Printrbot – day4

In the previous post, Printrbot – day3, the printer assembly was completed and the Z probe was adjusted mechanically and calibrated so that the initial print bed level would be correct down to 0.1mm precision.  This was done using repeated calibration prints of a 3mm box and observing the result.  Also a fan shroud was printed successfully.

After this success, I noticed that some of the online images of the same printer seemed to have a shorter hot ends than my printer. Since I had a standard hot end, this meant that even though it worked, I had probably not inserted the hot end into the extruder assembly as far as intended.  After some deliberation, I found the reason: The hot end must be inserted into the extruder before inserting the top right screw indicated with red below. In that image, it is done in the wrong order, resulting in the hot end only partially inserted.

image

The fix was easy, simply remove the screw, insert the hot end all the way and insert the screw again.  Obviously, this implies that I had to mechanically re-adjust the Z-probe to fit the new location of the hot end nozzle, and then perform a new round of calibration prints.  But after having done it once, the second round was much easier.

The time had now come for something slightly more challenging. I needed a filament spool holder, so why not design and print one to sit on top of the vertical bars? This is not a new idea with this printer, and an alternative is to download such a solution from thingiverse, but it is more interesting to design your own, I thought. I used the open source program OpenSCAD and designed the following slightly futuristic looking spool holder.

image

The holes under it are just large enough to match the 12mm vertical bars of the printer, with some slack. The top is designed to take a 32mm PVC tube that I already had. The spool holder is designed to allow a reel radius of up to 110mm and a reel width of up to 80mm. It is also worth mentioning that the design is intended to be printable without support material, since there are no low angle overhangs to speak of. The top of the bar holes can be covered by the printer automatically by means of “bridging”, the printer drags strings of plastic across the hole and the string is instantly cooled.

Would it work to print this design? It was estimated by Cura to take 5 hours with 15% infill. To attempt this as your second print is perhaps foolish, but who cares? All I had to lose was some time and pride, and there was no-one around to observe it happen :-)

Thus far I had used only the sample PLA filament provided with the printer, and I doubted it would be enough to complete the long print. I therefore opened the PLA filament I had bough from filament.no . This turned out to be made by eSUN in China, and as far as I can tell it is very good quality indeed. The prints look much better than the sample filament prints.

So I set out to do this print, but when I got as far as the image below indicates, the print just stopped, and the connection to the printer was lost. I rebooted Windows 7 and tried again, but the same thing happened once more. This was rather frustrating, the suspicion is on the Windows serial port over USB driver. Could it be that the stepper motors generate electronic noise that the Windows driver cannot manage?

image

Since I also have a Linux Kubuntu desktop, I decided to try Cura on that machine instead and ditch Windows for controlling the printer. Ultimately, the idea is to use OctoPrint on a Raspberry PI, so running Cura under Linux is anyway closer to that goal.

Printing from Linux turned out to be a very useful idea. Even though the software (Cura) was exactly the same as on Windows, and with the same USB cable (now with an extension), no more connection dropouts were observed. The print proceeded uninterrupted for the next 5 hours. Half of the base has been printed in the image below. The 15% infill can be seen as crossed lines inside the print volume.

image

image

In the image below, the bar holes have been bridged and closed. The arms have started to “grow”.

image

The fancy bottom arm supports are complete and the arms have gained some more height.

image

Print nearly complete. Everything went beyond expectations, the performance was really impressive. However, the keen observer will notice 3 horizontal lines in the spool holder arms. These lines are not in the design, and each represents a “dislocation”, a small shift in negative X direction. Some minor “clunks” when the shifts occurred could be heard. I think it has to do with slippage in the X-axis, either in the X-axis pulley, the X-axis GT2 belt or the metal clamp that holds the X-axis linear bearings down. After the print, I removed the print-bed and applied some Loctite to the pulley set screws and re-tightened them. I also tightened the GT2 belt and the 4 clamp screws. They were somewhat loose, so perhaps they were the cause of the problem.

image

In spite of this issue, the printout was a complete success! I now have a spool holder and it just needed a slight trim with a sharp knife to fit on the vertical bars. A quick test with the 32mm PVC pipe and the eSUN filament spool is a good demonstration.

image

The spool holder is adequately stiff, but the connection to the bar is slightly wobbly.  I will therefore print some  extensions to fit around the top of the bars and glue them to the spool holder, to make the connection more rigid. Then trim the PVC pipe to the required length and print end caps for it, plus an adapter to centre the spool on the  PVC pipe. Then it will be complete!

One thought on “Printrbot – day4”

Leave a Reply

Your email address will not be published. Required fields are marked *