Re: differential threads for extreme precision movement

The application we used was a micrometer spindle on a laser.
The original design had two micrometer heads at 90 degrees to each other
that pushed against springs to return. These aligned the beam up. Problems
were :-
At 40tpi they were too course and with high gas cutting pressures the down
force on the 'O' rings was making the spring return very stiff.
We replaced the micrometer heads with ones we made having 20 tpi on the
barrel and 22 tpi on the spindle. I did work out what the movement was but
this was immaterial as the operator doesn't look at the spindle, only the
spark array whilst it's cutting.
By locking the spindle we were able to make these pull and push and do away
with the springs. Backlash which was present didn't matter as this was only
an adjusting method not measuring.
Due to the lasers 'moving' with thermal expansion during the day, and night
as these run 7 / 24/ 6 .5 the operator are playing with the adjustment all
day. If the spark pattern goes to one side they just 'tweak' the adjustment
to give a even array. In about 7 years we have had to replace the outer 20
tpi barrels once and they are in brass.
--

Regards,
John Stevenson
Nottingham, England