Fixing Z Wobble from 20$ Ball Screws with that simple device

These fine looking metal pieces are ball screws  they are used into linear motion applications   where precision speed heavy loads and endurance  are needed this type of equipment is normally   very expensive therefore not accessible for  hobbyists just like myself luckily low cost   alternatives exist but they might bring other  issues into your project in this video i will   show you how i managed to obtain excellent results  using low cost ball screws on my 3d printer Before we dive into the world of ball screws let's  understand the difference between a lead screw   and a ball screw and why would you  even want to have those ball screws   lead screws are very simple they only consist  of two parts a threaded rod and a matching nut   the lead screw will transform a  rotation movement into a linear movement   via the continuous sliding slope created  by the threads of the nut and the screw in   general lead screws will use a shape of threads  called acme they are also called trapezoidal   these threads are better for power transmission  and they are also stronger who says sliding and   slope also says friction therefore lead screws  require excellent lubrication not only in quality   but also in interval if you're operating into an  open environment this nut has been printing on my   hypercube evolution for a period of six months  even with good lubrication the brass from the   nut has suffered from severe wear and erosion  due to the considerable weight of the bed from   that printer lead screw nut are made from brass  brass is a lot softer than steel and it will act   as sacrificial material which means that the nut  will take the hit of wear and tear not the screw Just as ball screws lead screws can be  back driven meaning that when a force   great enough to overcome the thread friction  and the unpowered motor torque the nut will   transfer that linear force into rotation of  the screw this situation will create your bed   from going down when the motors are powered  off the difference with lead screw is that this   force required to enter that mode is much greater  than the ones you would find on all screws the   simplicity of lead screw makes them easy to be  manufactured into a fairly small form factor   the most popular size for lead screw  in the consumer's 3d printing market   is eight millimeter being small has the advantage  of being flexible this flexibility will help   a lot in case of misaligned installation  or even in the case of a screw with axial   deviation or what we call axial run-out since most  obvious 3d printers are made from 3d printed parts   the rigidity of the system will not be able to  digest the axial run-out of a very rigid screw   they will bend to the required shape more  easily and therefore not winning the rope   pulling contest with the rest of the printer's  components in summary lead screws are simple   therefore low cost they are also forgiving due  to their flexibility they are also very silent   in operation but on the other hand they require  higher maintenance they might suffer from a higher   degree of wear and they are also limited into the  load capacity they can carry for the same size Now let's see why ball screws are so special ball  screws are a lot more complex than lead screws   they consist of a screw with a thread shape made  to interface with ball bearings so far this is   not rocket science now let's have a look at the  nut this is where all the magic happens the ball   screw nut contains multiple ball bearings that  are used to eliminate the friction between the   screw and the nut as the ball bearings are being  carried over by the screw rotating inside the nut   they will eventually need to make an exit  at one end of the nut a ball screw nut is   equipped with two plastic inserts one of these  insert will scrape the exiting ball bearings   in order to direct them into the recirculation  path the recirculation path then realigns the   balls into the threadway at the opposite end  of the nut using the second plastic insert   this cycle repeats over and over along the screw  length back and forth since friction is the number   one contributor to wear you can understand  that such a system is not only very durable   but it requires very little maintenance while  being able to carry much higher loads at higher   speeds than a lead screw would for this high  demanding application i use my favorite lubricant   category a pure Canadian maple syrup i  almost got you on this one right no seriously   i use a mix of heavy synthetic oil and this Lucas  stabilizer additive into all my linear motion   application it is a 50 50 mix that benefits from  the motor oil fluidity and lubrication performance   and from the stickiness of the Lucas additive look  how sticky this stuff is it stays on very good to   the components and will not turn into hard gunk  over time although friction seems to be the enemy   of all it is actually helping the printer's heated  bed from back driving its way down when stepper   motors are unpowered it is true that ball screws  require very little effort to be back driven   in the industry this is usually being addressed  with a braking system but for small and relatively   simple machines like our 3d printers this can be  prevented using bigger motors which have a higher   detent torque or by introducing a higher gearing  ratio with geared stepper motors or pulleys and   belts as i mentioned previously the ball screws  are quite complex therefore manufacturing a tiny   ball screw assembly while maintaining its quality  and accuracy at comparable