Using a rotary table to cut an approximate ellipse?
 

Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

Using a rotary table to cut an approximate ellipse?
 

axolotl wrote:

Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

I expect you probably have to break it down into 4? separate arcs and
cut each one in a separate setup with the part and mill positioned the
proper distance from the center of the rotary table.

Using a rotary table to cut an approximate ellipse?
 

I would use the "Egyptian CNC" method, it is probably the easiest.

It took me less than 1/2 hour to cut a circle just turning dials
according to instructions from my perl script.

http://igor.chudov.com/projects/My-B...ian-Style-CNC/

i

On 2010-01-20, Pete C. wrote:

axolotl wrote:

Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

I expect you probably have to break it down into 4? separate arcs and
cut each one in a separate setup with the part and mill positioned the
proper distance from the center of the rotary table.

Using a rotary table to cut an approximate ellipse?
 

On 1/19/2010 7:43 PM, Pete C. wrote:

I expect you probably have to break it down into 4? separate arcs and
cut each one in a separate setup with the part and mill positioned the
proper distance from the center of the rotary table.

I was looking at the 5 centered arch graphical method, thinking that
given an ellipse bounded by a rectangle, one could mathematically
determine offsets and radii. My head hurt. It then occurred to me that
someone in the bad old days before CNC must have done this. Hence my
appeal to the collective knowledge pool.

Kevin Gallimore

Using a rotary table to cut an approximate ellipse?
 

Ignoramus8727 wrote:

I would use the "Egyptian CNC" method, it is probably the easiest.

It took me less than 1/2 hour to cut a circle just turning dials
according to instructions from my perl script.

http://igor.chudov.com/projects/My-B...ian-Style-CNC/

Does your method leave stair steps in the result? I can't imagine being
able to manually move two axes in small enough steps for a smooth result
without going bonkers. With a rotary table, the four arc will be
entirely stepless.



i

On 2010-01-20, Pete C. wrote:

axolotl wrote:

Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

I expect you probably have to break it down into 4? separate arcs and
cut each one in a separate setup with the part and mill positioned the
proper distance from the center of the rotary table.

Using a rotary table to cut an approximate ellipse?
 

On 1/19/2010 8:05 PM, Ignoramus8727 wrote:
I would use the "Egyptian CNC" method, it is probably the easiest.

No doubt. But the object is to use the new toy (rotary table).

Kevin Gallimore

Using a rotary table to cut an approximate ellipse?
 

On 2010-01-20, Pete C. wrote:

Ignoramus8727 wrote:

I would use the "Egyptian CNC" method, it is probably the easiest.

It took me less than 1/2 hour to cut a circle just turning dials
according to instructions from my perl script.

http://igor.chudov.com/projects/My-B...ian-Style-CNC/

Does your method leave stair steps in the result? I can't imagine being
able to manually move two axes in small enough steps for a smooth result
without going bonkers. With a rotary table, the four arc will be
entirely stepless.

It was actually not bad, due to the fact that the endmill is round and
its diameter is much bigger than the step. Think about it. Visually
the circle looked very round. Check the pictures.

i



i

On 2010-01-20, Pete C. wrote:

axolotl wrote:

Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

I expect you probably have to break it down into 4? separate arcs and
cut each one in a separate setup with the part and mill positioned the
proper distance from the center of the rotary table.

Using a rotary table to cut an approximate ellipse?
 

axolotl wrote:

On 1/19/2010 7:43 PM, Pete C. wrote:

I expect you probably have to break it down into 4? separate arcs and
cut each one in a separate setup with the part and mill positioned the
proper distance from the center of the rotary table.

I was looking at the 5 centered arch graphical method, thinking that
given an ellipse bounded by a rectangle, one could mathematically
determine offsets and radii. My head hurt. It then occurred to me that
someone in the bad old days before CNC must have done this. Hence my
appeal to the collective knowledge pool.

Kevin Gallimore

Since these are the good new post CAD and CNC days, I'd draw it up in
CAD and let the CAD measurement tools tell you the radii and whatnot.

Using a rotary table to cut an approximate ellipse?
 

"axolotl" wrote in message
...
On 1/19/2010 7:43 PM, Pete C. wrote:

I expect you probably have to break it down into 4? separate arcs and
cut each one in a separate setup with the part and mill positioned the
proper distance from the center of the rotary table.

I was looking at the 5 centered arch graphical method, thinking that given
an ellipse bounded by a rectangle, one could mathematically determine
offsets and radii. My head hurt. It then occurred to me that someone in
the bad old days before CNC must have done this. Hence my appeal to the
collective knowledge pool.

Kevin Gallimore

If you really want to do it mechanically without moving two axes
independently, you need two rotary tables mounted one top of the other. The
top is offset by half the distance between the foci of the ellipse. Then
rotate the two tables at the same rate.

Using a rotary table to cut an approximate ellipse?
 

On Jan 19, 9:55*pm, "anorton"
wrote:
"axolotl" wrote in message
On 1/19/2010 7:43 PM, Pete C. wrote:
Kevin Gallimore

If you really want to do it mechanically without moving two axes
independently, you need two rotary tables mounted one top of the other. The
top is offset by half the distance between the foci of the ellipse. Then
rotate the two tables at the same rate.

If you tilt the blank up at an angle a long vertical endmill will cut
a mathematically correct ellipse. The major axis ends will be beveled
so the thinner the stock the better it works.

jsw

Using a rotary table to cut an approximate ellipse?
 

If you tilt the blank up at an angle a long vertical endmill will cut
a mathematically correct ellipse. The major axis ends will be beveled
so the thinner the stock the better it works.
....

Glad I got a CNC so I just put in the Gcode and cut.

