4th Axis Concept (long)

It seems there just isn't enough time to ever get anything
done....... I thought I'd share what I have been trying to accomplish.

I got this idea when I set my little Ryobi Wood lathe on top of my
CNC Router table one day. I wonder what you fellas think..........

I have been searching for some type of Simple "Indexable" Clutch. This
clutch would be such so that once disengaged, a re-engagement would
force it back into the "exact same location" as it was prior to
dis-engagement. (start thinking (2) 360 degree circle/plates with one
single pin in it for engagement)

In the following explanation, picture in your minds 2 motors driving a
Sherline or similar Lathe spindle, First motor: a dis-engagable
stepper, The Other: A traditional spindle drive motor.

Concept: A rotary 4th axis that can be under computer control (lets
assume stepper and belt drive), acting in the typical sense of 360
degrees of motion. Yet, When desired, thru an assignable code in the
toolpath file, the 4th axis can be *disengaged* mechanically from the
4th axis and allow, again thru toolpath code, The operation of the 4th
axis like a typical lathe.

How it works: A workpiece is installed in the 4th axis. The rotary
axis "0" point is located and "set" in your control software. Typical
4th axis work can now be done to the part. OR, IF desired, Code in the
toolpath would dictate the separation of the Stepper motors clutch
plate, and a traditional DC motor would be selected (again by code in
toolpath) to start spinning the spindle of the lathe.

After the needs of traditional lathe turning are over, code in the
toolpath would shut down the DC motor and include dwell time for it to
coast down. Code then would send signals to the Stepper motors clutch,
to Re-engage the clutch. As this clutch, let's say with ball plungers
moves toward its counter part plate with the indentations, the balls
would retract into their spring loaded holders. Code would then
dictate that the stepper motor rotate the clutch 361 degrees one way
and then back, thus engaging the ball plungers balls into the
corresponding indentations. At this point, no matter how many
revolutions the 4th axis has turned in "Lathe Mode", The axis is again
aligned where "Part 0" was assigned originally.


Usage: Imagine using it for making spindles for furniture legs.

Picture This: Small lathe mounted on a 3 axis CNC Router table. The
raw stock is in mounted the 4th axis just like one would in a
traditional lathe, one end in a chuck or spur center, the other end in
a tailstock center.

Acting under stepper control, part 0 is set. Let's say The Toolpath
dictates that one end of this material gets a taper. The Z axis moves
into place and cuts the taper on one end. NOTE: This does not have to
be done using the router head ! Simply creating a toolholder on the
side of the Z axis plate with a fixed tool can do the lathe work. The
Router spindle could be used either on top or on the side of the
material if interesting "Patterns" are desired.

Now after the lathe work has been completed, Toolpath code commands
the lathe spindle to stop and the stepper clutch to engage. It runs
the routine placed in the code to rotate the axis 361 degrees to make
sure it engages (a brake on the spindle may be required). Once engaged
the control software can determine the location of the material and
rotate according to code to allow the router head to cut Flutes,
Mortises and or any other typical 4 axis work. From beginning to end,
the CNC Control in essence "thinks" the steppers axis has never moved.

If you could follow thru the above, you may agree that this would be
really neat. In my search for such a clutch I came up empty.

A typical 4th axis will not run near the rpm necessary to *be* a lathe
and if it could, there is virtually no known way to "post" code for
some unknown *SPOT* after the lathe spindle stops (note that Flashcut
for instance will run for hours in the 4th axis, running up "degrees"
from here to who knows where!) This Clutch would handle all of that.

For very obvious reasons, you could not leave the stepper engaged in
lathe mode!

I have drawn many clutch prototypes based around the use of it mounted
on the little Ryobi Lathe being sold with the DC feedback motor. The
only method that could possibly keep it affordable is to just slide a
step motor forward and back, subsequently engaging and dis-engaging.
The connection to the spindle would be of toothed belt and
suprisingly the existing OEM pulley has room for running 2 belts side
by side. The accuracy for this type of 4th axis is not near as
critical as the typical but certainly could be made so.

I have concluded that the best method would not be ball plungers but
rather a very, very, well fitting, tapered (slightly bull nosed) pin
in a tapered hole. This pin would very easily be pushed back when the
2 clutch plates come together by a thin piece of spring steel on the
backside of the clutch, and it would find its corresponding socket on
the 361degree move.

The problem is that it needs to be made of the same quality as some
of the working parts of commercial sewing machines (only way I can
describe it) Very Hard, smooth and accurate. My machinist friends
don't quite come to that caliber.

So, the search continues. To my knowledge this has not been done on
any level of Sherline to midrange homebuilt machines. Possibly it has
been done only on special built applications. It lends for an exciting
technique. I have machined both with the router spindle and tooling on
the side of my Z axis.... Works pretty neat. Now to take it this one
step further.


If any have some ideas I would gladly hear them. If you steal my
idea............ well, you read it here first folks !!! Then again,
maybe I have been in the basement too long and it's already been done.

Thanks for lettin' me express myself,

Chris Luebke
DATA-CUT