Building a MakerGear Stepper Plastruder for a Mendel Prusa

Since I’ve already received word that my write-up on the mechanical build was useful, here are some similar notes on building the hot-end and extruder.

The overview instruction page is on the MakerGear website. I’ll go through the sub-pages step-by-step. Again, sorry for lack of images, I’m happier writing than drawing (which is why I’m not much of an artist yet!)

Building the heat-core

Instruction Page

Third hand

The vital tool not mentioned in the tool list is a “third hand” or “helping hand”. Mine cost me about $12 from my local Jaycar store. Two ball-mounted alligator clips and a big magnifying glass. It earned its keep in putting all the crimps on the wires, which is impossibly fiddly otherwise. Nophead’s video shows how to do the crimping, but he’s a hard man and an expert and he doesn’t need no stinkin’ third hand. If your hands shake at all when doing fiddly stuff, you’ll thank me for my advice.

Cutting the nichrome crimps

When you go to cut the ends of the nichrome crimps, be careful since they deform easily. I cut one with diagonal cutters, then compared it with the un-cut version so I knew how to bend things back the way they should be. My eyesight is not the best, and I squished a part I shouldn’t have, but it was fixable.

Stripping the Teflon wire

The green Teflon wire coating is both tough and very slippery. My pieces did not have their ends stripped, and I screwed up trying to strip them with my cheapo wire strippers. The Teflon was so slippery I couldn’t hold the wire tight enough while the strippers did their thing. So I used a pair of flat-nosed pliers. Before the strippers worked their way through the insulation, my pliers slipped and tore a 10mm chunk out of the insulation. Oops.

Now we don’t get any spare high-temperature wire in the kit, and it isn’t available in my local hardware store (or Jaycar – maybe American electronics stores are better). So I was stumped. I thought about using heat-shrink tubing, but everything I read (and the markings on the heat-shrink) said it can’t cope with the temperatures the extruder gets to. I was reduced to asking for help on the MakerGear group, and within minutes (while I was having lunch) Rick suggested wrapping the tear in kapton tape (the really dark amber stuff you are going to be using later to tape the thermistor to the nozzle). A simple fix which kept my build humming along.

Talking of temperatures, electronics solder melts at the sort of temperatures the hot-end gets up to. I wonder if that is part of why we have to encase the crimped joint in the ceramic compound? It’d be annoying to have molten solder dripping down onto your prints. High temperature joints are usually crimped without soldering.

Crimps in general

I found I really had to concentrate, and zoom in on the photos to be sure I was using the right crimps. Male and female are different, and there seemed to be different sizes too, and different plugs for them to fit into. Keep the different crimps separated, and with their labelled bags to reduce the chance of getting them mixed up.

Before you add any ceramic

This step took a while. I wasn’t ready to open up all the other bags, but I couldn’t tell what was so important at this stage without learning what a groove-mount was, and I didn’t want to mess up another stage that couldn’t be undone. So here’s what I learnt.

The big metal washer isn’t part of the final product, and neither is the big bolt that the heat-core sits on while you put ceramic on it and cure it. The washer just helps to keep the green wires aligned and in the right place while you apply the ceramic. The bolt is just a stand-in for the bronze hollow tube that you’ll replace it with later once you’ve stopped fiddling with the goopy heat-cured ceramic stuff.

The heat-core itself is a bronze nut-like thing with a thread on the inside, a carefully wound layer of nichrome wire wrapped around it (Thanks MakerGear for doing that for us. I have unhappy memories of rewinding H.T. transformers back in the 1970s.) and a layer of ceramic over the wire that makes it look spherical.

The key thing to note is the flat metal faces on each end of the heat-core. They are going to have to but up hard against other metal parts, and the heat transfer needs to be good. That is, you don’t want any ceramic extending past the main body of the brass heat-core. You have to try to get the metal parts of the nichrome crimps, and any bits of nichrome leading to the crimps, between the top and bottom of the heat-core. This way you can cover them with ceramic without them getting in the way later. Try to keep the crimps roughly parallel to the bolt, and you won’t have any trouble routing the wires over the groove-mount later.

