Z Axis Leadscrew Bearing
My Sherline mill was pretty well used when I bought it. I had used it like this for a while, but it was getting a bit frustrating. There was excessive backlash in the X and Y leadscrews and the Z axis was binding on the dovetail column. I took everything apart (all the way to the threaded brass inserts for the X and Y axes) to clean and inspect. Nothing needed to be replaced, so I oiled and assembled everything. I adjusted the gibs, aligned the leadscrew supports and removed as much backlash as possible. The X axis has about 0.002" of backlash and the Y and Z axes are less than 0.001". Even with all the adjustments, it was still difficult to raise the spindle. The design places all of the weight of the headstock on the handwheel and there is only a thin layer of oil between it and the thrust collar. I decided to make a new collar with a bearing to make the handwheel turn much easier.
I took some measurements and drew the basics of my design on the whiteboard. Before I started, I decided to modify my original design slightly to accommodate a stepper motor. I made the walls around the bearing large enough to drill and tap for a mount. I may CNC this machine in the future, especially since it is moving smoothly now.
I started with a chunk of 2" aluminum and faced it. I turned down the small diameter to fit in the bore of the column. I flipped the piece around, turned the large diameter and faced it. Then, I drilled through the piece with a D sized bit and finished with a 0.25" reamer. This bore supports the end of the leadscrew (0.249"), so it needs to be smooth and concentric with the bearing. Next, I bored the piece out for the bearing. This bore was about 0.005" deeper than the height of the bearing and 0.001" smaller than then bearing diameter. I also bored a shallow recess so the inner race doesn't rub on the bottom. I drilled 0.125" holes to allow removal of the bearing if needed. I placed the collar in position on the column so I could mark the mounting hole, then drilled and tapped this hole for the 10-32 mounting screw. I finished the collar by pressing in the bearing.
The second piece was made to fit the inner diameter of the bearing, clamp on the leadscrew and extend the shaft for the handwheel. I started with a chunk of 7/8" aluminum and faced both ends. I turned the end to fit the inner diameter of the bearing and the middle so it would ride on top of the inner race. I drilled the piece with a D size bit to a depth of 0.700" and fiinished the hole with a 0.25" reamer. I flipped the piece and turned the handwheel shaft to 0.249". I placed the handwheel on the shaft and tightened the set screw so it left a mark. I used this mark as a guide to turn a shallow groove for the set screw so burrs don't make removal difficult. I cross drilled and tapped this piece for a 10-32 set screw that will clamp the leadscrew.
I am very happy with this modification. The handwheel turns smoothly and the force required to raise the headstock has been greatly reduced. A larger handwheel would make this even easier. I still need to make a pointer. It will probably be a bent piece of sheet metal attached to the collar. I might make bearing collars for the X and Y axes, but I'm not sure they're needed. Click the pictures for larger images.
I took some measurements and drew the basics of my design on the whiteboard. Before I started, I decided to modify my original design slightly to accommodate a stepper motor. I made the walls around the bearing large enough to drill and tap for a mount. I may CNC this machine in the future, especially since it is moving smoothly now.
I started with a chunk of 2" aluminum and faced it. I turned down the small diameter to fit in the bore of the column. I flipped the piece around, turned the large diameter and faced it. Then, I drilled through the piece with a D sized bit and finished with a 0.25" reamer. This bore supports the end of the leadscrew (0.249"), so it needs to be smooth and concentric with the bearing. Next, I bored the piece out for the bearing. This bore was about 0.005" deeper than the height of the bearing and 0.001" smaller than then bearing diameter. I also bored a shallow recess so the inner race doesn't rub on the bottom. I drilled 0.125" holes to allow removal of the bearing if needed. I placed the collar in position on the column so I could mark the mounting hole, then drilled and tapped this hole for the 10-32 mounting screw. I finished the collar by pressing in the bearing.
The second piece was made to fit the inner diameter of the bearing, clamp on the leadscrew and extend the shaft for the handwheel. I started with a chunk of 7/8" aluminum and faced both ends. I turned the end to fit the inner diameter of the bearing and the middle so it would ride on top of the inner race. I drilled the piece with a D size bit to a depth of 0.700" and fiinished the hole with a 0.25" reamer. I flipped the piece and turned the handwheel shaft to 0.249". I placed the handwheel on the shaft and tightened the set screw so it left a mark. I used this mark as a guide to turn a shallow groove for the set screw so burrs don't make removal difficult. I cross drilled and tapped this piece for a 10-32 set screw that will clamp the leadscrew.
I am very happy with this modification. The handwheel turns smoothly and the force required to raise the headstock has been greatly reduced. A larger handwheel would make this even easier. I still need to make a pointer. It will probably be a bent piece of sheet metal attached to the collar. I might make bearing collars for the X and Y axes, but I'm not sure they're needed. Click the pictures for larger images.