Tuesday, February 12, 2013

RepRapPro Mendel (part 4)

The RepRapPro Mendel is set up with a Bowden cabled extruder running 1.75 PLA. My other printers use a direct drive MakerGear system and have extruded only 3mm ABS. Because of this my learning curve has been higher than it should be with this printer.

Using the PLA profile in Skeinforge and the supplied PLA filament, I was able to print the test.

It’s not a great print, but the printer moved in the proper directions, properly extruded PLA and didn't spew out blobs or jam up. A much better result than my first printing attempt on my Prusa Mendel reprap build.

The next test, I decided to print a replacement gear for the extruder. This is where it became difficult. I spent a lot of time tweaking and adjusting, trying to get a decent print. The extruder seemed not to be working well. After adjusting the extruder gears and the tension idler, changing the extruder temp and feedrate/ flowrate,  and adjusting the stepper voltage driving the extruder , I started to get something working.

Cooling the PLA in delicate areas is very difficult without a fan. It's difficult not to end up with a melted blob.

It's obvious that much tweaking in the slicer profile is needed to nicely print this model

It  seems most of my problems centered on one specific variable which I wasn't aware of. My other 2 printers use Sprinter firmware and this is my 1st time using Marlin. Marlin adds a M109 command in the gcode which specifies a set starting temperature. In this case, it's 200 degrees C. Even though the temperature was set higher in Ponterface during the start of the build the temperature would drop to 200 C. This was creating my extruder problems. I wasn't getting enough filament driven because it wasn't melting well enough. This command isn't given by Sprinter firmware, so it took me a long while to notice this initial drop in temperature. It's easily changed by changing the M109 temp setting in the command window or by editing the gcode.

After experiencing the problems inherent with PLA, I decided to switch to what I am more familiar with: ABS. For the first print, I decided to use the same profile that was used for my PLA print tests.

Using the PLA profile created many problems, the most obvious one is stringing.

There’s a generic ABS profile included with Skeinforge, but it doesn't work. I added relevant changes that the PLA  profile utilizes and did some minor tweaking using portions from my own ABS profiles that I use with my Prusa Mendel.

Overall, I've made a good average ABS profile. Of all 3 of my printers, I think this printer is creating some of the best prints.


Saturday, February 9, 2013

RepRapPro Mendel (part 3)

I’ve put the MakerGear hot end through hundreds of hours of service without having any problems. Because of this track record, I’m wary of any other system. I've experimented with other hot ends such as the Budaschnozzle and J Head MKIV and I haven't found them to be as reliable.

The RepRapPro hot end will be an interesting new addition and I hope, as reliable as the MakerGear system.

Overall, the assembly was not difficult. The entire system is small and lightweight in comparison to the MakerGear hot end.

The compactness of the hot end assembly can be largely attributed to the system’s employment of a Bowden extruder. Instead of the typical Wades extruder or MakerGear Brutstruder which is attached directly to the hot end and carried on the X carriage, this extruder is mounted on the printer’s frame. The filament is then moved from the extruder to the hot end through an attached PTFE tube. This decreases the weight carried on the X carriage and allows for a greater print speed than the other systems can employ.

The major drawback with using a Bowden cable system is that there can be more oozing and this will leave bumps on the print’s surface. This is due to the increase of springiness in the length of filament that is compressed in the system.
This is my first experience with this type of system and I’m very curious to compare the print results with my other systems.


This printer uses the RepRapPro version of the single controller board called the Melzi. It's a board designed to be more plug-and-play and a lower cost alternative to the other controller systems out there. I am not so convinced of this.
RepRapPro Melzi controller

I followed all the test pre-checks with utmost care and found no deviating readings after installing all the electronics. I had full communication through the USB tests with Pronterface, yet when I switched on the 12v supply the drivers and the power supply MOSFET immediately burned.

After checking everything once again, I realized the only mistake I made was that I did not switch the jumper back from USB mode to power supply mode.

Red arrow points to the jumper

According to Adrian at RepRapPro, this should not have burned out the board. I am yet confused as to why this happened.

In the interim, I decided to assemble the alternative, Sanguinololu Rev 1.3a, ATmega 1284P. The drivers I purchased directly from Pololu Robotics. With connectors & USB cable, the entire controller system cost $97 USD.

I ordered a replacement Melzi board from RepRapPro for $139 USD. This is not a cheaper alternative. And coupled with the fact that it's supposed to be an easier controller to use (I have dated, yet formal training in electronics) I managed to burn mine out, so I'm not convinced in its plug-n-play capabilities.

Since my goal is to test this printer as a device that can be used “right out of the box”, I’ve waited for my replacement Melzi board. After carefully transferring all the wiring to the new board, I repeated my pre-check tests and USB communication. Making sure the jumper was moved back to the power supply position, I
turned it on.

Everything is working, all axes are moving smoothly and in the proper directions.