cutting spiral onto a rod

On Mon, 09 May 2005 23:40:59 -0700, in àõ Abrasha wrote:


You probably stopped using the lathe and mill, and your need to know disappeared.

I use my lathe and mill almost daily.

Didn't stop using them, though I need them much less often than you do. But I'm not
currently in an environment where I'm teaching their use, nor do I often read about
their use, so the precise vocabulary describing their use gets rusty. The actual skills
and knowlege needed to use the tools are not nomenclature based, I think...

Peter

Abrasha wrote in
news
Peter W.. Rowe, wrote:
On Sun, 08 May 2005 17:37:37 -0700, in ¸õ Abrasha
wrote:


The motor that typically cames with the Taig does not have enough
power to cut a 2 mm deep groove in a 15 mm diameter silver rod. The
cutting force would stop the spindle dead in it's track, or the rubber
band (the drive belt that comes with the Taig is no more than a big
rubber band) would just slip.

Abrasha
http://www.abrasha.com


Is that really an issue that would stop this? I don't have a Taig, but
my sherline mill can't be that different,

A Taig LATHE and a Sherline MILL are two very different tools!

And no, you cannot cut a helical groove on your Sherline mill, unless
you have one with an indexing head (dividing head), which is coupled to
the automatic power feed of the table. This is only possible on the
Sherline, if it is equipped with stepper motors. Which means a CNC
interface. And even if you have all of this, how are you going to hold
the 15 mm silver rod. You have to have an indexing head on one end and
a tail stock on the other end. Given that the table of the Sherline
mill in only 13" long, that won't leave you much length and room to
maneuver for the rod.

nor is my little old unimat lathe.

Your little old unimat lathe is good only for the most basic of tasks.
It not useful for the task that the original poster asked about.
Cutting a helix on a 10-15 mm diameter silver rod.

BTW, I realize that he posted asking how to cut a spiral. I assume that
he wants to do this on a cylindrical surface and not a tapered surface.
I quote the following from "Audels Machinists and Tool makers Handy
Book, New York 1941"

"The enlightened machinist will not erroneously use the word spiral or
helix as is almost universally done even by some writers. To correct
such error is almost hopeless and perhaps nothing can be done about it.
However:

By definition a helix is a curve generated by a point which both rotates
and advances axially on a cylindrical surface. For instance the lead
screw thread on a lathe is a helix.

By definition a spiral is a curve generated by a point having three
motions: 1, rotation about an axis; 2, increasing its distance from the
axis, and 3, advancing parallel to the axis.

When a cylindrical piece of work is placed between centers and rotated
by the index head as the table advances, the cutter will mill a helical
groove.

When a tapered piece of work is placed between centers and tilted so
that the top element is horizontal and then rotated by the dividing head
as the table advances, the cutter will mill a spiral groove."

neither can do deep cuts in
a single rapid pass, but with a slow feed rate,

When you are cutting a helix, the feed rate is determined by the pitch
of the spiral. You cannot just set your feed rate "slow".

Besides, both the Taig and the Sherline do not have lead screws, so what
feed rate are you talking about? Unless you have a lead screw and
change gears, you cannot set a feed rate. Your feedrate in only manual
on both machines. Not very useful when you are cutting a helix in any
set up.

and perhaps several passes as
successivly increased depth, it should be possible. I've cut things in
silver deeper and wider than that on the sherline, doing it that way.
The low power machines, which also suffer from less rigidity in the
machine, simply mean you need to have a lot of patience, doing the cuts
slowly with multiple light cuts. At least, that was my experience.
Yes, it's slow enough to be quite annoying to anyone who's used full
sized machinery, but it can be done, nevertheless. I had one poject
involving turning on the Unimat, with a bracelet shape starting around
3 inches in diameter in platinum. That was a bitch to cut too, and to
keep the lathe from stalling took a tool bit with very little radius at
it's point (to make the cut dig into less metal at a time), and very
small amounts on each pass. But it eventually worked.

I'd guess the big problems would be simply generating the spiral
desired without going over budget on the machine, as well as the
difficulties involved in cutting silver. Back in graduate school, I cut
pretty much this type of spiral in a slightly larger brass rod without
trouble.

1: You didn't cut a spiral, but a helix.

2: You cut a certain very special kind of helix, i.e. a screw thread,
which is not what the poster is after I think.

Screw threads are cut on lathes equipped with leadscrews. Helices are
cut on milling machines, in a manner I have now described in several
posts.

