As we all know drilling a deep hole in metal the drill bit will wander so why didnt I take steps to minimise this.
This came home to bite me in the last special rod joiner nut and bolt I'm making.
The first 5 went well with no problems except a couple werent drilled quite deep enough but that was soon rectified with no problems.
I used a 16mm bar of stainless and machined them one after another just setting the bar through a bit at a time depending upon the step to do.
1, turn 16mm down to 10mm 25mm long
2, centre drill then drill 55mm deep
3, turn the taper till it meets the edge of the hole
4, use the parting tool and make the run out groove
5, cut the M10x1 thread
6, loosen the collet and extend the bar
7, cut the knurl
8, part off
9, extend the bar, rinse and repeat.
The one that went wrong was one that had a 7mm deep hole left in the end of the bar so I just drilled it deeper.
As I got to the end the drill was flexing quite a bit where the hole had drifted off centre by at least 0.5mm.
I continued and finished the bolt but the 6mm rod it had to slide on wouldnt slide through due to the bend in the hole.
All the others were first faced the centre drilled.
Oh well, still enough 16mm bar left to make another