Metric and inch threads battle for ultra-precise positioning

When you're a machinist, your job is precision, with measurements to the thousandth of your favorite unit being common. But when you're a die maker, your precision game needs to be even finer, and being able to position tools and materials with seemingly impossible granularity becomes really important.

For [Adam Demuth], aka "Adam the Machinist" on YouTube, the need for ultra-fine resolution machinist jacks that wouldn't break the bank led to a design using off-the-shelf hardware and some 3D printed parts . The design revolves around a metric inch thread adapter that you can get from McMaster-Carr. The female thread of the adapter is an M8-1.25, while the male side is a 5/8″-16 thread. The pitches of these threads are very close to each other - only 0.0063", or 161 microns. To take advantage of this, [Adam] printed a cage with compliant mechanism springs; the cage holds the threaded parts together and provides axial preload to eliminate backlash, and allows precision steel ball mounting at each end to ensure that force in the ram is transmitted through a single point at each end.Each full turn of the ram moves the ends of the pitch difference, allowing for ultra-fine resolution positioning. Need even more precision? Try an M5 to 10-32 adapter for about 6 microns per turn!

While we've seen different thread pitches used for precise positioning, [Adam's] approach requires machining. And as useful as those jacks are on their own, [Adam] stepped things up by using three of them to create a kinematic base, finely adjustable in three axes. It's not quite a Stewart nanopositioning rig, but you can see how adding three more jacks and some actuators could make it possible.