Leave the ceramic overnight

I know it says ‘you can proceed immediately’ if you are stupid impatient, but I don’t think it is worth it. The fresher the ceramic, the wetter it is. Any water in the ceramic turns to steam and makes frothy bubbles. You don’t want frothy bubbles in your hi-tech robot do you? If you need to file or sand down any lumpy bits, you’ll see hollows in the ceramic where bubbles formed – which can’t be making it any stronger. Let it dry overnight and the curing process will be easier.

Heat curing the heat-core

The scary bold-face warning about not exceeding 240 degrees is specifically if you’ve already mounted your heat-core onto your hot-end. Which you haven’t yet. Regardless of that, since you will be curing it without temperature regulation, don’t leave 12V connected to the heat-core for more than 2 minutes at a time.

You need 12V at roughly 2 amps (unless my maths is wrong – the nichrome resistance was about 6 ohms on my heat-core). Since my only 2 plus amp power supply was 13.8V rather than 12V I decided to use the Eagle ATX supply MakerGear provided with the kit. My previous post talked a bit about the strangeness this entailed.

One thing I forgot to mention there was that I left the green two-pin plugs off the thick black 2-core power supply cables til after I finished curing the heat-core. I temporarily stuck the bare ends of the black wires into different holes on the white plastic 12-wire screw connector that will later be cut up for the stepper motor wiring. The black two-core power leads went into one side, and the pins on the end of the green heat-core wires went into the matching holes on the opposite side. Carefully, because I didn’t want to crush or deform the pins on the green wires.

[Update: Much more complete description of using the ATX supply for heat-curing]

The yellow leads on the ATX supply carry 12V, the black are ground, and the red are 5V (which you don’t need at all).

Trick your power supply into thinking you’re a PC

Yet another thing I forgot to mention. The ‘Differences’ file does cover this, but quite a bit later on. The ATX power supplies are designed for computers. The computers provide a special signal to say “I’m awake” or “I’ve shut down now”, and we have to fake that. Luckily its easy.

The largest of the connectors on the ATX wiring harness is at the end of the cable covered in black woven braid. The MakerGear kit includes a matching white socket that this big 24-pin plug fits into. Two adjacent pins on this socket need to be soldered together.

Look at the photo in the power supply section of the ‘differences’ file, and look at the white socket. On my socket the wonderful MakerGear folks had marked the two pins with green pen. I checked that against the ‘differences’ file (everyone can have an off day…) and since they agreed with each other, I soldered a piece of solid heavy wire across them.

Then I tested that the power supply started when plugged in and switched on. The fan spun, so I was happy. So I wrapped the connector up in self-amalgamating tape to guard against accidental short-circuits.

Mark your connector with polarity

Turn off the ATX power supply. Plug the small square white 4-pin socket into the matching 4-pin square plug on the ATX wiring harness. There is only one socket and plug matching this description. Really plug it in, so you know you’ve got the alignment right – they are keyed so you can’t connect them the wrong way round.

Now looking at the wires on the harness end, two are yellow (12V), two are black (Ground, 0V). You need one of the wires from your black twin-core cable soldered to a pin that lines up with a yellow wire, and the other to one that lines up with a black wire. Use a DVD marker pen to mark the white socket with a ‘+’ where the yellow wire leads to, and ‘0’ where the black leads to. (It might work to connect both the yellow pins together, and both the black pins together for extra current capacity, but I haven’t successfully tested that. I just picked one yellow and one black) .

Cut your power supply cables to length

Find your length of thick black twin-core cable. Cut it in half. Put one of the pieces away for building the heated bed, much later on. (I haven’t built mine yet, I don’t seem to need it for the PLA I’m printing with.)

Cut the remaining half in half again. One of these quarters will connect between the high current plug on the ATX supply and (eventually) the 11A connector on the RAMPS board. This is the cable we’ll use for heat curing the heat-core. The other quarter of the cable will go to the 5A connector on the RAMPS board, and we don’t need it just yet.

Prepare for soldering

Unplug the white connector and stick it in your third hand, or desk vice or whatever.

