CupCake CNC build, part 11: Building the Plastruder & finishing up

3D Printing & Imaging
CupCake CNC build, part 11: Building the Plastruder & finishing up

Building the Plastruder isn’t too difficult, but it does take about two hours. I’m highlighting the general build process. You are going to want to follow the official directions carefully, double-checking everything. It’s not hard to build, but having a short, or other problem, can lead to disastrous results.

I like how MakerBot Industries describes the Plastruder:

You can think of it as a souped-up, robotic hot glue gun.

Here is some interesting information about the Plastruder:


  • Accepts 3mm plastic filament
  • Maximum extrusion rate: 16mm/second
  • Maximum temperature: 260C

Usable Plastics

  • ABS – recommended polymer. cheap, ubiquitous, low shrinkage, strong objects. ABS == Acrylonitrile butadiene styrene.
  • PLA – excellent polymer. made from corn, transparent, eco-friendly, biocompatible and biodegradable in the body. PLA == Polylactic acid.
  • HDPE – cheap polymer. very smooth, relatively high shrinkage factor. HDPE == High density polyethylene.
  • CAPA – fairly expensive polymer. very low melting point. low friction. CAPA, aka PCL == Polycaprolactone.

Start be removing all the protective plastic from the acrylic. Warning: This is not fun! Use a small screwdriver to pick at the edges. It will make the process a lot easier.


Next it’s time to assemble the “weird dinosaurs.” You will have (2) left parts, (2) right parts, and (4) base pieces. You can read all the details in the official instructions. All the parts are laser etched, which makes assembly really easy.

Idler Pulley:


Next we have to make the idler pulley. The first step is to glue the bearing into the outer acrylic wheel. You need to lift the outer wheel up by resting it on a pair of washers. One you have everything level, apply a liberal amount of crazy glue, or any fast drying all-purpose glue, around the bearing.

Tip: Draw a few lines on the acrylic wheel, radiating out from the center of the pulley. This will make it easier to see the wheel spinning when extruding.

Barrel Assembly:


Now let’s start building the barrel assembly. The first step is to prepare the Nichrome wire. The wire needs to be cut to a length that gives it exactly 6 Ohm of resistance, about 300mm’s long. Grab your multimeter and start taking measurements!


Once you verified the 6 Ohm’s on your meter, attach each end to the heater wires with the included crimps. Once crimped, solder the connection and wrap in the supplied Kapton tape. Do this for both ends of the Nichrome.


Now we need to make the thermistor connections. Trim the leads of the thermistor to 25mm long and tin them with some solder. Next, solder on (2) separate wires to each leg of the thermistor, and insulate with Kapton tape. Easy!

Note: You need to add some extra Kapton tape to the thermistor so the leads do not touch each other. I used 2 flat pieces, front and back, and it worked fine.

Barrel Assembly:


Start by making sure all the barrel parts are super-clean. Wash them, brush them, check them, double-check them! When they are clear of any debris, screw the threaded heater barrel into the thermal barrier all the way. Not too tight! Next, wrap some Kapton tape around the bottom of the barrel, and add the brass nozzle.

Note: Every revision of the CupCake CNC changes slightly. This is how I assembled mine, and future version may be slightly different. Make sure to check the latest build instructions here.


Next, I layered the Nichrome wire around the tip a few times, followed by wrapping around the rest of the brass barrel. Apparently there is some debate about the layering method? Who knew! I layered it, and it works fine.


Next, wrap the entire barrel in Kapton tape, enclosing the Nichrome wire.


Now you can add the thermistor to the nozzle using some Kapton tape. You can see the thermistor in the picture above. It’s close to the tip. Again, secure the entire assembly with a nice layer of tape.


Now you need to insulate the barrel with the included ceramic tape. Once around, followed by another layer of Kapton and you are done!


Now you need to add the retaining washer. Start by unscrewing the threaded heater barrel form the insulator. Next, add the retaining washer. You might want to add some tape to the inside diameter of the washer. This will help prevent it from scratching, and shorting out, any wires. Add the washer and screw it all back together. You’re done!

Drive mechanism:


Start by attaching the pulley to the DC motor, followed by press fitting the 606 bearing. Make sure the pulley is oriented the same way as the picture above.


Next, add the first few layers of the drive mechanism acrylic sandwich, and attach the motor.


Followed by the next few layers and the idler pulley that we assembled earlier.


