Kossel 3D printer upgrade project

The dangling power cable for the hotend and the fan is now fixed again with this model (cable holder from thingiverse - my make of it), which is much sturdier than the one before.

I am sorely dissatisfied with the (optical) print quality but for one, the Amazon Basicfil has very good first layer adhesion and the print itself is solid as it should be. And the print was to measure without any scaling (the screws to fix it to the extruder cage fit in perfectly on the first try).

3D printing can be fun again ....

Before, I tried (mostly in vain) to print the Renkforce 1.75 mm PLA 'premium' filament from Conrad but it was supremely finicky on the first layer. Once you got it to print, it does have a nice surface finish but the printing qualities are pretty sub par (in line with all the reviews of it on Conrad.de. One guy got it to print with 100° bed temperature and 230° nozzle which is extreme, considering it is PLA and not ABS ). I only bought it because I had a gift voucher for Conrad.de. 

I still have most of the 1kg roll left and I will probably pick it up again once I have a perfectly levelled print bed - as said, once it prints, it is decent. Would be a pity to throw away an almost full roll of PLA.

Currently there is a weird issue where the first 5mm print totally fine but after that the layer quality degrades - which I still need to and will fix.

The much easier first layer with the Amazon Basicfil is a nice breath of fresh air though compared to the struggles with the Renkforce.

Things to do

For now there are a few basic upgrades that are next up in line to make room for further more dedicated ones.

• cut out a baseplate to mount the printer on. It will provide stability and also a mounting plate for the mainboard (which is currently mounted to the printer frame). The printer is already elevated by 5cm (~2") so now there is enough space to lower the mainboard onto a base plate and enclose it in a cooling tunnel.
• mount the extruder up top. Currently it is mounted to the side of the printer and the bowden tube through which the filament moves towards the print head is bent in a U-shape which introduces more friction to the filament movement. I hope, by mounting the extruder vertically, the filament will move more easily (especially important since I plan to print with flexible filament too which I suspect is more susceptible to friction).
• install extruder upgrade for flexible filament (TPU upgrade for extruder). the current top part of the extruder has too much space so that flexible filament can jam. I already printed the part, but did not have the time to install it.
• reprint the holding brace for the extruder power and thermistor wires. I downloaded one from Thingiverse (Make of holder brace) but it broke in the meantime. Maybe I'll redesign it to be a bit sturdier or just reprint.

Next batch of upgrades would include:

• spacers to offset the glass plate by a bit so that it does not lie on the LEDs from the heated bed anymore. This will make bed leveling easier since currently the glass plate bends a tiny bit into a curve (in the order of less than a mm).
• bed leveling screws (own design probably - did already a first take on designing and testing but quite a few improvements needed to be fully functional) to make bed leveling easier. The bed leveling mechanism needs to be designed such that it does not interfere with the glass plate spacers.
• mount the mainboard on new base plate and add a cooling tunnel over the steppers and also replace the current 50x50mm fan with a less noisy version
• redesign extruder pressure lever, currently I use a chop stick that I press against the extruder lever to ensure my extruder does skip as few steps as possible. The stock spring is way too weak to provide the correct pressure. I would like to have a new design with easily adjustable extruder pressure.

Done upgrades so far:

• PSU (power supply unit) replacement: switched from the power brick that it was delivered with to a PC ATX PSU (Corsair CX500). The Corsair power supply has only one 12V rail which is important for using it to upgrade a 3D printer. Most modern power supplies have two 12V rails which means that their 12V output is split (unevenly mostly) between two 'power lines'. This is not good for 3d printing since the heated bed for example pulls a lot of power. With modern PSUs (unless they are in the 600-900W+ range), one 12V rail might not be enough to power the heated bed.
• updated the stepper motor drivers: to Trinamics TMC2100. They put out almost pure sine waves so the steppers run almost inaudibly! But: They also run hotter than standard stepper drivers so some active cooling is a good idea (see planned upgrades, i. e. cooling tunnel on mainboard).
• installed a power MOSFET to move the heated bed supply from the mainboard to the outside of the printer. This should decrease possible fire hazards through molten onboard connectors to a minimum and increase the longevity of the mainboard in general
• coated the extruder heat block in a few layers of thermo-isolating kapton tape - now the heating curve is a bit smoother and the extruder keeps its temperature more steadily

• designed and printed
• a preliminary fan funnel to cool the stepper drivers and plopped in a 50x50mm fan (a bit smaller than 2"x2") powered by the new PSU
• braces (Filament brace) to plug into the sides of a filament roll which take 608Z standard skateboard bearings. Now the filament unrolls much more easily (almost too easily ^^)
• and installed a filament filter
• a small retainer to prevent the bowden tube from moving backwards while the extruder retracts
• holding brace for the heated bed that mounts to the 20x20 extrusions of the printer

• downloaded and printed
  • a new and a bit fancier dial wheel (dial knob) for the control unit
  • elevated feet (elevated base stand) for the printer base that lift it up by 5cm (again, about 2").
  • cable holder (cable holder - my make of it) for extruder power line and thermistor wire. It snapped a while ago, need to print (and / or redesign) a new one

The printer still has a few calibration issues, mainly due to the heated bed. The heated bed has a few LEDs to indicate it is working but unfortunately, these LEDs protrude a bit so the glass plate on top of it is at a very slight angle. For small prints, this does not matter much but for larger prints, it makes a decent first layer almost impossible. See ToDos for planned improvement.