumstance) argument, that circular movement on the Z threaded rod won't be felt on the Z smooth rod and affect X stability.... he is correct. I was going to go on to say that in this case it would then make no difference if your Z threaded rods were tied at the top or not, but, thinking about it, they would need to be tied as having no mid point of lateral stability provided, usually, by the fixed X-carriage mount would mean the only thing holding them straight is the flex coupler,...and that is an oxymoron if ever I heard one.

So, my conclusion, if your Z rods are bent so bad that they affect your print even when allowed to properly move freely at the top. Try this method, it doesn't use much plastic if it doesn't work.

I do spot some other potential issues however;

  • How does it respond to Z hopping, can it return to correct Z level quickly enough through gravity alone?

  • If there is any rotational play at all between the slot on the Z thread block and the smooth rod(s) then Z travel could be affected, especially if Z hopping.

The weight of the X axis + the head in the original design is pretty high (1,3 kg) and I found it is enough to keep Z ok. But there may be a problem with tilting the carriers which will bring small shifts in z. This is why I already started to design a slightly different version which has much less and circular contact around the threaded rod position. This involves a new X axis element too and needs much more modifications than the design of this version. But it is far from a "release" and I am busy with my day job, playing prey and also want to finish the final PR to include Anet support directly into Marlin as I am maintainer of the SkyNet3D Firmware too :)

I simply can let this stay as is:

A flex coupler is only a flex coupler if you don't let the rods touch inside.

"The smooth rods and leadscews will still work against each other to some degree because even with your design there is not enough angular freedom of movement (and if there were the X axis assembly would be unstable, you can't have both)."

Above assumptions are totally wrong and show that you make wrong assumptions about how it works.

How can smooth rod and lead rod "work against each other"? You seem to not understand the design at all.

If your lead rods are bend in a way that the move more than +/- 3 mm you may run into trouble but even then one could widen the holes in the x carriage as contrary to your believe, there is nothing getting unstable from that.

Again: Don't tell people about your theoretical believes if not used it for yourself. Stuff like this lets people adjust steps with 10 mm cubes instead of 100 mm, fine tune extruder filament transport with mounted nozzle, lets them decrease jerk instead of fixing their belts and re-tighten their screws. Understanding things in detail is key to giving advice.

The risers work well, but are the top rod holders a 'must' do they improve the print quality?

No, the top holders are to be avoided at all costs.

Why would you say something so incorrect? The top caps do nothing negative. Their purpose is to tighten the tolerances at the top of the lead screw and make sure it has a harder time wobbling...

On my machine they tightened the movement at the top from about 1mm to less than half a mm. In my book, the caps are one of the best, fastest, cheapest options to add.

This is the best and cheapest upgrade you can do to improve print quality. The difference is amazing! Thank you for designing/sharing this thing.

Not bad, but keep in mind, placing these isolation risers under the lift carriages will limit the build height, because now the x-carriage can't start in a lower position.
These could be much thinner. The best option is to not use bolts or nuts. Use the thread guides as inserts, sliding them onto printed knobs in the risers. Gluing them in would allow for isolation risers no thicker than the thread guides.
I'm gonna remix the Hell out of these. Thanks for the start.

let's be honest, do most of us get anywhere near the top of the machine most of the time?
I went to 220mm once for a vase, that's it. the rest has stayed under 100mm

Sure, I just printed an Eifel tower. I would have built higher if I could. I've also built an Apollo rocket, a space shuttle, & dozens of tall or cylindrical pieces... I compensated by designing a carriage which moves the nozzle closer to the bottom x-axis rail, regaining 15mm of height, so it's all good, even better actually.

It did not change the build height at all for me. Simply mount the clamps a bit lower if it does not touch the bed anymore.

My carriage goes so low, that my bearing blocks come within 1mm of the spring couplers. The brass nut is 16mm high, so moving them underneath the bearing block moves everything up by 16mm. This makes my maximum build height drop from 260 to 244mm. I see now there's no way around it, unless the brass nut is shaved down. Not as if there's any worry of backlash, since the z-axis only moves in one direction until the print is finished.
Still, I'd rather have an isolated z-axis than taller prints. It was only a 240mm stock build height in the first place, so I've still gained space even with the brass nut under it.

Well you are not talking about an stock A8 extruder then I guess. For "high" stuff I have a delta :)

Correct, I designed a carriage mod. It works very well.
http://www.thingiverse.com/thing:2031671
I also lowered my bed by removing space between the bearings & bed carriage. My build height is over 265, but I still need to tweak height limits in firmware.

i3 A8 Badass DiggityDank MK8 Carriage

My Z axis wobble was intermittent which was weird to me but when it happened it was annoying and sometimes REALLY bad. After thinking about it your solution seemed like the most logical solution and I'm glad to say it WORKS!!!! Thanks for coming up with this relatively simple yet very effective solution.

Hi,

Did you use the z-axis bearings that came with your printer, or did you buy additional ones for your supports?

Thanx in advance.

The original ones.

Hello,

I made them but for me they are not really works, they make my print worst than before :/ .
You can take a look on my video when I trying to make my prints looks better :

https://youtu.be/TRv6fuOE_4k

I'm sorry to display some ignorance here, but I have to ask as it may be useful for my Anet/Alunar (always looking for ways to improve it!), and I want to understand how it works.

Is the X/Z-axis meant to 'float' atop this assembly and be lowered by gravity only? Is the weight of the X/Y carriage alone to ensure accurate Z-axis placement?

Was wäre denn, wenn ich oben auch noch welche einfüge ?
Ist das denkbar ? Oder versaut es das Prinzip ?
Gut, du kannst dann nicht mehr so schön das Filament wechseln, aber das ist ja nicht die Frage ^^

Ich habe keine Ahnung was Du meinst :)

Hans, nutzt du diesen anti z noch selbst ? Ich habe einen zweiten a8 für die Firma gebaut und da sind die Achsen Abstände der weissen Halterungen nicht korrekt. Man hat mir deine hier empfohlen ... Damit wäre meine Achsen Differenz gelöst. Was sagt du?

Ja. Mache ich. Ist übrigens auch super praktisch, wenn man mal schnell die Düse sauber machen möchte :)

Does this still work with the Z-Min switch??

I forgot where that was placed. I changed that on day one. I guess it may work though. Somebody with the original switch here to verify it?

Works if you put it really far down but its close

Best ANTI WOOBLE in combinasion with up anti wooble with bearing

Depends... I get to few response to judge its usefulness for others. My biggest concern was, that it harms. I got one report where it does, but from the circumstances I guess that the real problem was something else for his case.

For myself, with few to none z-wobble before the modification, it did not degrade quality at least. I build it for and back to tests different stuff and I could not link it to problems I had in between. So I guess for people with stronger z-wobble it may be a solution. But I also think that they may need to fix their guiding rods and/or make the "non z-wobble" spindle rod really elastic. Some people may even find this mod to fix their problems, but they would not have them when they had mounted the original construction correctly.

For myself it is helpful in another way (and originally the reason why I wanted to try a mod like this): It helps with development and testing of sensor solutions by avoiding that the nozzle is driven into the bed. It also lets you mount an "emergency stop" z-switch which gets triggered by the carriers instead of the actual x-axis. This is because they go deeper down than the x-axis when a sensor does not trigger.

So for me it helps in different ways and I am decently sure that it does not harm. Besides that one can easily try it and build it back if it does not help or harm. People which consider such mods are used to that I guess :)

Great work - and it really helps! :)

Wow...boy did you add more meat to the frame...thing looks like it could lift the entire z axis with only one on there! Daggum!

Great design!

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