Printrbot – day5

This is another entry in the “Printrbot – dayN” series, documenting the build and initial use of the Printrbot Simple Metal Kit. In this post we will add some more notes on experiences so far, plus show some videos of the printer in action.

One of the first things I noticed after completing the spool holder print, was that the vertical bar hole diameter tolerance was too liberal, making the holder wobbly and unsafe sideways, especially with a 1kg spool on top.  But there is an easy fix, simply print some narrow tolerance collars to fit on the bars, with 2 M3 screw holes and then drill corresponding holes in the spool holder.  Problem solved!



Second issue was to do something about the operation of the extruder tensioner arm. When you change filament, you press down the tensioner arm to allow for the filament to be inserted. But since the arm is short and the pressure area is small with a screw head in the way, you get sore fingers.  I therefore decided to download and print a part to solve this problem:

When installing this printed part, you have to remove the tensioner arm by unscrewing the screw indicated in the image below. The screw is threaded into one of the 4 holes of the extruder stepper motor seen behind the extruder assembly. However, in my case, the screw was very short and hanging on to only a few threads in the motor, and I managed to strip those threads in the process. Maybe I used the wrong screw during assembly or perhaps this is a design issue, I have not double checked the build instructions yet. However, as I had same dimension M-screws in my drawer, I was able to find a longer screw plus suitable shims on the outside and solve the problem that way.  Problem solved again.


Another observation was that the fan shroud I had printed originally seemed to be a poor design wrt. airflow.  It seemed to blow more behind the fan than at the extruded plastic! The reason seemed to be a rather steep narrowing of the cone and a small hole at the bottom, creating an internal pressure causing blow-back. Clearly, this part was a candidate for an improvement.  I contemplated designing my own fan shroud, but then I found a part on thingiverse that looked rather promising wrt. airflow, plus it matched the way I had mounted the fan:

Both of these parts from thingiverse are shown installed below.  Also, If you compare the image of the hot end with previous images in this series, you will notice that the two horizontal “rings” on the hot end are closer to the extruder assembly than before, after I managed to install the hot end properly. More problems solved :-)


Both of the printed parts are working fine, the back-blow from the fan is much reduced, so most likely there is more and better airflow around the hot end nozzle to cool the plastic.  Also, the new fan shroud misses the black metal base with a tiny margin when the printer is in the home position (back/left/bottom in the image), so all is good.

What follows are videos from the new fan shroud print, with the old fan shroud still installed. The videos are made with an old Phillips webcam, so VGA resolution only. The video speed is real time, the printer really moves this fast!

First the “critical” start sequence where the metal/orange Z probe detects the bed level in 3 points, allowing for automatic compensation of slightly unlevelled beds. In this phase, the challenge is to get the first print layer to stick to the bed, that is what the blue painters tape on the bed is for.

Printrbot Simple Metal Z probe start sequence


The second video shows the print as the shape is getting more complex.  The dent in the front is intentional to avoid collision with the printer base when in home position.

Printrbot printing a complex shape


The final video shows the final phase of the print, and homing of the hot end.

Printrbot finishing up the complex shape


After this print, some minor clean up was needed, there were some plastic stringers inside that had to be removed, but that was trivial to do.  The print was not 100% perfect, something I attribute to the old fan shroud, but the new part was certainly usable.  I have printed a couple of end caps for the 32mm PVC tube on the spool holder and they look very good, so the new fan shroud appears to be doing its job.

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