Spindle, Micro Mill, ER-16

Finally found a direct replacement spindle that fits the SX1 micro mill perfectly – the ER-16 collet nut threading is exactly right. Ran it for a few hours and the runout seems minimal, definitely an improvement over my worn-out original.

The M22x1.5 thread on the collet nut mates perfectly with my ER-16 collets, and the runout is noticeably tighter than the stock spindle I had before. Swapping it in took under an hour, and the finish on my aluminum parts is way cleaner now.

Finally got around to swapping the stock spindle on my SIEG SX1 and this one fits the ER-16 collets without any fuss. The M22x15 thread on the collet nut side engaged cleanly and the whole assembly runs true when I chuck up a 1/8" end mill. Took maybe twenty minutes to install and it’s been solid on