In article ,
"DoN. Nichols" wrote:

On 2008-02-24, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:

On 2008-02-23, Joseph Gwinn wrote:

[ ... ]

OK. What acme thread were you cutting? Given the delicate nature of
the application, one assumes that this leadscrew is quite dainty.

It was something like 1-1/4" diameter IIRC, and perhaps 5 or 6
TPI, I think.

Sounds plausible.


Shouldn't this been the excuse to buy a larger insert holder and insert?

Not an option. The shanks on large enough holders would not fit
in the toolpost holders on my lathe. I'm limited to 5/8" shanks. I
think that the next size up of inserts required 1" shanks, but I'm not
sure, and the MSC catalog is too deeply buried for me to dive into it at
the moment.

I would have thought that a 5/8 shank would suffice.

Nope -- there were inserts in the pitch range, but only stub
Acme, not full Acme profile. The anvil needs to be enough bigger so the
head of the holder needs to be bigger too. And remember that what I
really had to make was an internal thread.

Another factor for thread cutting inserts is that there is not a
single anvil -- there is a range of them, each tilting the insert to one
side or the other by a specific angle to match the thread pitch angle
for the given diameter.

Clearly intended for large production of a specific thread, not a series
of one-off jobs.


That's also the size of the slot in the lantern toolpost that comes with
the Clausing 5900 series lathes. I got the toolpost, but missing the
crescent-shaped rocker.

O.K. I wouldn't know, because mine came without a toolpost at
all. (And, I didn't miss it. :-) I had an old turret toolpost which I
could use while waiting for the Phase-II clone of the the Aloris BXA to
arrive, but I was very glad to retire it as soon as possible.

My theory is that it is useful for use with big knurlers and the like,
which come up used for small dollars, and they don't fit Aloris B-series
toolholders.


This piece was lost some time ago, as I found a
rocker of the wrong curvature to fit the post, heavily marked where the
edges of the concave seat cut into the convex surface of the too-shallow
curvature of the rocker. I bought a used replacement, and it fits
better, but still not quite right. The real Clausing rocker is double
curved (being a toroidal surface, like the outside of a donut, it
appears), and hardened. The one I bought is cylindrical, not toroidal,
and matches only one curve, not both. (Does anyone have a spare of this
rocker?)

Hmm ... sounds like you need to combine a radius turning tool
with a small toolpost grinder. Start with a collet-held fixture which
has a slot for the rocker-to-be, add setscrews tapped in from the side
to grip the blank rocker, then turn the end of the fixture to a sphere
of the proper radius. If necessary, stop with the radius just a little
long, remove the rocker-to-be, harden it and draw appropriately, then
put it back and use the toolpost grinder mod to the radius turning
fixture to take it to final dimensions. (I would suggest you rig some
kind of holder for a small air-driven die grinder, and mount it to serve
as the die grinder.)

I've been thinking about this a bit. I think the easiest way is to hold
a piece of octagonal 5/8 thick plate in the 3-jaw chuck by means of a
large bored hole in the center, or bolt the octagonal 5/8 plate to the
dog driver plate, and machine the outer edge of the 5/8 plate to fit,
using a sphere-turning tool of some kind. When done, cut crescents from
the edge of the plate, and mill the sawn surface flat in the vertical
mill. Harden to taste. Given that one plate will yield multiple
rockers, hardening is probably not required.

Joe Gwinn