Large dial upgrade - opinions wanted
Surprisingly I belong to the mass who are not getting younger as time goes by. I recently observed that the closer I look the less sharp the picture I can see. I bet there should be something with my eyes. Anyway that is one more reason why I'm thinking on to replace both dials on my 9C. I've read the excellent thread from Tex-VA about making the ACME screw and the dial HERE and it seems to be doable. However I have some questions regarding that upgrade.
1. As far as I know the large dials was offered from SB, so replacing the small ones wouldn't hurt too much the originality of the machine, would it?
2. Since I'm in metric system I would chose the thread pitch and the micrometer scale to fit to it. What is the best combination for that?
3. Is there something against making the sleeve and the dial from stainless steel (apart from its poor machineability)? What about brass or bronze?
4. I understood the advantage of the longer sleeve is the enlarged travel of the cross slide. Does this applies also to the compound rest? To what operation it is useful?
5. What is the recommended way to make the screw, from one or two piece?
1. Nope, over time, the size of the dials on the 9" lathe increased to what we now call the "large dials".
2. My 1940 catalog talks about the metric option and states, "All metric feed screw collars have graduations reading 0.02mm per graduation." The pictures show a collar that appears to be graduated from "0" to "2", which I guess implies a screw pitch of 2mm. I don't know if that's optimum or not, but that's what SB was using at that time. Wondering how that will fare with an English leadscrew? One thing to consider is that you'll have to make your own matching nut if you go metric on the compound and cross slide. That implies either single pointing the thread with a tool that you'll have to grind yourself, or buying/having made a tap. I don't know if a 2mm tap is standard/cheap. With a 10tpi screw, you can buy the nuts, aftermarket.
3. You can make them out of anything; brass/bronze may not be aesthetically pleasing, however. Most of the guys are making this stuff from 12L14, I believe.
4. The longer sleeve is necessary to preserve the cross slide travel when retrofitting the large dial - I'm not sure that it adds any travel when compared to the standard sleeve and small dial. The compound, no matter the size of the dial, doesn't suffer from the same interference problem as the cross slide. It's travel is limited by the nut coming into contact with the casting.
5. Given that you don't have power cross feed, I would say make the screw one piece.
I think I have a large metric dial for the 9" and maybe a CF nut. I do have the metric CF screw for the Heavy 10 that you can use the threads for the 2 piece option.