"Robin S." wrote in message
.. .

"Harold & Susan Vordos" wrote in message
...


You apparently have never honed a reamed hole. The typical reamed
hole
is
scarcely qualified to be considered precise, let alone VERY precise.
I'll agree that a well reamed hole is drastically improved over the
typical
drilled hole, however. Reamed holes are a distant second to properly
bored holes and aren't even in the running when compared to honed bores.
Reamers are notorious for generating multi-sided holes with bell mouthed
conditions.

I thought boring and honing were fairly bad for leaving bell mouthed holes
(although they're certainly round)? Not to say it's impossible to get a
correct profile with a boring or honing tool, but they're not exactly
perfect.

Regards,

Robin

There is no reason for a boring bar to leave a bell mouth in a hole. A
hole that is bored with a sharp instrument and proper feed should yield a
roundness in keeping with the bearings of the spindle. Cutting pressure
should remain constant from one end to the other, thus should yield a bore
that is round and parallel in all respects, assuming the cutting edge is not
dull and dragging. Tool wear can be the one variable, but is generally
not enough to effect a bore size unless one is boring particularly nasty
material.

Honing is extremely precise, but in the hands of a fool it surely could
leave a bell mouthed hole. My personal experience as a grinder and tool
maker have proven to more than my satisfaction that honing is likely the
most precise of all methods to achieve round, straight holes. I would place
an internal grinder next. One of the projects I had to make was a set of
3/4" ring gages with a tolerance of only .000020". Holding the bores
straight and round on a hone is absolutely no problem is you apply the tool
properly, and it was the tool used to size the bores of the gages. They were
inspected by a certified secondary standards lab and were within limits.
By their very nature (by design), honing mandrels have a constant truing, or
correcting action. A hole that is out of round and tapered is easily
brought round and straight. Understand that the mandrels must be of the
rigid variety. The spring loaded cylinder hones one uses for cleaning up a
brake cylinder are virtually worthless, and yes, they do yield bellmouthed
holes. They have no reason not to.

If in the process of your apprenticeship you have the opportunity to run any
grinding and/or honing equipment, I think you'll quickly come to understand
the things I've mentioned. Grinding and jib bore/grinding operating are
the ultimate expression of precision work.

Harold