I've started work on a motorized indexer for my rotary table.   At this
point I am not calling this a fourth axis.  The way this will be used is to
(1) rotate the table, (2) clamp it down, (3) perform the drill or mill
operation (4) unlock) then if not finished go to #1.

A fourth axis would required more mechanical precision.  I plan to drive
the table only on one direction and clamp down the clamps when cutting.
It should work well for making bolt circles and the like.

Later I can see if my low-cost table can be used for more.

The project adds a stepper motor to replace the crank because I am not good
at counting or finding holes on an index plate.   The motor connects via
direct drive to a a worm that drives a 72 tooth wheel.  I can micro step at
about 8:1.  This gives me about 0.0001" of resolution at the edge of the
table and a lot more near the enter.

For your amusement here is a photo of the controller electronics, computer
and all working on my electronics bench.   The user interface is a rotrary
knob that you can "push to select" and there is a small LCD for a display.
https://www.dropbox.com/...ElectBenchTest01.jpg
<https://www.dropbox.com/s/rlyhhmjvr2qm88f/IndexerElectBenchTest01.jpg?dl=0>

The little 8-bit computer can drive the stepper at almost 10,000 steps per
second.  The steps have 105 uSec period with only a few tens of nanoseconds
variation.  I'm currently using a 12 volt plug-in power cube to power the
stepper.

QUESTION:  Before I get further along, within the limits of this hardware
what features would be good to include?   The memory has tons more room for
software and many unused pins on the Arduino.  I wonder if I missed any
useful features?

1) selectable units, either degrees/minutes/seconds or fraction of a circle
2) A physical button to set the zero point
3) A physical "step" button to move to the next point
4) can set the step size with rotary dial
5) controls lock out automatically when it does not make sense to use them
to avoid accidental activation
6) A fine motion mode where the table moves 1 second of arc per click of
the rotary dial, for fine tuning the zero point
7) the display will show the current position and the step size in
selectable units


Is there anything I missed?

PS.   This is only tangentially related to LinuxCNC, connection to that
comes later.   Another project I want to do is to add a replica of the
physical hand wheels that go on a manual machine tool.  It would be self
contained not using a PC.  Likely just three wheels with one of those small
LCDs above each one to serve as a digital readout.   Basically what you see
in that photo times three.

-- 

Chris Albertson
Redondo Beach, California
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