In article ,
"DoN. Nichols" wrote:

On 2008-02-28, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:

[ ... ]

O.K. I've found a URL which gives some images:

http://reno.craigslist.org/tls/563369567.html

but it is short on description, since it is simply someone selling a
used one, and it is presumed that the purchaser already knows what it is
and how to use it.

The picture helped a lot.

It does, typically. Even better is holding one in your hand. :-)

Someday.


So -- I'll do the description here.

1) Picture something which looks like a 4-jaw chuck with strange
levers coming out radially.

[ ... ]

8) At this point, you can withdraw the ram of the turret with the
workpiece still spinning at 800 RPM. When the turret ram
reaches its full back travel, it will rotate to bring a new
station and tool into position. However, if you are using the
rough/finish lever, you flip the lever from rough to finish and
use the red ball handle to close it again for another stroke.
(Without the rough/finish lever, you complete the whole thread
in a single stroke. And because the form of the chasers is
correct, you can simply check the setting by measuring the OD of
the finished thread, instead of having to use a thread pitch
micrometer, or a set of thread measuring wires.

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.




As I said, this would be a real asset in production.

And -- you (ideally) need a bed turret for the lathe to make
most efficient use -- though you can fit it to a boring bar holder for a
quick-change toolpost if you take the time to properly center the bore
in the toolholder to the spindle axis. For that matter, you could
precede that with a roller box tool in another holder. Put a turret
carriage stop on the bed to stop each tool at the right place.

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.


I don't think I will add much to the wear already experienced by the
Clausing in production use versus HSM use.

Well ... the cross-slide leadscrew (which had been mostly used
under power feed for parting off) on my Clausing looked like this in
the middle:

__/\__/\__/\__/\__/\__/\__/\

instead of like this:
_ _ _ _ _ _ _
_/ \_/ \_/ \_/ \_/ \_/ \_/ \

thanks to long service. And that was a leadscrew which was just being
used for parting off. The lathe did not even have the threading dial
mounted, because it was being used with Geometric die heads in the
turret for threading.

I assume that this crossfeed screw has been replaced by now.

Oh yes -- it was one of the first things to be replaced, along
with a broken pinion gear (one tooth broken off) in the turret,
resulting in a hitch in the feed. I got a new nut at the same time, of
course. But I got the leadscrew without the gear, and pressed on the
old gear from the previous one -- a significant difference in cost. :-)

Mine
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.


I don't quite visualize your proposed approach.

1) Make a ball on the end of a sufficient diameter rod to match the
radius of the ring around the lantern style toolpost.

[ ... ]

Now I understand. This will yield a section of a sphere, not a torus.

That is what I would expect to fit the ring. It should be a
section of a circle to allow the rocker to rock through full range of
adjustment.

That said, it would make mechanical sense if the surface were in fact a
sphere, not a torus. I will remeasure the two curvatures. It's hard to
measure the radius across the thickness, and I may have it wrong.

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".


The reason to use a torus is to allow toolbars that are not perfectly
rectangular to nonetheless be clamped quite firmly.

Oh -- you want to relieve the center of the top of the crescent
so it contacts at the ends. I thought that you were trying to match the
compound curvature of the support ring around the toolpost. And that
would be difficult to do with anything other than a section of a sphere.

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.


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.



Joe Gwinn