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
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link into the video description thank you for watching see you soon and meanwhile happy printing