Critiques for a cheap rostock-like design

So a few weeks ago it occurred to me that we had 2 old HP printers sitting around the house, so I decided to try to build a 3D printer. Since this is my first real foray into electronics and mechanical engineering, I would love some feedback.

My plan is to build a short rostock-style printer using the main inkjet cartridge axis of an inkjet printer for each "axis". I'm not sure yet how accurately I can make these move because they are driven standard DC motors, but they do have a pretty accurate feedback sensor built in. I wired the oldest one of them up to an Arduino and I get almost 8000 steps from a movement distance of about 320 mm, which would be 25 steps per mm. I haven't tried the other two yet, but I suspect I'll get something pretty similar.

For the motor controllers, I'm building a custom solution with an ATTiny84 and an H-bridge out of MOSFETs for each motor. That way I can have each one handle any non-linear movement necessary, which should take a lot of burden off the master Arduino controller. If I end up having to use stepper motors, I can also program them as stepper motor controllers instead with the same parts.

For the hot end, I have ordered a "High Temp Mini Detail Glue Gun" which I'm hoping will have a small enough tip to be useful, since the ones we had around the house had a nozzle diameter of about 1 mm. I'm planning to tear the thing apart and figure out how to manage the temperature myself. The main problem I have with the hot end is that I didn't want to pay ~$60, but I also don't have a lathe or even a drill press to make my own. If it doesn't work I'll be looking for suggestions.

I'm going to need to build a bowden extruder, and I have a few little motors with a built-in feedback disk and several gears. I also have a small stepper motor if I end up needing it. All that's left is to figure out how to build some kind of enclosure, or at the very least a way to hold the filament and tubing in place.

I haven't decided what to do about everything else:

I need a bed to print on, and I'll probably get a PCB heatbed eventually.

I have to find something to mount the axes on, which is going to be tricky since there isn't much to mount with. We've got a bunch of particle board and 2 by 4's in the garage I'm going to try to use.

The ink cartridge carriages are oddly shaped and I need to find a way to mount the universal joints for the arms of the print head onto them.

I'm also not sure what plastic I want to use. PLA seems like a good beginning choice. I wanted to use ABS, but without a heated bed and good ventilation, I think I'm going to wait. I also have a pile of plastic from the printers that I'd like to figure out how to recycle, but I have no idea what types of plastic they are. Any ideas?

Thanks!

Such efforts are always good, you might have more fun with building a proven design first, though. For example, there is no electronics dealing with DC motors and position feedback so far, one had to put a lot of work into getting this going ... to save some 20 dollars.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

I think I'm actually saving over $100 so far. I'll probably make a detailed comparison at some point. Another advantage is that I will get to learn much more about how these things work by creating one myself rather than just working off someone's well tested design. You're right that I would have more fun with a proven design right away, but I won't get the same satisfaction of having created my own.

Hello!
I know how to get infinite amount of second hand printers that nobody uses anymore. I am just wondering, if it is a big trouble to connect these motors to adurino and the software? Where could I find information about that and maybe you managed to do that already? I would appreciate a few tips!
Thanks!
Mat

I can't say I recommend this route for building 3D printers. I did manage to get an Arduino hooked up to the position sensor and getting feedback, but when it comes to printing, accuracy is extremely important, not just *eventually* hitting the target position. I decided that the strength and accuracy of a stepper motor is vastly superior to that of any kind of DC motor with feedback, enough to warrant paying ~$15 each for them.

As for how I figured it out, I recommend trying to find the part number on the feedback sensor and looking it up. I was able to find where someone told how they work. It's been a while, but IIRC, one side has an LED, and the other side has 2 feedback sensors that toggle out of sync with each other. I just hooked them up to the Arduino and used interrupts to increment/decrement a counter based on the state of the pins.

That's all the advice I can offer.

I have used an old printer axis and used the print head carriage as my x carriage via many cable ties. However I modified it to accept a stepper motor (basically I just drilled holes to directly mount a stepper where the gearbox from the dc was) . It worked really quite well, I used this machine to make parts for a proper axis, which does work a little bit better. The belts used in printers are fantastic though, you can drill out the tiny pull to 5mm and stick it on your stepper with a drop of superglue. Comes off quite easily with pliers.

One thing I will mention is that the linear rod in the printer I used was 9mm. I couldn't find linear bearings or even bushings in this size so was stuck with the bushings on the print head carriage which are near impossible to mount to anything else. Eventually I purchased some 9mm inner diameter bearings, removed the inner race and these are working superbly as some low cost bushings. I keep them very well lubricated, but see no sign of wear. There is zero slop, they really are great bushings!