2026-09-20

Last modified: 2026-09-20 21:28:49

Cyclecar spring shackles

I started making the 80mm spring shackles this evening.

I gang-drilled them, bolted them together, and then put in the CNC machine to round the ends.

The first side went OK but the end mill snapped on the other side, unsure why.

It was a 6mm 4-flute brown-coated end mill, at about 4200 rpm, 260 mm/min, 1mm depth-of-cut, and varying width but going up to full-slotting at the corners.

I thought this should be fine? It's possible the end mill was already worn. Shortly before it snapped I notice some chip-welding, which I removed before continuing, and then just before it snapped I heard it stall but didn't have time to stop it.

ChatGPT suggests that coated carbide end mills actually want to get hotter so counterintuitively it may help to increase the spindle speed.