Replace the X-axis Idler on Your Prusa I3

Introduction: Replace the X-axis Idler on Your Prusa I3

About: Hi! I'm a technology nut, dabbling in everything from mobile electronics to computers to 3D printing to website design and hosting. I work for Gridpoint, an energy management company, and I enjoy riding mot...

I have enjoyed my FolgerTech Prusa i3 3D printer. It has presented very little trouble and taught me a great deal about 3D printing, parts design and troubleshooting... in a good way.

This Instructable walks you through replacing the printed X-axis idler with a couple bearings to eliminate the wear you see in the first photo.

Here's what you'll need to get started:

  • 1x M3x20 socket-head bolt (already installed in your printer)
  • 1x M3 locknut (also in your printer)
  • 2x M3x6 flat washers
  • 2x F623ZZ Flanged bearings (3x10x4)
  • 2.5mm hex tool (Allen wrench, screwdriver, etc.)
  • Hemostat or small, long needle-nose pliers
  • Scotch tape (any brand really...)

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Step 1: Hardware Assembly

Here is how the hardware assembles.

The two flanged bearings face together to form an idler pulley that is a perfect fit for GT2 timing belt. The washers go on both sides to separate the flange from the surface inside your X-carriage, and the nut and bolt holds it all together.

Bolt > Washer > Bearing > Bearing > Washer > Locknut

Step 2: Remove the Old Idler

The old idler is easily removed by using the 2.5mm tool to unscrew the M3x20 bolt from the X-axis end. Be careful not to lose the M3 locknut from the back, as it will be used later. The GT2 belt can be left connected to the X-carriage. My printer had a 10mm bearing with two printed covers that formed a 15mm idler pulley. These can be discarded or kept for another use.

Step 3: The First Washer

Place the M3x20 bolt slightly into the hole, just enough to place the first washer onto it. I used a hemostat to perform most of this work, but small, long needle-nose pliers should also work fine.

Note that the washer probably has a rougher, or sharper, side and a smoother side. This is from being machine stamped. I prefer to install them so that the smoother side is toward the bearings, but it really shouldn't make a difference.

Step 4: The First Bearing

Repeat the same technique with the first bearing, making sure to install it so that the flange is nearest the head of the bolt. You will need to push the bolt in a little farther to go through the bearing once it in aligned.

Step 5: The Second Bearing

Again, repeat the same technique with the second bearing, this time making sure to install it so that the flange is away from the head of the bolt. You will need to push the bolt in a little farther to go through the bearing once it in aligned.

Step 6: The Second Washer

Here's where frustration usually begins. The remaining space in the hole is too small for any tools to hold the second washer, and it is nearly impossible to get it aligned with the screw when all of the parts are vertical.

I will spare you the trouble by teaching you a very handy trick!

Grab a small piece of transparent tape and stick it to one side of the washer, leaving the hole unobstructed. You can now use the tape as a tool to put the washer just where you need it and push the bolt through the hole.

Wow! that was easy :)

Step 7: Install the Locknut

Here's where the hemostat really comes in handy. Most pliers are too thick to get between the X-axis end and the printer frame, so using tweezers or a hemostat is suggested.

Just put the nut behind the X-axis end and thread the bolt into it. Go ahead and tighten it pretty snug.

Step 8: Almost Done

Now you can step back and inspect your work.

I suggest using your finger to roll the newly installed idler, making sure it isn't binding or wobbly. If it is good, disconnect the idler end of the GT2 belt from the X-carriage and loop it around the new idler. You'll not that there is a little extra belt now, since the idle diameter was reduced from 15mm to 10mm. This does not pose a problem with your alignment or printing, but you'll need to trim off the extra length of GT2 belt once you're done to avoid noise from it rubbing against the other side of the belt behind the X-carriage.

Hope you enjoyed this Instructable and can put the tape trick to good use on other projects!

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    4 Discussions


    5 years ago on Introduction


    I have been asked that same question several times... I installed the X-axis ends so that the stepper motor would be on the right, nearest the majority of my wiring, and I didn't want the back of the stepper to protrude forward. Thus, I had to install the ends in this orientation. The 5mm nuts are secured with epoxy.

    I intend to redesign both x-axis ends at some point to relocate the stepper behind the frame, and integrate photo-interrupt end stops.

    Thanks for the inquiry :)


    Reply 5 years ago on Introduction

    Makes sense. I've seen your build pictures on - nice job on the wiring. We used the same braided sleeving and shrink tube on our i3 builds. Makes everything tidy.



    5 years ago on Introduction

    Just wondering why you have the M5 nuts on the top vs the bottom on your X-Motor and X-Idler, i.e. they are upside down compared to the usual Prusa i3 build. Though mine were a press fit into the plastic gravity helps keep them in place.