Here’s a reminder of what the apron interior looks like. The blue piece on the left is the threading dial, and is easily removed by removing the grub screw from the outside. The jaws next to that are the half nuts. The silver sheetmetal part in the middle is an oil bath where the drive clutch and the main worm screw live. The cog sticking out the top is the power-crossfeed drive, and the coarse-tooth cog on the right is the carriage drive pinion, connected to the handwheel and the rack. (I’m probably using all the wrong words)
This is one of the half-nuts. The thread is supposed to be acme, and they should have flat tops. They are sharp due to wear. I have had to order two new half-nuts from Mal at Australian Metalworking Hobbyists. The price was $138 + $22 for fast delivery. I have heard people renewing these threads by adding some material via. brazing, or boring out the threads, fitting a bronze insert, and then recutting the threads, but I don’t have a working lathe or milling machine to do either of those. I’ve also read about people putting a release-agent such as petroleum jelly onto the leadscrew and re-casting the threads using some JBWeld epoxy. I’m not sure I would be as happy with that as with new half nuts, so I have bit the bullet and ordered the parts.
Tubalcain (aka. mrpete222 on Youtube) has a fantastic video demonstrating the teardown, cleaning and rebuilding of the 9” Southbend apron. I’ll be using his 9 part video series as my guide during the clean up of my lathe.
His videos are about the Southbend lathe, but my lathe is a Hercus, but for all intents and purposes, they are indentical down to the last grub screw. The only difference I’ve found so far, is the keyway-type slots and felt wicks in the gear shafts on the Southbend machine, used for oil retention. These have been replaced (upgraded? downgraded?) in the Hercus with an oil-hole directly fed through the shaft to the bearing surface, fed from the outboard end of the shaft. I have no idea which is the better system. As long as the oilways are clear, and they are regularly fed with oil, I suspect either system works perfectly well. I imagine the felt system works better when new, but would it be more prone to clogging?
Here’s the inside of the oil bath mentioned before. It’s clogged with thick mostly dried out grease. I’m pleased that there are barely any chips and swarf in here, very different to Tubalcain’s southbend. He was pretty sure that the use of compressed air pushed the chips up and into the apron on his lathe.
Here are all the parts from the apron, along with the tailstock and carriage. Everything in here, although not yet cleaned up, looks to be in great condition, except for those half nuts. I suspect the wear on those is due to a previous owner using the half nuts (which should only be used for threading), as a general purpose carriage feed. The clutch and feed lever mechanism should really be used for that.
Here’s the casting minus most of the internal parts. I can clean in and around the feed lever mechanism and the handweel gear, no problem. It may even get a coat of machinery grey epoxy enamel. I’m not too fond of the blue. The original colour was a machinery grey, but with a hint of pale green. I’m quite keen on the pale grey on its own though.