I’ve been printing a lot lately with a couple of extruders. On my ORD bot, I use a MakerBot MK7, and on my cupcake, I use a MakerGear stepper plastruder. And what I’ve come to realize is that I don’t really like either of them. Or rather, I really like some elements of each, but not really the whole package for either.
The MK7 is very compact, and I really like that, especially for a smaller printer like the ORD bot. And the hot-end is uniquely short. It is about 20mm shorter than the MakerGear. That being said, the drive sucks. The filament “idler” is a piece of delrin that is held pressed into the filament using not a spring, but the flex of the drive housing. There’s a lot of stress there, and no adjustment. It is also driven directly off of a NEMA 17 stepper motor. That would be great if it needed to turn at high speeds, and it does mean thet there’s no gearbox to take up space. But it doesn’t turn at high speeds, and to get the needed torque It sucks down about 1.6A. That means the motor gets really toasty (so there’s a heat sink to cool it, which takes up space), and the driver gets so hot that I have to fan-cool it or it goes into thermal shutdown. Not good.
The MakerGear, on the other hand, uses a geared stepper. It has awesome torque, even with the driver turned almost all the way down (so the driver and motor are always cool to the touch). The only problem is that the gearbox takes up a lot of space and weight. But the filament drive uses a proper ball bearing driven by springs, and the drive gear is accessible so you can clean it without dismantling the extruder. My only real kvetch is that the hot-end is long (and unlike the MK7, not all-metal).
So I have two extruders, and in the end, I don’t really like either of them. Frankly, I can’t find one I really do like, but that’s just because I’m very picky. But I have tools, so I’m not allowed to complain. I need to design my own extruder. I started with the hot-end. I wanted something like the MK7, but lower friction. The MK7 has a relatively high-friction thermal barrier, which is also made of the somewhat thermally conductive stainless steel. I don’t plan on extruding any crazy polymers (such as ploycarbonate… yet), so I shouldn’t ever need to go above 280ºC. This means that I can use a plastic thermal barrier. Stainless is alright (an order of magnitude less conductivity than brass), but something like PTFE or PEEK (an order of magnitude less than stainless) is even better. PTFE also has crazy low friction. But it’s not strong, so I can take a page from MakerGear and make a hybrid insulator. I came up with a PEEK shell and a PTFE liner. The PEEK provides structure, and the PTFE provides low friction.
The heater block was fairly simple. I took a block, and added a threaded hole for attaching the nozzle and thermal barrier. I used a power resistor for a heating element, since they’re cheap and easily available. And just for kicks, I threw in a divot to stick a thermistor in. I spent a while trying to decide if I wanted a thermocouple or a thermistor. Thermocouples are good to 1600ºC (not necessary) and need no calibration (nice). But they’re incredibly noise sensitive. have one on the MK7 extruder, and even with tons of filtering can’t get all the noise off the signal. So I decided on a thermistor, which is pretty much noise-proof (nice), and cheap (even better).
And so the last component is the nozzle. I have no engineering background, and so I don’t really have any way to quantify the design of something like a nozzle. So I went on intuition and drew out something that just looked right. But now enough blathering, it’s time to make this beast.
Here’s how the thermal barrier came out. I single-point cut the M8 threads on the lathe because I didn’t have a die, drilled it out to 4mm, and slipped in a bit of PTFE tubing. That was pretty easy.
The heater block was another easy one. It has two holes, and was a nice quick job on the mill.
This was the hard one. I turned the nozzle out of hex bar. The threads were cut on the lathe again, but the nozzle hole was drilled on the mill. I just can’t make the lathe go fast enough to use a 0.4mm bit.
And here it is assembled, with a US penny for scale. I assembled it, cemented in a resistor, and fired it up. I don’t have a drive for it yet, so I just pushed filament through by hand. It went through easily, so that’s a success. And it came out 22mm shorter than a MakerGear hot-end, so that’s a success. I guess now I have to build a drive for it and really put it through it’s paces. Or make a bunch more. Or both.
I got another 3D printer. Although really, given how much I love those machines, it was only a matter of time. But this one is different. This is the new hotness in 3D printers, the Quantum ORD Bot.
