[modeleng] Re: coarse threads

Here's how modern CNC does it in a nutshell.

rotary table (with rifling cam blank chucked in rot table and between 
centres) mounted under mill spindle
cam blank  rotated by rotary table while table moves in X
cutter cuts spiral groove in cam to whatever rifling twist is programmed

Cheers Jeff Dayman


>From: Allen Messer <al_messer@xxxxxxxxx>
>Reply-To: modeleng@xxxxxxxxxxxxx
>To: modeleng@xxxxxxxxxxxxx
>Subject: [modeleng] Re: coarse threads
>Date: Fri, 26 Jan 2007 13:06:48 -0800 (PST)
>
>Previously, I mis-spoke about using it for cutting
>grooves in rifle barrels.  This machine would not do
>it, but now the question arises, in my mind, at least,
>is HOW are the correctly pitched groves, say one turn
>in twelve inches, cut in the guides that control the
>cutters that actually do the work?  Old timers carved
>them into a cylinder of wood with chisels, following a
>spirally wound string, but how now??
>
>Al Messer
>--- Alan Stepney <alan@xxxxxxxxxxxxxxxx> wrote:
>
> > Very interesting, however, one thing is certain, I
> > wont be trying to make
> > one of them.
> >
> > I am gradually restoring an old lathe I bought a
> > couple of years ago, and
> > although lack of time has limited the amount done so
> > far, the other day I
> > did clean one part, to find a brass plate detailing
> > changewheels for thread
> > cutting.
> > The threads listed are:
> > 1,2,3,4,5,6,7,8,9,10.11,12,14,16,18,19,20.28 tpi.
> > Some are the usual ones I would have expected, but
> > the others are unusual.
> > I was wondering / hoping that the threads might have
> > given a clue to the
> > purpose as it appears to have been built for a
> > specific use, although thus
> > far it has been impossible to identify the maker
> > thus far.
> >
> >
> > Alan Stepney
> >
> > http://www.alanstepney.info
> > Model Engineering & steam engine information pages
> > ----- Original Message -----
> > From: "Edward Bean" ebme@xxxxxxxxxx
> > [modeleng] Re: coarse threads
> >
> > The
> >
><http://www.vcalc.net/cu.htm>Curta<http://www.vcalc.net/cu.htm>
> >
> > mechanical calculators of the 1950s,
> >
> >  Edward Bean
> >
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>
>
>
>
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