Update 2022/04/19

After a long time, one small update:
You can now find a remix of the arms for the 2020 VSlot aluminum extrusions I made:

https://www.thingiverse.com/thing:5359057

Update 2019/01/10

Added an image showing in which position the single parts should go.

You can also explore the object interactively on A360 following this link.

https://a360.co/2DbpG7G

Update 2018/04/20

IMPORTANT NOTE: If you have an Original Prusa i3 MK2.5 or an MK3, print the Mark 3 version! Due to the redesigned extruder unit on both versions, the print head will hit the Mark 2's mounting on high Z positions. The Mark 3 is specifically designed to avoid this and fits the MK2 (non-2.5) version!

Update 2018/04/14

I added a revisited version of the screw/bolt, calling it Mark3_SpoolHolder_Bolt.stl, and of the spacer, calling Mark3_SpoolHolder_Bolt.stl. It is a cleaned-up version that fits better into the spool holder arm's holes. Many complained that the bolts are a pain to get into the arm's hole, and I heard you loud and clear. However, sometimes it's hard to get the time reserved for these projects.

Don't worry if the bolt sits too loose in the arms now!
The provided spacer goes between the arm and wheel. It keeps the wheel from contacting the arm and locks the bolt when you tighten the nut—the nut and the spacer press against the bearing on its inner ring. Therefore, continuous mechanical tension keeps everything locked in place without hindering the rotation.

This SpoolHolder's history goes far back into mid-2016 when I received my first Original Prusa i3 MK2 with its terrible spool arm. It was a pain to switch spools, primarily if their width differed. Adjusting the arm on the frame was tedious, and one arm even broke at some point.

Therefore, I looked on Thingiverse for alternatives and found the top-loader spool holders like mine ended up being too. However, all of these designs back in the day had some flaws that bothered me — for example, some needed tools; others required hardware like real screws. However, the most significant weakness was the design of the mounting mechanics for the frame assembly. There was always that tight fit and the force one needed to clamp the arms onto the frame.

So I designed Mark 1 of the arm, which you can still see on most of the pictures and downloads as a legacy zip archive.

I was surprised by the success of my design throughout the community. However, this supported my bad opinion of the stock spool holder arm.

The Original Prusa i3 MK3 is out for sale, with some significant geometrical changes. My Mark 3 version of the arm takes them into account and also fits nicely on an MK2 and MK2S (most probably even on an MK2.5, but mine is still not delivered).

I hope you like my continuous efforts to make this arm better. I read every comment coming from you and try to react as quickly as possible. Many thanks also to the incredible Thingiverse community for providing a lot of derivates of my designs for other machines and purposes.

I also have a side project where I release arms for other machines. I do not test these arm derivates because I don't own all of these printers. The process is that you send me your request for such an arm derivate and the measurements of the frame of your machine, and I try to provide you with the best experience.

You can find these arms here: https://www.thingiverse.com/thing:2356183

Please also look at my other designs, printer parts, and tools.

If you like to support me and my work, please consider following me on:

• Thingiverse
• MartinMajewski.net
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Sending a tip over Thingiverse is much appreciated and will provide me with coffee to stay productive.

Please also consider buying your next gear via one of the affiliate links found inside my Thingiverse project pages or directly over the following links.

• Amazon.de
• Amazon.co.uk
• eBay Germany
• GearBest.com

Thank you very much, and happy printing!

Martin