Wanhao i3 V2.1: more upgrades and maintenance

I did some maintenance on and upgrades to the Wanhao i3 V2.1 today.

Some cheap Chinese printers suffer from under-spec'd power connectors on their main boards. Over time, these can heat up, char, and eventually fail, causing fire. While none of my connectors have shown any sign of discoloration or impending failure after 75 days of printing time (6.8 km of filament), I decided to do a common preventative upgrade. Since the heated bed is the primary power consuming device, it makes sense to offload the heated bed's power. Since the heated bed is PWM'd to achieve different average power, you can add a MOSFET between the signal, power, and heated bed power wires, where the signal comes from the original heated bed connections on the controller board, power comes directly from the DC power supply, and the heated bed power wires are the original. Before doing this, I printed this thing, which is a nice holder for the MOSFET board. That gets installed on two standoffs under the Melzi, and the MOSFET board screws to it.

Upper right: MOSFET board installed

I used ~10AWG wire for the connection from the PSU, but it was pretty unwieldy. I'd suggest using 14AWG wire. Anyways, instead of just jamming the wires under the terminals, I soldered forked spade connectors to the ends and heat shrunk them. I did the same for the heated bed wires.

While in the safety mood, I installed a smoke detector on the ceiling of the room with the printer. 

The wires to the hot end heater cartridge come crimped from the factory. I found it annoying to have to work on the hot end with it attached to the carriage, so I replaced the crimps with micro-Deans (micro T) connectors. These are rated up to 10A, but the Chinese knock-offs are probably not able to handle that much current. Since the heater cartridge only uses ~40/12=~3.3A, it should be fine. 

I also re-built the hot-end again. In a previous post, I detailed all the things I tried to get back to how it would print previously (no blobs, no initial under extrusion, etc.). All of that failed, and I ended up applying software band-aids, but the last physical thing I tried was spacing the nozzle off the heated block and using the original PTFE tube, which was too short. This time I rebuilt it with a new nozzle, hex edge flush against the heated block and using a proper-length PTFE tube. I made sure everything was tight to prevent leaks, then put the whole hot end back together. 

I then oiled the bearings and greased the z-axis threaded rods.

I also printed a new Diii Cooler, this time out of PETG, which has a higher temperature limit than PLA. Before doing that, I printed a temperature test tower, with increments of 5 degrees from 250-200C (+10 from markings on tower). These are great for finding the optimal print temperature for a filament. 

Settings were 0.2mm layer height, 40 mm/s (20 mm/s outer wall), 0.1 extra prime, 0.15 coast, 0.4mm nozzle, 0.5mm line width, 1mm walls, 10% infill, 100% fan after 1st layer, 70C bed temp, etc. I forgot to use a brim, so the little side bridge part popped off, and I had to pause the print to tape it down. Ignore the lower 3 bridges because of that. I started to hear some skips at 225C, and I had to stop the print at 205C. The best combination of strength and quality seemed to be about 245C. I could probably print at 230-240C if I cared more about quality than strength. Using less fan would probably let me print at a lower temperature, too, but since the DiiiCooler has huge overhangs that can't be supported, I need the fan. I then printed an XYZ calibration cube using those settings, 245C, and a layer height of 0.25mm.

It came out great. The first layer was smashed too much, so I lowered the bed slightly. Small warping at the downward facing points of the X and Y, but that was almost always present with PLA. Good layer adhesion. Might be slightly overextruding because the X and Y were ~20.2mm instead of 20. It popped right off the bed, so I increased the bed temp to 75C. Interestingly, the PLA DiiiCooler has had no problem with the high extruder temps...no signs of warping or melting. The PID controller isn't as steady at the higher temps, ~-2/+1C instead of +/-1C. But I figured that was good enough. Then I printed the DiiiCooler:

Sporting some CA on the side

The extruder was skipping on the long path inner walls (40 mm/s), so I turned speed down to ~65% to stop the skipping. I guess flow rate is more limited with PETG than for PLA. The slower speed throws off the extra prime and coast settings, i.e. you need less of both. This caused the blobs and inconsistent extrusion near the right side of the fan opening, which is where I set the Z change location. I think the layer thickness was too high...only two layers on top and bottom, and it was clearly not air tight on the top (CA to the rescue). If I were to print it again, I'd use 0.2 mm layer height or lower and go slightly faster (~30 mm/s).

Summary of PETG-specific settings:

• Same speed settings as PLA
• Use PLA prime and coast values
• Only use fan if printing overhangs/bridges, otherwise don't need it
• Strong temp: 245C (maybe lower if 0 fan?)
• Good quality temp: 235C
• 75C bed
• Max flow: 40 mm/s @ 0.2 mm layer height, 0.5mm line width. For long continuous extrusions, that will probably cause skips, so turn down to ~30 mm/s. Needs about 25 mm/s max for 0.25 mm layer heights. When reducing speed, reduce prime and coast approximately proportionally.

I'm using PLA next, so I'll need to heat the extruder to ~225C, remove the PETG, insert the PLA, and extrude a bunch to get all of the PETG out so it doesn't clog. 

One of the last things I need to do to this printer is replace the worn X-axis belt and install the belt tensioner. However, the belt is tight and still functional, so I'm going to wait on it to wear out more before doing that.