Some tips and tricks I've developed building and upgrading Crystal Palace, my Prusa i3 V2 3D printer clone.

Notes on the Reprap Guru Prusa i3 V2 3D Printer Clone

August 2017

Contents
  1. Fixing the Heated Bed
  2. Cooling Nozzle
  3. Cable Chain
  4. Upgrading the Linear Bearings and Rods
  5. MINTEMP Errors

In the summer of 2017 I bought and assembled a 3D printer kit from an outfit named Reprap Guru, which sells, among other things, clones of Prusa open-source designs. I would have happily bought from Prusa directly, but their top-of-the-line i3 V2 was back-ordered at the time, and I really needed a new printer quickly. This was a very cheap machine, and came with a certain number of problems, some expected, others surprising. This page exists to document my fixes for the benefit of any other owners of this machine (and so I don't forget things myself!), and is likely to be updated frequently for some time to come.

I named this printer Crystal Palace, in reference to its clear acrylic construction and in honor of one of the greatest feats of Victorian engineering.

Now this won't hurt a bit.

Fixing the Heated Bed

Right out of the box the thermistor on the heated bed PCB was shorted by a splash of solder, producing a MAXTEMP error in Repetier. The solder bridge was clearly visible with some magnification and was easy to clean up with a soldering iron.

About to resolder the broken thermistor wire.

After some running time I also experienced a failure of the thermistor wires where they join with the PCB; I fixed this by resoldering. Although without some method of strain relief for the y-axis wires I expect this will happen periodically.

Cooling Nozzle

The small amount of epoxy visible in the photo fixes a crack caused by rough handling.

One of the first improvements I made to this machine was to print and install a cooling nozzle. This particular design, from thingiverse user James McGall diverts a small amount of cooling air from the extruder heat sink to the end of the nozzle. You can download the part at thingiverse or right here:

Cable Chain

I've been steadily upgrading Crystal Palace by adding wire management, most importantly to wires that go to moving parts of the machine. For the x-axis I've adapted some cable chain parts from thingiverse; this version uses some snap-in cable retainers so that after assembling the chain, you can lay the entire cable bundle in the trough before snapping the retainers in place; this is much easier than feeding the end of the wire through.

X-axis cable chain.

I connected the x-axis cable chain from the x-axis stepper motor to the extruder stepper using two clamp-on adapters I designed. They use a 6-32 x 3/8 panhead machine screw and a 6-32 hex nut to provide the clamping force. The cable chain attaches to the adapter via a special male or female chain link that screws on with four #2 x 3/16 thread-forming screws.

Upgrading the Linear Bearings and Rods

After not very many hours of operation at all I discovered that the printer was losing its position along the x axis multiple times during a typical print. At first I attributed this to insufficient current to the x-axis stepper and played with the potentiometer, trying to power my way out of the trouble. I also rigged a temporary cooling fan so that I could comfortably push the stepper drivers even harder.

A fan kludge.

None of this really worked for long however, and I shortly discovered the real problem: there were noticeable grooves worn into the guide rods! This is down entirely to the low-quality parts shipped with the RepRap Guru kit; it turns out that the rods are ordinary non-hardened stainless steel and are quickly worn down by the hardened balls in the linear bearings. Those bearings aren't great either; a few balls escaped at the slightest provocation during assembly and the bearings never felt or sounded smooth, even when everything was brand new.

So I sprung for top-quality Misumi parts. All the rods and bearings are 8 mm diameter; the rods are 52100 bearing steel with a hard chrome finish. If you wish to replace all the components, you will need:

Replacing them is straightforward, just follow the Reprap Guru assembly instructions and these parts will fit just as the originals did. There is a night-and-day difference in smoothness however, as the next video shows.

MINTEMP Errors

The extruder thermistor joints are sleeved in orange (original) and black (my fix).

After some more operating time, prints starting failing due to an intermittent MINTEMP error. I was seeing a lot of “cold extrusion prevented” errors in Repetier. After some research I discovered this was due to an intermittent connection to the thermistor wire at the extruder end. Fortunately I was able to resolder the joint without cutting or stripping any wire; the end that comes out of the extruder itself is very short and I don't want to have to make it any shorter.