Alt account for @mcdanlj
1st Fedora Project Lead. Co-author Linux Application Development. Sr. Director Engineering Pendo. Ex-{Linux Journal, Red Hat, rPath, SAS}. Christian. Father. Maker (including machining, 3D printing, and electronics). Books. Classical music. Aviation (PP-Inst-SEL). https://musings.danlj.org/
I've never before bored a hole this long with such a high aspect ratio through steel; ⅝" almost 5" long.
First try, I broke about an inch off the end of my pilot drill right in the middle and after a lot of work failed to rescue.
Second try, I used a larger 3/16" 6" aircraft drill as a pilot, but it wandered. I ended up using a 2-flute ⅜" end mill in both ends for alignment and drilling through, which got me close enough for final drill and ream.
I forgot to chamfer before starting my final reaming operation on this part.
Now I know why to chamfer before reaming. This chatter is intense, and it's definitely just as bad as it looks.
😅
Fortunately, I can start over from the other end and these chatter marks will, I think, eventually do me no harm.