Jim,
I have got from somewhere a 'circle cutter'. The difficulty with the plain fly
cutter is that it is inherently unbalanced and so has a tendency to dig into
the work and 'pick it up'. My circle cutter is effectively two fly cutters on
opposite sides of the central shaft: as they can be moved individually, they
need very careful setting up. Better to use than a drill press is a vertical
milling machine, because
a)you can get a much finer feed to avoid digging in and
b)you are less likely to have the drill chuck decide to part company with the
arbor or even the arbor itself get wrenched out and Morse taper damaged if it
does dig in.
If you have a variable speed drive, that helps a lot too.
Another difficulty you can get is the drill chuck coming off the arbor. With a
Jacobs chuck, a good way to avoid that is (using a lathe) drill through the
base of the chuck in the centre. Tap the hole 6-32. Then drill a corresponding
hole in the arbor and tap the arbor 4-40. A 4-40 screw and washer attaching the
chuck to the arbor and they won't come apart, but if you want them to, removing
the 4-40 screw enables you to use a 6-32 screw to jack them apart. The arbors
for my mill also have a drawscrew hole tapped 10mm, so a long bolt stops the
Morse taper arbor shifting.
A kit of suitable clamping dogs and spacers is a good investment: even then,
I've things move and as a result, break a half inch diameter end mill!
But yes, fly cutters can be dangerous. So can all workshop machines - other
really nasty ones include a revolving wire brush (it can spit wire bristles at
you) and a grindstone, especially if some fatherless wotsit has ground
aluminium on it clogging the pores!
Of course, there's always the nearest smaller size hole saw and a half round
file....
73
Peter G3RZP
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