If it were of importance then the material can then be set to run true at the jaws
whilst it is being supported centrally by the steady. I say, can, but this will
almost certainly attempt to move the material off centre at the steady. To over come
this the part should only be held using just the ends of the jaws, say 8mm. However,
this approach should only be adopted with caution and due consideration to the nature
of the intended machining, heavy or light, intermittent or continuous.
When the reverse in the case, that is a long but a small diameter piece of material,
the method of setting the steady is different. In this case the material is set to
run true at the chuck's jaws and the steady set at this point. With that done the
steady can be slid along the lathe's bed and secured towards the outer end. With
the material being slightly flexible the steady would easily pull it into line. If
your three jaw chuck is reasonably accurate, say within 0.05mm TIR then this should
be adequate for smaller diameters at longer lengths, say 10mm by 200mm long. The
viewer may ask why there has to be two methods of setting the jaws. This is because
small diameters will, if setting the steady at the end of a long length, easily deflect
when the first and second arms are set.
For a recent project it was necessary for me to set up the steady for three differing
pieces of material and I chose to carry out some tests.
In one case the diameter of the material was 20mm and projected from the chuck by
300mm. Testing this using the fingers I found it quite easy to deflect so chose to
be more precise. I set up a DTI and measure the deflection that occurred when I placed
a vee block weighing 700grams on the end. This resulted in a deflection of 0.1mm.
Unsupported, the end of the bar gave a total indicator reading of 0.3mm when turned
by hand and from these I considered the steady could easily pull the material into
Having taken the readings I set the steady adjacent to the chuck, Photograph 1 and
then moved it close to the end to machine the two bushes required, Photograph 2.
The task took a few minutes during which the arms became only slightly warm, from
which I concluded that the set up had been satisfactory.
A second task was to hold a 38mm diameter bar with a projection from the chuck of
150mm. Carrying out the same test with the vee block gave no readable deflection
and so was definitely a candidate for setting the material to run true at the point
the steady was to be used. A third task was with a 32mm diameter bar extending 280mm
which gave a reading of 0.02mm and again needed to be set true at the point the steady
was to be used.