Check the alignment, and spacing, of the entire assembly with the included steel rod. Once it’s aligned, tighten it all down.


Now you can attach the assembly to the “dinosaur’s” you made earlier.


Followed up by the extruder controller board.


Last but not least, attach the heater barrel with the included M3 x 16mm bolts, M3 x 50mm bolts, washers and nuts.


Now we can wire it all up and do some tests! The thermistor wires connect to the board at the location marked “Thermistor.” The heater wires attach to the board at the location marked ‘B+/B-‘. The red motor wire red goes to the location marked 1A, and the black wire goes to 1B.



No need to mount the whole assembly into your CupCake CNC. First, plug the Extruder controller board into the RepRap Motherboard with the included Ethernt wire. Install the ReplicatorG software and run through the test procedure outlined in the instructions here.

Note: I placed the extruder assembly on top of an old CD spindle cover to catch the hot plastic. Everything worked perfectly. It spit out a nice steady stream of hot plastic. Yea!


No you can go ahead and mount the whole assembly onto the Z stage we made earlier. A few bolts and you are done!

Next up: Installing the electronics & software

Ask questions! Do you want to see a better picture of a particular part, a different camera angle, a video perhaps? Maybe you have a suggestion for a cool mod or hack? Let me know in the comments. I’ll try to answer them as best as I can. Thanks!

Want to know when my next build entry is done? Follow me on Twitter @devinck!

Build history:


    Having just arrived home from a quick trip to the hardware store, I was pleasantly surprised to see a large, unmarked, cardboard box sitting on my front steps. This isn’t an uncommon event, since I am constantly checking out cool products and projects for the Maker Shed, however this box was a bit larger than normal.

    Oh wow, it’s the CupCake CNC kit from MakerBot Industries! I’d ordered it weeks earlier and had completely forgotten about it. (The truth is out: I have an atrocious memory, sad but true.)


    And so the adventure begins! I’m going to document my “out of box experience” with a MakerBot. How many posts will the series be? I’m not sure since I’ve never built one. How often will I post about the build? Again, not sure, but I’ll try to do at least one a week, maybe more, it all depends on how much free time I have between all my other maker-ly projects.

    A little background: My CNC experiences


    I’ve been tinkering with CNC for about 10 years, and consider myself an enthusiast, not an expert. I do own a few CNC mills, routers, and lathes. I have retrofitted old mills, and even build one from scratch. Pictured above is my mobile CNC machine, dubbed the “MobileC.” I stuffed all the components into a mobile tool cart so I could bring it to hackerspaces, workshops, and events, all in the hopes of helping out fellow makers.


    The mill is a Sherline 5400 that I retrofitted for CNC. Also, I added a few extra parts to make it even more useful. It has a longer reach, thanks to the headstock spacer block on the column, and a larger table that I simply mounted to the stock table. It’s a sweet machine. I love my little Sherline!


    All the electronics are housed in the cart too! There is a 19″ LCD monitor, wireless keyboard and mouse, desktop computer, and CNC controller. It’s a tight fit, but it works perfectly. There is even an extra full-size drawer for tooling and accessories.


    I’m thinking of replacing the computer, keyboard, and mouse with an HP TouchSmart, but I have to save a few more pennies for that upgrade.

    Does anyone want to know more about my MobileC? Let me know in the comments. After I build my CupCake CNC, maybe I should do a series of articles on CNC machining?


    I purchased the CupCake CNC kit with my own hard-earned cash. I waited several weeks for it to arrive, just like everyone else that placed an order. No favors, no freebies! Why did I buy one? Well, for two reasons.

    • Reason #1 – I like what MakerBot Industries is doing for the open source community and open manufacturing, so I wanted to support them!
    • Reason #2 – I am going to document the build for Make: Online, and if I like it, I’ll let you know, and if I don’t… well, I’ll let you know that too! No biased reviews here.
    • Reason #3 – I am a CNC junkie, and I had to have it, even if my wife was questioning whether I really needed another machine in my studio! “Ha!” I said, “You can never have too many machines!” Oops, only two reasons, right?! :)

    Questions & suggestions:

    Ask questions! Do you want to see a better picture of a particular part, a different camera angle, a video perhaps? Maybe you have a suggestion for a cool mod or a hack? Let me know in the comments. I’ll try to answer all of them as best as I can. Thanks!

    Build history:

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