Sanjay's Heater Cartridge (all sales donated to Sanjay's foundation)

One night at 3am on Discord, Sanjay taught a clinic on how heater cartridges are made. This sticker is from the finger-painting illustration he provided.

• Do you know how a heater cartridge is made?
• Sadly, the answer is two ladies with chopsticks packing MgO powder around a nichrome coil. I'm deadly serious
• So you thread it, then wind it back up the outside of the rod with the little windy go round machine
• So if we're making a 6 mm cartridge, we might have a 2-3mm diameter wound rod
• Then we take some steel tube, with an OD a bunch larger than your desired final OD, maybe 8-10mm or so for our 6mm hc
• You cut off a little length
• Then things get a bit weird and there are a few ways to do it.
• But most commonly you now take a little silicone rubber bung and jam it in one end.
• So tube plugged one end
• You hold your plugged tubing vertically, plug end down, open end up, like a test tube. Then you take some MgO powder, and sprinkle a little in the tube, filling it about 25% of the way up.
• MgO is used because it's got good thermal conductivity, dielectric strength, but unlike alumina it's weak and crumbly soft. This becomes important later.
• And just so we're clear, nearly everything has been done by hand thus far apart from the little winding machine doing its thing on the rod.
• So now you take your wound coil rod and put it in the tube, ends of wires poking up out of tube, bottom of the wound rod kinda pushed into the powder at the bottom which kinda holds it in place like a flagpole stuck upright in loosely packed dry sand. 
• So the [really] crazy thing at this point
• Is that you're really going to have a bad time if the wire touches the steel tube
• But there's diddly squat in the way, the nichrome is bare naked, and you have a human precariously inserting them balancing upright in the damned tubes
• So now the fun part
• You have the cartridge clamped in a little soft rubber jig, holding the upper mouth area
• So in your right hand you hold a pair of chopsticks
• And in your left a jug full of MgO powder loose
• And you pour the free flowing powder over the mouth of the tube, while using the chopsticks to rapidly tap the sides of the tube to help the powder flow into and around the coil+rod
• I'm not [at all] kidding here boys. This is legit how this goes down. A few places have got it more automated, but that's mainly for larger diameter heaters than our relatively small ones
• Now you have your coil inside an 8mm OD tube, hopefully nothing touching anything it shouldn't be touching (tube walls and any other part of the coil can't touch)
• Then this thing goes into a big rotary hammering device
• Yes, the rotary hammering machine is literally a repurposed CHF rifling machine, obviously with no mandrel form etc, just the smashy go round spin bash bosh bit
• This compresses the MgO powder very tightly around the nichrome coil. This is a good thing, as you want a nice dense pack to increase contact, conductivity, and constrain the wires within so they cannot wiggle and drift around in loose powder
• In the process however the central rod cracks and such. Again, it's chaotic, lots of moving parts etc. Remember that nothing must touch anything it shouldn't throughout all this compression too.
• So now different manufacturers diverge in approach a bit.
• The really cheap folks will leave the rubber bung in place to call the non cable exit end and call it a day.
• We weld on an end closure cap, automatic rotary Tig. Then the final touch we do that not many others do, is we take that compressed end cap welded cartridge (no cables attached) - and we centreless grind it. That's why when you look at ours vs nasty cheap ones, we have nice cylindrical round geometry. Others end up with a tapered uneven not quite round shape. We used to have this before we added the grinding step about 4 years ago (?).