In the process of trying to make an important print, I ran in to a series of maintenance problems with my good old home made 3D printer. The first problem was the failure of my extruder. I use a Stepstruder Mk 6 that I had purchased used through eBay. I think it was attractive to me since I wanted to get in to the the business cheaply back then, and I didn’t need to do the assembly myself. Since then I have assembled a brand new Mk 7 for my new Arduino based 3D printer. The Mk 6 extruder sporadically stopped heating. I finally broke down and disassembled it completely. I found that the wires connecting the resistors were in very bad shape. That should not be a surprise given that they are subjected to the high temperature inside of the insulated print head area (250 C in my case). I need to admit something here. After sort of carelessly pulling off the rotten wires, I reworked the unit with the two resistors in series, not in parallel. That seemed sensible to me.
I nicely wrapped it back up with my remaining new insulation from my Mk 7 build, and many layers of Kapton tape. It heated, very slowly, and topped out at 150 C. At first I assumed that one of the resistors or both might have gone bad. They sort of wiggled inside of their little metal cases. Then I thought about power delivery and realized that parallel combination must be the answer. This was clearly a case of RTFM since there was a beautiful, detailed post on the Makerbot site with exact instructions. I the mean time, I tried to order two new 10 Watt, 5 Ohm power resistors. Going to Newark or Allied was rather painful for their handling fee for such a small order and their shipping fee that cost as much as one of the resistors. I found a Chinese supplier that appeared to have a close enough resistor footprint and sold them for $3.50 each with free shipping. Sure, it takes a month to get them, but this is a matter of pride… and cheapness. Search eBay for “5 Ohm” 10 W so that it does not give you dozens of listings for 10 Ohm, 5 Watt resistors and you can probably find the same little green resistors that I did. Now they will just be spares since when I reworked the system in parallel, the extruded shot right up to operating temperature.
Here are the power specifications. I series, we have 10 Ohms and so 1.2 Amps at 12 Volts, which means we dissipate 14.4 Watts. That’s not enough to heat the extruded. In parallel we have 2.5 Ohms total, 4.8 Amps, and 57.6 Watts. So how do two 10 W resistors handle that? I guess because they are only on intermittently. They have only 20 W power handling on paper.
Next I learned that 250 C is enough to loosen up a solder joint if it’s inside of the insulation. I had a wire pop off about four times before I gave up and ripped off all of the insulation and Kapton once again. Once again, RTFM. The Makerbot blog describes just how to wrap your wires around the resistor terminals. You can solder if you wish, but the wrapping really holds the wire in place. Run the leads (I used bare, twisted copper) out of the heat shield and solder your input wires externally. I wrapped those too before soldering. The extruder has been working well ever since.
My next problem was a hard drive crash. My old Windows XP machine running Mach 3 suddenly and completely failed. Since then I have replaced the SATA drive with an old IDE drive. After a power failure, that drive is now also unresponsive. OK, time to retire that computer. I have a Smooth Stepper, so I could employ a much more modern (though still old) laptop, plugged in to my stepper controller through the Ethernet port. After rediscovering all of the proper Mach 3 settings (keep a backup copy of Mach3mill.xml!), I had my printer back up and running. Now it sounded strained, especially on the Y axis during a print job. I had recently replaced a flexible coupling that had sheared off from the Y stepper motor to the leadscrew, and now the motor made some noise. With the flexible coupling and the rubber gasket that I had used to remount the motor, the solution I found was to put a piece of duct tape across the back of the motor and fix it to the body of the printer under tension. That does not remove the flexibility of the mount, but it does prevent the motor from vibrating and making noise. I also generously greased both X and Y leadscrews and their rails.
This sounds like a lot of work, and it is! These sorts of problems made me step up my effort to build a second 3D printer. I am making more and more parts with my printer, and now I depend on it. When it breaks, I am in trouble. As you can tell, I am learning lesson after lesson in the school of hard knocks. That has always been the best way by far for me to really learn how to make things work and to remember the solutions that I find. My old printer will be a good work horse, and my new printer will be a sleek, awesome, problem free wonder! Stay tuned for that new post!
I laser cut Stepstruder Mk 6 parts that I have for sale. Please contact me and I can post them on eBay.