The ArmDrive is a 1.75mm filament bowden extruder, designed to work with the NEMA 17 stepper motor. It mounts directly to any OpenBeam or equivalent sized (15mm) extrusion. With the complimentary mounting bracket, it can also be attached at a 90° angle. The optional bracket is located here: https://www.thingiverse.com/thing:2353189
The MK7 and MK8 versions are each designed to work best for those particular drive gears, or gears with similar dimensions.
The extruder is designed to be robust and reliable, while using as much easy to find hardware as possible.
These files are the result of a surprisingly large amount of work, I hope you find they work as well for you as they do for me.
Update - January 6th 2015
Slightly increased the diameter of the post holding the 608ZZ bearing to reduce play and allow more clearance around the outside of the bearing near the swivel shaft area.
Increased the radius of the bearing cutout near the swivel shaft area by an additional .2mm to allow for more clearance for problem described above.
Significantly strengthened the input filament alignment post.
Added more support behind the spring retainer arm on the base-plate to reduce warping over time when under high spring tension.
- Increased height of the three standalone posts on the base-plate by .2mm to allow for more torque when installing the screws without causing the binder arm to jam.
Update - October 24th 2015
Revision 3 is now available!
- Increased the rigidity of the upper and lower arm segments in response to feedback about occasional cracked and broken arms.
Update - May 29th 2017
- I have designed a 90° mounting bracket to make alternate angle installations a breeze.
The ArmDrive was designed to be printed at .2mm layer heights, any other setting may result in less accurate vertical layering.
Suggested print settings:
Layer height: .2
Solid layers Top and Bottom: 4
ABS plastic is highly recommended. PLA will work in a pinch, but tends to warp over time, especially due to heat created by the NEMA 17 stepper motor.
Drill bit sizes: (confirmed working)
15/64" for the upper and lower arm pivot holes
1/8" for all screw holes excluding the lower arm
7/64" for the two lower arm screw holes
I don't have any metric drill bits for testing, but the hole diameters once drilled should be approximately:
6mm for the upper and lower arm pivot holes
3.2mm for all screw holes excluding the lower arm
3mm for the two lower arm screw holes
Use caution when installing the lower arm on the swivel post! The post is narrow, and will break easily. Be sure to deburr the post and check for roundness. The post is quite strong once the screw is installed. If the post does break off, it is still completely usable as long as it is complete and located in place when assembled. The post merely acts as a standoff.
One binder clip arm is often enough to provide more than adequate tension. There are four spring slots available for your super filament crushing desires, but beware, too much pressure can cause premature failure of the swingarm, and deformed filament.
The alternate lower arm is designed to work with an M4 nut threaded directly on the bowden tube, whereas the standard lower arm uses the 4mm push to connect fitting. Take your pick!
The 608 size bearing is a standard that fits in most scooters, skateboards, rollerskates, fidget spinners, etc... You can find them everywhere!