Re: 4th Axis Concept (long)

Chris,
Interesting idea! I have a Sherline, so my comments would apply
to it. Sounds like you have pretty much thought this through. Have
you considered installing a toothed pulley on the outboard side of
the existing drive pulley? Mount it on a ball bearing on the end of
the spindle shaft, (where the threading drive gear would normally go).
Have a tapered drive pin mounted to it which would engage a hole
in the existing drive pulley. Use an overcenter (snap action) spring
to toggle the drive pin into or away from the spindle drive pulley.
Fix a sliding ring to the pin and use a yoke shaped lever to actuate
the overcenter spring. The yoke would ride on the perimeter of the
ring, but not touch it except during the actual toggle. Would use
a solenoid or ? to actuate. The ring would slide free on the spindle.
The toothed pulley would be fixed axially, the stepper would also
be rigid so as not to affect belt alingment or tension. Also no
sliding splines, etc, to add play. The only thing requiring a
tolerance would be the fit of the drive pin to the toothed pulley.

What do you think?
AL

PS I'm thinking of a combination of the concepts of the sliding
start/run contacts of an electric motor and the overcenter
spring of your Lucas impulse type fuel pump. Ever replaced the
points in a MG fuel pump?
al

--- In CAD_CAM_EDM_DRO@y..., datac@l... wrote:
> 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