Look closely at your thick black twin-core cable. You’ll see one wire has embossed writing on it, and the other has hard-to-describe lengthwise ribbing. I use the ribbing side as +12V and the other side as 0V. Make a choice and stick to it througout your build. Getting the ends of your power cables mixed up will trash your electronics in a major – possibly fire and smoke – way.
Ideally you now want to separate the twin-core wires for an inch or three, and slide a half-inch piece of the green heatshrink tubing over each wire, so you can slide it back over the joint when you’ve done soldering. You can see the end result in the photos in the last photo in the ‘differences’ file.

Soldering the pins

Solder the +ive side of your twin-core to the + pin on the connector, and the 0V side to the 0 pin. It’s tricky because these connectors aren’t designed for soldering (misusing technology is part of being on the cutting edge!) Use a multimeter to confirm there is no contact between the + and 0 pins (that would be very bad at 11 Amps). Check that there is contact between the pins on the socket and the corresponding wire at the other end of the twin-core.

Connecting the heat-core ends of the power cable

Find the white plastic screw-terminal block with 2 rows of 12 shiny screws in it. Each of the 12 screws on one side of this block connects to the screw directly opposite it, and not to any of the others. We’re using it temporarily here to make our connections safer while heat curing.

Plug the bare end of your black twin-core into the block (one wire into one hole, the other into the one next to it, not the one opposite it). Do the screws up firmly. Confirm with your multimeter that the pins on the socket are not connected to each other. Confirm that the wires can’t accidentally pull out.

Plug the square white connector into the ATX wiring harness. Turn on the ATX. The fan should spin. Use your multimeter (on voltage setting this time) to check that you’ve got 12V (or 11.something) on the screws of your connector block. Yay! This is enough to cure your heat-core.

Turn off the ATX again. Put the pins from your heat-core into the holes in the screw-terminals opposite the ends of your black twin-core cable. Gently tighten the screws til the pins are held firmly but not squished.

Start heat-curing

Start your stopwatch, turn on power, turn off power after 2 minutes. Let cool.

When I started the curing process I measured the voltage on the white screw terminals going to the heat-core. There was voltage, and it had dropped from 11.65V to, I think, about 10.5 V. This was a relief because it meant the heat-core was soaking up current. After a minute or so I could feel the air getting warmer and smell a plastic smell. When the stopwatch reached two minutes, I turned off the power supply. Yay. Iteration one completed.

After about 10 minutes I gave it another 2 minute burst. Repeat til the new ceramic you applied looks the same colour as the original ceramic on the heat-core. For me, I think 4 heating cycles got the colour matched.

Now you’ve finished the heat-curing, and turned off the ATX again, you can disconnect the black twin-core and the heat-core from the screw-terminal block.

Attaching power cords to RAMPS board

Find the strange green connectors that fit into the RAMPS 11A and 5A sockets on the RAMPS board. Note which way they fit into the sockets, and look on the PC board next to the sockets. The size of the huge + and – signs are a hint that you need to get this right! On my board, looking down from above with the sockets nearest me, + is on the left and – is on the right. The left-most socket is 11A, the rightmost is 5A. I labelled the tops of my connectors (11A, +, -) and (5A, + -) so I’d never get them mixed up.

Plug the bare ends of the black twin-core into the plug that you’ve just labelled (11A + -). Remember which side of the cable is +. The other side is 0 (or -, compared to the +. We don’t have any true negative voltages in this system, and people familiar with electronics often use ground, GND, 0V and – as synonyms).

Now you’ve got half of your power supply needs wired up. Follow the same proceedure using  the rectangular (Molex) connector in place of the white square one. Though obviously you won’t be heat-curing with it. The rectangular connector goes via the other length of black twin-core to the green plug which you labelled (5A, +, -).

Once you’ve got both the green plugs wired up, but not connected to the RAMPS board, turn on the ATX again and do a last paranoid check that you’ve got the right voltages, and they are the right way round (matching your labels). Then turn off the ATX again, and leave the green plugs unconnected to the RAMPS until you are ready to test your extruder or motors.

Now we can go back to building the plastruder.

Attaching connector to heat-core (crimps again)

When you put crimped wires into connectors, there should be a distinct ‘click’ that you may feel through your fingers rather than hear. If the lead doesn’t set fast and resist being pulled out, there are four possibilities.

