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The arm had a fair amount of backlash in the 2nd joint when I originally built it. The reason for which I'm not quite sure, but I think it was a combination of the tolerance stack up within the J2 spindle and gearbox shaft and spline / key.
The solution
Chris was able to source a new, higher precision, gearbox for the J2 stepper (link to the blog post). When I saw this I jumped on the opportunity to order the new parts and attempt to reassemble Joint 2 properly, hopefully eliminating the excessive backlash.
The process
1. Remove original J2 Stepper
Steps to remove J2 Stepper:
Remove J3 in order to access J2 grub screw.
Loosen J2 centering mount and remove screws at base of J2 mount.
Using a wooden dowel and a hammer (if necessary), gently tap on the J2 motor shaft through the J2 Spindle from the opposite side.
2. Prepare new J2 Stepper
Using the two plastic covered ports on the side of the new J2 gearbox, loosen the coupling screws that are holding the motor to the gearbox.
Remove the motor from the gearbox.
Remove the 4 screws that are holding the back of the gearbox onto the rest of the gearbox.
Carefully slide/pull the rear of the gearbox off the rest of the gearbox assembly.
Slide the new J2 motor mount over the gearbox, making sure the orientation is correct.
Slide the 3D printed spacer (J2 Spacer YGS.STL) onto the gear box (contoured section facing towards the open end of the gearbox) (Note: this isn't shown in the photo)
Re-install the rear of the gearbox and motor by reversing the above steps.
Using a clamp or a press, insert the key / spline into the J2 gearbox output shaft (make sure it's fully seated, otherwise inserting the motor into the J2 spindle will be difficult / impossible)
3. Install new J2 Stepper
Thread the stepper motor and encoder wires through the J2 motor mount.
Trim the wire to the correct length (as described in the assembly manual)
Solder / attach the new motor and encoder wires to the existing cables
Make sure grub screw in J2 spindle is clear of the key spline
Insert J2 motor into J2 spindle until you have ~1mm of clearance to J2 retainer / endstop
Using thread locker screw J2 motor mount into base of arm.
Using 45mm M4 machine screws, bolt the motor and gearbox to the motor mount
4. Finish up
Check wiring continuity
Tidy up wires / cabling
Check to make sure the arm has full range of motion without binding
You're done 🥳
Thoughts
The combination of the new J2 Gearbox and a new J2 Spindle greatly reduced the amount of backlash I was seeing in the joint. Looking forward to doing some new accuracy / repeatability tests in the near future.
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The problem
The arm had a fair amount of backlash in the 2nd joint when I originally built it. The reason for which I'm not quite sure, but I think it was a combination of the tolerance stack up within the J2 spindle and gearbox shaft and spline / key.
The solution
Chris was able to source a new, higher precision, gearbox for the J2 stepper (link to the blog post). When I saw this I jumped on the opportunity to order the new parts and attempt to reassemble Joint 2 properly, hopefully eliminating the excessive backlash.
The process
1. Remove original J2 Stepper
Steps to remove J2 Stepper:
2. Prepare new J2 Stepper
3. Install new J2 Stepper
4. Finish up
Thoughts
The combination of the new J2 Gearbox and a new J2 Spindle greatly reduced the amount of backlash I was seeing in the joint. Looking forward to doing some new accuracy / repeatability tests in the near future.
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