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When I heard about the square hole drill I assumed it was
a joke, I have drilled triangular holes in sheet metal but
a square hole drill sounded like it should be kept in the
same draw as the glass hammer.
The first time I bought drills at Drill Service[DS] in Horley,
I got one of their drill catalouge's. They have more types
of drill than you can shake a stick at. Next time I went there
I asked to see a 1 thou drill, they were out of stock but
they showed me a 2 thou drill, what can I say, it was very
small. I found the polygon hole drill quite fascinating it
was so simple, why hadn't I heard of it before. Well that
was in 1982 and I still have only seen them in the DS catalouge.
This system for drilling polygon holes was introduced in
1891, it can be carried out in a variety of machines: drill
press lathe etc.
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Figure 1. Complete setup for polygon hole
drilling in drill press. |
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The drill has one less flute than the number of sides to
the polygon. the drill is held in a floating chuck allowing
radial movement whilst held axialy aligned. One cutter edge
is lodged in a corner and the next corner sweeps around untill
it lodges in a corner, this is the cutting action.
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Figure 2. Square hole drill and form plate. |
