"Snag" wrote in message
Phil Kangas wrote:
"Phil Kangas" wrote in message
Say you've laid out the end of a shaft for a center hole
to take a dead center and the hole comes out a bit off
center. How would you go about 'moving' the hole
back to center?
Phil Kangas
Guess I'd better add some more info on this. The bar is
1.75" 4140 B7 , rough finish surface, too big to pass
through
the spindle, 30" long, no extra length. I managed to do
it
but
got curious what others would do.
Phil
Brass bush , steadyrest , and a very pointy lathe bit .
And as Grant said ,
a PITA . I've been turning some 4140 lately , what fun !
Almost as much fun as the Ampco 18 ...
--
Snag aka OSG #1
'90 Ultra , "Strider"
The road goes on forever ...
none to one to reply
Voi ye, this dumb 'ol Finn went and did it the hard way,
again, but then I
have a lot of free time sometimes! So what's my story? Ok.
The original
holes were actually quite close to the center of the bar
ends but when the
bar was first placed between centers it rotated on its own
to a certain
spot, time after time. ? Shouldn't do that, eih? The bar is
rough all right,
lots of fat spots, a belly along its length and a very
slight bow. The bow
would not come out even in the press at 24 tons and 0.130
displacement!
Some tough iron this is but at $24/foot it better be! And I
don't plan to
shovel off pricey metal to get a good usable bar. So the
center holes even
though they were good for the ends they were not in the
natural centerline
of the bar! So they have to be moved to that line but how?
heh heh .......
now the fun begins:
First thing, replace the spindle dead center with a combined
drill / csk
( mine is a #6 mounted directly into a salvaged 3MT drill
shank) then
move the faceplate dog to the tailstock end but left loose
for now.
Then a steady rest was mounted close to the faceplate with a
DI on it
reading at 12 o'clock position. A wood v-block was placed
near the
tailstock for convenience. Another DTI w/mag base was set on
the rear
apron for test measurements along the bar. The bar was then
set in place,
run up on the center drill with the rear on the tailstock
center. The bar was
turned watching the DI's and figuring where are the errors.
The high spot
was set at 12 o'clock and the dog set at the tailstock end
to stop rotation .
At the steady rest the rollers at 4 and 8 were brought in
contact then
backed off ever so slightly. The roller at 12 was then
brought in contact
and the DI zeroed. With the gearbox in lowest gear the
spindle was
started and the top roller turned down hard while watching
the drill cut
and the DI reading changing. It didn't take a lot of
pressure to do this
and as soon as the required distance was reached the
tailstock was
nudged ahead to clean up the hole back to round. Worked
pretty
good actually and set me to gloating about it. The bar can
stay in
place and readings can be taken to assess the situation. The
bar
can be swapped end for end to take care of anomalies at that
end
if needed. I gotta admit I spent a lot of time playing with
this but was
worth it! Here I am, 60 years old and still learning a fun
hobby!
Hope you youngsters out there learned something today too,
eih?
Phil Kangas
--
Posted via a free Usenet account from
http://www.teranews.com