1. You are plugging it in to the wrong end of the connector (just as illustrated on the instructions d’oh!)

2. You’re plugging it in the wrong way up, or sideways. These crimps are keyed – they have bits that stick out (usually on the sides) that mate with invisible notches inside the connector. You nearly always want the wire side up as you slide the crimp into the connector, otherwise it won’t lock in place.

3. You haven’t pushed it in far enough. This caught me out with the thermistor. My thermistor had been working fine, then it ‘failed’. When the RAMPS system loses touch with the thermistor it refuses to heat the hot-end, to avoid disastrous overheating and burning down your house. I couldn’t work out what was wrong, so I wiggled all the wires and the thermistor wires pulled right out of the connector. I blame it on the horrible slipperiness of those PTFE coatings. The solution is to use a jewellers screwdriver and push the crimps in further. When I felt the crimps ‘click’ I was a happy man again.  When Pronterface started reporting ambient room temperature readings again I was even happier!

4. You’ve got way too much solder on the joint and the crimp can’t fit into the connector – there should not be any metal visible at the back of the connector. You’ll have to use your solder sucker to remove the excess.

Building the Bruthead filament drive

Bruthead instruction page

Now I’m no expert here. I’m having real troubles getting the filament past the geared head and into the hole in the groovemount. I didn’t find a 3” metal rod for checking the filament guide alignment. Maybe I should have taken the hint. The biggest of the Bruthead plastic pieces was by far the least well-printed of the printed plastic in the kit. I can see it is a hard part to print, but the inside was quite rough. I’ve taken it apart once, and fed PLA into the gear-head from underneath. That worked fine, and that piece of PLA worked well in the extruder, but it’s not a long term solution. I’m wondering if I’ve done something stupid Sad smile

[Update: Maybe I am an expert after all. I’ve developed a method for loading filament into a bruthead. It works, it extrudes nicely, I’m happy.]

Building the Hot End

Hot End instruction page

Lock-nuts

Follow the instructions and the photos. Use two small wrenches/spanners to tighten the lock-nuts, close to the nozzle. I have two small adjustable wrenches that have been invaluable for the whole build. Don’t put the lock-nuts far away from the nozzle, as you get too much chance to bend things. The hollow brass bolt-thing is not strong against bending forces, and at least one person has snapped theirs in half by applying force in the wrong direction.

Ok, don’t follow all the photos. Never use pliers to hold onto a nut, always use a spanner or wrench.

PTFE tape

I’m ignorant here – I don’t know what this is supposed to do, and I hate working with PTFE tape. It creases and kinks and catches on things and blows away in the breeze from the fan, clogs up when I’ve got too many layers. Hate it. I can’t remember whether I ended up with any on my hot end at all, but I sure remember trying. At some point the red mist descended and I gently put everything down and went away. Be patient. Eat chocolate. (Wash your hands first – who knows how toxic some of this ceramic stuff might be.)

Hand tightening the Groovemount onto the heater barrel

Important note: recent kits have a steeper nozzle which results in a gap of 2mm or so, rather than the 1mm mentioned at the beginning of this section. I spent a lot of time assembling, disassembling, re-wrapping with evil PTFE, etc. trying to match the gap in the photo before I scrolled down far enough to see a different photo, and realised that the gap I had was ok for the new nozzles. Maybe I didn’t hate the PTFE tape the first time after all – memory hazy.

Securing the thermistor

It’s not obvious to eyes as old as mine, but the thermistor has a flat side and a round side. Put the flat side against the nozzle and it’ll be much easier to wrap the kapton tape around it snugly.

Simplified Mount

Simplified Mount Instructions

I have nothing to say here except make sure that the bolts you use to fasten the groovemount and extruder are the right length to not contact the motor, and don’t leave out the wooden piece – it is important thermal insulation to stop your printer bits melting when you print at ABS temperatures.

That’s all folks

Comments and corrections encouraged.

Next post should be on getting the electronics up and running.

