Thanks everyone.  This is a lot of help.  Coming from S Scale standard gauge, I am more comfortable with larger radii.  I am leaning towards code 83 rail, but I am not sure yet about MicroEngineering On30 versus living with HO.  I will check the referenced On30 Layout in SN&NG.  I have a subscription, so its sitting on my desk.

Does anyone have any suggestions on where to find a suitable turntable or alternatively how to build a relatively simple one from scratch?

From this, it seems that the Bachmann On30 flanges are sufficiently shallow to allow code 83 track.  I have been thinking that the MicroEngineering track would look good.

It also seems that a 14-15" turntable might be more appropriate.  Does anyone make one in On30, or will I need to get an HO turntable with suitable rail?

Alan,

Thanks.  This is perfect.  I am thinking I will use some combination of the 4-6-0 and 2-8-0 locomotives, so a 12" turntable should work.  The other dimensional information is really helpful.

I was thinking that larger curves might be better.

Do you have any preference in track for On30? 

A recent move has created an opportunity to build a new model railroad.  After looking at some Bachmann On30 locomotives and cars at a local hobby shop, I think I would like to give them a try for this project.  I have a few questions about On30 modeling, and I hope someone on this message board can help.  My initial questions are related to layout planning:

   1. What are the recommended minimum curve radii?  Bachmann's catalog suggests 18-22" depending on what steam locomotives I choose to buy, but I suspect that I would be happier with 24-30".  Any opinions?  I assume the limitation on workable radii is locomotives rather than the passenger or freight cars.  Is this correct?
   2. Do people actually just use HO track or do people choose to buy the On30 track offerings from PECO or Microengineering?  What are the pros and cons of either approach?  Do the Bachmann models need the more common code 100 rail, or can code 83 or code 70 rail be used successfully?  What brand and type of On30 track do people recommend?
   3. How long are the locomotives, passenger cars, and freight cars?  I need to figure out the required track lengths for a turntable and for runaround tracks.  The cars looked to be 9-12" when I looked at them at the hobby shop.  The locomotives with tenders (looked at a 4-6-0 and 2-8-0) appeared to be about 15" long.  If someone could provide some rough lengths it would be helpful and more convenient than the hour drive to the shop that carries On30 here in Houston.
   4.  One last question for today.  What are the recommended center line spacings for parallel curved tracks?  How about parallel straight tracks?  I am guessing 3-4" would be fine, but advice would be most appreciated.

Thanks for any help you can provide.