Water Cooled Hotend
Greg Frost's Water Cooled Hot-End
This is the current state evolution resulting from about 2 years duration of sporadic work on home made hot ends for 3D printer extruders.
Key features are:
- Rapid heating (I’ve chosen a 5W 4R7 resistor as the heating device)
- Aluminium foil wrapping of heater resistor for efficient heat transfer to the block.
- Water cooled top end. Ensures the transition zone stays cool to keep tye required extrusion force low. The requirement for a fan mounted on the X carriage to keep the hotend insulator cool is eliminated.
- PTFE sleeving inside the shaft right down to the melt zone.
- Necked shaft to reduce the upward leakage of heat.
- Interchangeable extruder nozzles.
- Short profile – 40 mm from undercarriage mounting surface to the nozzle tip (maximises build height).
- Thermistor sensing close to the melt zone
- If your Z screws are long enough – the cool end and mounting block can be mounted on top of the X carriage increasing Z build height further.
Combined cool end and mounting block
An aluminium block 60mm x 25mm x 6mm with 5/16 UNC tapped hole in the center and 2 x 4.5 mm holes for mounting. Within the block 2.5mm dia x 40mm deep holes are drilled from each end and from each side the 2.5 mm holes are drilled to intersect and join with the end holes. They are then plugged at the sides and set with Araldite to be watertight. The end holes are drilled out 3mm diam to 4mm deep to allow fibre glass tube 3mm OD x 15mm long to be fitted and sealed with Araldite.
A 5/16 UNC threaded shaft 30mm long is drilled 4mm right through. In about 13mm from one end is the start of a necked down section of 5mm dia x 10mm long. The lower end of the shaft is carefully faced off to mate with the nozzle part.
An aluminium block 24mm x 18mm x 10 mm is drilled 6.5 mm dia through and tapped 5/16 UNC to allow for screwing in both the shaft and nozzle to mate together about 8mm from the top. A hole is drilled parallel to the tapped hole and is suited to accommodate the heater resistor. A 2.5mm hole is drilled from the side of the block and is carefully placed between the tapped hole and the resistor hole to allow the thermistor to be fitted. Care taken to ensure that the hole does not break through into the previously drilled holes.
A 15mm length of 5/16 UNC aluminium threaded rod is drilled 1.5mm dia 14mm deep, then followed up by a 2mm hole 12mm deep and another at 2.5mm to 10mm deep and a 3mm dia hole 5mm deep. From the other end a 0.4mm hole is drilled through. The end is faced off at 30° to allow clearance around the nozzle hole. Two flats are machined or carefully filed to about 4mm from the end to suit the use of a spanner on the nozzle.
1 x 5/16 UNC half nut (can be sliced from a full nut)
1 x 5W 4R7 resistor
1 x thermistor (I use EPCOS B57560G1104)
1 x 18mm x 100mm x 1.5mm thick strip of Silicon Bakeware Pot holder/Heat mat
2 x zip ties
Copper Plus – high temp, sensor safe gasket maker.
PTFE tube 4mm OD x 3mm ID
Water Pump Alternatives:
Wrap 25mm wide Kapton tape around the resistor leads Wrap the resistor with enough aluminium foil to provide a snug fit to the heater block. With the resistor set in place – a little dab of super glue will help keep it there. Bend the resistor leads such that they will be clear of the nozzle depth and also the rest of the assembly.
Wrap one of the thermistor leads in 50mm Kapton tape and fit about 40mm of heat shrink over both leads. Bend the leads almost 90º near the sensor glass bead and place bead in the hole provided in the heat block. Use a little Copper Plus around the bead to hold it in place assisted by a dab of supper glue on the heat shrink with the leads aimed to the top.
Wrap the Silicon Bakeware strip around the heat block and tie it in place with zip ties.
Fit the PTFE tube firmly into the shaft and bell it out at the top of the shaft, then face it off to match the bottom shaft face and bell it out at the top of the shaft
Add a little Copper Plus to the bottom shaft thread and screw the shaft 8mm into the heat block. Add some Copper Plus to the nozzle thread and screw the nozzle into the heat block until it engages with the shaft. Tighten the engagement with a spanner on the nozzle.
Screw the cool end mounting block onto the shaft and then screw on the half nut and tighten it in position on the shaft to suit the orientation of the hot end.
Below are images of the components and their assembled form: