On 12/3/2011 10:32 AM, Ed Huntress wrote:

I'm assuming that you want the binding effect that prevents the gear
from driving the pinion? Or you're looking for more smoothness than
you can get with ordinary-quality bevel gears?

Or what?

Ok, full description:

As I mentioned in the original thread, I wanted a focusing block that
mounts on a round shaft, but haven't found any in my price range. The
Sherline Z slide offers all the vertical travel I need.
I was just going to use the column as-is until I realized it would be
rather slow to run it up and down it's full range.

I'll make a new thrust plate at the top to move the screw away from the
column a bit. It will pass through a closely fitted hole in a block that
is also fastened to the back of the Z slide.
90 degrees to this screw, will be the gear I just hobbed, on a shaft,
with a knob at one end. There will be a provision to clamp this shaft.

When the vertical screw is stationary and the gear's shaft unlocked, it
will allow raising and lowering the slide just like a rack and pinion.

When I lock this shaft and rotate the vertical screw, it will function
just like the original screw, allowing for finer adjustment.
To sum it up then, it will function as both a pinion on rack, and a
leadscrew w/nut.

My brother, having more $$ to spend on his rig, is using a crossed
roller slide with micrometer head for fine adjustments, mounted to a
post for course adjustments. I have a lower budget for my rig and was
looking to use stuff I have on hand (the Sherline slide). I'm also
probably not going to be working at the extreme magnifications he's
going after and a 3/8-16 thread will offer sufficiently fine control.

The gear rolls over a 3/8-16 bolt just as smoothly as a regular pinion
over a rack. I chose it as it rolled over the tap almost as smoothly
before hobbing.

I'll post pics when done, but that will be well into next year. Still
have a lot of work to do on my brothers setup.


Jon