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[Shop-talk] Identifying taper and threading attachments on a

Subject: [Shop-talk] Identifying taper and threading attachments on a
From: neiljsherry at talktalk.net (Neil Sherry)
Date: Sat, 22 Oct 2011 00:20:40 +0100
References: <mailman.18.1318960808.11683.shop-talk@autox.team.net><1B9FB4B4C85C43988CF6533A293A8F6D@EnergyKinetics.EKnet><65884CFF6F01482B99CD50CD5947BC69@HP62011><7520E99DCA554F72827DAE1E259B3768@EnergyKinetics.EKnet><B8677E2507954B69BD9E4BD02B86E23F@HP62011><4E9F8126.3000707@frontier.com><053901cc8eed$60943220$0501a8c0@randall> <4EA14BD4.5000009@talktalk.net> <06b401cc9009$5a63d820$0501a8c0@randall>
mmm, makes sense.
On 21/10/2011 16:51, Randall wrote:
>> My recollection is that for ANY thred you can re-engage the
>> nut on the
>> same point that you were on the dial (eg if you were first
>> engaged on 1
>> - you can always re-engage on 1).
> You got me wondering, so I looked it up.  On a lathe with Imperial threads
> on the leadscrew, engaging on 1 works for any thread that has an integer
> number of threads in 2 (or 4 for some lathes) inches.  But metric (and BA,
> which is what I was thinking of when I said Whitworth before) threads
> typically don't have an integer number of threads in 4 inches, so the
> standard Imperial threading dial cannot be used when cutting those threads.
>
> Imagine the lathe stopped, with a long threaded bar between centers.  Start
> with the half nuts engaged, the threading dial on '1', and the tool bit
> exactly in the thread groove.  Now imagine moving the carriage to the right
> until the dial comes back on '1' and closing the half nuts again.  The
> carriage has moved some number of inches (2" on my 10" Atlas).  If, for
> example, your bar has 11.5 tpi, then the tool will be exactly 23 threads
> away from the original position and still at a thread groove. (Assuming
> you've taken up the slack correctly and so on.)  But if, for example, your
> bar has 25.4 tpi, the tool will now be 50.8 threads away from the starting
> position, and not lined up on the groove.
>
> The rules are different for a metric leadscrew, of course, but similar
> limitations apply.  From what I found on-line, most metric lathes come with
> 3 different gears for the thread dial (and still don't cover BA threads).
>
> Here's a neat little device that apparently includes the gears for both
> metric&  imperial on the same leadscrew
> http://www.dgrdesigns.co.uk/metradial.html
>
> But it still doesn't appear to cover 4 BA (38.46 tpi)<g>
>
> -- Randall
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