"Ned Simmons" wrote in message
...
On Sat, 28 Nov 2009 02:20:12 -0500, "Ed Huntress"
wrote:


"Mark Rand" wrote in message
news
On Thu, 26 Nov 2009 16:51:38 -0500, "Ed Huntress"

wrote:



Now I'm getting confused. If the HLV has a pair in front and one in the
rear, why is the rear bearing an angular-contact type? I can see that
for
the HLVH, based on what's been said here.

Ditto.

I can only put it down to the fact that the HLV seems to incorporate
quite
a
lot of design decisions that don't make sense from an engineering point
of
view, unless you assume that more expensive is automatically better.
Like
my
case earlier where three C3 or two C1 bearings would outlast three C1
bearings
on a shaft and other oddities. I guess it is a 60 year old design and
there
were many improvements made over the years.

If all of this is sinking in correctly, it sounds like the outer spacer is
designed to heat and expand at the same rate as the inner spacer -- or
close
enough for it to work. Because it still looks to me like the whole
assembly
is going to break or unload if one of them expands significantly faster
than
the other.

With the outer spacer, it saves one bearing but adds the spacer. And the
whole thing, I'll bet, was developed experimentally.

The HLVH layout is extreme, but some space between the front bearing
pair is not unusual. I'm looking at a cross section of a 10EE
headstock and it appears the spacers are about 2-1/2" long. The
support at the tail is an unspaced pair of angular contact bearings.
Top speed of an EE is about 1000RPM higher than an HLVH.

The bearings at the nose of a Bridgeport spindle are separated perhaps
1-1/2". In this case there's a single deep groove bearing at the top
of the quill. A BP spindle running at top speed gets much hotter than
an HLVH.

Grinder spindles typically have the bearings pairs mounted directly
back-to-back.

--
Ned Simmons

That generally agrees with what I've seen, although I haven't had any
spindles apart for a few decades. Thirty degrees F produces about 0.001 in.
of growth in about 5 inches of length. That shouldn't be a problem for
ordinary bearings, which are less that perfect all around; there's a little
room for elastic compression.

As it's been explained to me, the problem becomes more critical as the
bearing class goes up. The Class 9 bearings in a Hardinge HLVH must be very
touchy in terms of the growth they'll tolerate.

--
Ed Huntress