On 2008-03-02, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:

On 2008-02-28, Joseph Gwinn wrote:

[ ... ]

This sounds very useful in a production environment.

It is, indeed. Even a batch of 80 (from one 6' 3/4" brass rod)
counts as production enough to make it worthwhile. It is especially
nice for threading up to a shoulder, because once you preset the travel
stop on the ram for that particular station, you have no problems with
things shifting. The Shoulder is made by the previous station in the
turret, with a similar stop. A roller box tool is what is used for
that.

I'm still doing one and two, mostly for educational value.

Understood. When I got the lathe with the bed turret as part of
it (matching serial number) I had to get more tooling so I could use it
fully. I already had experience with various lathes from around that
size on down to tiny, but no turret experience. The turret came loaded
with three 1/2" Jacobs chucks and two floating reamer holders -- end of
list. :-)

[ ... ]

Hmm ... I wonder how repeatable the location of the boring bar
hole is from holder to holder. If you were going to use it that way, it
would be important.

The boring bar hole in various holders is probably pretty good, as
Aloris makes them on some kind if production line, but they make no
claim of repeatability between holders.

And if you mix manufacturers, the difference may be much
greater.

[ ... ]

didn't look that bad, although the corresponding nut did seem a bit
loose. What kind of backlash is reasonable?

Well ... that particular leadscrew had something like 0.070"
backlash, so it was obviously problematical. I would think that
anything under 0.005" would be very good for a used one, and probably up
to 0.015" would be acceptable.

Mine appears to have 0.048" of backlash, judged by turning the handle
and reading the dial drum.

O.K. Mine as a bit over 0.070" -- nearly 3/4 of a turn, and the
leadscrew was going to start wearing a lot faster.

Compare the backlash in the middle of travel to that at the ends
to see how much is in the leadscrew and how much is in the nut. If you
go to the point where the leadscrew is just barely fully in the nut you
should be measuring just the wear in the nut, since the leadscrew is
very seldom used in that range. And the more difference in backlash
between the ends and the middle, the more cumulative error in the dial
reading. I got both leadscrew and nut at the same time.

[ ... ]

There may simply be small errors in the curvature turned in the
ring, and if there is any error, I would expect that the rocker should
make contact at the OD first. I wonder whether it was turned with a
form tool, or a radius turning tool.

The slot appears to have been made by plunging a form cutter held in a
horizontal mill into the stock about 0.25".

Huh? I thought that we were talking about the curvature in the
ring which surrounds the lantern toolpost. That can be slipped over the
toolpost for measuring the radius with the toolpost out of the way.

[ ... ]

Right. I'm wondering if it's a torus, or a sphere. A sphere would make
mechanical sense, and is easier to machine as well. Maybe I'll make a
disk out of thin aluminum, for fit testing.

O.K. No radius gauges in the proper size range? :-)

Not that big. Nor that narrow at the tip, to allow use at the bottom of
a narrow slot perpendicular to the slot.

Again -- slip the ring off the top of the toolpost and measure
it free standing.

As for a tool to measure the radius -- try three rods on a set of
three collars which can allow the rods to both pivot and to slide back
and forth to set a radius. The extension of the rods which allows the
rods to pivot throughout the range of the curve and have all three
continue touching would be set to the true radius. I've seen such a
tool in an old Machist's toolbox.

Note that the rockers which I have seen were forged, and have a
diamond pattern grip surface on the top.

I have one of those. It almost fits, but is a cylinder, not a sphere or
torus. It is also hardened, making trimming arduous.

Of course. I wonder whether the cylinder instead of the proper
curvature is intentional? That would cause the edges to dig into the
ring and make it less likely to slip sideways under cutting loads.

I think that the cylinder is intentional for sure - the cylinder is
cheaper to make. With a section of a sphere, clamping is firm and
distributed over a broad area even if the bar being clamped isn't quite
rectangular. Which is why Clausing went to all that trouble.

Have you seen a true Clausing one to be sure that this was the
case? I don't think that Clausing made the toolposts for their lathes
-- they just bought from Armstrong. The parts are all forged, and it
makes more sense to get them from a vendor who is already set up to make
forged tools than to make one yourself for the machine in question.

But -- I wouldn't worry about it anyway. My Clausing came to me
without a lantern style toolpost, and I have been happy to keep it like
that. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---