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 also fits for the MK2 (non 2.5) version!
I will reorganize this project asap to lower the confusion.
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 which 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 kinds of projects.
Don't worry if the bolt sits too loose in the arm. The provided spacer goes between arm and wheel. It keeps the wheel from having contact with the arm and locks the bolt when you tighten the nut. Both, the nut and the spacer press against the bearing on its inner ring. Therefore, there is a continuous mechanical tension keeping everything locked in place without hindering the rotation.
I have to update the pictures and the video at some point!
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 the spool's width differed. Adjusting the arm on the frame was tedious, and at some point, one arm even broke.
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, other 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 download 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.
Now there is the Original Prusa i3 MK3 out for sale which has 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 of making this arm better. I read every single 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 as well. These arm derivates are not tested by me, 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 your machines frame and I try to provide you the best experience.
You can find these arms here: https://www.thingiverse.com/thing:2356183
Please also take a look at my other designs, printer parts, and tools.
If you like to support me and my work, please consider following me on:
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.
Thank you very much and happy printing!
10% for all small parts, 20% for the arm, and optionally 100% for the bolts.
You'll have to print the following parts in the following quantities.
First off, choose an arm version:
Then the rest of the parts:
- 4x Mark2_AxisNut.stl
- 4x Mark2_SpoolHolder_HexStyle_Tire.stl
Optionally you may want to print the SpoolHolder_HeyStyle_PressingHelper.stl to press the bearings into the printed tires.
Note: users have reported that the bolts are breaking easily during the assembly. To avoid this from happening I highly suggest that you print them with 100% infill!
To make the spool holder work, you need four 608 bearings for one set, which you can get from a local skate shop or from Amazon (by using the provided links you can support me and my work):
You often find eight bearings inside a set, which is enough for two spool holders.
The spool holder is designed in a way, that you can use all parts on both sides of the holder and also switch the axis bolts from back to front and vice versa. If you like to have the "smooth bedside" oriented to the outside, you have to mirror the right arm along the x-axis.
For the infill, I used a honeycomb pattern because it matches the hexagonal style of the holder and my filament is quite translucent. Honeycomb gives good mechanical support in general.
I printed three perimeters for all small parts. Four parameters were used for the arm and six perimeters for the wheels to avoid infill there. Each part has four top and bottom layers on my prints - except for the arms, where I printed without any top and bottom layer to achieve the honeycomb look.
Even though I printed my final design in 200µm (0.2 mm) layer resolution, I also tested 100um (0.1 mm) for the wheels. That gave them a smooth finish, but it did not affect the mechanical properties. You can also use smaller layer heights for the bolts to make the threads more smooth.
Bolts, Nuts, and Spacer
The bolts, nuts, and spacer should fit nicely with a small clearance. Nevertheless, it can be hard to get the nuts screwed onto the bolts the first time around. So give them a gentle press and try to find the sweet spot where the threads match up.
For the Mark 1, I used a small amount of PTFE grease on the threads to make handling easier (see affiliate link below).
The Mark 2 and Mark 3 have more clearance between the threads of the bolts and nuts. Therefore, you should be fine even without PTFE grease.
However, if you still want to use grease, here is my recomendation:
Finish Line Fett Synthetik Casual Grease
This PTFE based grease is also very useful for other mechanical components.
- Put one bolt into one of the arm's determined hole and press gently. The bolt should fit nice and tight.
- Put a spacer on the bolt and move it all the way to the arms surface.
- After you assembled a wheel with a bearing (see next section) tighten everything down with a nut-wheel. However, don't use your force! This is just molten plastique after all!
Bearing and wheel assembly
Print one single wheel/tire first! Then check, if you can press in the bearing. Bearings and wheels will always come with variances. What works for me, might not necessarily work for you. If you have a hard time to press fit the bearing (I mean a really, really hard time - I took the back of my screwdriver to press them in) into the tire, scale the tire up by a tiny amount (something of 0.01%) and try again.
I've printed the tires with 0.1 mm layer height for best results!
The wheels are modeled with a small clearance. Therefore it is not always easy to press the 608 bearings into them. But here is how you will succeed:
If you are printing Mark 2 or newer, proceed to step 2!
On the Mark1, the wheel has a wider side (asymmetrical wheels). This side is oriented towards the holder's arm. Lay the wheel with the larger side flat on a table.
Place the bearing on the wheel. Try to push the bearing slightly into the wheel. It is enough if the bearing just barely sticks.
Flip the wheel with the bearing around and press with your hand hard on the wheel's backside. The bearing should pop in and be level with the wheel outer edge.
- Place the pressing-helper tool onto the bearing and flip the wheel again, so that the pressing helper rests on the table. Now you can push again hard onto the wheel, and the bearing should pop completely into the wheel.
The pressing helper tool has a smaller diameter than the wheel's inside diameter. Therefore, it should be easy to remove.
Starting with the Mark2 the wheels become symmetrical. However, there is still an entrance side for the bearings, but it should not affect functionality if you put the wheels in reverse onto the axis.
Mark1: Be aware that the wheels are asymmetrical. They have a wider side regarding diameter. This larger side should be oriented towards the arms.
This spool holder was designed in Autodesk Fusion 360 and optimised to be printed on an Original Prusa i3 MK2s - because that is what I have. :-)