I repeat. To cut a helix, you need:

1 A milling machine,
2 A universal dividing head (indexing head)
3 The ability to couple the dividing head to the automatic table feed,
so that the work rotates as the table advances.

To cut a spiral you need:

Everything above, plus

4 A tilting table so you can create a horizontal cutting surface.

But it was a full size rockwell tool room lathe doing it.
It was quite capable of that sort of thread,

Threads and spirals are two very different things.

Abrasha
http://www.abrasha.com



A Four axis cnc machine with steppers, an air spindel that runs up to 50K
and the fourth axis is full indexed to the other three is available in the
$2000 range from www.maxnc.com. A closed loop machine similar to the above
with servos instead of steppers is available for about another $1000.
http://www.maxnc.com/page12.html



--
James C. Woodard
"Too many laws make scofflaws of all"
http://home.comcast.net/~gwyddon/

"Andrew Werby" wrote in
:


"Abrasha" wrote in message
...
Andrew Werby wrote:
"norwick" wrote in message
...

I need to cut a spiral onto a silver rod.
The sides of the cut can be at 90 degrees/and/or inclined. I envisage
this to be done by a lathe (milling machine?).
Diameter of rod could be 10-15mm,
spacing between edge of the next groove ca 3mm,
groove width & depth ca 2mm (ideally there should be some scope for
visual considerations).
Non electric system would be acceptable (or very slow speed lathe),
machine size should not be more than 1m, weight under 50kg.
Cost should not be more than $1000-1500, but this assumes that it can
be used for other applications, eg cutting tool steel etc.


[You could do this on a miniature CNC milling machine (like the Taig
mills I
sell) equipped with a rotary table, chuck, and tailstock. You'd need
to program the toolpath to advance the tool along the X (long) axis
while rotating the A axis (the rotary table) so that the grooves were
properly spaced. A ball-end tool would give you a round-bottomed
groove; a regular endmill would give a flat-bottomed groove. The
weight and size of this machine would be about what you're asking for
above, but the price would be
higher - about $3k, with the accessories you'd need. These machines
can be
used for many other things, but for best results with tool steel
anneal it
first, and use carbide cutters.]

The motor that typically cames with the Taig does not have enough power
to cut a
2 mm deep groove in a 15 mm diameter silver rod. The cutting force
would stop
the spindle dead in it's track, or the rubber band (the drive belt that
comes
with the Taig is no more than a big rubber band) would just slip.

Abrasha
http://www.abrasha.com

[Want to bet? Taig recently started providing a bigger motor with their
mills than previously. The 1/4 hp Franklin motor now standard would have
no problem cutting a 2mm groove in a piece of silver - or a piece of
steel, for that matter, in one pass, if one went at an appropriate speed
using a 2mm 2-flute cutter. It could also make multiple faster cuts at
shallower depths. The Gates drive belt, while it may superficially
resemble a "big rubber band" is actually quite resistant to slipping,
when tensioned correctly. The pulley settings can be changed to provide
more torque, or more speed, as needed. Have you ever actually used one
of these mills?]

Andrew Werby
www.computersculpture.com







Does Taig also now offer 4th axis capability?

--
Saint Séimí mac Liam
Carriagemaker to the court of Queen Maeve
Prophet of The Great Tagger
Canonized December '99

"Abrasha" wrote in message
...
Andrew Werby wrote:


[Want to bet?]

No. However your reply seems to indicate your need to be right by trying
to
bluff me into a bet.

[Bluff you? I was just correcting your misperceptions, and providing a
little new information you may not be aware of. But I wondered if you'd be
willing to put a little money where your mouth was - guess not...]

So I challenge you to produce the helix, the original poster asked about,
on
your mighty Taig mill. I say, it can't be done. Go ahead, prove me
wrong.
You've got the Taig. If you succeed, (which I know you won't), you have a
strong selling point. If I am not mistaken, you are after all trying to
sell
these things, which seems to make you a bit biased. I find that rather
amusing.

[Yes, I sell these things, which is one reason I don't like seeing them
unfairly disparaged. I imagine you're "biased" about the things you sell,
but I'm not churlish enough to assume you'd lie about them. I don't claim
the Taigs are the best mills in the world, but they're quite capable within
their limitations.]

Don't get me wrong. The Taig is a very valid and verstile tool and a
useful one
at that.

[Thanks for that...]

And it cannot do what the original poster asked. You can try to bluff
me all you want, it can't be done. You can't do it.

[Unfortunately, I don't have a silver rod 10-15mm in diameter - care to
provide one? Or would brass be okay?]

