Advertisements

Archive for January 4th, 2010

Micropositioner Rehabilitation: Z-axis Slide

With the planetary reducer off, I could remove all the bits and pieces holding the Z-axis slide to the rest of the positioner.

Rack drive casing

Rack drive casing

Note carefully the three spacing washers near each mounting screw. They hold the slide off the casting body by a very precise amount: they’re each 4 mils thick and prone to vanish in a light breeze. I discovered that each screw had three washers when I flicked one off the workbench and discovered two on the floor.

The metal plate holding the pinion in place has two flat-head screws to the left and two ramps to the right. The conical points of the two long setscrews on the right bear on the ramps, providing a convenient, if obscure from the outside, way to adjust the slide friction by clamping the pinion shaft. One of the setscrews was partially removed, so a previous owner had evidently tried to reduce the overwhelming stickiness.

With the washers in a safe place, the pinion cover comes off with only slight encouragement.

Pinion parts

Pinion parts

Plenty of congealed lubricating oil to be found.

Even without the pinion gear, it was exceedingly difficult to urge the two parts of the slide apart: more congealed oil. Much to my surprise, the slide does not have adjustable gibs: it’s one of those precision-ground gadgets that Just Works. This picture shows all the parts in their gunky glory. Note the random dirt in the rack teeth, along with the goo on the pinion shaft.

Rack and pinion - disassembled

Rack and pinion - disassembled

With everything apart, removing the gunk was a simple matter of toxic solvents and mechanical poking with wood picks and splints

I filed off the burrs on the shafts, thought briefly about grinding some flats for the setscrews, and decided to leave well enough alone.

A few dabs of clock oil here & there, reassemble everything in reverse order, and the Z-axis moves gracefully with minimal knob torque. It’s very sensitive to the clamping force of those pointed setscrews, though.

It’s now easy to discover that the planetary reducer has a 5:1 ratio and the Z-axis moves about 6 mm per turn. Because the reducer uses balls, it slips when the slide jams against something, rather than strip its gears.

I should clean the other two slides, but a dot of clock oil on each cheered them up enough to let me punt that for a while…

I like it!

Micropositioner

Micropositioner

Advertisements

Leave a comment