Finally, in terms of sharpening the cutter, the cutting edges should be honed to
achieve the best possible cutting edge. This is particularly important in the case
of small boring tools as the sharp cutting edges will cut more freely limiting the
load placed onto it and therefore the amount that the tool deflects. Also, a small
radius (say around 0.2mm) should be honed onto the cutters tip making it stronger
and able to produce a better finish.
If the viewer is interested in the grinding rest I am using this enables the angles
to be precisely set and includes facilities for controlling the feed in two directions
so that the depth of cut can be increased gradually as the tool is ground.For more
detail see below, right.
An Alternative Form
The shape of the boring tool discussed so far is essential where the end of the bore,
or a step within it have to be faced so that they are at 90° to the bore's axis.
An alternative form though can be considered that will more easily produce a superior
finish when a through hole is being made. In this case the side rake (1) is replaced
with top rake (2) as is illustrated by Sk. 3. The tool also includes a larger radius
on the tip than that suggested above for the blind hole tool. Being larger, say 0.5
to 1mm radius depending on the cutter size. Shaping this form of tool follows almost
exactly the sequence above with only the angles changed for the operation shown in
I mentioned at the commencement that I also use the method to produce other tool
shapes some of the most useful of which are seen in Photograph 11. On the left is
a very small parting tool (0.8mm), very useful when parting off workpieces of say
3mm diameter and less. Being so small it can be used on the top slide rather than
the rear tool post. The next two are grooving tools, such as used for making a groove
to accept a Circlip. The pointed one is used to make lines on a dial, such as one
for a machine tool lead screw. The final one is a very small bull nose tool for finishing
It is obvious from the photograph that only small tool bits are required
and very little grinding is necessary making it economical in terms of both time
and money. It can also be seen that I produced many of my earlier cutters from broken
centre drills, not that I am vary careless and break a large number, they were obtained
from a firm having a large number of capstan lathes.
I hope the viewer has found this interesting and been prompted to consider the method
described for producing boring tools.