Re: I'm impressed - and a GCode question.

Ballendo,

Speaking of threadmills...

Sometimes in an emergency an acceptable thread mill can be made from
a tap. For instance, take a four flute tap and completely remove,
grind away, 3 of the flutes. Then relieve the remaining flute behind
the cutting edge to leave a very micro "land". The land area left
behind the cutting edge must be minimal so there's as little as
possible chance of the tap's helix angle causing rubbing in the cut
as the thread is milled.

Choose a tap with the smallest helix angle and that will still fit
into the hole to be threaded. Example, if the hole to thread is 1"-
20tpi, a 1/2-20 tap would be a better choice than 1/4-20 since the
helix angle is less on the 1/2" tap.

Doug

--- In CAD_CAM_EDM_DRO@y..., "ballendo" <ballendo@y...> wrote:

(snip)

>
> P.S. Your description of turning a dovetail cutter to a "single"
> tooth threadmill is correct. Don't forget to "dubb" off the tip for
> the flat at the minor diameter. Many controls allow arc/helical
moves
> greater than 360 degrees. Haas allows up to +/-8380. On those which
> only allow 360 (or 90!), yes, you would program subsequent blocks,
OR
> use a loop, if the "L" word is allowed. BTW, using a dovetail
cutter
> is not ideal for the reasons you mention; most threadmills are
SMALL
> diameter, to keep the cut more constant, AND to minimise "trailing
> edge" interference problems resulting from the helical path. Also
> allows one threadmill to do larger variety of threads.
>
> --- In CAD_CAM_EDM_DRO@y..., "Graham Hollis" <ghollis@m...> wrote:
> > Alan, It sound to me you are seeing things that are not there.
All
> the
> > curves I can see are the result of a intersection of simple bored
> holes at
> > 90 degrees to each other. Lathe bored or CNC milled, the result
> will be the
> > same.
> >
> > Graham
> >
> > ----- Original Message -----
> > From: "Alan Rothenbush" <beer@s...>
> > To: <CAD_CAM_EDM_DRO@y...>
> > Sent: Sunday, February 03, 2002 9:16 AM
> > Subject: [CAD_CAM_EDM_DRO] Re: Re: I'm impressed - and a GCode
> question.
> >
> >
> > >
> > > A dovetail cutter, yes, certainly with extra relief.
> > >
> > > A flycutter, yes, again, with appropriate relief.
> > >
> > > And both under CNC control. Mind you, the GCode to do such a
> thing
> > > escapes me. A LONG series of appropriate G02 commands with
SMALL
> Z
> > > increments could do it, I suppose. I'd think that there would
be
> some
> > > decided "staircasing", no matter how fine the Z move.
> > >
> > > This brings up another related GCode question. Say you took
> your
> > dovetail
> > > cutter and ground it like so < instead of the standard /_ ,
> with the
> > > angle now being 60 degrees.
> > >
> > > Is it possible to use this cutter in a mill and program the
> GCode to
> > > cut a thread ( more than just a single rotation ) all in one
> go ? I
> > only
> > > know of G02/G03 commands, and they're limited to 360 degrees,
> aren't
> > they ?
> > >
> > > To cut 10 threads, you'd need to tell the G02 command to
rotate
> 3600
> > > degrees ...
> > >
> > > There would also be finish problems as a result of the
> discontinuous cut,
> > > but continuous motion. Again, I guess with a SLOWWWW feed
rate,
> this
> > could
> > > be minimized.
> > >
> > > Still sounds like a job for the lathe, though.
> > >
> > > An endmill ( which was the initial "boast" <G> ), is a no.
> > >
> > > Alan
> > >
> > > >
> > > >Dovetail cutter. Extra relief ground in if needed.
> > > >
> > > >Hope this helps.
> > > >
> > > >Ballendo
> > > >
> > > >--- In CAD_CAM_EDM_DRO@y..., Alan Rothenbush <beer@s...> wrote:
> > > >Have a closer look. The insides of the cube are curved.
Can't
> for
> > > >the life of me figure out how to do that with an endmill and a
> three
> > > >axis machine.
> > > >
> > > > The cube was almost certainly bored on a CNC lathe, with the
> boring
> > > tool
> > > > taking a curved path as it proceeds through the piece.
> > >
> > > --
> > >
> > > Alan Rothenbush | The Spartans do not ask the
> number of the
> > > Academic Computing Services | enemy, only where they are.
> > > Simon Fraser University |
> > > Burnaby, B.C., Canada | Agix of
> Sparta
> > >
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