Today I Finished my design for my new hotend this will take three power resistors and three thermistors or thermocouples, The power resistors will be fire cemented into short (15mm long) sections of thin walled brass tube, this will then be installed into the hotend, one for each nozzle. with a little heatsink paste.
the nozzles slip into place from above and will also have a interference fit, and some heatsink paste, i will be trying out a variety of nozzles so this hotend is fairly easy to remove once i complete the mounting plate for it.
Below are some screenshots from solid works showing the construction of the pieces, this section is by no means printable.
the height of the hotend is 29mm this is 4mm more than the height of SC10UU linear bearings that i have used for my X cariage. this wastes no Z axis movement.
here is a bottom up view of the Hotend, the nozzles are 10mm apart and the white holes are mounting holes M3 will probably counter sink them to help clear the printed plastic. The grey holes range from 1mm to 3.5mm (except for the 5mm that power resistor's home) are to try and keep the heat from wandering between the nozzles, a probably feeble attempt but hey, this is going to be CNC machined from brass as there is no hope i could get all those holes right in a drill pres.
Here is the New extruder mounted onto the X carriage. its not fully mounted i will decide how that happen when i build the prototype, i have to raise the axles up 3 or 4 mm more from the plate to allow for the 20toothed gears that will be used to drive the axles.
in this Design all running surfaces have been replaced with tiny 703, 7mm OD 3mm ID bearings that i get from the hoby shops at a ok rate for 2 at a time, this design will require 9 of these and 4 1608 bearings. but the wont wear too fast. this design is also missing the springs that will push down on each of the tension arms. the plate that the springs will press against is not in the drawing but will be added later.
here are the screen grabs.
this is a side view, looking along the X smooth rods.i will be able to bring the motor in a little more maybe 5mm before they will start to interfere with the filament too much. the area outside the worm drives is where the belts will run, i have to make a new idle axle and some extenders for the X axis to spread the belts to all this to mount up.
A 3d angle shot to help you get the picture. the two motor are not exactly in line with each other, this was done to give me a little more leverage on the camshaft.
i will be driving both the filament and the filament select camshaft with Nema17 2300g/cm stepper motors ( with a 20:1 worm drive reduction to get enough torque..) they will be driven by a pololu stepper driver. with 1/16th the motors have 200 steps per rev and 2300g/cm so that's
64000 steps per rev, and ~46Kg/cm of torque if an can convert half of that into grip i will be off to a good start. thats for both the feed and the camshaft which should be suffcient.
Update : The pictures here show a single piece heater block, the idea here was that there would be holes drilled between each of the three sections of the block to provide simple mounting and thermal isolation between each heater, this is too hard to manufacture for my liking, all those 0.5 and 1.0mm holes are a PITA to get right with out a decent MILL and plunge bits. so i have changed the design to use three separate pieces of brass, one for each nozzle, that will be 8mm thick this will give me 2mm of air gap between each of the heated sections that can be packed with ceramic insulation tape if required, this does complicate the installation of the nozzles but simplifies changing of the nozzles as each one can be removed and replaced/repaired without disturbing the others, one drawback to this is that each nozzle can be installed into a slightly different position if the mounting holes are not the perfect size.