Prusa i2 MK8 Extruder Mount
Description
This is a drop-in mount for an MK8 metal extruder (I obtained mine from "MYSWEETY" on Amazon) and 40 mm fan for a Prusa i2 printer. There are no mounting holes on the MK8 extruder, so this mount is designed to hold the extruder in place via a clamp around the motor, and then bolted onto the stock carriage. The 40 mm fan mount is held in place by friction between the carriage and its bearings. This mount is designed to be able to mount in place without having to remove the carriage and rods from the printer. You just need to raise the z-axis enough so you can install the bolts from below the carriage. To assemble the mount: 1. Place an M4 nut in the cutout in the bottom motor clamp. Then use 2 M3x12 bolts and nuts to fasten the clamp around the motor (make sure the extruder head is on the same side as the bottom of the clamp). Don't tighten the M3 bolts yet, as you may have to adjust the clamp position. 2. Place an M4 nut in the cutout on the extruder base, and test fit the clamp in the extruder base by sliding it in the slot. The extruder heat block should be below the base. Slide the motor in the clamp such that the extruder fan housing is over the raised portion of the base (this raised portion is intended to act as a support for the fan side of the extruder. You can now tighten the M3 bolts for the clamp to secure the motor. 3. Place the extruder assembly on the carriage, and securely bolt them in place from below with 2 M4x14 bolts using the middle holes in the carriage. The bolts should screw into the nuts you placed in steps 1 and 2. 4. Mate the 2 halves of the 40 mm fan mount together, and use the screws provided with your fan to secure them to the mount. The screws are fastened from inside the fan mount - the holes in the bottom of the mount are there to allow you to access the screw heads. Make sure the fan is oriented so it blows air down into the housing from outside. The "scoop" shape of the inside of the housing is intended to direct air horizontally towards the extruder head and print. 5. Snap the fan mount onto the front of the carriage. You will have to use a bit of force to spread the legs open enough to allow them to open around the bearings. Option: use zip ties to secure the top of the mount to the carriage bearing zip ties (see note b below). Notes: a. The M4 bolt on the motor clamp side might not capture the nut easily, if the motor magnet is strong enough to hold the nut away from the bottom of the clamp (at least mine was). If this happens, use a bit of foam or other spacer on top of the clamp nut (between the nut and motor) to separate the nut from the motor before assembling the clamp around the motor. b. The fan housing may start to sag toward the bed over time due to the weight of the fan bending the legs. Using zip ties to hold up the top of the mount against the carriage ties will prevent this. c. I printed this using PETG, as I was concerned about the extruder motor softening the clamp. My geared Gregs extruder (which used 3 mm filament) used to get REALLY hot during operation. However, I found that the MK8 direct drive 1.75 mm extruder motor doesn't get hot at all. I might have been able to get by with printing the mount in PLA. Perhaps the geared extruder motor with 3 mm filament is under a lot more stress than a direct drive 1.75 mm motor? d. You will have to recalibrate your extruder steps-per-unit rate (either in your firmware or send a M92 EXX gcode in your slicer program). And of course readjust your bed height for Z=0. e. If you get the "MYSWEETY" MK8 extruder, make sure the threaded feed channel and teflon tube is set correctly so the nozzle forms a tight seal. When I first got mine there was a gap between the teflon tube and nozzle. The nozzle was all the way up against the heat block so I couldn't tighten it any further. When printing, PLA would exit the gap and seep up around the feed channel and heat block, causing a big mess. Solution was to screw the feed channel down more so the nozzle butts against the teflon end, and not against the heat block. See https://www.youtube.com/watch?v=OoShQSrrYdA. For me, replacing the Gregs 3mm extruder with the MK8 made a big difference in the quality of my prints. The printed reduction gears in the Gregs had a bit of slop in them - I think a direct drive motor has finer control over the filament feed and retraction. Also, my other (newer) printer uses 1.75 mm filament, so I no longer have to stock up on 2 different sizes of filament. 3 mm filament is starting to be hard to get hold of.
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