Go Back to Instructions for Original i3 Upgrade Kit

1. Preparation

1.0 Introduction


  • Since you are upgrading an existing Original Prusa or clone, if you have experience in assembling Original i3, that’s perfect! if not, don’t worry, follow this guide, everything will be smooth and fine. Also feel free to contact us.
  • Disclaimer: We share these guides to make your experience as smooth as possible. However, you are responsible for your upgrade, assembly, and any damage you cause to your hardware.

1.1 Check before Upgrade

Make sure you have the following tools and things available:

  1. Your Original i3 
  2. 4mm, 3mm, 2.5mm, 2mm, and 1.5mm hex keys for disassembly, you can find one 1.5mm hex key in our accessory pack if you do not have one.
  3. A cutting tool for cutting zip ties 
  4. Your Prorifi3D upgrade kit 
  5. A box for keeping the screws 
  6. Printed parts from our GitHub
  7. Open the Original Prusa i3 MK3S kit assembly Guide for reference(https://help.prusa3d.com/en/guide/1-introduction_24976)
  8. Make sure you have a flat surface such as a polished marble top, or a big ceramic tile. This surface will be your base level.
  • Make sure the filament is unloaded before the upgrade. You will have to turn the printer over during the process so the filament spool and spool holder need to be removed before the upgrade.
  • Make sure your printer is Not powered, the nozzle and heated bed are fully cooled to room temperature! Otherwise, you may injure yourself!
  • Make sure both ends of the power cord is unplugged to allow the printer to be placed sidewise.
  • For disassembling the Original i3 you can refer to this guide:https://guides.bear-lab.com/Guide/02.+Preflight+check+and+disassembly/42?lang=en

Table of Content

2 Assemble the Main Frame

3 Disassemble your Original i3

4 Build the Machine

5 The Dual Belt system

6. Replace the E motor

7. Electronics

8. Install the control box

9. Spool holder

2 Assemble the Main Frame

2.0 Check before the assembly

  • Make sure you have the following parts: All the aluminum profiles, your Hex Keys, Accessory Pack 1
  • A measuring tool for screws, you can find the STL file here
  • Make sure you have a flat and big enough surface such as a polished marble top, or a big ceramic tile. This surface must be able to fit the longest Aluminum profile in any direction. Clean the surface to remove any dust or small debris.
  • Check the inside of the two longest beams, there should be two plastic plugs been pre-installed at both ends. If not, please contact us.

2.1 Assemble the gantry

  • Take the left and right vertical beams (the longest ones).
  • Check the beam and make sure you have the correct orientation. The side with chamfers should face downward, against the flat surface. The side indicated by the blue arrow should face outward.
  • Take the short 4040 profile and place them as shown. The side with Chamfers needs to be facing down, against the flat surface.
  • Use one 2040 beam as the jig, place it as shown
  • Note the orientation! The 4040 should on the side with 3 screw holes. 
  • Use M5*45 screws from Accessory Pack 1 and tighten the screws as shown on both sides. Note the Upper one is for adjustments. Do not fully tighten it.
  • Adjust the upper screws on both sides evenly to make sure the 2040 beam used as a jig can just about move freely up and down at the open end of the gantry

 2.2 Assemble the base

  • Take the rest 4040 and 2040 profiles
  • Check the beam and make sure you have the correct orientation. The side with chamfers needs to be facing down, against the flat surface. The sinkholes should face out as the green arrow shows. The front and rear 2040 profiles are the same, just make sure you have the correct side facing out and chamfered side facing down.
  • Place them as shown. Note that for the 4040 profiles, be careful with the position of the screw holes. Make sure you have the correct relative position!
  • Insert 2 T-Nut in the bottom inner slot of the 4040 profile, do this for both left and right 4040 profiles. These will be used to fix the footpad later.
  • Insert 6 T-nut in the upper slot of the inner side of the rear 2040 profile and insert 1 in the lower slot.
  • Insert 6 T-nut in the upper slot of the inner side of the front 2040 profile and insert 2 in the lower slot.
  • Double-check if you insert the correct amount of T-nuts and they are in the correct position!
  • Now we can build the base. Make sure both sides are aligned. You can use a piece of a flat surface, such as the jigs you printed to help you align these beams.
  • Take the M5*25 screws, you need 16 of them. Use them to fix the front and rear profiles. Make sure you tighten them in a diagonal order. When tightening the screws, do not fully tighten a screw before you tighten the next one. Screw them in evenly. Make sure all the aluminum profiles are not moved or have gaps with the flat surface. This is very important!
  • Turn the base over and install the footpad. Use M5*10 button head screws to fix them. Turn the base back and if it shakes, adjust the screws on footpads until they are all in the same plane.