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20 Responses to Building a MakerGear Stepper Plastruder for a Mendel Prusa

  1. MC says:

    Brazen,
    Can you clarify on two things: D1 and curing the ceramic? The former is straightforward: do we need D1 on the RAMPS board or not? I’m reading both yes and no from different sources. As for the adhesive, I’m not clear on how you got it to work with the power supply. I gently stuck the heat core pins into the red and yellow sockets of the PS, turned it on, and nothing. Am I missing something? Thanks.

    • MC says:

      Nevermind, I guess yellow is apparently the 12v and black is ground. However, I’m rereading your previous post and it sounds like the Eagle PS has to be terminated onto the RAMPS board before it will output 12v to cure the ceramic?

      • BrazenArtifice says:

        I could have been more clear with my explanation of the power supply connections.
        You are right that the yellow leads on the ATX supply carry 12V, the black are ground, and the red are 5V (which you don’t need at all).
        I’ll update the plastruder post with a much more complete description of what I did. The short answer is that you don’t need to terminate the PSU to the RAMPS to do the heat-curing. You just have to ensure you only connect one cable to the PSU, not both of them, for the heat-curing.

    • BrazenArtifice says:

      You don’t need D1 at this point. I’m not using it. Leaving it out means your RAMPS board gets its power (for the arduino electronics) from the USB connector to your PC, not from the ATX supply. The 12V from the ATX supply just drives the stepper motors, heat bed and extruders. If you later want to run the printer from an SD card and not have it connected to the PC at all, then you might have to look into using D1.

  2. Pingback: Using an Eagle ATX powersupply to cure a MakerGear heat-core | Brazen Artifice

  3. Mark C says:

    Thanks for the update! After I took a break this morning, I looked back and noticed I had skipped the part in Brock’s article about the PS. Even though the 24-pin connector referenced is not included in the kit, I eventually figured out the PS needed to be tricked into turning on.

    This is probably by far the most interesting/frustrating/educational project I’ve embarked on so far. Can’t wait for more of your write ups!

    • BrazenArtifice says:

      There should have been a 24-pin ATX connector in your kit. It fits onto the biggest of the power supply plugs, the one that has a black braided plastic sleeve leading to it. My connector was white, and the MakerGear folks had kindly marked in green pen which two pins I needed to solder together. Once I’d soldered them together, checked for shorts, and tested that the PSU worked, I covered the connector in self-amalgamating tape to guarantee no nasty surprises if I let it touch my metal bench legs by accident.
      In fairness to Brock, he tells us how to wire the PSU up when we need it for the ramps, not at this early stage where we’re bodging it up to cure the heatcore.

  4. Pingback: More ATX power supply hacking | Brazen Artifice

  5. “On my socket the wonderful MakerGear folks had marked the two pins with green pen. I checked that against the ‘differences’ file (everyone can have an off day…) and since they agreed with each other, I soldered a piece of solid heavy wire across them.”

    fyi, this is a logic signal, any wire will do

    “You don’t need D1 at this point. I’m not using it. Leaving it out means your RAMPS board gets its power (for the arduino electronics) from the USB connector to your PC, not from the ATX supply”

    If you do later want to power your ramps from the ATX supply, you could use the 5VSB signal from the big connector. I think it’s the purple wire. This wire provides 5v at all times that the supply is connected to mains, regardless of whether or not it’s “on”.

    My electronics is set up like this, and I also connect that magic green wire into my arduino so I can turn the power on and off via firmware 🙂

    • BrazenArtifice says:

      Thanks Triffid, that’ll be useful when I get round to running off SD card independent of the laptop. I’m not exactly happy with the idea that the big solid-looking ‘mains’ power switch on the PSU doesn’t really disconnect it from the mains 😛 More things to unplug during thunderstorms.

      I’m glad to know you read this, hopefully you’d catch any stupid mistakes or misunderstandings I might make. I had wanted to get up to meet you at the Gold Coast hackerspace Saturday, but it sounds like both our better halves had higher priorities 🙂 Maybe I can come see you sometime?

