Prusa i3 3D Printer – Initial Build


I initially built the Prusa i3 from a kit starting in December 2014.

The kit was purchased from a company called Semi-Utilitronics via the eMakerShop website. The kit cost just £399 plus £12 p&p. It arrived on 18th Dec 2014 packed in 2 pizza boxes (unused I hasten to add).

The printer boxed, as it arrived in the post.
Unboxed – the full contents of the kit.

I checked the contents to ensure all the parts were present, which they were then went to the suppliers Facebook site for instructions. These were fairly basic, consisting of a series of pictures. Although this was helpful I also trawled the web for more detailed instructions. I found some good instructions for similar printers but the best place I discovered was the Reprap Wiki.

I have added links to the Reprap Wiki and manufacturers’ websites throughout the text where possible.

Suitably armed I set about building the y axis.

Y Axis Assembly

The y axis consists of the horizontal frame that supports the moveable print bed which is moved from front to back.

The y axis components.
The front including the y axis idler.
The long edge threaded rods.
All connected via printed corner pieces. Shows the long edge smooth rods that the bed slides on.
The linear bearings are tie-wrapped below the bed.
Top view. The frame is adjusted so the bed slides all the way along with minimum friction. The motor mounting bracket is in the centre of the left-hand threaded rod.
Close up of front.
Bottom view. Printed part in centre of bed is where the motor belt attaches.

X Axis Assembly

The next step is to assemble the x axis. This moves horizontally from side to side and carries the extruder assembly.

prusa _xmotor_01
To assemble the x motor mount I needed to cut out a small section of plastic in the centre that was stopping the two bearings from sitting flat and in-line.
The tie-wraps needed to be curled tightly at the end in order to get them to bend round and come out of the exit holes.


 The bearings were then mounted and the tie-wraps tightened. I used one of the smooth rods while doing this to ensure they were perfectly in-line.
The bearings were then mounted and the tie-wraps tightened. I used one of the smooth rods while doing this to ensure they were perfectly in-line.
The same was then done for the x idler.


…and the x carriage.


The idler bearings were installed in the x idler.
The M5 nuts for the z-axis drive were then inserted in the x idler…
…and x motor mount
The x axis smooth rods were then carefully inserted into the three x axis components.

Z Axis Assembly

The z axis is the vertical dimension. It allows the x axis to be raised and lowered moving the extruder assembly up and down. This axis is the slowest moving when printing is taking place as it only steps up when the next layer is to be printed.

The z axis lower left & right mounts installed on the plate.


The z axis smooth rods installed through the holes in the brackets. The holes are very tight so needed widening carefully with a round file. The brackets did bend slightly once the rods were inserted but once the motors are mounted it will give them strength.


The x axis assembly slid onto the smooth rods and the upper pair of brackets installed. The x axis length needs to be adjusted while doing this to ensure that it runs smoothly along the z axis.


The z axis threaded rods installed. These are driven directly by two z axis motors and move the x axis up & down via the M5 nuts held captive in the x motor mount & x idler.


Stepper Motor Installation

Four stepper motors are used on the printer frame to provide the 3-axis movement. One on each of the x and y axes and two on the z axis. The z axis needs two in order to ensure that the x axis is kept exactly parallel to the print bed.

The z axis motors connect to the drive rods via a plastic coupling which is also tie-wrapped to prevent slippage.
One of the z axis motors installed on the left lower bracket.


The other z axis motor installed on the right lower bracket in the same way.
The z axis endstop clipped round the smooth rod and secured.
The y axis motor mounted at the rear of the y axis assembly.
The pulley wheel for the toothed belt attached to the y axis motor spindle.
The x axis motor mounted on the x axis motor mount.
The y axis mounted to the bottom of the frame via the M10 bolts on the y-axis.
The M10 bolts attaching the y axis to the frame.


Toothed Belt Installation

Toothed belts are used on the x and y axes only. They need to be fairly taut but not so much they restrict the movement.

Toothed belt attached to the x carriage. The belt is looped around the left and right hand ends of the x axis and fixed in the centre using tie-wraps.
The x axis belt passing around the idler at the right hand end.
The x axis belt passing over the motor pulley at the left hand end. This is where it is driven from.
The y axis belt passing over the tensioner at the front of the y axis.
The y axis belt passing over the motor pulley at the rear of the y axis.
The y axis belt attached to the base of the print bed and secured with tie-wraps.

Extruder Assembly

The extruder is the business end of the printer. It consists of two main components:

Cold End

The cold end is responsible for pushing the solid filament into the hot end at a controlled pace. In this printer it does this by means of a ‘hobbed bolt’. This is an M6 bolt that has grooves cut into the sides that digs into the filament and drives it into the hot end. A small idler wheel keeps the filament pressed against the hobbed bolt to ensure a constant pressure is maintained.

