The steel “rolling pin” part shown has a precision 8mm boss on the secured end. To mount this in the Microarc, I took on old ER20 TTS holder and 8mm collet and chucked it up in the 3 jaw. There’s about 0.015" of total runout measured at the point shown … which isn’t good enough for my purposes. The 3-jaw chuck itself has only about 0.002" of TIR.
Solutions:
Loosen the securing bolts where the 3-jaw mounts onto the microarc and tap it to bring the part into true.
Get a 4-jaw (independent) chuck.
As I have the ER40 collet chuck, get the requisite 8mm collet and skip the 3-jaw altogether.
From my point of view, option 3 looks like a stand out leader in this race.
I have looked around for a 4 jaw chuck for the microarc and haven’t found anything that would bolt right up. Granted, this wasn’t an exhaustive search. I found a few options that would need a base plate in-between.
Definitely swap to the ER chuck. Faceplates for the microarc are easy enough to make so you could certainly put one together for a 4 jaw without much trouble but the cost of a single collet is going to be far less than a 4 jaw and material for a faceplate.
And ordering the collet is likely to take less time than ordering a 4 jaw, measuring it up, designing the faceplate, fabricating said plate, then getting everything set up.
Granted then you’d have the 4 jaw for future projects but still doesn’t seem like the right approach to getting the current part finished.
