That's a much more reasonable price But again it looks like a worm driven so I'd ask them what is the backlash and whether it's adjustable.

Dan

All the standard rotabs are worm driven and will have backlash.  You can adjust it out to some extent, but you wind up with binding the gears until they are hard to drive and wear quickly (needing frequent readjustment).  The cheaper the rotab, the more trouble will be caused along those lines. 

So, you have to decide between two courses:

-  Modify an off-the-shelf rotab and be prepared to live with the backlash.  You'll adjust it as well as you can, but it will always be there.  This is the quick and easy approach, and one the vast majority go with.  It's very straightforward to slap a stepper on one of these import rotabs.  For a lot of kinds of operation, it'll be fine, and yours sure seems to fit this category.

-  Build your own 4th with a no-backlash drive.

The latter has been done a fair number of times, but its a lot more work.  You just missed being able to buy a nice prototype from this chap: 

http://www.machsupport.com/forum/index.php?topic=11422.new

But, it's not to late to see how he approached building his 4th.  Given your application, I'd personally be tempted to go the latter route even though a rotab would work.  Start out just creating an indexer and a tombstone, manually indexed if need be.  You can worry about the drive later, and you can deal with the complexity of it as needed. 

You need to engineer a spindle and bearings, and a brake or indexable lock to get started.  Leave provision for a motor in a later iteration as needed.

Your spindle and bearings can be real simple.  You are essentially engineering a lathe headstock.  BTW, you could just buy one from Little Machine Shop or Grizzly if you're willing to spend the money.  Or you could buy the spindle and bearings and machine the headstock out of cast iron or aluminum.  Personally, I'll probably build something like this with bronze bearings.  Press fit a couple oilite sleeves into a couple of pieces of Fortal, bore them with a boring head, provide drip oiling, and you're done with a nice smooth but very tight axis.

Cheers,

BW

PS I keep some design notes here for my long-term project: http://www.cnccookbook.com/CCMillCNC4thAxis.htm

Thanks for the tips.  I've got some thinking to do.  I'm mainly an artist here, and some of that is over my head;)

Barry