Hot End

The hot end is essentially a heated metal tube that melts the filament which is forced out through a nozzle forming a thin stream which is laid down to make the print. The heating is done via a 12V heater cartridge. There is also a thermistor attached to the hot end in order to monitor and control the exact temperature. This printer uses a commercially available E3D V6 hot end. The hot end has a heat-break where it joins to the cold end to ensure the heat stays where it should. A small fan is constantly keeping this area cool to stop the heat creeping up and damaging the cold end which is made from plastic.

The extruder motor with pulley attached.
The idler with idler bearing installed
The extruder body with main bearings in place.
Idler attached to main body. The bolt used to attach it is inserted incorrectly as indicated. This was later reinserted correctly.
The hobbed bolt inserted with drive wheel attached. Note the horizontal cuts around the centre of the hobbed bolt which grip the filament and drive it into the hot end.
Close up of hobbed bolt.
Close up of hobbed bolt.
The two tension springs installed on M4 bolts. These ensure the idler is always pressing the filament onto the hobbed bolt.
The extruder motor installed and adjusted so gears mesh smoothly.
Side view of motor.
The hot end assembled. The aluminium heater block contains the heater cartridge and thermistor.
Rear view showing the heat break.
Bottom view showing the 0.4mm brass extruder nozzle.
The heat-sink attached to the heat break.
The 30mm fan and duct which cools the heat-sink.
The hot end fully assembled , fitted to the extruder and mounted on the x carriage.

End-Stop Installation

End-stops play a vital role in the operation of the printer. They ensure the control electronics can sense when the three axes are at one end of their travel. In this case they are set at the ends of the axes that represent zero. Some printers place them at the maximum travel positions and some even have them at both ends. This printer has a print area of 200mm(x) x 200mm(y) x 180mm(z). The control system is set up with the maximum dimensions ensuring it never goes beyond.

The z axis endstop installed.
The x axis enstop mounted on the x motor mounting. Note the z axis adjustment screw that sets the z axis zero height.
The y axis endstop mounted on the rear smooth rod.

Heated Print Bed Installation

The print bed is heated to ensure that the part being printed sticks to the print surface. It contains a 12V heater and also a thermistor to ensure the temperature can be controlled.

The heated bed. The supplier had already soldered the heating wires and taped the thermistor to the lower surface.
The heated bet fitted to the aluminium base using m3 bolts and springs.
Close up showing bolts and springs. These allow adjustment for levelling the bed.

Power Supply

The Power Supply that comes with the kit is a standard ATX style PSU as used in desktop PCs. This supplies the high currents needed by the printer at 5V and 12V at a very good price. It requires some modifications though before it can be used with the printer. The main issue is that these types of PSU are designed to be connected to a PC motherboard and will not suply any current until there is a certain electrical load on the various outputs. Also the usual PC on/off switch needs to be simulated by grounding one of the wires.

The PC ATX PSU rewired for the printer. The motherboard connectors have been removed and the individual wires connected as required.
Any unused wires are insulated with heat-shrink.
The power resistors provide the correct load on the 5V and 3.3V lines for the PSU to function correctly.
The power resistors get fairly hot so are tied to the rear of the PSU case where they are cooled by airflow from the internal fan.
The Ground and +12V lines connected to the RAMPS power connector. These are split between the two 12V inputs to the separate RAMPS circuits.

Control Electronics

This is done by a combination of three components.

Arduino Mega 2560

This is a microcontroller which is programmed with the Marlin printer control firmware. Its role is to accept printing commands from a host program, in most cases this will be running on a PC and control the printer movement to produce the print. The outputs of the Arduino are too weak to control the printer so it needs some help.


This is a shield which is piggy-backed on the Arduino Mega 2560 board. It is controlled by the Arduino and gives the necessary power and control to actually control the movement and heating that the printer needs. The RAMPS also has four Pololu stepper motor drivers plugged into it. These provide the high powered control of the individual stepper motors. Five are supplied in the kit and there are room for five on the board; the fifth is only used if you have a dual extruder installed which we do not.

Marlin Firmware

This is a piece of dedicated software that is flashed to the Arduino providing the actual control of the printer. It accepts commands from the host software running on the PC in the form of g-code and convert those into the required movement and control of the printer.

From L to R: Arduino Mega 2560, RAMPS 1.4, Pololu Stepper Drivers.
The RAMPS board installed on the Arduino Mega. Care must be taken to ensure all the pins are inserted correctly.
Pololu stepper driver showing the adjustment trimmer pot on LHS.
RAMPS connected up to the various components of the printer. The Pololu drivers have been inserted to the RAMPS board.
All the connectors were labelled to ensure they were connected correctly.
The printer with all connections made and connected up to the PSU. A bit untidy at the moment but OK for an initial test.