This is a new version of my previous, never published spring mandrel / spring making guide with several improvements over V1

It is used to produce very small springs out of music wire for self-made solenoids.

Libraries

The old version relied on Douglas Peale's spiral_extrude library which renders incredibly slow (like glacially slow).

Version 2 passes to Phil Schatzmann's spring implementation which renders way faster.

Formulas

I also found several different spring calculation which turned out to be unreliable for small springs (giving negative lengths for mandrel diameter (?!??!)). They all seem to rely on " 'Helical Springs' by Kozo Hiraoka, in Home Shop Machinist, May/June and July/August issues, 1987" but I couldn't find an original source. I ended up estimating the mandrel diameter and approaching the final result through several iterations. Please, if anyone knows pertinent literature to this topic, leave a comment.

Printing/Slicing

I printed the mandrels with 0.1 mm layers. To reduce printing time I applied variable layer height for the base.

Lefties may want do mirror the mandrel (also included in OpenSCAD file.

How to coil a spring

Follow this video.

You need music wire, pliers, an M5 extension Nut and a driver. The video shows my self made Wrench Rod. Instead of using an extension nut you may also adapt the file to used any kind of screwdriver bit

Please be aware, that your spring will open up and

• get longer than the mandrel's spiral height
• have less coils than the mandrel's spiral has.