D.Howard@kid0110.wins.icl.co.uk wrote:
> The manual calls for some less than typical drill bit sizes, e.g.
> 3.3mm.
Standard drill sizes are now metric dimensions in most countries. The usual
series goes in 0.1 mm steps (eg I have a set of 1 - 5.9mm by 0.1mm, total
50 drill bits) However, the old number (& letter) sizes are still not too
hard to get hold of as they are still used in imperial :-) places like USA.
I'd recommend buying a metric set if you have the choice, though. They will
make life easy when drilling holes for tapping in (coarse) ISO metric screw
threads; you subtract the pitch dimension from the nominal overall thread
diameter to get the tapping size (eg M4x0.7 requires 3.3mm, M10x1.5
requires 8.5mm).
Thanks to D (Dave? Doug? Dilbert?) Reed for posting that handy list of
number to decimal equivalents. You can buy in most engineering supply
houses a little pocket booklet which gives that list, with imperial
fraction and metric decimal equivalents and near-equivalents. It also
covers tapping & clearance drill sizes for all the popular machine-screw
thread sizes and other good engineering titbits (= tidbits in USA). Mine is
called "Zeus Precision" data charts & etc, but it is not a recent edition
as it claims to be in use by such firms as DH, AVRO, Saro, Folland, Handley
Page, Hunting, BEA, and BOAC. Get yours from the same place as the drill
bits (see below).
The pocket calculator can provide some of the functionality of this
booklet, but can't compete when you need to make a tapped hole for some
strange thread, or even to find out what thread is on the bolt you're
holding.
> Clearly such bits are not available down the local DIY store.
Actually, _my_ local DIY shop _does_ stock a good range of the metric drill
bits, but they are a proper shop, not a chain warehouse. Buy a copy of
Model Engineer, Engineering in Miniature, or Model Engineer's Workshop, and
select a supplier from the ads therein. Either pick one nearby, or choose
one of the many mail-order houses. I've used most of them at various times,
and can't remember any with bad service. It's the wrong time of year to
mention it, but the other place you should frequent is the Model Engineer
Exhibition in London, first week in January. There are similar events
elsewhere (advertised in the above mags) at other times of the year, and
you may find them more convenient to attend. Just watching the indoor
flying displays is worth the MEE entry fee alone, even if you don't come
away with a rucksack weighed down with bargain goodies. Our friends from
Perma-Grit are always there, other outfits are selling Dremel tools at
discount, etc, etc.
(Sorry to be so wordy - I strongly agree with the comments about
_selective_ quoting of prior postings; I'd also like to see more
disciplined use of the subject line - ie change it if the subject changes!)
cheers
Rowland
... that's Rowland with a 'w' ...
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