[Jewelry making - Article 00915] - Re: [Orchid] Quick change handpiece advice

[Peter W . Rowe]

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>      Don't be too quick to condemn the size of the chuck bore for the
>     problem you encounter occasionally. While it's true the bore  size
>     could be at fault the problem could also be with the tool you're
>     inserting into it. 

    Good thought, Dave, but in this case, it's the chuck bore.  These
    are standard HSS setting burs, which may be slightly oversize.  
    That's why they jam in the chuck.  With the lever open,  the shank
    slips easily into the jaws of the chuck, and the chuck is properly
    adjusted to properly grip the normal range of 3/32 shanks.  My old
    Techno-X (any of the three I have had) never had a problem with such
    burs, when the chuck was properly adjusted like this.  If the bur
    would go into the jaws at all, it could go all the way in.  With
    these new handpieces, apparently the manufacturers weren't aware of
    the possible variations in spec on burs and other points one might
    use, and have apparently bored the inside of the shank appropriately
    for really on spec tools.  That means that though the jaws of the
    chuck open enough for oversize burs, the bur won't go into the
    chuck. It's very annoying.  And these are not bent or damaged bur
    shanks.  Just made to slightly looser standards than I would have
    hoped for companies like Dedeco and Spearhead (at least, the
    spearhead that it used to be, years ago.  now, they're not worth
    beands.) 

>        If the problem only seems to happen with a limited set of
>     tools, I bet on the tools being at fault. The diameter could be out
>     of spec or the shank damage in some way. 

    That's just the point.  Busch burs, and similar ones are accurate
    and on spec. Most other types, including several brands of high speed
    steel burs from several sellers, as well as the typical shanks on
    various bristle brushes, mandrels, and various other wheels, are not
    this accurate.  Properly designed quick change handpieces for the
    jewelery industry should take this into account.   I've qot a bit of
    a collection of various such handpieces from over the years, and
    almost all of them work just fine with these out of spec burs, other
    than a few that are so very under sized that the chuck can't tighten
    down on them enough when properly adjusted for the average burs.  
    I've seen a few of the bristle brushes do this now and then, but it's
    not common.   The problem with the QC handpieces seems isolated to
    the badeco I recently tried (and a visually similar one, not marked
    badeco, that I bought on ebay a couple years back, and returned,
    which I was told was made in the U.S. for the dental tech crowd), as
    well as these two new versions of the techno.  Never had this problem
    with the old technos, nor with any of the Faro types.  

    Yes, the problem is that some burs are over sized.  But the
    handpieces should take this into account.  Oversized shanks on burs
    and points, other than the busch type, are common. 


>            If the shank has a little bend or other deformation in it,
>     that would cause the same type of problem you've described. The
>     chuck bore has a hole of the same diameter end to end. A small bend
>     in the shank of tool has the effect of making the sides of the
>     shank non parallel from end to end. This explains why the tool goes
>     in O.K. for a distance then gets tight. 

    Yeah.  i know about bends.  Remember my mentioning that very
    occasionally I find a bristle brush that's undersize, and won't quite
    go tight in a QC chuck? A slight bend in the thing is my fix for
    those.  Doesn't work for actual burs, since with a bend, it doesn't
    turn quite true, but for a brush, that's not a problem.    The burs
    that I'm having trouble with now, are normally made high speed steel,
    as well as some of the other types of brushes and mandrels. if the
    chuck is adjusted so it properly grips an on spec bur,  the jaws
    will open enough to allow an oversize one to begine to enter, but
    then jam.  This simply means that the bor is too close to the
    specified shank diameter.  That just isn't the right way to build
    such a chuck.  It needs a bit more internal clearance.  The bur is
    only  held tight at the chuck jaws, so having only too little
    clearance, versus a bit more, makes no difference to the security of
    the bur, or the trueness with which it turns. 


Peter




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