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
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 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
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
[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
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.
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.
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.