There are many incarnations of the Prusa i3, the one used in this example is but one of them, accordingly there may additional or redundant steps in this guide. Please familiarise yourself with the steps in the guide and establish if it is relevant and possible on your printer before choosing to continue.

The plethora of Prusa i3's available makes assuring compatibility hard.

This guide assumes the following:

  • 8mm Rods using LM8UU Bearings (or similar).
  • 45mm Rod Spacing, ~15mm Belt Spacing.
  • One bearing on the top rod, two on the bottom, or the other way around.
  1. We are going to remove the old carriage and HotEnd.
    • We are going to remove the old carriage and HotEnd.

    • Cut the cable ties holding the LM8UU linear bearings in the X carriage.

    • Cut the cable ties holding the two ends of the belts in place.

    • Remove extruder and carriage assembly.

    • Keep the old assembly away from bed to work without risk of bed damage.

  2. Gather the nozzle, heater block and heat break:
    • Gather the nozzle, heater block and heat break:

    • Nozzle

    • Heater Block

    • Heat Break

    • Before starting work on your heater block, make sure that you'll going to screw your nozzle into the correct side.

    • You should be looking at the side of the heater block with three holes in it

    • Screw in the nozzle all the way into the heater block. Don't worry about tightness yet.

    • Then, unscrew the nozzle by a 1/4 of a turn. This will leave a little space to tighten after screwing in the heat break.

    • Screw in the heat break until it touches the nozzle.

    • Tighten the nozzle against the heat break. No need to over tighten, we'll be hot-tightening later.

    • Double check that your nozzle is still almost flush with your heater block.

    • If there is significant space between the nozzle top and the heater block you should re-adjust your nozzle and heat break to eliminate that space.

    • Gather the parts you'll need to install the thermistor:

    • Thermistor Cartridge

    • The Smaller, 1.5mm Hex Wrench

    • M3 Grub Screw

    • Heater Block

    • Slide in the thermistor cartridge.

    • You can slide the cartridge in either direction so that the wires extend from one side or the other of your heater block. Think about how you'll be organising your wiring to decide which makes sense for your printer.

    • Screw in grub screw until it just touches the thermistor.

    • Tighten M3 grub screw by an 1/8 of a turn.

    • Do not over tighten the screw. The thermistor cartridge is soft, and you might deform it if you over-tighten the screw.

    • Gather heater block, heater cartridge, 2mm hex key and M3x10 screw with washer:

    • Heater Block

    • Heater cartridge

    • 2.5mm, Hex Wrench

    • One of the longer M3x10 Screws and M3 Washer

    • Slide in the heater cartridge. Typically you'd want the wires to come out the same side as your thermistor wires.

    • Tighten the M3 x 10 socket dome screw (with the M3 washer on it) with 2 mm hey key until the clamp deforms slightly (as shown in the second picture).

    • Gently tug the heater and thermistor wires to check they won't slide out

    • Thread the M3 grub screw into the pinion gear slightly so you don't lose it

    • Slip the pinion gear onto the motor shaft with the grub screw facing down, towards the motor.

    • Slide it about 3/4 of the way down the shaft and tighten the screw.

    • Gather the motor

    • Titan body with the hob gear placed into the bearing.

    • I3 x axis mounting part

    • 2mm hex key

    • M3 x8 mm screw

    • place the m3 screw in the titan body and fasten it into the motor through the i3 x axis.

    • At this stage the assembly should look like this. (Image 2)

    • Make sure at this point that the pinion gear and hobb shaft acetal gear line up. If not adjust the pinion gear up or down as per step 13

    • Gather:

    • Titan Aero heat sink

    • Assembled Heater Block

    • Thermal Paste Sachet

    • Apply the thermal paste to the heat break.

    • You don't need to use the whole sachet

    • Screw in heat sink and tighten by hand—no need to over-tighten.

    • Wipe away any excess thermal paste.

    • Don't use thermal paste on any other parts of the HotEnd.

    • Wash your hands after working with Thermal Paste

    • Insert the 9mm diameter bearing into the the back of the Aero heatsink, this is designed to be a tight fit but you should be able to push it in by hand.

    • Gather:

    • Filament Guide 1.75mm

    • PTFE Tubing

    • Cut a 23mm length of PTFE and insert it fully into the top of the heatbreak.

    • To reduce the possibility of jams, ensure that both ends of the PTFE are cut squarely and the ends are not deformed, we recommend using a sharp knife rather than scissors for this.

    • Slide the 1.75mm filament guide over the protruding PTFE. The flat side of the guide should be flat with the back of the lid.

