I have a cnc lathe with a2-6 spindle nose and have recently purchased a new marquart collet chuck. The collet chuck fits very nicely but the sliding portion that closes the collet is 3.385" diameter at the rear and the bore of the spindle nose on my machine is 2.75 diameter. The a2-6 spindle nose is aprox 4" in diameter at the small end of the taper. The sliding portion of the collet chuck would need to slide aprox .23" inside the spindle nose .

I am assuming since marquart sells this chuck that it must be farily common for the a2-6 spindle nose on some machines to have the clearance . Need thoughts/advice on what to do . I am considering opening up the spindle nose slightly for clearance . Any downside? Thoughts?

Any one with same spindle taper know what the bore size is on your machine?