2.3 Assemble the mainframe

  • Check if the T-nuts are correctly inserted again before this part!
  • Make sure the reference surface (the side with chamfers) for the base is facing downwards, against the flat surface. At this point, the reference surface should be flat and directly touching the flat surface with no gaps between.
  • Take the gantry, make sure you have the correct orientation!
  • As you can see, on the lower end of the gantry there are 4 screw holes on each side, and they are shaped differently. Viewed from one side, the upper left one is the pinhole. And the 4 screw holes match the holes on the base.
  • Carefully match the gantry and the base. Take a shoulder screw(the one with steel case) and insert it into the upper left pinhole to the bottom, slightly tighten this screw. It is ok if you feel some force or resistance when inserting this screw.
  • Do the same for the other side. Now the position of the base and gantry are locked and make sure the gantry stands against the flat surface, there should be no gap between the gantry end and the surface, or the base and surface.
  • Now the gantry is perpendicular to the base, take the M5*70 screw (the longest normal screw) and install them to the lower right hole on each side. 
  • Take 4 M5*50 screws to fill the rest screw holes. 
  • Now you should tighten the screws evenly in a diagonal order. Note that the shoulder screw is for positioning thus cannot be tightened much. Make sure the rest M5 screws are fully tightened!
  • The main frame is now finished, if perfectly assembled you should see no gap between the base and the flat surface you have. And if you shake the gantry, there should be absolutely no relative movement between the gantry and the base.

2.4 Prepare the next phase

  • At this point, we just finished the main frame and are moving to the next phase. It is time to take the accessory pack 2. There are many screws in it so be careful. You will find screws with the socket head cap, the button head cap, the flat head cap, and the countersunk screws. You can use the measuring tool to help you classify the screw.
  • If you found anything confusing or are not sure, you can always reach out to us!

3 Disassemble your Original i3

  • For disassembling the Original i3 you can refer to the bear guide:https://guides.bear-lab.com/Guide/02.+Preflight+check+and+disassembly/42?lang=en
  • The Bear upgrade is also a decent frame upgrade and we took some inspiration from it despite using a completely different approach and mechanical design principles.
  • The part you need to keep and reuse later:
    • The entire X-axis and E-axis
    • The PSU
    • The Y-axis, including the rod, but without the belt system
    • The Control board and the control box
    • The Z rods
    • The Z motors, if you did not get the full upgrade kit
    • The LCD
    • The Control Box

4 Build the Machine

4.0 Screws and nuts

4.1 Z-axis

  • Let us start with the Z-axis first. Take the Z rod from you recycled from your Original i3 and the left and right Z Motor Mounts
  • First, put the Z motors into the motor mounts firmly and install the steel rods first. Z motor here is used as a jig.
  • Then, remove the Z motors. Make sure the rod stays firmly on the motor mounts and the bottom end of the rod does not stick out the printed parts.
  • Insert flat head M5*10 on the Z motor mounts, then hook T nut on the screws.
  • Slide the Z motor mount into the slots from the top. Make sure you have the correct orientation.
  • Press the printed part sideways against the profile and slide them to the position where printed parts are just about to touch the base, as shown in the picture below.
  • Tighten the screws to make sure it does not move freely. Do this for both left and right z motor mount.
  • Now carefully reinstall the X-axis, be careful with the linear bearings! You should lower the X-axis evenly. Do not proceed if you feel too much resistance or force, the linear bearings are very very easy to break!
  • Take the Left and right Z top, insert M5*10 flat head at the front and M5*12 flat head at sides. Hook hammer nuts on the screws and then install the Z top. The Z steel rods should be in the slots on the Z top and will not fall out. Then tighten all the M5 flat head screws.
  • Use M4*5 set screws to fix the back end of the Z top.
  • Do this for both left and right sides.

