As this was unlikely to be a requirement in my case I made my cutters, Photograph
3, to their nominal diameters, 12 and 16 mm. This enabled silver steel of that size
to be used, rather than a larger diameter that would require reducing in diameter.
As commented earlier, the outer diameters were though skimmed to ensure concentricity.
In the case of the larger this has been used to cut some 600 mm of slot without any
sign of deterioration of the cutting edges.
When turning the head to width using left and right hand knife tools, as a final
measure, set them round by a degree or so and skim each side very lightly with the
full width of the cutting edge. This slightly under cuts the two faces ensuring that
the cutter is widest at the cutting edge.
With the turning complete, transfer the cutter to the milling machine and mount in
a dividing head set up to give six cutting edges. Make sure that the flat (if made)
for the driving dog is in a position that will be machined away. Sketch 1 shows how
the end mill is set relative to the cutter to create a rake angle on the cutting
edge. Set the depth of cut to around 1 mm and make six cuts around the cutter.
Then, lower the cut in stages until there is only about 1 mm of the original outer
diameter left at each tooth Photograph 4.
The need for the cutter to be made to rotate in the required direction when eventually
used results in the cut having to be taken such that travel of the workpiece and
rotation of the end mill coincide. To ensure that this does not cause the cutter
to snatch and take up the backlash in the table movement, the table locking screw
should be slightly tightened to stiffen the movement. If the cutter head being made
is appreciably larger than its shank diameter then the end mill can move from the
shank end to the outer end this eliminating the possibility of snatch.
Mark the 1 mm of the outer diameter remaining with marking blue to aid visibility.
Then, using a small fine file, add a degree or so of clearance to the outer diameter
leaving just the slightest amount of the outer diameter visible, say 0.2 mm maximum,
preferably less, see sketch 1.
Hardening and Tempering
For one who does not carry out the task of hardening and tempering, and I suspect
that this is the case for most home workshop owners, completing the task, resulting
in a workable tool, was very satisfying. This process alone makes the project worthwhile
even discounting any financial savings.
For the viewer who needs guidance regarding this, see my pages on the subject of
hardening and tempering in the processes section.