cost is very difficult   therefore most of the ball screws we find on the  market are 12 millimeter in diameter and more   this is a rolled 12 millimeter ball screw and  we will see in a minute what rolled means but   all that is important right now is that this guy  is super rigid i am applying all the force i can   and it barely flexes remember our rope pulling  contest from earlier with the printer components   well this time around the printer is not going  to win this one and for that reason it is very   important that the ball screw be as straight as  possible in a nutshell oh i like this one in a   nutshell you get it nut shell anyways a lot of  bearings in that shell but that leaves us with   the following summary for ball screws ball screws  are wear resistant with a very high durability   they require low maintenance and they have  a very high load capacity on the other hand   they are a lot more complex and therefore a lot  more expensive they are not flexible and will not   forgive any misalignment into the installation  or any defect into the ball screw will never   be compensated by the 3d printer and they will  operate with a lot more noise since there is a lot   more parts moving inside of them before we bring  back the lead screws for decision making matrix   we need to establish our requirements let me first  put a few images into your heads before we do so music See where i'm going with this what if we could do  the same with the abort non-planner printing is   getting more and more focus and the evort project  does not want to miss that boat big thanks to my   buddy mental one for this fantastic display of the  evorze bed capabilities and big thanks also to him   for all the amazing work he's bringing among the  awards community you'll find a link up here to his   youtube channel so where were we with our story oh  yeah requirements with the non-planner printing in   mind and the fact that the awards printing  area can be quite large with a heavy bed my   picks would be low maintenance high durability and  high load capacity clearly this is now pointing us   in the direction of ball screws let's see if we  can deal with the downsides associated to them   as one of the downside the noise level i think we  are covered by the fact that many of us are using   bird air compressor to cool our parts and this  is much noisier than what a ball screw could be higher costs yes but that depends on the  precision grade that you are selecting   bold screws level of accuracy and precision are  usually tagged with a c0 to c10 grade c0 being   the most accurate and c10 the worst so let's try  to source some high quality for our 3d printers   let's not be too crazy and go conservatively with  a c3 or even a c5 perhaps the price tag associated   with these better ball screws made me fall of my  chair this is serious money when you multiply that   by the amount of screw you need for a triple  z-axis printer that nice dancing is fine but   might not justify that price in order to achieve  the grades c0 to c5 we normally machine them by   grinding a first pass will remove the bulk of what  needs to be taken off and then a precision grinder   will remove the remaining in order to achieve  the right dimension and right finish this process   requires special tooling and is time consuming  hence the price tag that comes with this and it   will be the same impact on price no matter where  you buy them even china sells c3 ball screws for   good amount of money fortunately there is another  manufacturing process that is able to produce ball   screws for much cheaper this process produces  ball screws that are called rolled the rolling   process consists of squeezing a metal piece in  between two larger diameter barrels on which the   ball screw pattern is imprinted progressively  as the metal rod makes its way between those   two giants it is being crushed to shape and  when i say crushed i mean it listen to this it sounds like this crew being formed is  screaming for its life being much faster   and less complex this process will produce screws  with two characteristics first the screw surface   has been cold formed by this crushing process  and therefore has been hardened it is now more   resistant to wear and also more rigid remember  what i told you before about the screw rigidity   the second characteristic is not so positive  squeezing and crushing the material like this has   left a lot of stress into the screw that stress  may even have created permanent deformation that   will now affect the accuracy the runout accuracy  seems to be generally the most affected by this   run out is the actual deviation of  the screw compared to the normal axis   i have purchased some very cheap ungraded  yeah that's right ungraded not even c10 grade   balls cruise to proof my initial evort z-axis  concept after a few prints i quickly realized that   this was not working what was happening is that my  screws were not straight at all they were wobbling   around their axis and due to their rigidity they  were also pulling and pushing the build plate   this situation was causing serious z wobbling that  had a pattern matching perfectly the ball screw   thread pitch i made myself a small installation  to measure what kind of run out i was getting this is probably the worst one of all getting  a six thou of an inch of variation which   translates to point fifteen millimeter looking  at the specification table a rolled c7 grade   ball screw should not have more than point  zero fourteen millimeter of axis deviation   this means this unit has more than 10 times  the allowed amount of deviation that