It’s small, cute, and and neat. It’s made of makerslide, which is an aluminum extrusion with v-rails on it. When combined with v-wheels, it’s pretty much instant linear bearing. And like anything made of linear bearing, it’s rigid and smooth, and that combination leads to fast.
I got my hands on this one for beta testing, and it wasn’t long before I took the nice clean aesthetic and draped it in tangled masses of wires.
I started with a heated build platform. I took this one off my cupcake, because the ORD bot prints with ABS and ABS doesn’t work without a heated bed.
With the addition of the heated bed and a thermocouple amplifier for the extruder, my RAMPS board quickly got all messy. But hey, it’s still pretty dang neat.
But the proof is in the results, so let’s skip to those.
This herringbone gear was one of the first things I printed. At this point, I had a poorly aligned z-screw, which was causing a ripple in the z-axis. But the print quality was still miles better than what my cupcake had to offer, so I pressed on.
Here’s a heart gear. It’s a very complex profile, and it printed almost flawlessly. I’m happy.
And here’s a quick video of an early print, printing more heart gears.
I will be bringing the ORD Bot to CNC night at Pumping Station:One (Chicago’s hackerspace) on the 14th.
I plowed through the rest of the extruder daughterboard and just finished it up.
Here’s what I added. The header on the right is for the thermistor. It has a pull-up resistor and a filtering capacitor. The header in the middle is for the heater. It connects to the MOSFET in the middle.
And here’s the finished board. There’s not a whole lot there. And to think that this replaced my whole extruder controller. It’s not quite Moore’s law, but it’s close enough for me.
Here’s a short video showing the printer running.
Success!
With sprinter, thanks to the acceleration, I was able to boost my print speeds from 30 mm/s to 80 mm/s. I can go faster, but it gets pretty scary. Additionally, the reversal works millions of times better than the reversal in my hacked makerbot firmware before. As in, it actually works. I think now I should print something big to celebrate. Maybe another 3D printer?
I’ve been steadily printing on my trusty cupcake for a long time. And I’ve gotten my prints tweaked well enough, but I’m definitely falling behind in the print quality game. No one really writes Gen3 firmware anymore, and so I began looking for other ways to update my printer. I didn’t want to build a new printer (not out of the question, but expensive), nor did I want to put other electronics on my cupcake (also expensive). And so the game was on. What could I cobble together with what I had laying around? So I began by researching firmware. And I found that kliment’s sprinter firmware can support Gen3. So I popped it into arduino and started tweaking, and with only a little while of tweaking the pin definition file I could run the x, y, and z axes. Great. That was easy. The only problem was that I can’t use the extruder controller. No big deal there either. Just build one. And so I began.
Here’s the stock motherboard. It has a row of blank pads on either side of the AVR chip. These are for adding things on, which is exactly what I want to do.
So I soldered on some headers. Now it’s like an arduino, and I can just make an extruder “shield” to fit on top.
And after soldering some more headers to a piece of protoboard, I have my very own blank shield.
The only problem is that in all those headers, there isn’t a single voltage supply pin. There are three grounds, but not a single +5 or +12. So I needed to wire some in. This is the solder side of the ATX power connector on the motherboard. There is a very convenient hole to run wires through next to it.
I have some nice 4-conductor cable that came off some fiber-optic receivers, and it happens to fit perfectly here. So I took 3 conductors and soldered them to +5, +12, and an extra ground. It’s not especially pretty, but it’s plenty solid.
And the cable exits cleanly through that hole I mentioned earlier.
I wired the other end into the protoboard. I also added some headers and wiring for a pololu driver.
I still need to install the heater and thermistor control, but I was able to test the motor as is. And it worked!
Here’s a short video demonstrating the motor running under computer control.
Previously, I discovered that I had made the internal thread in my boring head too large. There was no way it was going to fit accurately on a standard 3/4 – 16 thread. And then some members on the HMEM forum pointed out what I had been overlooking: I have a lathe. If I screw up and make an over-sized nut, I can just make an over-sized bolt to match. So that’s exactly what I went about doing to make an arbor.
I started by turning a 0.5″ diameter shank 1.5″ long from some 12L14 mild steel. I also turned down a small section right next to the jaws so I would have a reference surface that is concentric to the shank.
I then turned it around and used the reference I made before to center the part in the 4-jaw chuck. Since the whole boring head will spin around this part, it is important to make this as concentric as possible. Any runout here will transfer down the line later.
