On 12/2/2011 10:40 AM, Lloyd E. Sponenburgh wrote:

He pivoted the blank on a shaft on a vertical member in his mill vise,
then used a common tap of the requisite thread as a milling tool. He
simply advanced the tap sideways into the edge of the blank a few thou,
and let it cut all the way around, then advanced again, etc., until the
profile was cut full depth.

Yeah, that's the technique I'll be using if I end up making it.

The intended use btw, is a vertical column for my macro photography rig.
I'm big into recycling what I got, and I happen to have a Sherline Z slide.
I'll use a different screw with a RH thread. The worm wheel will have a
knob at the end of it's shaft and when this knob is turned, it'll act
like a rack and pinion. When this shaft is locked, I can use the screw
for fine adjustment. Loads will be very light and use rather infrequent
really. I hesitated to mention intended application as that just invites
a lot of input on other ways to do things. I have a lot of options and I
know what they all are. But I like to do things a bit different. I know
what I'm doing and why I'm doing it and not really open to debate.
(however, if someone has a focus block like the vertical one pictured
below they would sell REALLY cheap, I'd jump on that!)

Overall, this is more or less what I'm building:
http://www.photomacrography.net/forum/viewtopic.php?t=8247

Except I'm using linear slides instead of expensive focusing blocks for
linear movement. And the slide my bellows/camera mounts to will be
driven by stepper motor via a dedicated and purpose built controller.


Jon