On 13 Nov 2010 04:56:28 GMT, "DoN. Nichols"
wrote:
On 2010-11-13, wrote:
On 12 Nov 2010 06:01:52 GMT, "DoN. Nichols"
wrote:
My WML hates you. It swallowed your post again. OTOH it is not
prejudiced, it swallowed my last reply, too.
:-)
It knows that I do not trust Windows and reciprocates. :-)
This one it let through. The Forte Agent formats better. OTOH it has
other issues.
[ ... ]
I put the chuck back in. The dowel pin run 0.002 at "zero" and 4"! But
then I repositioned it slightly and re tightened and the wobble
appeared - 0.004" at 4".
Since you are using ER style collets -- you should be able to
cover the whole range that the chuck can hold (assuming a full set of
collets), so why not *use* the collets?
How do you drill a e.g. 7/64" hole with a collet? I guess start the
hole with a spotting drill in a collet and then switch the
arbors...OTOH if one has a proper spotting drill with a long enough
shank the procedure might not be necessary (see below). It certainly
seems the way to go if starting the hole with the center drills. Which
I won't 'cos I know better now.
I tried the center drills: No.3 was better initially at 0.003", but re
tightening I could make it 0.005".
No. 4 was 0.007"
For the sake of comparison I put the dowel pin in my drill press:
0.0035" and 0.007" at "zero" and 4".
How much could you move the stationary spindle by pushing
sideways on the chuck in various directions? Usually, the fit of the
quill to the headstock in a drillpress -- especially an import one --
can be pretty bad.
A fair bit.
[...]
I thought it would be helpful to check the run-out of the JT33 arbor
and tried to remove the chuck. I made a wooden jig to support it but
it seems that the helpful Chinese glued the thing in so I desisted
before things got out of hand.
The normal method for removing a chuck from an arbor is to use a
set of Jacobs chuck-removal wedges.
Check MSC part number 08592941 to see an example. (These are
for the #3 Jacobs taper. There are four different sizes depending on
the size of the Jacobs taper being removed -- and for some of them you
need two different sets to make a removal set for a particular size.
These are tapered in thickness (narrowest at the tips of the tines) and
are placed between the chuck and the shoulder of the Morse taper adaptor
from opposite directions, and are squeezed together with a vise. If the
Morse taper big end is smaller than the Jaobs taper in the chuck, you
may not have a shoulder to work against, and will have to destroy the
arbor by drilling a cross hole for a pin for the wedges to work against.
The MSC catalog page may list what combinations are needed for
what Jacobs tapers -- or it may be that I saw it on the Jacobs web
pages.
OK, what is wrong with my method?
1) Prop the chuck upside down on two blocks of wood by its shoulders
(where the wedges would go, too)
2) Open up the chuck to its widest.
3) Use an *aluminum* cylinder of a diameter just slightly less than
the diameter of the JT33 arbor through the open chuck jaws.
4) Hit with a BFH
[ ... ]
Jacobs style chucks are made to grip all the way down to the end
of the shank -- and if your tool won't seat fully back for whatever
reason, it will not be as good a grip, and the jaws may move in their
guides.
There is less than 3/4" of intact shank between the ends of the No. 4
center drill. The flutes start either side of it. This is enough for
the collet but clearly not enough for the chuck. It gets worse as the
center drill gets smaller. I think I mentioned that with the No. 1 it
is ridiculous. Never again No. 1 in a chuck!
..
You might look at MSC item # 08592545 -- which is a rebuild kit
for some particular sizes of standard Jacobs chucks. (Replacement jaws
and replacement split threaded ring which feeds the jaws.) Since MSC's
web page has just gone offline, I can't tell more about it at the
moment. The best thing is to visit Jacobs' web site and read up on
rebuilding their chucks, then make the tools needed to press the chucks
apart and actually *see* how they work.
Would they then work any differently on the center drills?
[ ... ]
1) Do not use digital indicators for this sort of work.
You had been using a digital one? I don't remember you saying
this. *Some* digital ones are more accurate than some mechanical ones.
The Starrett "Last Word" mechanical if the bias spring is not applying
bias throughout the range. (A bump on the side of the point can cause
it to skip in the spiral, so there is a major deadband in the range.)
I did the first time. It was a part of an existing set-up. They are
nice for some things, axis movement, measurements over 0.1", but for
this analog is better IMHO.
:-) A good analog one can read to a tenth of a thousandth.
What? You mean my $9 ones won't?
2) Change the center drilling procedure as outlined above.
3) Grind a spotting drill?
How about *buy* at least one, so you know what it needs to look
like? I recently got (from a sale flyer from MSC) a couple of 1/4" x 60
degree spotting/centering drills (MSC #FJ71332167). If the sale from
that flyer is over, the "FJ" won't do any good, and the price will be
back up to whatever it was.)
Probably right. Getting the point exactly co-axial is probably
something I could not do with a Dremel.
Exactly co-axial with the spindle -- *sure* until you remove it
from the chuck. :-) But generating the flutes down to the point is a
major trick.
Probably not worth the effort spending the time producing inferior
result. Fastenal show some US made ones. I shall see if the local
branch will sell me one (rather than a packet of 100).
Michael Koblic,
Campbell River, BC