David's Hotend (Bowden and Direct)
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Mechanical: Overview | Mendel solid model files | Procurement | Preparation of materials | Assembly notes | Extruder | X-axis | Z-axis | Y-axis | Circuit boards | Frame | Squaring the axes
Release status: Experimental
| Description | Dual-purpose Bowden or Direct Drive Extruder Hot-End
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| License | GPL
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| Author | |
| Contributors | |
| Based-on | |
| Categories | |
| CAD Models | not available
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| External Link |
- Ignore the picture, it's just a placeholder - I've yet to upload photos of it **
Contents
Features
A dual-purpose hot-end which can be used in either Bowden or direct drive extruder, using a Wades extruder to drive either mode.
Advantages
- Removable nozzle - so size can be varied in seconds, and cleaning is easy
- Suitable for Bowden and Direct Drive setup without modification
- Approx 2mins to switch between either Bowden or direct setups
Disadvantages
- Not quite so light on tools as the later versions of the geared extruder
Time Required
3 hours (2 to make holder, 1 for 2 nozzles)
Raw Materials
Brass rod: 16mm diam (for heater block; if buying I'd get copper or aluminium as better heat conductor) Brass rod: 6mm diam (for nipple; ditto re copper) or M6 Grease Nipple (you'll have to braze the tip close then redrill to smalled diameter) or gas nipple, but couldn't find where to buy them Wire wound resistor Thermistor (100k) PEEK block (which I cut from a bit of rod) PTFE Tube (6.4mm OD x 3.2mm ID) Block of wood to make tip jig (I used 5x5cm, but pick anything similar scrap off the woodpile) Thermal paste or fire cement (see below re this) Kapton tape (for electrical insulation)
Tools Required
Drill press,
Drill clamp
Drill bits: 2.5mm, 3.2mm, 5mm, 6mm [16mm drill for jig)
Tap: M6 (ideally x3 - taper, 2nd and bottom to thread right to the bottom of the hole)
M3 (taper only OK)
Dremel-type metal cutting wheel (mounted in drill press)
Optional
Collet to fit 6mm rod
Bench mounted belt sander (else use drill and file)
Making the Heating block
Cut your 16mm rod to length (mine happened to be 27mm, but I'd probably aim for 25mm)
Drill 16mm hole vertically in scrap wood. This will be used to hold heater block perpendicular to the sander to tidy the faces.
Sand the ends flat on the bench sander (by dropping down the hole in the block
Clamp the heater block in the vice with one face upward
Mark 4mm in from each side on a line passing through the centre of the circular face
For the filament hole: From one mark drill 3.2mm hole through the entire block out the other end. make sure to regularly clear the hole and drill slowly to keep it perfectly vertical (I rotated my heater block in the vice, I'm not sure thats essential but my hole had less angle when I did so)
From each end drill this hole out to 5mm (5-6mm deep at one end, 10mm deep the other, leaving a 3.2x10mm section joining the two holes). The longer hole is unnecessary unless you wish to use a Bowden rod - which would thread into it.
Tap these holes out to M6 (I unplug my drill press and hold the taps with it then turn by hand)
For Heating Resistor: From the other mark (4mm from side) drill a hole that will just allow the heating resistor to fit inside (5mm with my resistor). Drill until you just break through the other end to allow the lead to pass out of the block. You could overdrill your hole and bring it back inside, but you'll sacrifice close contact and therefore heat transfer.
For Thermistor: Drill a hole to fit your thermistor from the side of the block at a point close to the nozzle, and away from the heating resistor
For attachment to PEEK block: 2.5mm in from edges, Drill 2.5mm holes 10mm deep at the points of the cross away from the resistor and tap them out to M3.
The heating block is now done!
Making the Nozzle
Drill 6mm hole vertically in your scrap wood (for facing ends). Drill another one at 45degrees (for the taper) This should ideally go corner to corner to ensure the collet has a stable support when rotating the rod.
I would suggest doing each stage following to both ends of the rod simultanesously so you will end up with two nozzles without having to change tools too often.
Sand the ends of the 6mm rod to ensure flat face at the centre as per heater block (only the centre as the edges are about to be removed)
Lock the collet onto the rod mine is 53mm to get the taper nearly to the centre of the rod - experiment to get it correct with your setup.
Placing the rod in the 45deg hole rotate it on the sander until the collet sits flat against the jig. This will get you a nice conical taper. DON'T taper right to the centre - leave about 1-2mm flat. (this will depend on the angle of your 3.2mm drill bit tip, how long you want the length of the narrow hole in your nozzle, and how much you worry about the nozzle catching on the print), and how worried you are about botching it and drilling out the other end.
Unplug your drill press, and open the top to expose the spindle head so you can turn it by hand. If you don't mind the risk of losing your fingers if the drill accidentally starts you can leave it plugged in - I quite like mine attached and I already have an uncle and a grandfather with "micro-digitorum" secondary to power tool exposure, so choose to invest the extra few seconds. Much less time than brushing your teeth and you do that don't you!
With the nozzle still held in the drill chuck place your M6 die on the press table so it is flat, and pressing gently down manually rotate the drill to cut the M6 thread on the nozzle up to the point you have cut the flats.
Adjust your spindle to slow the drill down to the slowest speed (approx 600rpm on mine)
Close your spindle cover and plug the drill back in again.
Clamp your fine nozzle drill in your drill vice so it is pointing vertically. These bits are quite fragile, so be careful here. Align it directly under the centre of the nozzle held in the drill press, and gently and slowly drill out the nozzle hole by lowering the nozzle onto the drill bit.
Check the hole by eye and if it the hole is messy then gently hand twist a slightly larger bit to clean it off.
The nozzle is now done!
Making the PEEK insulator
Thermal Paste
In initial testing instead of fire cement, I used silicon grease mixed with some brass swarf from construction to improve heat conduction from resistor and to thermistor (it's teardrop shape means contact with the wall is poor, and I didn't want to cement things in during testing). With this my hotend got from 25->260degC in approx 5mins
Heat Conduction Values for reference
Fire cement and Silicon (even as grease) are poor conductors (<1w/(m.K))
copper = 400
aluminium = 250
brass = 110
(steel = 45, iron = 80, glass = 1, air = 0.024)
