I didn't know the thread dial gear was missing. Mine is in fine shape so I haven't bothered to replace it. What was worn on mine (but still working) was the bronze power feed worm gear. The power feed worm gear is pretty essential for using power feed for both longitudinal and cross. You could get by without cross power feed as long as you don't have too many large facing cuts to do. Nice to have for parting off also. For long. feed you could just use the threading halfnuts... but that would be a terrible abuse of the halfnuts and leadscrew.
I made my own power feed worm gear from SAE 660 bearing bronze. I reverse-engineered the original and also got a copy of the original drawings from Rockwell*. It was difficult to do because it was the first gear I ever made. I needed a mill with a dividing head which I had. Fortunately I was successful. My new power feed worm gear has been in operation for 89.1 hours of motor time (I have a digital Hobbes meter on the motor) and is still going strong. I made careful measurements of the gear before installing it, including its mass to within 0.01 grams, so I could determine the amount of wear.
I was also trying to figure out how to make the power feed worm gear with only a lathe but I lost interest in that project once I got mine made. I know that some people have had success making such gears with only a lathe. Best way is to make your own hob. Problem with that is the RW 10" does not have the correct gearing to make the correct pitch hob. I think one would need a lathe that can do diametral pitch threads (or something) in order to make the hob. Not sure about that because it has been a while since I looked into it.
Back to your thread dial gear: Fortunately the thread dial gear would be easy to make a hob for. Simply cut an ACME profile 8 TPI thread on a piece of O1 of adequate diameter. Harden. Grind some longitudinal slots to make the teeth and you have a crude hob. Turn the gear blank from 360 brass. Mount the hob in the spindle. Mount the gear blank on the compound so that it can turn freely on an axle. Feed it in to the hob with the cross feed. Crude, but many people have done it with success. Done carefully you can make as good a gear as the factory ever made.
You also may be able to find a gear off-the-shelf that will work. It doesn't need to be anything fancy because it doesn't drive anything but a dial.
For thread pitches that are multiples of 8 (8, 16, 24, 32, 40,...) you don't even need a dial. Any place the halfnuts will engage will work.
* Rockwell is a bit unusual. Though the company has gone through many changes and has dropped the Rockwell name for Delta... they still carry some parts for machines they no longer make. The only part still available for the lathe is the Reeves drive belts and that because the same size belt is still used in a machine they still make (a bandsaw I think.) However... I called their tech support line: 1 800-223-7278 and asked politely if they could send me copies of the drawings for these part numbers:
Worm Gear 414-02-051-5037
Power Feed Worm 414-02-351-5004
Bracket for Power Feed Worm 414-02-014-5006
Clutch Shaft 414-02-406-5009
on lathe model number 25-700.
They said fine and emailed me PDFs of scans of the original drawings within an hour! Next best thing to getting the actual parts.
I know of no other companies that would do that.
-DU-
