Revolving Tail Stock Chuck or Rotating Tail Stock Chuck

[jjr2001]

Had to stop the progress on the little steam engine model I was building due to small parts.
This particular shaft has a very small .093" section and another at .064".
Well after one attempt I found that a standard live or dead center would not work,
at least not for me. So I found some ideas using a revolving chuck in the tail stock
to hold the end of the shaft. Seems like a good idea so I made one.

Just used a Jacobs chuck with a 3/8-24 thread and some bearings along with
a MT2 taper blank that I made a year or so ago and some mystery metal. I think
the mystery metal is just some hot rolled steel that was left over from another project.

I turned the parts for an interference fit so that I would have to cool (freeze) the MT2 arbor
for the inner race of the bearings and in the last step the housing was heated with a propane
torch so the outer race of the bearings would slip into it. Worked out great. I figured this was
a one time build and that if it went together properly it would never be taken apart.

The pictures show the story. I used 3 surplus bearings that I had in stock and fired up the lathe.

First use will be tomorrow when I make that tiny shaft.

Cheers, JR

[Frank S]

Jr I used to have a dead center that instead of a point it was bored to accept a point made from a .125" tungsten tig tip spun ground to a sharp point it worked beautiful for small parts.

[jjr2001]

Thanks for the tip Frank. Sounds like a good idea. I may have to try that if my rotating chuck doesn't do the job.

Cheers, JR

[Toolmaker51]

JJR2001's solution is well founded; when a center isn't feasible, often due small diameter. Frank S's tungsten is excellent alternative. A 60 degree pointed drill blank and high pressure grease is another. Dead centers don't run any RPM long if dry before galling. https://www.google.com/search?q=lath...utf-8&oe=utf-8

We often have to bore ends of long rollers used in printing industry. This is to repair bearing fits after sleeve is inserted.
Before anything can start the end usually needs a narrow area turned for the steady rest to run. This is done with the left end in a 4-jaw, and a 4-jaw in the tailstock.
Both chucks are 'timed' together, visually and then with a torpedo level, oriented so they mirror the same clock position. Tailstock chuck is a soft #5 taper dead center, turned to fit dual bearings, and a 10'' chuck [reversible jaws, no back plate] bored to fit the bearing OD. This was shop made decades ago; they are also sold by toolhouses. https://www.google.com/search?q=4+ja...utf-8&oe=utf-8

Can't make much recommendation as to sizes, readers have too many possible combinations of equipment. But three independent ball bearings is good enough for typical live centers. Another combination might be needle roller and angular contact, positioned 'inboard' for thrust. Also possible: to mimic a live center with live bearing at each end, or sleeve a center with a bronze valve guide.
The main fabrication issue will be attaining near perfection in concentric axial and radial surfaces.

[mklotz]

A rotating tailstock chuck is certainly a great addition to the lathe armory but allow me to offer some alternate thoughts on tiny model shafts gleaned from years of model engine building.

Shafts with turned down sections on the ends of the parent stock can be turned without benefit of TS support by feeding just a small bit of the parent out of the collet, turning it to size, then feeding a bit more out, turning, etc. until the desired length of turned diameter is reached. A turned down section in the middle of the parent can be done by a similar process.

If the turned diameter matches available stock sizes it's sometimes easier to drill into the parent and solder/Loctite in a bit of smaller stock to make the requisite assembly.

Which engine model are you building?

[Toolmaker51]

Modelling in general and engines specifically are distinct versions of toolmaking, encountering processing that are not so difficult with 'normally' sized materials and equipment.
Marv's turning at short intervals is a good example. Attaching a larger sacrificial portion works in small and immense projects, critical at small scale when tooling presents unavoidable restrictions.

[mklotz]

Attaching a larger sacrificial portion works in small and immense projects, critical at small scale when tooling presents unavoidable restrictions.

Yes, one thing one learns quickly in the model engine building undertaking is...

NEVER REMOVE THE PART FROM THE PARENT STOCK UNTIL IT IS ABSOLUTELY NECESSARY TO DO SO.

Leaving yourself something to hang onto is essential. Model engineers should scratch the above on the inside of their safety glasses lenses.

[Frank S]

Yes, one thing one learns quickly in the model engine building undertaking is...

NEVER REMOVE THE PART FROM THE PARENT STOCK UNTIL IT IS ABSOLUTELY NECESSARY TO DO SO.

Leaving yourself something to hang onto is essential. Model engineers should scratch the above on the inside of their safety glasses lenses.

Marv the same holds true for a lot of things even in the larger scale. and especially when dealing with things like spool valves for hydraulic manifolds and such.
I had my own propitiatory valving that I used on the elevators I used to build. Later I went to poppet style cartridge valves but I made my own manifold bodies creating creating the dozen cavities on a pure mechanical very old Bridgeport without any DRO was laborious, it was much easier to do tool changes and complete 1 cavity at a time than it was to do all of 1 process then the next until the cavity was formed. the last step was a special ground burnishing tool for each size cavity

[jjr2001]

Thanks for all the great info guys. I see that TM51 had a link where they are putting a large 3 or 4 jaw chuck on the tail stock.
Marv's solution is eye opening....Why did I not think of that....Pull out only the part that you need and then extend the blank
and continue keeping the part close to the collet or chuck.....I will try that method....

So far it is little piece of steel 2 and hobbiest 0.....Tomorrow I will try again.

I think my lathe tool bits were too dull. Sharpened all of them today and we should have a part by tomorrow night..

Cheers, JR

Oh, the model I am working on is Gerry's Beam engine. I posted a few of the parts completed so far here:
http://www.homemadetools.net/forum/g...m-engine-60782

The interesting part I am working on is the shaft for the steam chest valve.

[metric_taper]

<snip>
Just used a Jacobs chuck with a 3/8-24 thread and some bearings along with
a MT2 taper blank that I made a year or so ago and some mystery metal.
<snip>
Cheers, JR

I'm curious how good the runout of the 3 jaw drill chuck is?

I like the idea of the 3 bearings that will average out the radial play to near zero, as well support the cantilever forces from the 3 jaw chuck.