[ATM] Threading

[don clement]

Berthold,

Speed is an issue for me but typically by not having a low enough speed. The lowest speed on my 12x36 lathe is 70 rpm. ( at least  until my lathe gets a VFD  controlled 3 phase motor ) The problem for me is threading up to a shoulder or lack of  space at the end of a cut for external threading. Sometimes even 70 rpm is not slow enough to disengage the half-nut or stop the lathe motor, especially on coarse pitch threads. My lathe has an imperial lead screw of 8tpi so I can't use the threading dial and disengage the half-nut for cutting metric pitch threads. For internal RH threads that problem is solved by using the reverse helix method (spindle runs CW) where the cut can start from an internal blind shoulder and thread towards the tailstock at high speed. (i.e. the upper limit of the lathes speed 1400 rpm.)  Vardex carbide threading inserts work best at higher speeds than can practically be used on a manual lathe. For me the advantages of full profile
 carbide inserts far out weigh the speed requirement though. YMMV. A full set of ID and OD inserts plus tool holders can be quite expensive though.

I highly recommend the chapter on screw cutting by George Thomas' " Model Engineers Workshop Manual" He covers many issues for cutting threads on a small manual lathe including plans for a retracting top slide for screw cutting that I wish I had. Also I follow Geo. Thomas procedure of using the top slide to advance the cut and then zeroing using the cross slide. 

http://www.walteranderson.us/hobbies/book_reviews/metalcraft_book_reviews/model_engineers_workshop.html  

 When I go to CNC lathe conversion or hopefully a Hass TL1 CNC lathe those kind of threading issues that plague threading on a manual lathe will be moot.

Don Clement
Running Springs, California 
  


--- On Wed, 9/30/09, Berthold Hamburger <b-hamburger at artinso.com> wrote:

> From: Berthold Hamburger <b-hamburger at artinso.com>
> Subject: RE: [ATM] Threading
> To: "'don clement'" <donald_clement at yahoo.com>, atm at atmlist.net
> Date: Wednesday, September 30, 2009, 12:29 AM
> Hi Don,
> 
> What speed do you run your machine at for threading
> operation. Minimum speed of mine is 150rpm which is a bit
> fast I guess for full profile tools?
> 
> Regards
> 
> Berthold
> 
> -- 
> Berthold Hamburger - Cellist/Spain
> Email: behambu at artinso.com
> http://www.artinso.com
> http://www.astro.artinso.com
> 
> 
> > -----Original Message-----
> > From: atm-bounces at atmlist.net
> [mailto:atm-bounces at atmlist.net]
> On Behalf
> > Of don clement
> > Sent: miércoles, 30 de septiembre de 2009 6:16
> > To: atm at atmlist.net;
> Berthold Hamburger
> > Subject: Re: [ATM] Threading
> > 
> > 
> > Hi Berthold,
> > 
> > I use Vardex full profile inserts to cut threads on my
> lathe. Full
> > profile have the benefits of perfect thread form,
> Thread OD is
> > concentric with PD, helix angle can be accommodated by
> using a different
> > anvil, and it is easy to get a new cutting edge by
> just rotating or
> > replacing the insert. The draw back is higher cost and
> an insert for
> > each pitch is needed for both ID and OD. I use a
> Vardex AVR075-3 holder
> > for both external RH threading and internal RH 
> threading using the
> > reverse helix method. The reverse helix method uses an
> IL insert and
> > feed is towards the tailstock so threading can be at
> high speed from an
> > blind shoulder. The inserts I use are Vardex 3/8”
> size. Also Vardex does
> > make a 3/8” size partial profile insert that fits
> the same tool holder
> > just in case one doesn’t have the exact insert 
> pitch size needed or to
> > thread sharp V threads for baffling. I like the
> AVR075-3 holder because
> > of the machined flats so the holder fits my KDK 156
> >  bar with the proper orientation. See:
> > http://i72.photobucket.com/albums/i163/miltons_stuff/VardexTTKDK156bar.j
> > pg
> > 
> > 0.5mm pitch is quite fine. I routinely thread 
> 40UN , almost as fine  a
> > pitch,  in stainless steel using Vardex inserts
> with good results.
> > 
> > Don Clement
> > Running Springs, California
> > 
> > 
> > 
> > --- On Tue, 9/29/09, Berthold Hamburger <behambu at artinso.com>
> wrote:
> > 
> > > From: Berthold Hamburger <behambu at artinso.com>
> > > Subject: [ATM] Threading
> > > To: atm at atmlist.net
> > > Date: Tuesday, September 29, 2009, 6:20 AM
> > > Hi,
> > >
> > >
> > >
> > > What do you guys use for cutting exterior threads
> on the
> > > lathe? Do you use
> > > inserts (full profile)? I am asking because I
> have a hard
> > > time to cut usable
> > > M12 0.5mm pitch metric threads.
> > >
> > >
> > >
> > > Thanks
> > >
> > >
> > >
> > > Berthold
> > >
> > >
> > >
> > > --
> > >
> > > Berthold Hamburger - Cellist/Spain
> > >
> > > Email: behambu at artinso.com
> > >
> > > http://www.artinso.com
> > >
> > > http://www.astro.artinso.com
> > >
> > >
> > >
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