Taig recently started providing a bigger motor with their
mills than previously. The 1/4 hp Franklin motor now standard would have
no
problem cutting a 2mm groove in a piece of silver - or a piece of steel,
for
that matter, in one pass, if one went at an appropriate speed using a 2mm
2-flute cutter.

We weren't talking about a groove. We were talking about a helix! That's
what
the original poster wanted. Something very different.

[He was talking about a helical groove:

" I need to cut a spiral onto a silver rod.
The sides of the cut can be at 90 degrees/and/or inclined. I envisage
this to be done by a lathe (milling machine?).
Diameter of rod could be 10-15mm,
spacing between edge of the next groove ca 3mm,
groove width & depth ca 2mm"

I understand this as a cut wrapped around the long axis of the rod, somewhat
like an elongated Whitworth thread. Did you envision something else?]

However, you claim that the Taig, does a 2 mm depth of cut cut in steel,
on a 15
mm diameter (original poster's measurement) in one pass? Prove it!

[How - are you going to come over and watch? Or would pictures be
sufficient?]


SNIP

Have you ever actually used one of these mills?]

No, I have no need to. I have a real mill, with a 3/4 HP, 3 phase motor.
Actually, it is a rather wimpy mill as far as true power is concerned.
I'm
ready for something more powerful, like a Bridgeport.

[I've got a Bridgeport. There are some things it is best for, and some that
are better done on the Taig.]

But a Taig, gimme a break, why would I ever want to use one of those when
I have
a Clausing 8520?

[Is it retrofitted for CNC? Do you have a rotary table for it? If not, it
wouldn't do the job we're talking about here, while the Taig will.]

Now go and make that helix, you claim you can make on it. I say, you
can't do it!

Abrasha
http://www.abrasha.com

[If you're wrong, will you at least eat your yarmulke?]

Andrew Werby
www.computersculpture.com

Andrew Werby wrote:

[Unfortunately, I don't have a silver rod 10-15mm in diameter - care to
provide one? Or would brass be okay?]

No brass is not OK. It has a much higher sfm than silver. You said the Taig
could do it in steel. Well, do it in steel then.


However, you claim that the Taig, does a 2 mm depth of cut cut in steel,
on a 15
mm diameter (original poster's measurement) in one pass? Prove it!


[How - are you going to come over and watch? Or would pictures be
sufficient?]


Pictures would be sufficient. I trust you. Include setup, process as well as
finished work pictures. You could post them on your site.



[Is it retrofitted for CNC? Do you have a rotary table for it? If not, it
wouldn't do the job we're talking about here, while the Taig will.]

I never claimed that my mill will do the job.



[If you're wrong, will you at least eat your yarmulke?]

No.

Abrasha
http://www.abrasha.com

Andrew Werby wrote:


[If you're wrong, will you at least eat your yarmulke?]


Be careful with remarks like that!

Abrasha
http://www.abrasha.com

""Séimí mac Liam"" wrote:
Does Taig also now offer 4th axis capability?

--
Saint Séimí mac Liam
Carriagemaker to the court of Queen Maeve
Prophet of The Great Tagger
Canonized December '99

[They've had it for quite a while. The rotary table is actually made by
Sherline; Taig adds their own base and stepper. The standard Taig control is
now wired to run the 4th axis; they used to require a return trip to the
factory to activate it, but now that's not necessary.]

Andrew Werby
www.computersculpture.com

"Abrasha" wrote in message
...
Andrew Werby wrote:

[Unfortunately, I don't have a silver rod 10-15mm in diameter - care to
provide one? Or would brass be okay?]

No brass is not OK. It has a much higher sfm than silver. You said the
Taig
could do it in steel. Well, do it in steel then.

[While I'm not going to invest the time and effort to do the spiral cut
(although I would if you cared to back your bluster with your bucks) I did
an experiment yesterday; cutting a slot across a piece of mild steel 3/4"
wide. I set up a 3/32" 2-flute carbide cutter (a little bigger than 2mm
diameter) and set the depth of cut to .08" (a little deeper than 2mm). The
spindle was set to the second-highest speed (about 8000 RPM). The feedrate
was .5 ipm. The Taig mill, with its stock spindle motor, had no problem at
all cutting that slot. The motor didn't slow down. The belt didn't slip. I
think this proves my point.

It's not generally considered good practice to cut slots this deep in one
go; the usual recommendation is to choose a depth no greater than half the
cutter diameter. This is not because the machine can't do it, but because
it's likely to break the cutter. That's why I went with a conservative
feedrate. ]



However, you claim that the Taig, does a 2 mm depth of cut cut in steel,
on a 15
mm diameter (original poster's measurement) in one pass? Prove it!


