Upgrading Kossel Carriages

After some research and testing I've come to the conclusion that current rollers on my kossel mini where hindering my printer's performance. It so happens that a single bearing design like the one I have is not the best solution for my printer.





These single bearing wheels dont properly grip onto the 2020 aluminum extrusion and cause the carriage to tilt back and forth whenever the printer moves the right way. This has caused my prints to come out about 1 mm too large in one dimension. Circles are not round and squares become rectangles.
I was looking to replace it with some of these rollers but I am concerned that they might not work properly. On the website it says that the outer diameter of the rollers is 15.5 mm. My current wheels happen to be about 20 mm.



On top of that the new bearings also have an inner diameter of 3 mm, they use 623 bearings. My current wheels screw onto a M5 screw. My concern is that if I was to replace the old wheels with the new rollers that the rollers would be too small to grab onto the 2020 extrusion.



I'm not sure if an M3 bolt would even work on my carriages. If anyone has had experience with this kind of conversion I would greatly appreciate it.

One ugly (but working) hack would be:

If the M5 bolts are sticking out long enough on the backside you could use something to tighten them there, like a steel wire or cable, a small rod of some kind (thin allenkey, M3 threaded rod...), and some cable ties.
Put the wire between the bolts and tie it together somehow, stick the rod in there and start twisting until you get the tension you want and the fasten the rod along the wire with the cable ties.

Should be enough at least so you could print other carriages accurately enough that can use other rollers.

Like these perhaps: [www.thingiverse.com]

Rollers like those black delrin V rollers you linked to came with my mini kossel kit from T3P3 and they work well for me.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

DC42 uses these rollers too and remixed a carrier to match 2020 extrusion.

You could try to print it with your wobbly carrier, maybe have to align the part on the slicer table in a direction, where the 1mm difference wouldn´t matter much.

You can also design a similar roller that matches your 5mm thread and diameter requirements. Although, you don´t want to use oval rollers, but with a spring loaded clamp it might work too.
-Olaf

Hello mrmuffin,

I have the same printer as you. I fixed your particular problem by implementing a tightening mechanism on the back side (as others here also suggested). Mine features a spring. It is not a particular sophisticated design but it does give a firm grip. Maybe you can use it for inspiration or if you are interested I can of cause give the files.



As you can see my printer is currently out of order because I have been unable to fix a bigger problem with the K800. As soon as I try to print anything just a little big and wide it will after some time disconnect it self from the magnets at the effector/spider end. I believe it is a design flaw. You can read more about this here: [forums.reprap.org]

I want to redesign the carriages and effector for use with rod-ends and get rid of the magnets, but I have too many other good projects on my plate these days. If you do decide to make a big makeover I will be very interested in your findings so do not hold your self back from posting.