Making Micro Screws Threads

Production of micro threads can be challenging, but using the most suitable tools for a given application can simplify the task.

Six different processes can be used to produce micro threads: tapping, conventional turning, thread chasing, thread rolling, grinding and electrochemical grinding (ECG). 

Thread chasing and thread rolling are performed on lathes, with tools other than a conventional v-groove tool.

Tapping

Micro taps are available in special alloy high carbon tool steel, hardened high speed steel, TiN-coated HSS, and in TiCN-coated HSS. As many as eight different tap geometries are available in some sizes.

Hard to machine materials often require the use of the upper end of the allowable drilled hole tolerance to prevent tap breakage. To be successful, a shop should establish its own minor and major diameter limits, 

but it could be restricted to working with only about half of the allowable tolerance to prevent breakage, yet still produce an acceptable “complete” thread form.

Cutting taps with ground flutes, but unground threads, though less expensive, break more often than those with ground threads. 

But these taps can be successful on aluminum parts. Micro-size fluteless cold forming taps, effective in soft materials, typically break in harder materials.

Miniature Lead Screw Tappers

Lead screw tappers can easily produce some of the larger micro sizes, but few, if any provide that capability for the small sizes. 

The most sensitive tappers have adjustable torque limiting controls that automatically reverse the spindle, clear chips and then resume tapping to preset depths.