On Sun, Sep 25, 2016 at 11:28 PM, Marcus Bowman < [email protected]> wrote:
> > 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. > I can figure out backlash without a PC. In fact I can do it automatically the way inkjet printers do with a self calibration on power up. Run a metal tab past an optical sensor in both directions. For now this is an indexer. Unlike a mill table, I can get to any location by driving in just one direction. I'll connect it to Linux CNC later. But the PC box is huge and not so portable. The indexer controller can be 1/3rd the size of this 4" table. > > > Later I can see if my low-cost table can be used for more. > > > Better to address that during the design stage, I think. > I'm stuck with this rotary table. It might be good enough that it can move while the mill is cutting metal. It's a small Chinese table The design of the table is fixed. > > > 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)? > I think angular resolution might be a derived requirement. The base requirement is the tolerance on the hole placement, then you compute what angular resolution you need to get the hole in the correct spot. At least this is the way I think about it. Even with a gear. You might look at one that is poorly made and say " that one tooth is .010 to wide". You's not say "the left side of that tooth is radially displaced 17 seconds of arc". Even if the two happen to be equivalent. But in any case, My goal was to have the table's mechanics be the weak link. > > > > 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> > Looks like a non-HTML aware mail reader hacked the link. There is only one link, the first is the text to be displayed to the reader, the second is the actual link. The bottom one SHOULD show the photo to anyone. > > > > > Depending on the inertia of your table, you would need ramped acceleration > and deceleration at the beginning and end of each set of steps. > Yes, thank you. I have a motor setting on my bench and it jumps when I go abruptly from zero to 10,000 steps per second. So I find that even a bare motor with nothing connected to its shaft needs to ramp up to speed. What I do, under the hood, where the user does not see is give an end point, maximum speed and a maximum acceleration. The motor only gets up to full speed if it moves a certain minimum distance. So I could add the requirement "don't miss any steps". But I only wanted to list user facing features > > > 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. > I just looked, the ShuttleXpress is about $50 and it lacks an LCD display. I'm into about $8 in parts for a single axis control with a two line text display. (Not counting the motor and driver) Is the Xpress cheaper some place else? I'm still astounded at the low cost off Chinese electronic parts, example I just got a bag of 10 push buttons in the mail for $1.85 shipped. I can't see how the postage alone is that low. > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > ------------------------------------------------------------ > ------------------ > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > ------------------------------------------------------------ > ------------------ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