  6. Pingback: My Mendel Prusa 3D printer is brazenly extruding plastic | Brazen Artifice

  7. ed says:

    Hi Brazen,
    I have been following your instructions thankyou! I was wandering if you might be able to help me with a problem with my ATX. (i am building a makergear prusa mendel). It will not turn on! I have soldered the indicated pins together but it will not turn on!? Do you know why this might be? It’s the atx voltas 500W.
    Thanks
    Ed

    • BrazenArtifice says:

      Hi Ed,
      I’ve certainly had a few times when my ATX power supply wouldn’t turn on, so I know the feeling.

      I’ve written two posts that include information on getting the power supply working,
      electronics assembly notes, and Building a MakerGear Stepper Plastruder (which is the one you commented on). Maybe reading both will give you some extra insights.

      Getting down to brass tacks: –

      First, check that you’ve got the voltage switch on the power supply’s metal casing set correctly for your region.

      I’m assuming you soldered the indicated pins on the loose socket that came with the kit, rather than directly on the plug on the power supply loom?

      Plug the socket onto the end of the power supply plug. Check the color of the wires leading to the pins you’ve soldered together – one should be green, the other should be black. If in doubt, look at the photo in the ‘Differences’ file.

      Disconnect the socket from the power supply plug. Check with a multimeter on resistance range that the two pins you soldered together really are connected, and that all the other pins are not connected to anything (ie that you don’t have any accidental solder bridges). You can’t judge this by eye, you need a multimeter, even a cheap one is fine. If you find a problem, fix it!

      Re-connect the socket to the power supply plug, and make sure none of the pins on the back can contact anything conductive during testing. (You’ll wrap them up safely in insulating tape once you know the power supply is working).

      Unplug any other sockets you may have connected to the power supply wiring harness. Seriously. You should have nothing attached to the power supply at this point other than the big socket with two pins soldered together.

      Lastly, plug the power supply’s mains plug into a wall socket and switch on. If the fan comes on, hooray! Once you know that you can make the power supply run, you can go on to the next step of the assembly.

      Please let me know how you get on.

  8. raster says:

    I took John Ridley’s advice and just clamped the heatcore into a small vice grip, and put it in my toaster oven at 200 degrees for an hour. No messing with the power supply! I did let mine sit overnight before I did this, but it sounds like you don’t need to do that if you don’t want to.

    • BrazenArtifice says:

      I haven’t heard about that way of curing the heat-core ceramic, and I just failed completely in finding any reference on the web, apart from the photo on your google+ post at https://plus.google.com/103170712877279687994/posts/BvsXHqPiz6z

      BTW, in that photo, what have you done to the end opposite to the heat-core? Is that tape? Was that just to stop the wires moving while you applied the ceramic goop?

      I have an ancient toaster over somewhere in a cupboard but I wouldn’t trust its heat regulation at all!

      I did my best to let the ceramic goop dry out fully before curing it. I didn’t want bubbles in the cured ceramic reducing the physical strength of the ceramic coating. If you find you need to file the cured heatcore down a bit you’ll see what I mean.

      • Toaster oven comments:

        And yes, it’s just some masking tape to hold the wire in place.

        I’d also recommend letting the ceramic drying for a day before toasting it, but I think it worked well.

  9. raster says:

    Oh, I also found the instructions about the crimps *very* confusing, and I’m still not sure I used the correct ones. I guess I’ll find out later on in the build. 😐

    • BrazenArtifice says:

      Heh, yes. I was stressed out enough about the crimps while building that I didn’t have the mental energy to take the photos that might have made it easier for other people to understand. Sorry ’bout that.

      And now that it’s all assembled, I can’t, because they’re hidden inside the connectors. Documentation writing and photography are two different highly skilled occupations, and really need access to the manufacturer’s stock of raw components.

      You've got the photographic skills down. Your photo of the bare prusa frame was gorgeous. I'm guessing you used a curved background and professional lighting?

      In the end, pretty much anything on a mendel prusa is fixable. I keep telling myself that.

  10. I should really do more photos… We have a photo studio where I work, but the Prusa shots were just in my home studio. It just barely fits on my table. I’ve just got a roll of white paper for a sweet and I either use two off-camera flashes and some reflectors, or occasionally just hot-lights. (And the poor shots I do with my iPhone.)

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