On Mon, 2 Oct 2006 15:05:53 -0400, (Arch) wrote:


4. Is a Jarno taper used on a Jacob's chuck arbor because it's short or
there other reasons? Which best prevents mating parts from rotating, MT
or JT? I've had both tapers slip by deliberately overstressing cheap
chucks. I let them rust to prevent slipping. Is there a better way to
'tighten' Morse & Jarno tapers?

Hi Arch,

I've done a little judicious snipping to skip the things I don't know
about to hit this one-

First part, I'd guess that the MT does a better job of preventing
mating parts from rotating. More surface area = more holding power.

Next, ever seen a machinist's Bohr blocks? If you haven't, they are
two blocks with perfectly flat surfaces that hold together with no
adhisive or fasteners. This is because the machined surfaces are so
precise that they allow the two pieces to sit so closely together that
the atoms in each can swap electrons (and possibly other forces, I'm
not an expert on the subject by any means)

In a perfect world, the mating surfaces between the MT or JT and it's
mating socket should work on a similar principle. Granted, most of
them have some dings and nicks, so it's not going to be quite the
same, but getting it close must be good enough. Allowing the two
parts to rust introduces a failure point that should not be there-
that doesn't mean it doesn't work in application, but the best way to
get the full performance is to make sure both the taper and the socket
are perfectly smooth and shiny. To help things stay rust-free, a
little oil goes a long way, and also adds to the bond between the two
mating parts.

As far as "tightening" goes, I've always fully opened chucks, then
inserted the JT, and put the assembly into a vise. Seems to work well
enough, and you're not pounding the guts out of your chuck.