Gyros Miniature Circular Saw Blade & Mandrel Tinkering

The Small Envelope o’ Slitting Saw Blades also disgorged several Gryos Ultra-fine blades and their mandrel with a broken screw jammed in place. Unlike similar Dremel-ish cutoff wheels with a mandrel threaded M2×0.4 mm, these blades have a 1/16 inch = 64 mil hole fitting the mandrel’s screw:

Gyros mandrel - broken screw size
Gyros mandrel – broken screw size

The 1-72 brass screw came heartbreakingly close to fitting and the M2 SHCS obviously won’t play. I can’t measure super-fine threads, but I can count: 16 threads on the stub occupy about the same distance as 18 threads on the 1-72 screw, so 72 × 8 / 9 = 64 tpi and it’s a 1-64 screw, not the far more standard 1-72.

The blade hole just barely fit a #51 = 67 mil drill and measuring my assortment of mandrels produced one with the only M1.8×0.35 (OD = 71 mil) screw I’ve ever seen, so I drilled the blade with a #50 = 70 mil drill:

Gyros miniature saw blade - hole enlarging
Gyros miniature saw blade – hole enlarging

Should the oddball screw in that mandrel break, the next step will be a #48 = 76 mil drill to fit the blade around the M2×0.4 screw for cheap and readily available mandrels.

So, being left with a broken screw stub in the original Gyros mandrel, I soaked the scene in Kroil overnight, then applied a tiny screw extractor with amazingly good results:

Gyros mandrel - broken screw extraction
Gyros mandrel – broken screw extraction

I did eventually find one 1-64 screw in the Big Box o’ Tiny Screws, although its infinitesimal head seems intended for gentler duty than clamping a saw blade to the end of a whirling shaft.

Hand-held Dremel mandrels have, as far as I can tell, no particular runout specs, so chucking them in a Sherline spindle collet pretty much guarantees only a few teeth on one side of the saw will do all the cutting. Which, I hope, will suffice for my simple needs.