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Posted by John Martin on April 23, 2008, 10:51 am
Please log in for more thread options
> When you cut threads by feeding straight in, you're cutting both flanks of=
> the thread at once. That produces twice the tool load for a given depth of=
> cut.
>
> If you have a good lathe, your tools are sharp, and you're cutting aluminu=
m,
> it may work just fine. But cutting clean internal threads depends on getti=
ng
> things pretty close to right, so the extra tool load is something to watch=
> out for if you get some chatter.
>
> --
> Ed Huntress
Of more importance is that cutting on one flank loads the cutter
against the lead screw. Cutting both flanks at once, the carriage can
float instead on being driven by the leadscrew, and you can end up
with a drunken thread.
John Martin
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Posted by Ed Huntress on April 23, 2008, 11:07 am
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> When you cut threads by feeding straight in, you're cutting both flanks of
> the thread at once. That produces twice the tool load for a given depth of
> cut.
>
> If you have a good lathe, your tools are sharp, and you're cutting
> aluminum,
> it may work just fine. But cutting clean internal threads depends on
> getting
> things pretty close to right, so the extra tool load is something to watch
> out for if you get some chatter.
>
> --
> Ed Huntress
>Of more importance is that cutting on one flank loads the cutter
>against the lead screw. Cutting both flanks at once, the carriage can
>float instead on being driven by the leadscrew, and you can end up
>with a drunken thread.
>John Martin
Maybe you can answer something that's bugged me for a long time, John: Why
do the traditional lathe books say you should advance the cut when cutting
Acme threads by plunging straight in, rather than on the appropriate angle
for cutting one flank at a time? I don't recall ever having seen an
explanation.
--
Ed Huntress
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Posted by Stupendous Man on April 23, 2008, 7:45 pm
Please log in for more thread options Thanks guys. I got 25 pieces done today, only 3 more days to go!
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty
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Posted by John Martin on April 23, 2008, 10:01 pm
Please log in for more thread options >
>
>
>
>
>
> > When you cut threads by feeding straight in, you're cutting both flanks =
of
> > the thread at once. That produces twice the tool load for a given depth =
of
> > cut.
>
> > If you have a good lathe, your tools are sharp, and you're cutting
> > aluminum,
> > it may work just fine. But cutting clean internal threads depends on
> > getting
> > things pretty close to right, so the extra tool load is something to wat=
ch
> > out for if you get some chatter.
>
> > --
> > Ed Huntress
> >Of more importance is that cutting on one flank loads the cutter
> >against the lead screw. =A0Cutting both flanks at once, the carriage can
> >float instead on being driven by the leadscrew, and you can end up
> >with a drunken thread.
> >John Martin
>
> Maybe you can answer something that's bugged me for a long time, John: Why=
> do the traditional lathe books say you should advance the cut when cutting=
> Acme threads by plunging straight in, rather than on the appropriate angle=
> for cutting one flank at a time? I don't recall ever having seen an
> explanation.
>
> --
> Ed Huntress- Hide quoted text -
>
> - Show quoted text -
Some may say that, some don't.
Machine Tool Operation, Burghardt:
"5. The side of an Acme thread is 14 1/2 deg., therefore move the
compound rest 14 1/2 deg. to the right when cutting a screw, to the
left when boring an internal thread. Set the thread stop and feed for
successive cuts by moving the compound-rest handle."
Perhaps the audience has something to do with it. Most of the machine
tool books were written by and for guys using big, heavy lathes. The
heavier the carriage, the less likely it is to jump ahead due to soft
spots in the work or the alignment of the planets. With a lighter
lathe, and less friction and mass in the carriage, it becomes more a
factor.
John Martin
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Posted by Ed Huntress on April 23, 2008, 11:38 pm
Please log in for more thread options
>
>
>
>
>
>
> > When you cut threads by feeding straight in, you're cutting both flanks
> > of
> > the thread at once. That produces twice the tool load for a given depth
> > of
> > cut.
>
> > If you have a good lathe, your tools are sharp, and you're cutting
> > aluminum,
> > it may work just fine. But cutting clean internal threads depends on
> > getting
> > things pretty close to right, so the extra tool load is something to
> > watch
> > out for if you get some chatter.
>
> > --
> > Ed Huntress
> >Of more importance is that cutting on one flank loads the cutter
> >against the lead screw. Cutting both flanks at once, the carriage can
> >float instead on being driven by the leadscrew, and you can end up
> >with a drunken thread.
> >John Martin
>
> Maybe you can answer something that's bugged me for a long time, John: Why
> do the traditional lathe books say you should advance the cut when cutting
> Acme threads by plunging straight in, rather than on the appropriate angle
> for cutting one flank at a time? I don't recall ever having seen an
> explanation.
>
> --
> Ed Huntress- Hide quoted text -
>
> - Show quoted text -
>Some may say that, some don't.
>Machine Tool Operation, Burghardt:
>"5. The side of an Acme thread is 14 1/2 deg., therefore move the
>compound rest 14 1/2 deg. to the right when cutting a screw, to the
>left when boring an internal thread. Set the thread stop and feed for
>successive cuts by moving the compound-rest handle."
>Perhaps the audience has something to do with it. Most of the machine
>tool books were written by and for guys using big, heavy lathes. The
>heavier the carriage, the less likely it is to jump ahead due to soft
>spots in the work or the alignment of the planets. With a lighter
>lathe, and less friction and mass in the carriage, it becomes more a
>factor.
>John Martin
Maybe. I just never could see why they'd recommend the angled cut for 60
deg. threads, and then the straight-in cut for Acme. It seems to me that the
Acme is going to produce a much heavier load on the tool.
I've only cut 10 tpi Acme threads (because I have only one Acme tap, and
it's 10 tpi), and it's not a big deal on my South Bend to cut those. But
bigger, coarser ones would be a real challenge.
--
Ed Huntress
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