a grade   c7 ball screw can have we could rename the snow  grade c20 20 as 20 bucks here's another one of   the same 12 millimeter ball screw batch that i  bought for cheap money this one is much better   with just under one thou of an inch but still  not cutting it for a c7 grade by looking around i   found multiple articles on the web making mention  of ball screw decoupling devices some very simple   made of flexible material and some very complex  involving expensive air bearings if the industry   is ready to spend large amount of money developing  air bearing decouplers this might mean that a   better quality ball screw is not always the answer  there had to be a solution available somewhere i have tried a few solutions  that were not fulfilling the job   because i do not have access to a precise  manufacturing tool such as a milling or a   lathe i had to rely on my 3d printer for producing  the parts required for my system this system would   have been great but making the parts out  of plastic would not provide the adequate   surface finish for smooth operation and would also  degrade pretty quickly let's get back to basics   we have two parts one that pushes the other one up  our problem is that the part providing the thrust   is oscillating on a plane perpendicular  to the pushing force on the other hand   the part that needs to consume that trust has to  remain stable on that plane the pushing up vector   is the only movement that needs to be transmitted  from our actuator to our carriage what if i was   to imitate the air bearings by using a simple  ball bearing inserted between those two parts   we could use small metal discs such  as magnets for better wear resistance   one of the advantage of using magnets is that the  magnetic field will ensure that the balls gets   re-centered after every deviation move this way  they will not fall off from the dense floor now   because we have our ball screw at the  center of the vertical thrust vector   let's use three sandwich assemblies like that one  to spread the load around the ball screw nut will   attach to the three bottom magnets while the upper  magnets will be transmitting the force associated   to the vertical vector only the ball screw will  be able to wobble as much as it wants without   affecting our carriage let's print the parts and  assemble one unit this assembly feels awesome it   is holding altogether very well thanks to the  magnets but it is also allowing without much   resistance the two pieces to slide one on top  of another after testing and observing the nut   on z axis direction changes i have noticed the  ball screw nut tends to rotate with the screw   although ball screws offer very little friction  it was still enough for the nut to lose a bit of   rotation degree momentarily while the magnets  were working their way back to being aligned   i did not want to introduce any hard attachment  between the upper and the lower part of my system   so i thought of using more magnets magnets  are cool anyways aren't they by installing   two magnets very close and attracting each  other could provide additional resistance   to rotation by extending the distance between the  rotation axis and the magnets we are increasing   the rotation resistance of our assembly without  increasing the resistance to wobble i have added   another pair of those anti-rotation magnets at the  opposite side of my system this would ensure that   the increase in wobbling resistance on one side  only would not transform into rotation deviation   there it was the concept of my wobble wings was  born since i keep referring to the magnets as   a dance floor for the ball bearings why don't  we bring back that little music from before dj the wobble wings have definitely helped me in  getting great printing results using very low   end ball screws the print quality given the  amount of run out on those very rigid screw   is very impressive wobble  wings are a great band-aid   but they will never be as good as high  quality ball screws yet they will allow   you to benefit from low maintenance and  high durability screws for a lot cheaper   i hope you enjoyed this video i have put quite a  bit of effort making it so if you have not done   it yet i invite you to subscribe to my channel  and don't forget to hit the bell to be notified   of new content if you would like to support my  work furthermore you can donate to the paypal   link into the video description thank you for  watching see you soon and meanwhile happy printing

Channel: MirageC

Views: 146,057

Rating: 4.9695783 out of 5

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Id: mqSQhwqSzvg

Length: 18min 26sec (1106 seconds)

Published: Sun Feb 07 2021

Reddit Comments

[u/Dora_Nku]

Given the facts that mk3/mini:

• have much less weight on the z-axis
• aren't using brass but nylon
• keep the servos powered during printing

I'm wondering how much of the artifacts you/anybody are seeing is due to the z-axis choices. You could start by replacing the trapezoidal nut and maybe the z-axis bearings.

[u/pandore60]

The Hevort have 3 z screws, mk3 have 2 and mini have 1. Compensation would probably not work the same way, probably not scalable to 2/1 screw.

[u/OttoGershwitz]

I’m definitely having some z-layer artifacts in my prints. I’ve ignored it to this point because it appears to be a mostly visual defect and not a terribly unappealing one at that. Nevertheless, I found this system interesting. I’ve never measured the wobble in my z axis screws but I would expect them to be of relatively low tolerance. It got me thinking about how this system could be adapted to the prusa.