    • Ensure that the guide sits flush against the Aero sink. It is preferable to get the tubing too short, rather than too long

    • Gather:

    • M3x30 screws

    • M3x25 Screw (the shortest M3 screw)

    • Shake-proof Washer

    • Assembled Body

    • Assembled Lid

    • The mid-sized 2.5mm Hex Wrench

    • Press the heatsink onto your extruder. It's a bit of a tough fit, but it will all fit in.

    • It will not be flush like the plastic Titan lid would be, as the heatsink is flat on the backside. It is intended that there will be small gaps between the extruder body and the heatsink where the old lid would have fit in.

    • Screw two of the longer 30mm M3 screws you're using on the two holes on the lid. (thumbscrew side)

    • Because the extruder is only attached to the motor by one screw at the moment, you may need to wiggle it a little to get them to thread into the motor.

    • Screw your short screw into the lower right hand corner of the lid.

    • This screw goes into the brass insert on the back of the extruder body, not your motor.

    • Slip the shake-proof washer onto the screw with the blue patch lock on it.

    • WARNING - this screw goes through the bearings and so when it is tightened it creates an axial load on the bearings, if this screws is overtightened even once it may cause permanent damage to your bearings which will result in bearing failure -PROCEED WITH CAUTION.

    • Screw in this screw until it is finger tight and no more.

    • The shake-proof washer will prevent this screw from coming loose.

    • There may be some slight visual misalignment of the idler and teeth, this is due to an inconsequential machining error of the filament drive gear. The toothed portion of the shaft is wide enough to accommodate this minor misalignment with no effect on how the teeth engage the filament.

    • If you find that the screw is not biting it may be due to the teeth on the slip proof washer protruding slightly which increases the thickness, try to flatten out the teeth before trying again.

    • Try to rotate the large acetal gear to see if it moves smoothly.

    • If it is hard to rotate, check the position of the steel pinion gear, it may be too far forward. Adjust it so that it is flush with the front face of the acetal gear and try again.

    • If this does not solve the issue, then the screw with the shake-proof washer on it may have been overtightened. If loosening this screw allows the acetal gear to run smoothly then the screw has been overtightened and permanent damage may have been caused to the bearings; seek replacement bearings if this is the case.

    • If the large gear exhibits “backlash” (there's play between the large plastic gear and the metal one on the drive shaft), loosen all screws on the lid and rotate the body such that the gears fully mesh.

    • Re-tighten the screws as described in the previous steps.

    • Gather:

    • Aero Asembly

    • 4x 2.9x13mm Self-Tapping Screws

    • 40mm Fan

    • Place the fan on top of the heatsink fins and use the 2.9x13mm self tapping screws to secure it in place.

    • Do not over-tighten the screws as this can crack the fan.

    • Make sure that there is adequate airflow over the heatsink. If your printer setup blocks the fan, you'll have printing problems.

    • If you're printing 1.75mm filament, you can guide it a little better by putting a length of PTFE tubing in the top of the idler lever

    • Press the tubing into the lever.

    • It may be a very tight fit. You can file down the tube if it helps.

    • The whole X-Carriage can now be offered up to the parallel rails.

    • Locate the LM8UU bearings into the bearing slots on the rear of the carriage.

    • Thread the 2.5mm cable ties though the small slot, they should re-appear on the opposite side of the bearings.

      • Secure the cable ties tight to hold the X-Carriage in place.

    • Release the X-Belt tension pulley then loop the belts around the teardrop anchors and back on themselves so that the belt teeth lock against each other.

      • Slide the belt loops all the way into their respective slots on the back of the X-Carriage.

      • Try to get this as tight as you can, then use the X-Belt tension pulley to achieve final tension required. You may want to refer to the documentation that came with your machine for this step.

    • Gather the Fan mount

    • Radial fan

    • x2 40mm screws

    • Fasten the two screws

    • Plug in your HotEnd where the old one was plugged in. Same with the thermistor, cooling fan, and motor

    • Update your firmware by following the Aero Firmware Guides

Finish Line

One other person completed this guide.

Attached Documents

Gabe S.

Member since: 08/08/2017

13,090 Reputation

41 Guides authored


It would be helpful if there was a link to your example replacement X carriage for Prusa i3’s having the required x carriage 45mm Rod Spacing, LM8UU bearings and ~15mm Belt Spacing.

Jonathan - Reply

There seems to be a step missing - Step 22 shows the extruder complete with the the pressure arm and tensioning screw but there are previous steps which describe this part of the assembly

Chris Wallace - Reply

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