RepRap Prusa Mendel 3D printer

March 2013 (edited February 2015)

I made one… then I stripped it for parts (see February 2015 update at the bottom of this page).

I made one because I was frustrated with the fabrication capabilities of my existing machines: hand tools and a pillar drill. Also I was attracted by the ability to design in CAD software, and then print the result without relying on my kak-hands to create what I had designed.

Halfway through making it I realised that what I really wanted was a mill. The parts the printer could create would not be robust or accurate enough for the kinds of things I make.

After researching mills I realised that what I really needed was a small lathe with some milling capability (as I usually work with small parts). I did eventually buy a small precision lathe (Hobbymat / Prazi MD65), that also came with a mill.

However, I very much enjoyed building this 3D printer, and if I had my time again I would still have built one. I learned a great deal about CNC, steppers, CAD and CAM software, electronics and soldering. I have not used it to produce anything useful yet, much to the amusement of friends and family who were subjected to starry-eyed, “it’s the way the of the FUTURE” proselytizing during the extended period of its construction. Ho hum not the first or last time…

There are many, many buildlogs available for RepRaps so I am not going to write one here. My build took about 60 hours including soldering up the stepper control board and configuring the software (however this was spread over several months).

I do have some (hopefully) helpful tips for people who wish to make one:

  • configuring limit switches in the software is tricky
    • expect to crash your print carriage into the chassis several times as you work it out
    • to avoid panicked pulling of power wires out of sockets, fit a large emergency stop switch – the first time you use it you will be very grateful for it!
  • the printed parts of the chassis need care when assembling
    • where the rails in the X-axis are a ‘push-fit’ into the chassis components to the left and right, these components cracked/delaminated on mine – I had to drill them out to 8mm, which means they are not tightly held in place
    • the same chassis components cracked along their long (vertical when installed) length, I had to splint them with some epoxy and a wooden stick
    • the compression ‘U’ fittings that clamp onto the threaded rod and rails are prone to cracking – do not over-tighten
  • use stainless fasteners
    • for the M3/M4 bolts and nuts use stainless – I found that plain steel fasteners of this small size are poorly made and/or prone to stripping, and easily damaged
    • for the M8 fasteners ordinary nuts are fine, as is plain threaded rod for the chassis cross-members – ordinary steel threaded rod is cheaper and much easier to straighten than stainless (your threaded rods will not be dead straight no matter where you get them from)
  • getting the chassis aligned correctly is impossible without a flat surface to work on
    • a granite kitchen worktop or piece of plate glass (5mm or thicker) is good, I used an offcut of a chipboard kitchen worktop that I had checked was flat (other parts of the same worktop were definitely not flat)

Here are some photos of my completed printer (RepRap Prusa Mendel Iteration 2):


Wade’s Extruder – printing gears is something that really attracted me to 3D printers, however they require some filing/finishing before they run smoothly.


Driver board – I bought the components individually and the board separately, in hindsight it would have been much cheaper to have bought a complete set of components with the board off one of the many eBay sellers (solder the board yourself however, as soldered boards are much more expensive than the component parts).


Cracking of the X-axis mount – you can see the crack running horizontally and also where I have epoxied a wooden splint to the vertical member: because of the way a part is built up in layers, and the relatively poor adhesion between layers (at least in the printed parts I bought), these plastic parts will fail via delamination if they are stressed too much.

print head

Bed and print head – oooh look at that cool “I am a spaceship” yellow mirror… I like Kapton tape, very useful for any number of jobs.


Heated print bed and wooden base – wood is fine for the base, I used a piece of mirror scavenged from Mrs Naut’s hoard of junk collection of potentially useful objects for the bed (yes yes, pot-kettle-black and all that…).


Stepper specifications – these are NEMA17 steppers, I don’t know a great deal about steppers but these are pretty pokey little beasties, even running on 12v. I believe you can increase the effective speed by ramping up the voltage to 24v, however the 1.2A limit must be respected or you will give your stepper (and possibly your printer) a Viking burial.

Update February 2015

I have started disassembling this printer as I have not used once it in the two years since I built it. It is looking rather sad on my projects bench, having been harvested for parts for other projects over the last two years – everything from nuts and bolts to the stainless rods and even one of the steppers.

I am going to use the steppers, electronics, belts and bearings to build a A2 desktop CNC router. The extruder assembly, print nozzle and heated bed will go onto eBay to raise some funds to buy the aluminium extrusion for the A2 router. The printed structure will go into a box, and may never see the light of day again – I don’t want the hassle of selling it as it has some cracks as detailed above. The rest will be added to my materials store.

And so it goes…




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