MKS SERVO42B Sensor Magnet Placement Tool

I recently acquired some Makerbase MKS42B closed-loop stepper motor drivers after seeing them used on someone else's project. The stepper controller uses a Magntek 6816 magnetic angle sensor (BOM lists Allegro A1333 and AMS OSRAM AS5047D but the PCB was populated with the Magntek part) for sensing the rotation angle of the stepper with 12 bit resolution (4096 counts per revolution). Since I already had a bunch of StepperOnline NEMA17's on hand I bought the controller board-only version. The StepperOnline NEMA17 steppers also have 50% higher holding torque than Makebase's bundled motor + controller version. 

The disadvantage of using your own stepper is the fairly complicated assembly process. Makerbase supplies a complete set of parts including the sense magnet, which is a 6mm diameter x 2.5mm thick with N/S polarization oriented as North semicircle and South semicircle, unlike the typical North top/South bottom orientation. This magnet needs to be accurately placed on the back side of the stepper shaft (obviously does not work with dual-shaft steppers). On my steppers I had to cut away the label covering the 9mm hole in the back of the stepper. The NEMA17 has a 5mm shaft and the bearing face the shaft is pressed in has an 8mm diameter that rotates with the shaft. This tool has a 6.2mm pocket 2mm deep and 8.9mm OD. The actual print I made came out a bit tight for the magnet so some trimming was needed. You want the pocket just tight enough to hold the magnet until pressed to the shaft, where the magnetism should overcome the friction fit, or at least I preferred this until I verified the placement was centered on the shaft. For final placement of the magnet, apply a dot of superglue to the center of the magnet. It is critical to use a small dot lest you glue the magnet into the tool or glue the stepper's shaft in place. Precise placement without accidentally gluing the shaft in place is the reason I made this tool.

The Makerbase kit includes spacers and M3x40 machine screws to replace the ones in your stepper, however my higher torque NEMA17 steppers have a thicker stack and a longer M3x50mm screw is needed (48mm would be ideal but is not a common length). I use washers to prevent the 50mm screws from using up all the mounting threads. The screws extend through the entire motor and will go completely through the mounting face mounting holes if the screws are too long. You need to leave enough thread at the mounting face to mount the motor!

The kit includes a jumper to connect the controller to the stepper via 4-pin connector; unfortunately for me, my steppers had hardwired 1m cables, not a connector socket. Choose connectorized steppers for simplicity! The kit also includes a DIP socket to cable connection to allow you to plug into the “standard” RAMPS stepper driver socket.

Product link: https://www.aliexpress.us/item/3256803194135222.html?spm=a2g0o.order_list.order_list_main.17.16fc1802L3M8rj&gatewayAdapt=glo2usa&_randl_shipto=US