Mark - thanks for the comments. Thing is - the controller/interface is independent of the size of stepper/power supply you use. I plan to rebuild that and use the same interface but tie it to a somewhat bigger motor and use the motor to drive a rotary table. With a little gearing down of motor-to-table, I should be able to cut an spacing for 1 to... whatever and not have to be bother with dividing plates. With the big ratio I should be able to the the error down (like in a 35 tooth gear) to be pretty much insignificant. It will be pretty slow stepping from space to space, but that is OK!
Yes exactly, only the motor and driver need to be bigger. I am considering the backlash issue however if worm gears are used- don't have a good solution for that that doesn't require an adjustment between the gears that would have to be periodically re-adjusted, just like a legacy indexing head.
Perhaps it is better to just have a Gilmer belt drive with a large ratio and large stepper motor, the motor would stay energized for the entire operation. Not clear about that.
I do understand the backlash issue with rotary tables. However - working with an electronic control SHOULD reduce or eliminate the possibility of having to back up and recover backlash error.
Once the table begins moving in one direction there should be no backlash to consider. Plus the stepper is under power and has a locking or holding ability. Of course this is all my THEORY - and may go out the window in real life - but I'll start that way.
I have a 'jog' feature and if that is done first, it will take out all backlash in that direction - then just begin by setting the cutter, make a pass, press "STEP" - rinse & repeat. I also want to have a second counter to show where you are in the step cycle - probably just a down count of the divide-count.
I'd be interested in the code you wrote to control the stepper drive.
I bought an Carroll dividing indexer off of eBay some time back, but it had only one plate when it arrived.
I too figured it would be much easier (and possibly more accurate) to use a stepper motor to drive it.
In my case, I went with Yuriy's Toys Touch DRO system for my DRO (still work in progress). This project has been on the back burner since the dividing head didn't have a chuck and has a 6 TPI spindle nose thread.
My thought was to try and develop a code for either an Arduino and/or TI Launchpad to control a stepper motor drive that could be used on an indexer or rotary table.
If it can be interfaced with the Touch DRO App with selectable inputs like indexer/table drive ratio, diameter and number of teeth, or degrees for arc cutting, this should make cutting arcs, circles, and gear teeth a breeze.
Be glad to send a copy. I created some special library's for it and it uses the I2C bus to talk to the display.
I lusted after Yuri's project initially for my mill - but it ended up for just another $100 in cost I got a "real" DRO with glass scales. IMHO, a good DRO is a must-have for small mills. Complete game-changer they are!
Go to my web site (http://www.avrdev.net) and there are 3 sections in the "Special projects" column that will give you some idea of the parts needed. If you are new to Arduino coding this could be a bit of a challenge - when you are ready, let me know and I'll zip up a copy of the project folder for you.
Glass scales weren't a real good option for me that's why I went with the Touch DRO set-up with some prodding from a friend at work.
I initially bought iGaging Absolute scales, but found out too late they were incompatible with Touch DRO. Turns out the refresh rate is too slow for my use anyway.
The friend from work is helping me hack the protocol they use, but it's been slow going. He's a wiz at programming and helps me a lot with anything I don't understand.
I bought another set of quadrature scale from The Little Machine Shop that I'm currently setting up to install.