FILENAMES:

Sherline_Mod.dwf 
Sherline_Mod.jpg

DESCRIPTION:

These are a drawing and photo of Sherline Mill modifications.  
Posted by Al Lenz <alenz@cmq.com>. Al provided the following 
description:

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Hello All

Here is an improved Sherline Mill Z-axis bearing assy which uses preloaded
ball bearings in lieu of the current setscrew to control backlash.  Several
fellows have mentioned backlash problems caused by the setscrew slipping.
This mod eliminates that problem.

The drawing is in .dwf format. If you don't have a reader, I suggest Whip 4.0
which is a free download from www.autodesk.com/whip.  Use the right mouse
button to display the menu, then zoom in on the area that you wish to view
or print.  

As you will see, the new bearing assy is interchangeable with the original,
all components are maintained in their same relative locations. The material
for the housing isn't critical, since it has no bearing surfaces. I used a
piece of 1 in. Alum rod.  The R188ZZ bearing is a standard size and widely 
available.  MSC has them in 440C for about $5.00.

No special tolerances are required.  The center hole has to be big enough to
clear the shaft but still provide a shoulder for the bearing outer races.  
The bearings should be a slip fit in their bores. The leadscrew should be
threaded only far enough for the nut to contact the upper bearing but still
leave enough unthreaded to center the bearing inner race. If you have the
locking saddle nut, you can use it to hold the leadscrew for threading.

The preload adjustment is set by feel during assembly, (it's easy).  Install
the bearings, housing and nut on the leadscrew.  Leave the housing an inch 
or so above the top of the column.  Back off the preload nut slightly. The 
housing should now spin freely on the leadscrew.  Now adjust the nut until a s
light to moderate drag is felt.  It may not need it but I put a drop of 
loctite on the nut to make sure the adjustment held. If you ever want to 
check or re-adjust the preload, you will have to remove the flathead screw 
and lift the bearing assy clear of the column and repeat this process.  
There is just too much friction in the system to feel the preload when 
everything is all together and loaded.

After adjusting the preload, install the handwheel and check for clearance
between the index ring and bearing housing. It should be close but not
rubbing. I used a paper shim to set this clearance.  Note, this just positions
the handwheel while tightening the setscrew, there is no axial load.

Cheers
Al Lenz