Printrbot – day3

In the previous post,  Printrbot – day2,  we completed assembly of the mechanical parts of the Printrbot Simple Metal Kit. We ended up with something that looked finished, but nothing was connected to the controller board. In this post, the topic is connecting the motors and sensors to the controller board (Printrboard Rev. F5 in this case), calibration of the Z-probe and initial printing attempts. It gets more exciting!

First, we hook up the four stepper motors. From bottom, the sockets are for X, Y, Z axis motors and the top one is E for extruder motor. The black motor connectors are not polarity safe, so it is very important to pay close attention to the orientation of the blue wires as shown in the image below. The Y and E motors are connected in the opposite manner, compared to the X and Z motors. Since I labelled the motor connectors consistently, the Y and E labels end up on the back in this image. All the other connectors have polarity safe connectors, so all you have to do is identify the various sockets on the board.

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After the motors are connected, the fan and hot end thermistor are connected at the top of the board. The X and Y end stops are connected to the right, counting from bottom. The Z-probe is connected to the Z-stop socket above them. A word of caution for the Z-probe : Make sure the extension cable is connected correctly to the Z-probe cable. It is possible to get the polarity wrong and the Z-probe is then going to say “goodnight”, needing a replacement. Follow the printrbot instructions with full attention to the details. 

What remains is then to connect the hot end to the socket at the bottom of the board, followed by the large red/black power input connector. We should now be hooked up!

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The final step is to route all the wires through the opening between the two base “compartments” and close the opening with a zip tie. Then collect the wires in the bottom compartment with one or more zip-ties and tuck them away. Make sure there is no excessive  tension on any wire. Similarly, I found it useful to use a couple of zip ties to collect the wires in the board compartment.  I used no force, but simply carefully  collected the wires and made sure  they were not sticking out or under any strain.

Done! This should in theory now work.

In the future my setup is likely to be different, but for the purposes of calibration I decided to go completely mainstream and and follow the printrbot calibration procedure in every detail. That means I used a laptop with Windows7 and installed a serial port driver and the Cura software.  I would recommend reading those instructions carefully and do exactly what they say. Initially, i didn’t and had some scary moments, but all went well :-)

One should read and follow the procedure, but it is useful to understand the overall concept of calibrating the Z-probe. You power up the printer and connect it to the PC using the USB cable provided. You then start Cura on the PC and connect to the Printrbot. The idea is to first mechanically adjust the position of the Z-probe to be approximately one mm higher the hot end (which must be hot) when the hot end is “a paper thickness” above the bed. This is done using the wooden wrenches (or use better tools, the wooden wrenches are mostly useless).

By repeatedly printing the provided calibration cube and observing the result, one can determine the required Z-offset of the probe. There are YouTube videos demonstrating how to analyse the printouts during calibration.  This offset changes are entered by means of manually typing G-code commands such as “M212 Z-0.2” (to offset the Z-probe –0.2mm) and then “M500” to save the value into the board firmware. This process is repeated by changing the Z-offset until things start to look right. Remember that the hot end must be hot during the calibration, since heating it will change its dimensions enough to affect the settings.

After a few completely failed attempts of the 3mm calibration box , I was getting closer, however things were still not perfect, the bottom was a bit messy. But at least we could see what it was supposed to be.

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In the above image, it is possible that the offset is too low, causing the first layer to be squeezed too flat. It is also possible that the extrusion isn’t completely correct. But at least we are getting something. In the image below, the offset is –1.0mm (I think). Now it starts to look good.  However, it is still this is not a perfectly calibrated printer.

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The print box ended up looking quite good, so I had a go at printing the Improved Fan Shroud available from Thingiverse.  This worked out rather good as the following images illustrate:

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The print completed in about 48 minutes. After a little bit of cleaning up, the printer got a new part! The fan will now blow on the freshly extruded plastic, not on the hot end itself. This should help improve print quality even more.

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I consider this a complete success so far. There are probably a few more adjustments that can/must be made, but being able to print a part like this proves that everything is working and that was the goal at this stage.

3 thoughts on “Printrbot – day3”

  1. Those can be pretty nice. They have a pootntitmeeer on them so you can get a little bit more voltage out of the power supply. This is useful for pushing more current through the heated bed. With a twelve volt power supply you may not be able to get the bed hot enough for ABS (V=IR), but with this or a 15V power supply you should be fine to getting to a higher temperature. Remember to do your automatic PID calibration if you change out your power supply. Your temperature ranges might be all over the place if you don’t. The GCODE to use is M303 S185 . This will tune your PID for 185 degrees Celsius.

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