Having the top slide at the required angle making it possible to place on very small
radial feeds all is still not plain sailing. It should be obvious that it is not
possible to make a very fine cut if the cutting tool has a blunt cutting edge wider
than the amount being attempted to be removed, for the depths therefore being considered
the cutting edge has to be perfect. For this a HSS tool will be required and honed
to an extremely fine edge, my preference being a round nose tool but of course this
is not practical if machining to a step. The tool should also be set a little below
centre height, just to ensure that it is not above, because if above, even minutely,
it will just rub at these very shallow depths. The viewer should take note that a
tipped tool will not be suitable for the task as they do not have the fine edge required.
With the top slide set and a finely honed cutting tool, the process is only a little
more complex than normal turning, resulting in the gauge for the bore, and eventually
the bore itself, being made with comparative ease.
From this point in the article I should make it clear that the dimensions now given
relate to my Myford mandrel and am of course giving them as Imperial sizes, the viewer
will, when machining for a different mandrel, have to work to his or her own requirements.
With the item needing to be machined suitably mounted, machining can now commence.
If at this stage you are machining a casting, machine the mounting face using a tungsten
tipped cutter to break through its outer skin as you will not want to carry out this
task with an HSS tool. Next, centre drill and drill through with a large drill to
avoid excessive work in machining the bore followed by boring to a diameter of 1.045",
the significance of this diameter being explained later.
With that done, set up a finely sharpened HSS boring tool and with the tip of this
against the face first machined set your saddle stop for a depth of 5/8" when machining
the parallel bore can now commence Photograph 4.
Having set the top slide to 0.6° for machining the gauge there will be a temptation
to reset the angle so that forward movement of the top slide increases the diameter
of the bore being cut. this though should not be done. When the bore is very close
to the final diameter and the top slide advanced to increase this, this will defeat
the purpose of setting the saddle stop as the forward movement of the top slide will
increase the depth.