Ceramic Heater Core - Instructions
Do not use these instructions for the partially assembled HeatCore provided with the Stepper Plastruder Kit. See the Stepper Plastruder instructions instead.
Please read all the way through these instructions before starting. There are a couple of short videos at the end of the instructions.
Your kit includes the following items:
2x Brass core threaded M6
2x Nichrome wire (300mm each)
Ceramic adhesive with popsicle stick applicator
PTFE (Green) Hook-up wires
Molex Connectors with Crimp Pins
Crimp pins for attaching nichrome to hook-up wires
M6 screw (drying stand and holder for heating)
**Important Note – earlier kits have 30ga nichrome and some of the more recent kits have 31ga nichrome. You should measure the resistance of your nichrome. If you have 31ga, the resistance will be ~8.2 ohms per foot. 30ga is ~6.5 ohms per foot. If you have 31ga nichrome, you can shorten the piece by 50mm (to an overall length of 250mm) to improve performance. Then just follow the instructions but since the piece is shorter you’ll have a few less loops. Otherwise the process is the same.
You’ll need the ceramic adhesive, stirring stick, brush, nichrome, and brass core. Stir the adhesive slowly (don’t whip air into it) but thoroughly. A little bit of thinner (water) was added to get a smooth consistency. Place one end of the nichrome in the slot located on one end of the brass core. The calipers in the following photos are set at 25mm for reference. For all of the talk about 6 ohms of nichrome for the heater, all that really matters is that you are in the ball park (5.5 – 6.5 or so ohms works fine – the only difference is that it will heat a little faster or slower depending on the length.) The included nichrome is 300mm in length with the expectation that about 250mm will actually get used for the core. You are welcome to carefully measure 6 ohms but it is unnecessary.
With one end of the nichrome in the slot, carefully wrap the nichrome around the core following the thread. You should have one loop around the slotted end – before the thread – and then follow the thread down. Once you’ve reached the end of the threads – add two more loops around the end. Though it is not critical, for best results, try not to have the nichrome overlap. You want the nichrome to have good contact with the brass. Check to make sure the nichrome is in the threads (not crossing over threads, the ridges are sharp and can fray the insulation. With the nichrome pulled taught, you should have about 25mm of extra nichrome on each end. It may take a couple of attempts to get it right. Just take your time and get an extra set of hands if you have trouble getting and keeping it wrapped. Once it is wrapped, bring the ends of the nichrome together and twist a couple of times. This will keep it in place while you add the ceramic and the ceramic cures.
It is not critical that the two ends be exactly positioned. After you put the ceramic adhesive on and let it cure for an hour (or so) you will be able to free the ends and place them where you want them. So, at this point, just get it wrapped with the ends lightly twisted together.
Now that your core is wrapped it is time to add the ceramic. You can apply the ceramic using either the stick or brush. I’m using the stick. Dip the tip of the stick or brush into the ceramic adhesive. Slowly spread the ceramic over the nichrome. Spread a thin layer over the nichrome so that all of the nichrome is just covered. Try and keep the ceramic out of the inner threads but don’t panic if you get some inside as it is easy to clean up – even after it dries at room temperature. If the ceramic makes sharp points when you pull your brush away add a few drops of water to thin the mixture.
Let it cure for about an hour at room temperature. We just need it to cure enough so that when you unwrap the ends it does not come apart. (Note: If you are in a hurry, you don’t have to wait, you can proceed to the heating process immediately – it is just a bit more of a challenge.)
After sitting for an hour, the ceramic should be pretty smooth (maybe a few bumps) and firm. Carefully untwist the wires and align them so that they are both on the same end of the core and about 5mm apart. (having the leads aligned along one end of the core simplifies the placement insulation over the core when the core is mounted on your heater barrel.) You may need to touch-up the ceramic after moving the nichrome around. (To avoid getting the wet ceramic all over the place, you should probably continue to get your heater core mounted and wired up for the initial heating, then touch it up before applying power.)
If you break off a bit of ceramic, just touch it up prior to heating it.
Place an M6 screw into the brass core and place it in your metal “helping hands” or some other device that can handle 200C - 300C. We are going to heat up the core to quickly cure it.
Use a 12V power supply to heat your core. Apply power to the core, using alligator clips or another method. Heat the HeatCore until it begins steaming, let it steam for 15-20 seconds then let it cool for a few minutes. Repeat the process.This process removes the liquid and hardens the ceramic. The amount of steam and time it takes to cure the core depends on how long you've let it sit. If the ceramic is fresh, it will steam and bubble a lot - go slowly repeating several times. If the ceramic has been sitting over night or several days, there will not be a lot of steam and bubbling.After hardening the HeatCore will be somewhere between gray and gray-white. (cured core shown in the next step)
The HeatCore assembly instruction continue here