[Jewelry making - Article 01640] - Re: [Orchid] Drilling Dilema

[Ian W. Wright]

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    Most sources such as manufacturers websites, machinery handbook etc.
    say that you should use small drills at high speed but this data is
    only really relevant where the drills are used in precision
    industrial machinery for drilling shallow holes and with bags of
    coolant. In practice in a small workshop slower is better and,
    indeed, very slow might be best. Any hole which is more than 3 times
    the drill diameter is classed as 'deep drilling' and is a different
    ball game to normal drilling as factors such as chip removal, side
    friction, difficulty of cooling the drill tip etc. come into play. I
    regularly drill holes down to 0.1mm diameter through carbon tool
    steel in making parts for watches and so I have, over the years,
    tried every combination of speed, pressure, coolant etc. Trying to
    use a high speed with a High Speed Steel drill or a Carbon steel one
    will just blunt and glaze the point very quickly. The temptation (or
    one could almost say 'reflex') then is to increase the drilling
    pressure to make the drill cut which then, inevitably, causes the
    drill to break. If this is in iron or steel you then have the
    almighty and often insurmountable problem of trying to remove the
    broken pieces from the hole. In brass or similar metals this is not
    too bad a problem as you can dissolve the broken drill away by
    soaking it in an alum solution for a few days. Carbide drills, on the
    other hand, do need quite a high speed - though not as high as
    usually quoted for the same reasons as above, but they need a very
    light pressure or they will quickly dig in and snap. The only way I
    have found to remove them is to try to break them up with a little
    punch - not easy at small sizes and often still leaves debris
    impacted in the hole which prevents further drilling. In any case,
    an accurate drill press is needed for such small drills and drilling
    should be done by 'pecking' gently at the hole with the drill
    running at a fairly low speed - patience is the key!! Coolant is
    optional but, in a deep hole, can cause the chips to clog together
    and sieze the drill into the hole - I prefer to work dry and blow the
    chips away with an air jet. An alternative way to produce the holes
    may be to make a simple spark eroder - there are several plans on the
    web for making such a machine. 

Best wishes,
Ian
Ian W. Wright
Sheffield UK
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