Topic: Replacement hot end guide
This guide shows how to change the hot end for a setup which should be more reliable, more durable and above all, much easier to take apart.
The setup is also designed to use as many of the original parts as possible, making it a simple and cheap upgrade.
The Problem
The factory hot end is a maker gear model, which requires the forming and curing of a ceramic material around a nichochrome wire. To unscrew this heating element, force must be applied to the outside of the ceramic, and in my case trying to disassemble to clear a blockage destroyed the heater. The brass barrel also sheared when trying to get everythng apart:
The default thermistor is also placed delicately and simply taped to the outside of the nozzle. Temperature readings for this are questionable. Pulling apart the whole thing to change or clear the nozzle is a big pain.
One considerable advantage of the hot end, however, is how slimline it is.
Step 1: Parts & Tools
The minimum needed are these parts or equivalents:
Brass barrel https://www.bilbycnc.com.au/DisplayProd … rrel175xM6 (I ordered two in case)
Aluminium heater block kit with resistor and thermistor https://www.bilbycnc.com.au/DisplayProd … erBlockKit
0.34mm nozzle https://www.bilbycnc.com.au/DisplayProd … PtNozzle34 (I ordered two in case)
Tools required:
Soldering iron
Heat shrink
Thread tape
A hacksaw and file
A drill and ~6mm or countersink drill bit
Replacement wiring plugs and a crimping tool (optional)
Step 2: Prepare Metal Parts
The aluminium heater block needs to be shortened to stop it from touching and melting the plastic extruder motor carriage. It may be possible to shop around and buy an aluminium block that is smaller and does not require this.
Cut approximately 6mm off the rear of the block with a hacksaw as shown. Quickly file the freshly cut surface to remove any burrs.
The brass barrel also needs shortening. If may be possible to reuse the original brass barrel or buy one which is the right length to begin with.
Cut down the new barrel until it matches the old one. File the end clean, taking care not to damage the thread. Now drill slightly into the freshly cut end to give it a filament friendly conical opening.
Step 3: Wire Up Heating Resistor
The new hot end does away with nichochrome wire is favor of a heating resistor (like the bed uses). Simply snip the old wires just past the nichochrome wire, and solder them to the ends of the resistor. Clearly you will need to thread the resistor through the aluminium block and have heat shrink ready before you do this.
It is important to insulate the wires coming out of the resistor well. Don't let them short on the aluminium block.
Use the thermal paste from the kit to either coat the resistor or fill the hole the resistor will sit in. This helps the heating performance.
Please note that in my image I chose to rewire the plug for the heater to be more reliable. This is an optional step.
Step 4: Mount Thermistor
The thermistor reads the temperature of the heater. Although the hot end kit comes with a new one, the original one is better to use so firmware changes can be avoided. As a bonus it also fits snugly in the small hole. Push it in with some thermal grease and use 6mm kapton tape to wrap it in place.
Please note that in my image I chose to rewire the plug for the thermistor to be more reliable. This is an optional step.
Step 5: Assemble Barrel and Nozzle
While you have it handy, use the 6mm kapton tape to wrap the aluminium block a few times sideways. This hold the resistor wires in place and stops the first section of tape coming undone.
Now Place some thread tape on one end of the brass barrel. This should NOT be the end you drilled the conical shape into.
Screw on the nozzle as tight as you can with your fingers, and then screw on the aluminium block from the other end against it. The beauty of this system is that you can place the block in a vice and then use a spanner to screw the nozzle aganst it.
Step 6: Prepare PEEK and Complete Assembly
Take a file to the sides of the PEEK barrel so that they become flat and a spanner can be reliably placed. This is a simple step that makes assembly and disassembly much easier in the future.
You can now use a spanner on this and the nozzle to screw the hot end assembly into the PEEK barrel tighly. When pulling everything apart in the future, just reverse these steps starting with this. It is immensely easier than pulling apart the old system.
The completed assembly is pictured below. Note that the PEEK barrel spins freely in the acrylic extuder, so take advantage of this to get the wires coming out the right way.
Step 7: Minimal Software and Firmware Tweaks
Firstly, if your nozzle is anything other than 0.35mm, set the new value in your slicing software. Mine was 0.34mm.
Secondly, the heating performance of the new unit will be terrible because the PID settings in the firmware are optimised for the old heater. Fortunately this is an easy fix, and requires no firmware flashing thanks to the Sanguinololu's on board EEPROM. This stores some configuration variables, regardless of power outages or firmware upgrades. Using the screen below is the best way to make calibration changes.
Send the manual command in Pronterface or Repetier-Host:
M303 S200
The firmware will now test the heater by cycling it to the temperature you specified, and then give you the best PID settings.
Look for the message pictured and write down the values. You may need to reset the machine at this point. For me I receive errors afterwards.
Navigate to 'Config > Firmware EEPROM configuration' in Repetier-Host. The dialogue box below will appear. Enter your PID values and click 'Save to EEPROM'. A confirmation message will appear in the log.
Please note that even when upgrading the firmware, values stored on the EEPROM are prioritised. The 'Restore factory settings' button will wipe the EEPROM values and then read from the firmware values.
Step 8: Print!
Don't forget to recheck your z-height with the new nozzle. Avoid any silly mistakes where the nozzle crashes into the bed. Apart from that, the new hot end should work exactly as the old one did.
I've found that the temperature needs to be set higher for good printing with the new hot end. I put this down to the thermstor no longer reading so far under. This means that the actual temperature is probably similar, but the reported temperature is now more accurate.
I used to print at 200 but now 210 is required.
Since the new hot end is compatible with the old PPEK barrel, the acrylic extruder can be changed to another design without complication: