Next, the shank can be produced, which, as the cutter is to bore a hole larger than
the bit on which it is being ground, needs only to be a flat Photograph 6 with secondary
clearance added, Photograph 7 the greater angle for the secondary clearance should
be apparent by comparing the two photographs.
The viewer may question why the flat is needed if the cutter is to work at diameters
greater than the blank size. The reason being that initially, when creating the front
relief, a little will be ground off the diameter at the tip and then eventually when
the tool is sharpened using the side relief (6) the tip will retreat even further.
It also gives a little room for the swarf being produced when working near the minimum
Finally, side clearance (3) and side relief (6) can be ground in a single operation,
Photograph 8. The three being seen in Photograph 9.
Having restricted myself to a minimum diameter of 4mm, I see no reason why smaller
sizes could not be produced if using some form of mechanical assistance, as I have
done, 3mm would certainly be possible. No doubt, with a steady hand, smaller sizes
could also be produced manually but it will become increasingly difficult.
As most readers will not have the benefit of a tool rest such as I have shown it
is likely that when ground by hand the end result may not look so precise but there
is no reason why the cutter will not perform equally well, at least for larger sizes.
Photograph 10 shows three that I ground in this way in my very early workshop days
and that worked well then so do not be put off if this is the only method available
An important point to take note of when grinding a tool for the first time from a
blank piece of HSS is that a lot of metal, comparatively, has to be removed and therefore
a lot of heat generated. Because of this, grinding should be done in stages allowing
the tool bit to cool between each stage. Some will cool the tool by immersing the
hot end in cold water but this is considered to be a reason for tools to crack, personally
I have never experienced this though I do not do it now. If the viewer wishes to
speed up the process then perhaps frequently immersing the tool in cold water before
it get really hot would be an acceptable approach.