4.2 Z motors

  • Now it is time to install the Z motors. Make sure you have the correct Z motors. The one with shorter wires should be closer to the control box! (which is at left when viewing from the front)
  • Put the motors in from the bottom. Rotated the leading screw evenly to allow the motors to be in position. The printed parts have slots for wires to pass through. Make sure no wires are clamped or twisted.
  • Use M3*12 screws to fix the motors. You should tighten the screws evenly in a diagonal order.
  • Install the Bottom cover at the end of the gantry beams and fix them with M4*5 set screws on both left and right sides.
  • Collect the wires and proceed to the next step

4.3 Y-axis

  • Take the 4 Y rod holder, insert the square nut and pre-install the M3*12 set screws (the longest one) Make sure you have the correct orientation of the set screws
  • Install Y rod holder, be careful with the orientation. 
  • Use the positioning jig and hex key to slide the T nut to the correct position. Place the T-nut to where the screws holes hould be. Do this for all 4 positions.
  • Now carefully put the entire Y-axis back from the top. Slide Y carriage to make sure the movement is smooth.
  • Now use the M5*10 button head to fix the left 2 Y rod holders. If you feel the T nut is not in position, try using the hex key to help align the T-nuts first.
  • Slide the Y carriage back and forth to make sure the right Y rod is in the ideal position.
  • Tighten the screws of the 2 right Y rod holders
  • Slide the Y carriage back and forth and check if it moves smoothly. If not, untighten the screws on the right 2 Y rod holder and repeat the previous 2 steps to make sure the Y rods are parallel to each other.
  • Now take the Y motor mount and Y motor, first install the Y motor to motor mounts use M3*14 screws, make sure the wire comes out from the bottom
  • Now insert 3 socket cap M5*10 screws into the Y motor mount.
  • Adjust the pre-inserted T-nuts to an ideal position, hook the T-nuts with the M5 screws on your Y motor mount.
  • Slightly tighten the screw to make sure the printed parts do not fall off, make sure it can still move freely
  • Use the jig as shown to position the Y motor mount.
  • Press the printed part against the base and tighten the screws.
  • Take out the  Y-Belt-Idler-A, Insert one nylon nut as shown


  • Insert another nylon nut here
  • Insert 4 socket cap M5*10 screws. Hook the T-nut with the screws and then use the motor jig to position the idler.
  • Press the printed part against the base to make it parallel to the reference surface and tighten the screws.

4.4 The control box

  • Take the Electronics-Cover-Holder-C, insert 2 M5*10 button cap screws and hook the hammer nut on the screws. Install them at the back of the left gantry beam. Note the printed part surface should be at the same level as the base.
  • You can reuse most of your old control box. However, there are some additional parts.
  • Insert the hex nut into these positions and change the screws to M3*15 at these positions.
  • Insert one flat cap M5*8 screw, then hook 1 hammer nut on the M5*8 screw.
  • The final control box should look like this.

4.5 PSU

  • Take the PSU and PSU-Holders, Install the holder on PSU with M4*8 countersunk screws
  • Install M3*6 screws here and hook the M3 hammer  nut at the back If you have the black PSU
  • Insert M3*8 screws here and hook the M3 hammer nut at the back If you have the old version silver PSU. Replace the old bottom cap with the new one so that wires can go from the bottom.


  • Install the PSU on the frame, make sure the screws are tightened properly

4.6 LCD

  • Take the LCD supports, the installation for LCD support is the same as original ones. You can refer to the guide here: https://help.prusa3d.com/en/guide/6-lcd-assembly_172423
  • Connect the electronics first, make sure you have the correct wires.
  • Use the M5*10 button cap screws and hammer nut to fix the LCD on the main frame. The wires should be able to bend and go through the bottom of the base.

4.7 Endcaps

  • Install the endcaps with M4*5 set screws

5 The Dual Belt system

  • Take the Y-Belt-Idler-B, and accessory pack 3.
  • Insert the pin into the Y tensioner block about 2/3 as shown and be careful with the plastic, do not break it.
  • Put the bearings on it as shown. Make sure the bearings have the correct orientation and order.
  • Insert the whole pin into the Y tensioner.
  • Pass the two belts through the Y tensioner as shown.
  • Connect the timing belt as shown. Make sure the belts reach the end. Otherwise, the length will be different.
  • Insert the M3*32mm screw(the longest one in pack 3) into the Y tensioner.
  • Install the timing belt into the Y-Belt-Clip as shown. Put 2 M3*12 screws in advance.
  • Put Y-Belt-Clip into Y-Belt-Holder-B, the upper cover of the Y holder.
  • Attach Y-Belt-Holder-B to Y-Belt-Holder-A. Make sure you turn the screws on both sides evenly in turn.

6. Replace the E motor

Prorifi3D E motors have the same dimension as the original one. It is a direct replacement. You can refer to this section to rebuild the E axis:https://help.prusa3d.com/en/guide/5-e-axis-assembly_28536

7. Electronics

8. Install the control box

  • Hook the control box on the holder as shown.
  • Tighten the screws.

9.Spool holder

  • Install the spool holder with flat cap M5*10 screws and hammer nuts.