The end was turned down to 0.765″ diameter, and a relief turned.
And then I cut 16 TPI threads into it. I kept taking off small amounts until it just threaded into the boring head.
It threads in nicely. No binding, and no play. That’s one less scrap part, so It’s time to move on.
I finished cutting the threads, and when checking them with a 3/4 – 16 bolt, noticed that it was loose and seated at an angle. Not good. But at least I figured out what I did wrong. Earlier, I bored out the thread’s minor diameter to 0.7031″. That’s wrong. It should have been 0.6875″. That extra 0.015″ makes the fit sloppy, and causes the bolt to seat at an angle. So this one’s a failure. Time to start over.
I spent a couple hours pondering how to make an internal threading tool. And then I got bored, and started browsing through the archives of MadModder. And an answer materialized. So following (more or less) the guidelines in this post, I made an internal threading tool.
It isn’t pretty, but it does the job well. For scale, the diameter of the shank is 3/8″.
A couple very shallow cuts confirmed that the tool was cutting and that I was, in fact, cutting a 16TPI thread.
This is my setup for internal threading. The compound is set at 29.5 degrees opposite how it would be for external threading, and the cut is dialed in by retracting it. This ensures that the cutter is advanced into the face of the thread being cut. There’s a groove in the back of the threads for the tool to run into, but it’s very, very narrow. To help me not miss it, I have a dial indicator set up so I know where to end each pass. The lathe is set in the lowest back-geared speed (26 RPM) so I have plenty of time to react. External threading is one thing, but internal threading (to a shoulder!) is another entirely, and so I need to run the lathe slow. The fastest I would want to run it might be 100 RPM anyways, because the tool is silver steel, and can’t go very fast. I apply the tiniest drop of cutting fluid before each pass, and the threads come out nicely.
And here’s where I stopped. They’re getting close to done, but I don’t have a bolt to check them against. So now it’s off to find a hardware store that carries 3/4 – 16 bolts.
I cut off a couple 1.25″ lengths of the cast iron bar, and faced the ends to make them pretty. The big thing about this cast iron bar is that it isn’t round. So although the ends of the bar are flat now, they aren’t necessarily perpendicular to the length, or even parallel with each other.
I popped one in the 4-jaw chuck, and faced the end again. I now have an end that’s flat and straight as long as it’s in the same setup. I then turned down a section to 1.395″, as called for in the prints. That section is now actually round and perpendicular to the faced end. This end of the workpiece is now a datum, a reference that I know and can work off of for my next operations.
This end of the stock gets threaded 3/4 – 16. So I started by drilling out to the largest diameter I have, which is 1/2″.
And I then bored it out to 0.7031″, which is the required diameter for putting in 3/4 – 16 threads. Since the bore was done in the same setup as the facing and turning, the bore is concentric with the outside diameter.
And now I face a conundrum. I don’t have a 3/4 – 16 tap. And I don’t have an internal threading tool. I have some broken cutters I could grind into one, but they’re all carbide, which my aluminum oxide grinding wheel just can’t handle. So I’m stalled until either I buy one or think up how to make one. Stay tuned.
I haven’t been completely idle on builds like TinyMill.
I’ve just needed more tools.
One thing I’ve been wanting for quite some time is a boring head for my mill. And when I was re-designing the x-y stage for TinyMill, I realized that I actually needed one. So I’m going to build one, because I’m crazy. I’ll be following another one of Dean’s builds.
One thing that I considered in my decision to build this was cost. And because I don’t just happen to have large diameter pieces of steel lying around, that could be pretty high. And then, when looking at metals, I noticed that for some reason, fine grain cast iron was cheaper than steel. And after a lengthy discussion on the HMEM forums, I reached the conclusion that cast iron would be alright.
So this is where I am now.
I have a 1 foot length of 1 3/4″ cast iron, and some new hacksaw blades. Hopefully they’ll ease the process of cutting this monster.
And now, if you’ll excuse me, I have a date with a bench vise and a hacksaw.
I’ve been wanting a carriage stop for my lathe for a while. I just never liked that they often weren’t adjustable to a great deal of precision. So I set about designing my own. The drawings for the main block are here and the clamp here.
And here it is, complete with a Tumico micrometer head I scored on eBay for $5.
