Taunt wrote:
Proctologically Violated©® wrote:
Awl--

I'm sure I can "solve" this by being more vigilant, but that it
happens at all seems sort of strange.

Briefly, I'm drilling a 3/16 hole 3/4" deep in 1/4" round brass:
face, c-drill, then a 3/16 drill (tailstock/drill chuck, 5C collets).
Then, I'm turning down a piece of 1/4" round brass to 3/16" OD, for
about a 3/8" insertion into the other piece w/ the 3/16 hole, for a
"nice" fit. Using a live center.
Have DRO, Aloris tooling, good for half a thou, I'm pretty sure--at
least the DRO says so!

Problem is, the 3/16 OD pc gets in only about half way before it
hits some kind of "step"!!!
To achieve the full 3/8" insertion, the fit winds up being far too
sloppy! Still works, but annoys the hell out of me.

Seems like a simple no-brainer, and I'm sure I could solve it w/
sequential drill sizes, reaming, etc., but it doesn't seem to me
like this should be necessary, as there is nothing complicated or
exotic here. I would have anticipated any other type of problem--holes
too big,
holes too small, ragged/jagged sides, holes off-center, etc.
But an invisible step??

Any idears?
Mebbe on my next have-at-it here, I'll test the female portion w/ a
3/16" dowel, to at least try to identify the offending
piece/operation. It's pretty clear what the problem is (diameters!), but
puzzling as
to *why* this problem is occuring.

TIA.
----------------------------
Others have mentioned using a reamer to achieve an accurate hole.
I would suggest a 'D' bit for final dimensioning. They are rather easy to
make and produce precision results.
Use a twist drill out to a few thou (or next drill under - it is not that
critical, specially in brass) under required size and finish with the D bit.
A really simple type of D bit is a piece of drill rod of the required size
with one end cut off at a 45 degree angle. File, grind and polish the angle
flat to the best finish you can achieve - then harden and temper.
That's it. No relief or other fancy stuff.
Try it and you will love it!

Regards.
Ken.