[How - are you going to come over and watch? Or would pictures be
sufficient?]


Pictures would be sufficient. I trust you. Include setup, process as
well as
finished work pictures. You could post them on your site.

[If you trust me, take my word (above) for it, and apologize for disparaging
these fine tools in the absence of any actual experience with them. If you
don't trust me, even if I went through all the procedures you suggest, you'd
probably say I faked the pictures and lied about the rest.]



[Is it retrofitted for CNC? Do you have a rotary table for it? If not, it
wouldn't do the job we're talking about here, while the Taig will.]

I never claimed that my mill will do the job.

[Then we've answered your question:

"But a Taig, gimme a break, why would I ever want to use one of those when
I have
a Clausing 8520?"

The Taig will do this sort of job; the Clausing won't. Sheer horsepower is
only part of the equation when considering a mill's cutting function.
Spindle speed is also an important factor. When using small endmills like
this, one has to remove a certain amount of material with each flute, as it
goes by - this is called "chipload". If your spindle turns slowly, like on
your Clausing (or my Bridgeport) you can't remove enough material fast
enough to sustain a reasonable feedrate, no matter how much torque your
motor has. If you try to go faster than the rate at which the material is
being removed, the tool will break. On the other hand, if you want to use a
large tool, say 1/2" diameter, then you can spin much slower, since each
flute takes a bigger bite of material, but requires more force to do so. In
this situation, where you want to remove a lot of material in a hurry, the
larger mill with the slower but more powerful motor would be a better
choice.]



[If you're wrong, will you at least eat your yarmulke?]

No.

Abrasha
http://www.abrasha.com

[Well, you won't bet, you won't eat your hat, will you at least admit you
were wrong?]

Andrew Werby
www.computersculpture.com

"Andrew Werby" wrote in
news

""Séimí mac Liam"" wrote:
Does Taig also now offer 4th axis capability?

--
Saint Séimí mac Liam
Carriagemaker to the court of Queen Maeve
Prophet of The Great Tagger
Canonized December '99

[They've had it for quite a while. The rotary table is actually made by
Sherline; Taig adds their own base and stepper. The standard Taig
control is now wired to run the 4th axis; they used to require a return
trip to the factory to activate it, but now that's not necessary.]

Andrew Werby
www.computersculpture.com









Didn't find it on their web site today.

--
Saint Séimí mac Liam
Carriagemaker to the court of Queen Maeve
Prophet of The Great Tagger
Canonized December '99

thanks guys, you have been a great help!

Ben, I am trying to find a copy of the Amateurs Lathe to learn some
more...
Peter suggested how it is possible - while Abrasha convinced me how it
isn't.
- Thanks Andrew, it was a brave deed to take on the challenge - pity
that I just can't justify $3k for a Taig mill (at the moment).

Carl West's Firefox hint is intriguing ! I am all for low tech
solutions, if there is one. I kept on pondering how to rig up a system
where the revs are low enough to prevent silver tearing... I don't mind
shaving little bits off at a time to get the required depth. But if
there is a machine for it - why try inventing one? To save money?

The helix/spiral doesn't have to be absolutely precise in dept/width -
but visually it must be accurate, i.e. lines equidistance from each
other. Unfortunately the task must be repeatable, and cannot be
constructed (soldered).

Sherline UK have now responded to the same enquiry:
To meet your budget the only system I can offer you is a lathe with a
screw cutting attachment, cost UKpounds770.00.
This would entail setting the screw cutting attachment on its most
coarse pitch ( 5 TPI approx 5mm pitch) which would achieve your spiral.
As the screw cutting operation is fully manual this system of
generating the spiral would be very slow but on the other hand very
safe.
To generate the spiral on a mill would entail a very expensive system
costing UKpounds 2,500.00. The only way of achieving this on a Sherline
mill is to convert it to CNC and add a CNC rotary table supported on a
vertical plate. This is a far more accurate, quicker and versatile
system to produce spirals with very few limitations.

For those interested (re previous comments):
http://mathworld.wolfram.com/search/index.cgi?q=spiral
http://mathworld.wolfram.com/search/...helix&start=10

http://onlinedictionary.datasegment.com/word/helix
http://onlinedictionary.datasegment.com/word/spiral

So this is it, folks! Thanks again, I'm am only a step away from my
spiral/helix! Hopefully!

norwick