"I THINK" if you also tilted the head, the above suggestion would give you
an elipse with square sides.

Karl

Using a rotary table to cut an approximate ellipse?
 

"Karl Townsend" wrote in message
anews.com...

If you tilt the blank up at an angle a long vertical endmill will cut
a mathematically correct ellipse. The major axis ends will be beveled
so the thinner the stock the better it works.
...

Glad I got a CNC so I just put in the Gcode and cut.

"I THINK" if you also tilted the head, the above suggestion would give you
an elipse with square sides.

Karl

P.S. You'll have to raise/lower quill as you rotate to keep tool at same
depth.

Using a rotary table to cut an approximate ellipse?
 

"Karl Townsend" wrote in message
anews.com...

If you tilt the blank up at an angle a long vertical endmill will cut
a mathematically correct ellipse. The major axis ends will be beveled
so the thinner the stock the better it works.
...

Glad I got a CNC so I just put in the Gcode and cut.

"I THINK" if you also tilted the head, the above suggestion would give you
an elipse with square sides.

Karl


You can make the edge square on one end but it will be worse on the other.

Using a rotary table to cut an approximate ellipse?
 

On Jan 19, 5:09*pm, axolotl wrote:
Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

I can remember drawing an "ellipsoid" using a compass back in grade
school, was part of some kind of drafting thing, Was drawn as 4
separate arcs, I remember that Left some sharp points at the ends of
the major and minor axes, which could be dubbed off afterwards if you
were actually cutting stuff. Don't remember much more than that.
Maybe an old drafting text would have the procedure.

Or you could build an actual ellipse generator, I've seen some for
cutting photo matts, too. Isn't much more than a pair of cross slots
with sliders and a bar linking the two. As the bar goes around the
end traces out an ellipse that depends on how closely the two sliders
are linked for major and minor axis ratios I suppose it could be
hooked to some sort of pantograph linkage to get smaller ellipses.

Stan

Using a rotary table to cut an approximate ellipse?
 

There is a simple method for DRAWING one that involves the use of two pins
and a length of string, but after drawing it, you would have to manually cut
it. If anybody is curious enough, I'll write it up and post it; that is,
unless someone else does it first.


Flash



wrote in message
...
On Jan 19, 5:09 pm, axolotl wrote:
Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

I can remember drawing an "ellipsoid" using a compass back in grade
school, was part of some kind of drafting thing, Was drawn as 4
separate arcs, I remember that Left some sharp points at the ends of
the major and minor axes, which could be dubbed off afterwards if you
were actually cutting stuff. Don't remember much more than that.
Maybe an old drafting text would have the procedure.

Or you could build an actual ellipse generator, I've seen some for
cutting photo matts, too. Isn't much more than a pair of cross slots
with sliders and a bar linking the two. As the bar goes around the
end traces out an ellipse that depends on how closely the two sliders
are linked for major and minor axis ratios I suppose it could be
hooked to some sort of pantograph linkage to get smaller ellipses.

Stan

Using a rotary table to cut an approximate ellipse?
 

On Jan 20, 7:27*am, "Karl Townsend"
wrote:
"Karl Townsend" wrote in message

anews.com...



If you tilt the blank up at an angle a long vertical endmill will cut
a mathematically correct ellipse. The major axis ends will be beveled
so the thinner the stock the better it works.
...

Glad I got a CNC so I just put in the Gcode and cut.

"I THINK" if you also tilted the head, the above suggestion would give you
an elipse with square sides.

Karl

P.S. You'll have to raise/lower quill as you rotate to keep tool at same
depth.

If you mounted a tilt table on the rotary table, you could tilt the
head so one major axis end was square. After milling half the elipse,
you could tilt the tilt table the other way by the same amount. This
would make the other major axis end square and eliminate having to
raise/lower the quill.

Dan

Using a rotary table to cut an approximate ellipse?
 

Using a rotary table to cut an approximate ellipse?
 

On Thu, 21 Jan 2010 16:02:04 -0800, "T.Alan Kraus"
wrote:

wrote:
On Jan 19, 5:09 pm, axolotl wrote:
Years ago, Errol Groff posted some pictures of some packaging prototypes
he had made. The bottle top was shaped in an ellipse. Can anyone give
the procedure for fabricating an elliptically shaped object using a
rotary table, given a rectangle size that contains the ellipse?

Kevin Gallimore

I can remember drawing an "ellipsoid" using a compass back in grade
school, was part of some kind of drafting thing, Was drawn as 4
separate arcs, I remember that Left some sharp points at the ends of
the major and minor axes, which could be dubbed off afterwards if you
were actually cutting stuff. Don't remember much more than that.
Maybe an old drafting text would have the procedure.

Or you could build an actual ellipse generator, I've seen some for
cutting photo matts, too. Isn't much more than a pair of cross slots
with sliders and a bar linking the two. As the bar goes around the
end traces out an ellipse that depends on how closely the two sliders
are linked for major and minor axis ratios I suppose it could be
hooked to some sort of pantograph linkage to get smaller ellipses.

Stan
There is a device for a BP mill called a Volstro quill adaptor that will
allow you to mill an elipse.

Indeed. Leigh at MarMachine has two of them for sale IRRC. $1200 and
humm..$2000 for the bigger one.

Gunner

The current Democratic party has lost its ideological basis for
existence.
- It is NOT fiscally responsible.
- It is NOT ethically honorable.
- It has started wars based on lies.
- It does not support the well-being of americans - only billionaires.
- It has suppresed constitutional guaranteed liberties.
- It has foisted a liar as president upon America.
- It has violated US national sovereignty in trade treaties.
- It has refused to enforce the national borders.

....It no longer has valid reasons to exist.
Lorad474