On 26 Sep 2016, at 04:45, Chris Albertson wrote: > I've started work on a motorized indexer for my rotary table.
Like DivisionMaster? > 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. > Limiting rotation to one direction is a huge limitation on what can be achieved with a table like this. Why not drive it with LinuxCNC and address any problems of backlash through either (or both) mechanics and backlash settings within LinuxCNC? Bolt circles and simple division are fine, but bi-directional motion allows full machining. > Later I can see if my low-cost table can be used for more. > Better to address that during the design stage, I think. > 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. Is resolution on a rotary table not better defined in terms of angles (degrees or radians)? > > 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? > Depending on the inertia of your table, you would need ramped acceleration and deceleration at the beginning and end of each set of steps. > 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. A more practical solution might be to use a single wheel and three buttons. Or a ShuttlePro or Shuttle Express. The Express will be cheaper than the parts needed for your plan involving 3 or everything. Driver for LinuxCNC is available through the main LinuxCNC site. > > -- > > Chris Albertson > Redondo Beach, California > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
