I've build a new extruder. I started with a 'pre-owned' 1.75mm brass nozzle I acquired from a fellow Irish Reprapper ( AMK ), following terminal failure of it's PTFE insulator.
My new extruder consists of Greg's style cold-end, adding a raised tab to the idler block, similar to RichRap's mod here. That was my first exercise in modifying an existing design using Sketchup. It worked well.
I added an aluminium base plate to the cold-end to protect it, and to give me an anchor point for the stainless steel down-tube/support. I've been evolving the stainless steel down-tube for a while now and this variant consists of a 8mm (approx) rod, about 60mm long, threaded at both ends and drilled through with a 4mm hole, to take a PTFE sleeve of 4mm OD and 2mm ID. Note: I sunk a 4mm hole an additional 2mm into the brass nozzle to receive the sleeve beyond the joint of the stainless rod and brass. This is so the joints are not all aligned, reducing risk or leakage.
The aluminium plate is threaded and the stainless tube locked in position with a standard M8 nut on top. I had to file the edges off the nut to allow it to fit snugly in the hole at the base of the PLA cold-end. The 'standard' brass nozzle was threaded on to the stainless tube.
I re-employed an aluminium heater block, which I had cut and used previously in an earlier design (seen here ), but this time wrapped it in PTFE ('Teflon' oven tray protector). I cut the wrapper such that the brass nozzle would thread down through it, holding it neatly in place. I punched holes in it for the heater resistor and thermistor also. Neat holes were easily punched using a hobby leather punch. I'm hoping the little 'lagging jacket' will give better heat retention in the block and prevent undesirable radiating heat onto freshly printed surfaces below.
Photo shows 'teflon' jacket prior to fitting to heater block.
I learned a while back that it's important to support the wiring well. To do this I wrapped some heavy copper wire into a spiral and secured it with a bolt onto the aluminium plate (visible in photo above).
Here's a reverse angle shot of the entire extruder assembly. I'm still using my little salvaged stepper. It's smaller than a NEMA 17 to adapted a face plate. This stepper not as powerful as the NEMA 17 but seems to have no difficulty driving this extruder, especially with the advantage the gearing gives it. It's even easier for it to push the 1.75mm filament through. It is also lighter in weight.
Critical to this design is active cooling. I mounted a compact but powerful fan to the x-carriage and angled the bracket slightly so the air flow was hitting the heat-sink, stainless tube, and aluminium base plate, but avoiding the brass nozzle. In the photo above you can see the cooling fan, and the first item I printed on this new extruder, a 20mm single wall test piece.
I was printing with this new extruder within a few minutes of adjusting one of the delivered SFACT Profiles. I reduced the print speed, and turned Raft off. While I was doing that the heater block was warming up. I ran a few mm of filament through it in open air, then homed it and loaded the test object. I was very impressed with the quality from this .35mm nozzle. It will be excellent for detail work.
Here are some a last few additional general photos from this evening.
Printing an earphone holder from thingiverse.
At this stage I haden't even secured the extruder properly to the x-carriage as the little spring clamps testify, but it didn't budge and the print quality was excellent!