I had 8 off 15mm holes to drill in a 1.125" thick disc of mild steel on an 80 mm PCD. I have a 4" chuck mounted on my 6" Vertex rotary table and there was a 60mm recess in the back of my disc so the chuck was wound out to grip. The whole plot is mounted on the Bridge port, the 40mm offset dialled in and drilling commenced using a centre drill to start with, a couple of intermediate size drillings finally finishing off with a brand new 15mm drill. The indexing is done with one of those electronic thingummy bobby things, the name of which currently eludes me.
I then make the drilling bush to 15mm - .001ish and lo and behold they won't fully go home! Entered from the side that the drill entered they will go in 3/4 of the way, to the point of jamming they slide in nicely. Entered from the other side they bind 1/4 of the way in. Oh bugger. I have resolved the problem with an adjustable reamer so the job is done.
But......what went wrong. Any suggestions?