Time for next step in our YellowPrinter assembly process. Sorry that you had to wait for so long but a lot of thing are going on around here. Maybe not related to our FDM machine but for sure extremely interesting in field of prototyping. Please follow my Instagram if you do not want to miss latest news and if you are interested in combining different ways of prototyping.
Kinematically-coupled 3d printer bed
Next part of assembly we start with assembling ball screws for our heating bed. I decided to use SFU1204 ball screws with length of 370mm. Picture below shows one of three set of ball screw with bearing block which you get in the box.
As it is easy to see, almost all manufacturers of 3D printers use trapezoidal screws and nuts to drive the heating beds. YellowPrinter uses SFU1204 ball screws with a diameter of 12mm and a pitch of 4mm. This fact is related to one of the main features of the printer, namely the so-called “Kinematically-coupled 3d printer bed”. It is a table with three degrees of freedom, which apart from the up-down movement, can also tilt and roll, enabling its auto-leveling as well as the so-called non-planar 3D printing. This means that during printing, the screws rotate both sides, which has serious consequences in the form of low tolerance for clearances, the so-called backlashes. These in the case of rolled ball screws are negligible, and in the case of Tr screws very large and unpredictable. For Tr screws manufacturers use special nuts – backlash nuts, which are to reset this play, but their use causes excessive wear of both: the bolts and the nuts themselves. In order to guarantee the durability of the printer and the stability of its operating parameters, it is necessary to equip it with ball screws and this is why I decided to do during design process of the YellowPrinter. Ball screws are also equipped with two supports (fixed and movable) BK10 and BF10, which perfectly define the position of this element in the printer space.
I had to design plastic parts that will support kinematically-coupled coupled 3d printing bed. As always I keep in mind that my designs has to be simple and use only standard parts that you can get in metal shops but not sacryfying precision of the part.
What is cool in this design – position of the bed is holded in place by neodymium magnets. Thanks to this it operates smoothly and is perfectly aligned so none of vibration can change position of the bed. If you want to read more about magnets just look at this page:
Plastic block is screwed into rail carriage and ball screw nut using metric screws and special spacer that protect them against loosing over time.
Plastic element was printed using Black ABS+ filament and was designed in the way to print it without problem or any doubts regarding to how position them on the table.
As always, in places where it is critical, for properly positioning of 3d printing bed I decided to use ISO 7379 fitted screws.
Smart, cheap and clever solution. I always recommend to use those screws when you have to define exact position of the parts.
I use those screws to screw magnets into holder as well
Here you can see how heating bed lay on the side, perfectly round surface of ISO 7379 screw placed inside plastic holding bracket.
Holder is screwed into ball screw nut by six M4 screws. I used high quality ball screws which are really straight so I didn’t have to use any type of flexture here.
I use 6mm stainless steel plate for 3d printing bed. It is heavy, which is good for strength and inertia (but not for shipping 😊) and what is most important it doesn’t expend with temperature as much as aluminium twin part. To be more precise it expends 10 times less which is very important if you want to keep flat surface regardless operating temperature and if you do not want to spend hundreds of bucks 😉
I screwed into it three balls from standard ball joints DIN 71802 . Simple, precise and cheap solution.
Let’s go back to ball screws. We have two bearing blocks: BK20 and BF10 that have to be fixed to the frame somehow. BK10 is larger because it uses special bearing that is capable of supporting the weight of the screw itself as well as this heavy bed (and all your heavy prints). Thanks to BK10, bearings in stepper motors are safe and free from axial load. Bellow bearing block you can see 3d printed plastic part screwed into the frame using T-Nuts and M5 screws.
Top bearing block BF10 is much smaller but is also really important to properly define position of the screw.
Here the view from above. I think it looks really good and it’s rigid as a stone 🙂
And just a quick views from the front.
All ball joints are distributed by 120 degrees which is important if you are planning non-planar 3d printing in the future. Thanks to this Z stepper motors has to make same amount of steps to tilt or toll printing bed for the certain amount of degrees. It is important because Z ball screws have not the infinite length so I can imagine some use cases that we will want to make really tall part with non-planar ironing on the top. Without of 120 degree distribution of ball joints you could fail with this task because of lack of Z range. And it looks cool so, don’t blame me for this attention to details. They are important for me 😉
Ok, I have to be honest with you. Following design is not smart or simple but for sure is extremely overengineered. But it works soooo smooth. I’m talking about spool support/holder.
Ball bearings + fitted screws = no compromise
Spool turns like a dream 🤯
We have to make two of them because we have place for two spools inside the frame.
Let’s go back to something more important. Bottom plate is definitely one ot those parts because it holds whole mass of the printer and it has to provide enough air flow to prevent electronic from overheating.
I designed 3 places for fans but after first tests it seems that printer doesn’t need them actually.
In the 3mm stainless steel plate we have additional cutouts for stepper motors and power supply because otherwise we could have problems to fit them inside the frame which size is defined by aluminium extrusions.
YellowPrinter stays on four wheels with soft skin that will not scratch your flor. Once you have set up the printer where it suits you you have to block the position of the wheels doing black lever. Thanks to this it won’t roll or rotate around Z axi.
Wheels are screwed directly to the bottom plate into pretaped holes.
Result of 3rd step
And here we have result of 3rd step of assembling process. Now it looks pretty much like 3d printer 😊
See you in the next one 😉