With the ratio being 100:1 even a very small increase in the diameter being cut will
have an appreciable effect on the depth of the bore. The top slide should therefore
remain as originally set and the diameter of the bore increased, first by using the
cross slide, and then when close to the required dimension by winding the top slide
However, there is a potential problem with this approach that must be taken note
of even though the likelihood of it surfacing is very remote. As the top slide is
being wound back to increase the diameter being cut the pressure on the cutter will
be attempting to take up the backlash and as a result increase the diameter by more
than has been set. Even so, providing that the top slide is not set to move very
freely it is very unlikely that this will occur at such minute depths of cut but
if in doubt, use the slides lock to stiffen up the movement temporarily. However,
do not adjust the lock when very close to the diameter required as using the lock
is likely to make changes to the diameter being cut with the result that the bore
could become oversize.
Continue to increase the bore diameter using the cross slide and when within say
0.004" (0.1mm) hone the edge once more. If you do this whilst on the top slide place
a piece of cloth on the bed to catch any particles from the hone, removing the cutter
may be safer but you will then have to reset the saddle stop.
When the bore is close to the required diameter, as indicated by the short reduced
diameter portion of the gauge, now is the time to increase the depth of cut by winding
the top slide back and increasing the diameter in very small steps. Aim to get the
bore a very close but not tight fit on the gauge. If the gauge becomes a tight fit
make an extra cut without having placed on any more depth, this is particularly important
if you are machining the bore with a boring tool having a thin shank, that on the
right of Photograph 5 is definitely preferred for the task.
Having wound the top slide back to arrive at the required diameter the inner portion
of the bore will be undersize. To overcome this, remove the saddle stop and hand
feed the tool in just once more to bring the bottom of the bore to diameter, taking
care as the tool contacts the end of the bore.