Prusa i3 assembly 2: It’s ready (mostly)!

The purpose of this post is to show some of the actual steps of the assembly process, since its theory was already extensively documented. Additionally I explain how I resolved the issue of the missing and defective parts and how, by trial and error, I managed to deal with assembly steps that were not documented in the manual.

The assembled printer!

Cutting to the chase, the fully assembled 3d printer followed by photos of some of the steps leading to it:


One of the trickiest parts was to maintain the consistent distance of 162mm – dictated by the heatbed acrylic structure – between both smooth rods of the Y axis along the entire length of the chassis. To achieve it I used a strip of cardboard that I cut in the exact required measurement (see images below).

After gradually tightening each nut/locknut pair, this tool was used to make sure the distance between rods was ideal.

With a small mark on its centre, it was also useful to align the three parts that formed the the path through which the timing belt would pass: the toothed motor shaft on one end of the chassis, a pulley on the other end; and the centre of the heated bed base, where the end and beginning of belt are held together.

The defective and the missing.

new printed partIf you read the last post, you probably remember that one of the provided 3d printed parts was misshapen. I managed to print a new one after many refusals, I finally found a local company that agreed to print the 8cm³ part for R$20.00 (around $5.50 using today’s currency conversion rate). It was delivered quickly and the quality was quite satisfying. So, if you are also in São Paulo and find yourself in the same situation, I highly recommend these guys.

Also, because the assembly manual was so poorly designed and because the printer pictured in it was so different from the product I received, my estimates about missing fasteners were also off and thus I ended up buying a bunch of M2.5 x 16mm screws (read about fastener properties) for no good reason. Actually, after actually assembling the printer, it was clear the only fasteners actually missing were the M8 split lock washers (I gave up the M3 nylon washers as there was a chance that the extra 1mm added would render the provided fasteners too short).

Design deductions.

Lastly, in hopes that it’ll aid someone else, I’d like to register 5 cases where I had to resort to visual deduction in order to assemble the printer:

Two taller spacers were included and seemed to belong in the space between the extruder motor cooling fan and heat sink. Without these spacers, both parts barely fitted together.

Important: While most wires coming from the extruder assembly must be connected and controlled by the circuit board, the 12V fan shown facing the camera must be connected directly to one of the V+ / COM terminal pairs of the power supply.

Other four spacers were also tossed in the kit, without any explanations. I figured they probably were meant to keeping the circuit board’s soldered terminals from getting crushed against the acrylic structure when the fasteners are tightened.

The thermistor socket in the hot end is very small and easy to miss, specially if – like it was my case – it is assumed that the provided temperature sensor is for the heated bed. By the time I spotted the socket it, I had all 10 wires from the extruder assembly secured within the cable spiral wrap. I had to do it all over again, to include both thermistor wires and it was a painful procedure.
If that wasn’t enough of a hassle, I made yet another mistake that forced me to unwrap the cables a third time: the tiny temperature sensor cracked in two while I tightened the set screw that holds it in place inside its socket. I just assumed the sensor was tougher, since the screw hasn’t any type of cushioning at its tip. A 100K Ohms replacement was then purchased for R$3.75 (around $0.95). 100K of resistance are the ones that will work.
I also added a little thermal paste to improve heat transmission between hot end and sensor, just in case.

Notice the small pill-shapped openings present in the structure. They are meant to help with the organization of the wires. Unfortunately I’ve only noticed them when the printer was almost ready, forcing me to remove all motors to properly orient the wires toward these openings.

By screwing/unscrewing the screw inside the spring shown in the picture, it’s possible to calibrate the distance between hot end tip and heatbed. The more it’s uncrewed The spring secures the screw in place even if it’s not fully screwed.


From the experience acquired, I drew an alternative wiring diagram – less abstract than the one provided by the manufacturer – showing an approximate spacial distribution of every component of the system and the path that each wires must follow, going through each of the openings in the acrylic structure, in order to reach the circuit board. It’s not very simple to read but, when carefully studied, it should make wiring 3d printers of similar design a lot easier:


Extra Stuff.

While inventorying fasteners, I also predicted that a bunch of them would be left unused:

fastener    estimated  reality
--------------------------------------- screws
M3 x 8      6          0
M3 x 10     3          0 
M3 x 20     4          0
M3 x 25     3          0
M5 x 20     1          0
---------------------------------------- nuts
M3          25         12
M5          1          1
M8          4          0
---------------------------------------- washers
M8          4          0

spool supportBut after the printer was assembled, these numbers dropped significantly as a bunch of unused parts came together to create an acrylic support for filament spools (see it on the right) that was included in the kit without any sort of documentation. At least this time the surprise was a hidden feature, not a defect!

In conclusion: as I said before, the printer itself is pretty good and sturdy, but the lack of  a proper assembly manual added an unnecessary volume of guesswork and frustration to the process.

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