Chuck up workpiece in lathe (or clamp to faceplate), drill out 6mm or so, using drill in tailstock chuck. Small boring bar in toolholder, insert into hole taking light cut open hole out to required size. For what you want you can get accurate enough with boring if you use short tool to avoid tool shank bending and use a light cut can cut 0.05mm undersize then trial with stepper while still chucked until tight push fit (if its close enough you can heat workpiece with hairdryer to expand it and it will be a tight fit when it cools). I dont think you need to ream it, but if you do want to, bore out 0.2mm undersize then ream with reamer in tailstock chuck.