[Jewelry making - Article 00225] - Re: [Orchid] Burs tips and techniques?

[Ian W. Wright]

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    What no one seems to have mentioned is the reason you shouldn't try
    to use burrs for drilling. This is because the end of a burr has no
    teeth and so can't cut the metal. If you look at the end of a round
    burr you will usually see a small round circle, often recessed, which
    is just plain metal. If you try to use such a burr as a drill -
    pressing it in line with its shaft, the teeth will cut around this
    area leaving a small pillar of metal which will resist efforts to
    push the burr further in. Even where burrs have teeth cut right to
    the centre of the end of the burr, the 'peripheral cutting speed' of
    the centre of the burr is zero and so it will not cut - that is, at
    the centre, the teeth are not passing over the metal as is required
    for cutting. Shallow holes may be 'drilled' using the side of the
    burr but this is a little uncontrolled and haphazard as any end play
    in the handpiece bearings or burr collet will allow the burr to
    wander and cut an oval hole. Also, the depth to which you can 'drill'
    in this situation is limited by the diameter of the burr. 

Best Wishes,
Ian
Ian W. Wright
Sheffield  UK

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