Cross Drilling Holes in Round Stock

Cross drilling a round bar is something that always seems to give me grief, straight cross drilling is fine how ever take the example in the pics, on the bench I have centre punched a mark on a length of round stock and need to cross drill at the centre punch mark - the part on the right is out by 1 deg but if you ignore the 91 deg dimension it still looks ok and no different from the one on the left.

This is something I have never been able to get right - if the bar is small enough I can set it up in the rotary table and be sure that the holes are in the correct relationship, this is not always possible though and there are times when the position of holes is marked on the bench before being drilled.

Does anyone have a a good method that ensures a gross drilled hole will be exactly on a centre punched mark. The one degree error will matter if the bar has other holes/flats etc that need to be spaced with a certain number of degrees between them. I have in the past cross drilled two holes that need to be 90deg apart one of the holes was slightly out by just under 2 deg - put a rod through each hole and the error is visible.

Attachment 381303

Square collet block?

Hi Bob, Guys,

Bob you beat me to that one !
That is exactly what I do. I also set a length stop if I need the holes to meet precisely. I've also broken drills doing this a number of times.

Another helper is to put a dowel pin in one hole after drilling and position that against a square stop (like a parallel). A square collet block is probably the easiest though.

Michael

It could be your centre punches, for accurate holes i dont centre punch as they are not that accurate and only have to be off a bees and your drill heads off in the wrong direction.
If you are using a mill you dont need them anyway.
cheers, shed