At 10:40 PM 8/17/2012, Alistair Bell wrote:
>I want to add to this excellent description, maybe differing a bit...

Awww...I was hoping you'd go a little into how to actually find the
darn center in the first place.  And how to walk a punch mark sideways. ;-)

>I'd use a fine prick punch to mark the hole, then if you want punch
>again with 60 degree point pu[n]ch.

Good point (no pun intended).  But on the shaft we're talking about,
it's probably only held up by an E-clip, so we can't bang on it very
hard without injuring something; so we can't make a big hefty
center-pop with a hammer since we can't reach the back of the shaft
to back it up with a weight.  The fine punch wants a small hammer
(8-oz or less ideally, I think), and a spring-loaded automatic center
punch may be safer for increasing the size.

>  Then as Bill Monk has said, use a small (1/16") drill to enlarge
> punch divot. The small flexible drill does a better job in this
> case than a centre or spotting drill.

Yes, I agree.  Keep the center drill in the tool room.  It's actually
quite unforgiving with its little stiff point and rigid body.

>  You do not need to drill very deeply with the 1/16" bit, just make
> the punch mark a hole. Then go on to the 1/8" bit and follow with
> tap drill size.

I still like the 1/8" pilot point bit.  Probably can start right from
the beginning with it, the pilot makes it disinclined to wander
whilst drilling, and it's still quite flexible (but not as fragile as
a 1/16" bit).  I haven't measured the pilot but it's pretty small.

>Tapping the hole in situ is tricky. Hard to keep tap perfectly
>aligned, as is it is hard to keep drill bit aligned.

And of course whilst the drill bit will flex a bit, the tap is
practically glass hard and won't.  Which is why you use a proper tap
handle or die stock that lets you pull from both sides of the tap, as
you're much less likely to break it off short that way.  Don't use a
tee-type handle with its crossbar stuck out to one side, balance it.

Starting the tap is the trickiest part, that part you use a drill
press or other solid jig for if at all possible.  Getting the first
few partial threads to bite at all, and precisely straight in, can be
very difficult; and whatever angle it starts at it will continue
until the job is finished or it finally gets an impossibly large bite
of the wall, jams and breaks off.

>All in all, I'd say it is a tricky job to get a good tapped hole in shaft.

Amen, brother.

Yours,
David