Re: [CAD_CAM_EDM_DRO] 4th Axis Concept (long)

Chris Luebke wrote:

>
> Alan,
> Lets go thru some of your ideas.........

> I think the D shaped shaft may be a little tricky to engage and disengage,
> especially if there is some form of tension or part that is offset from the
> axis centerline like a crankshaft (crankshaft ??? what are you trying to do
> ??? Just illustrating!).

I think it could be made to work, with a little testing. Half flat,
then at the end a slight bit of flat taper away from the centerline, so
the flat of the D is away from center, but still pretty flat so it'll
catch. Spin once with little pressure and it should catch, then finish
pushing it in to lock. But there's a better way..

>
> I gotta think about this......... I think we would then need to index the
> part to be machined based on the hole in the disk from the getgo. I'm gonna
> print and then consider this more..........
>

Of course. You simply do a disengage/engage cycle before you start,
then you're lined up with the same index you'll use later. Would also
be easy enough to have the pic find and remember an offset from the
index, so you could simply chuck up the part, set it manually where you
want, and have the pic figure and remember the offset from the index for
this part through several engage cycles until it's next re-index. Not a
problem..
The key part is simply use a normal clutch with plenty of grab and not
worry about the indexing until after the clutch is in. For that matter
doing it myself I'd try putting an index system on the spindle, and tap
the spindle motor with short pwm pulses until it's aligned and then
engage, and be indexed before going together. But I think the engage
then index system will probably be more reliable.

Thinking about it, I see an easier way. Two round plates, one with
holes one with pins with a tapered edge, but basically straight pins and
with a good fit when engaged. Plate with holes is the spindle, and has
thin rubber sheet on the flat surface. Both plates have a flat piece
sticking off the edge for an index, and two opto-interruptors off the
system. Motor plate goes in till pins engage the rubber, then spin to
index the spindle, back out the motor a bit, spin to it's index, and
engage pins into the holes already aligned. Really guess you don't need
another index on the motor plate if you already know where the motor is,
but may as well put one there if the motor system doesn't already have
an index reference. Aligning both seperately then engaging with a solid
connection system will take a lot of possible problems and errors out of
the clutch assembly. And two simple interruptors are a lot easier to
deal with than some kind of complex clutch..

> I am picturing the versatility of keeping Square ends, like the legs of an
> old washstand. Flat spots for mortises and then rails to other legs.

I'd go with that too, and then try several alignment systems to find
something that works solidly. I think the above will work well, just
theory wise it looks much better than the other methods.

> I like the idea of an additional stepper motor for engagement. It does
> however add a bit to the overall project. I really think you could apply some
> fairly smooth motion for engagement with an air cylinder, sure you now need
> air, but who really doesnt have that if you have a CNC machine?

Well, stepper from an old full height 5 1/4" floppy drive, it's driver
chip, and a pic chip programmed to do the necessary tasks when it geta
an engage/disengage signal would be less than $20 cost, and you should
be able to do the mechanical part of the system very cheap with just
threaded rod etc, considering how light duty and low precision this task
is (at least the motor moving in and out part doesn't need much
precision at all..)
I'm trying to think of how to make this work with just a hinge point
and a single screw/motor at the other end. Move a hinge point a bit
away, and you can roughly approximate linear motion with just a screw
and hinge, no linear sliding arrangement required. High quality hinges
are cheap, good precision linear arrangements often are not..

> I am going to rip apart a floppy disk right now !

Have fun! Then try my patented 5 pound sledgehammer 'surplus printer
case removal' method, that is really fun!

Alan