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

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

> >>>Look at the bottom of a 3.5" floppy disk, and the spindle in the
> drive, that is by far the most common similar arrangement. I can see
> doing this, simply picture a stepper shaft with a half flat D, out to
> disengage, just barely touching (may need spring loading, may be doable
> without) and spin the shaft to find engagement, then in the rest of the
> way in to engage..
> I don't see an easy way to engage/disengage without having another
> small stepper to screw it in and out. You might could make a solenoid
> system that'd work, but I think an extra stepper would be more
> reliable. Easy enough to do a small PIC chip system to do this, all
> you'd need is an engage/disengage signal, and wait a reasonable time
> after the engage signal for it to get locked up..<<<

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!).

>
>
> >>>But, I can also see a better way. Use any clutch system, not
> indexed. Much simpler, just has to be locking type clutch so it won't
> slip, should be a lot easier to find one of these that will work. Then
> have an index wheel on the shaft somewhere, just a plastic wheel with a
> hole in it, and an opto-interupter. After the engage signal, send the
> command for a little more than one rev, at a low speed, then a wait
> period of that long again. Then just have a PIC chip so after the
> engage, it looks for the index hole. Soon as it sees the index hole, it
> disconnects the step signal for a fixed 1 rev time (that's why you need
> the extra wait time, the motor won't see pulses for up to one rev time
> afterwards if it sees the hole near the end of the first rev). Then
> you'll be set to the index hole, and the pic won't interrupt the signal
> again for anything until another disconnect/reconnect.<<<<

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..........

>
> >>>> Another question to ask, is absolute positioning really needed? If
> totally lathed, it wouldn't be at all, everything is relative around the
> piece. If you want to leave some areas square and have the work in the
> round match up to the square portions, it will be, OR use a larger
> starting block and machine it square after doing the round, but that'd
> be a bit wastefull. But if you're machining it square anyways, you
> really wouldn't need indexing, just good motion afterwards..<<<

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.

>
> >>>All in all I'd say it's easy enough to do, and you really wouldn't
> need a large stepper to control the engagement. Give it some leverage
> and I bet a surplus floppy drive motor would work great to move a much
> larger motor in and out, certainly a NEMA 23 type would be enough for
> most anything..<<<

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?

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

Thanks,

Chris

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