Geeetech A20M Chimear Clone (Semi) Direct Drive Mount by Abi_Jen

Last crawled date: 3 years ago

I got tired of blockages with the original 2-in 1-out hotend of my A20M and thought I'd convert to a 2-in 2-out setup, thinking of reduced waste from purging with each filament change and to have the ability to run different materials with varied temperature needs. I picked up a cheap chimera clone to play with and hit a snag with using a designed mount from here when i saw the heatbreak grub screws were in a different location to what other people have worked with. The hotend I got has the grub screws on the back face unlike the other designs where they appear to be at the sides, so using a design from here would make it impossible to adjust the nozzle heights due to the screw being impossible to access.
I ran the hotend initially bolting it directly to the stock x carriage with no parts fan or probe because the stock hotend blocked (again) and I needed to print some abs parts, and I found that running the chimera facing backwards worked well enough for me. The carriage has a cutout which is pretty much the perfect size for the 30mm cooling fan to mount to to get the machine usable again.
Designed in Fusion 360, This mount is designed to bolt to the original carriage, using the same holes as used for the stock hotend cage. The BLTouch mount is in the same position as the original so the offsets should be identical (ideally the mount needs adjusting in the vertical because the hotend is mounted higher that the original. This also requires the Z- endstop to be lowered sufficiently to allow the gantry to drop lower to reach the build plate). Another upgrade I had planned was to replace the 2 extruders as I didnt like where the release levers were mounted, having them inline with the filament made it awkward to feed material, and hold the lever while twisting my arm around the spool holders on the top of the frame. I picked up a pair of handed alloy extruder heads and decided to try running a semi-direct drive setup using a short bowden tube feeding the hotend.
The extruder mounts are slotted to allow for movement of the bowden tubes when adjusting the height of the nozzles. The thickness of the stepper mounts is set to allow clearance for the shafts of the stepper motors that came on my original extruders, but there may be some tweaking needed for others brands etc.
The parts fan is mounted on a hinge which allows it to be swung out of the way to access the grub screws, and also gets the parts nozzle away from the heat blocks if the fan is not running to prevent drooping with the heat (my stock fan shroud did this while printing with abs, the nozzle got hot enough to droop and strike the part). Ideally the fan mount needs to be a mm or 2 taller to move the fan slightly away from the hotend as it currently collides and doesnt sit perfectly flush which causes it to be abgled slightly. This makes no difference to how it behaves, its purely asthetic.
There are also 2 LED mounts which fit to the bottom bolts of the fan & Probe mounts, these were used for a pair of white 5mm LEDs which I plugged in to a spare cooling fan connector (with proper series resistor) for basic bed illumination. Cable clamps bolt to the Extruder mount bolts to keep the cabling tidy, which I've not used yet as I can currently only run 1 of the heaters at present (my A20M control board is a V4.1 model which doesnt have the components fitted to allow for dual heaters and is currently being replaced with a SKR GTR V1.0 and expansion board along with a TFT43 touch panel, but thats another story.
Theres also a mount for a drag chain which bolts to the reverse side of the base plate using the top 2 bolts for the extruder mounts, and is slotted to give adjustment to keep the chain level. The chain I used is a purchased one, I use larger chains at work so it was easier for me to order one from our supplier then printing my own. The chain setup I decided on runs above the x gantry and not through the centre of the frame as I found this limits the total travel height due to collisions with the top frame of the machine. This currently isnt an issue for me as my parts are small enough to not require a tall build area but i prefer not to limit the capabilities just because I dont require it right now. Chances are that if i did, then the next print i needed to do would be something that needed the extra travel. As it is right now, there is nothing that protrudes between the frame, so the gantry can travel to its full upper limit, and the carriage can travel past the 2 vertical rails, so nozzle wipe brushes etc. are an option to design if required. I've included a mount for the drag chain that bolts to the guide wheel mount on the end of the gantry too, and the mounting brackets are hopefully universal enough for other chains to bolt to without too many issues.
This is a WIP, which honestly probably wont get much of an update since I'm now toying with the idea of my own design for dual V6 hotends with servo operation to rotate the inactive nozzle clear to avoid parts strikes and ozzing, coupled with a single stepper, dual extruder setup. As it is right now, the chimera setup here works well enough for my purposes, at least until I get the SKR board fitted. Most of the tweaks I'd do to this are minor, such as moving the fan & probe mounts slightly. The 4 mounting holes to fit to the stock carriage are slightly out of position too (cheap vernier calipers with worn blades giving some poor measurements) but the base still bolts up without and major problems.
Everything was designed to be printer without supports, and to be pretty modular. It all bolts together, so if you want to change something then you dont need to redesign and print the whole thing, just the bits you want to replace. If you dont want the extruders mounted on the carriage (I have dual Z screws fitted and I dont try setting speed records with my prints so the extra weight doesnt cause issues) then its simple enough to trim down the base plate in Fusion 360 (file included). The Fusion file has everything included, the steppers, extruders, fans etc. since this is the first design I've shared here so I have no idea how it would work sharing a file with references to other designs (I'm used to Solidworks and files saved to a network location for shared access, not cloud based saving).
Assembly is using M3 and M4 nuts and cap head bolts in lengths up to 25mm (from memory), I have a couple of cheap selection boxes from eBay. The nuts are mostly captive so may require slight size adjustments to get them to fit properly. Sizing was based on the parts I had to hand.