Hello and welcome. Yes this the appropriiate place to ask!
Your lathe does have proper oilers for the headstock bearings so that is a blessing!
I lubricate the ways on my ML7 by cleaning them thoroughly with paper towels (kitchen wipes), puddling oil on the flat surfaces them winding the slides back over that. Not ideal but it seems to work.
I agree the diagram in the handbook is not ever so clear, but you should never need count wheel teeth because the proper change-wheels are marked with their tooth-counts. (As for any lathe with change-wheels rather than gearbox.)
When setting up a compound change-wheel train the two middle gears are connected by the keyed sleeve on the peg on which they revolve together.
The basic principle is [Driven/Driver = TPI/LS]
where the –
Driver and Driven are the tooth-counts of the gearing you need set up,
LS the Leadscrew (8TPI on the Myford)
TPI the turns count of the intended thread. That should never be coarser than the leadscrew, when driven conventionally, to avoid excess stress on the lathe. Even an 8tpi thread is quite heavy work for it.
Some sources quote the algebra the other way round: Driver/Driven, etc..
E.g. 60T wheel on the leadscrew / 30T driven by the tumbler gear, with an intervening idler of any convenient size to connect them and maintain the same direction, will give a 2:1 ratio so we now cut a thread of (2 X 8) = 16TPI (Which I see from my tables, is 3/4″ UNF and 3/8″ UNC.)
When you can’t obtain a direct single-stage ratio like that, the idler is replaced by a pair of wheels keyed together, and smaller wheel or a sleeve placed on the leadscrew end to put its wheel into mesh with the output wheel of that intervening pair.
There is, or should be, a table on the inside wall of the change-wheel guard to give the change-wheels for a very wide range of inch, and some metric, pitches with the standard change-wheel set. The latter might be approximations that become difficult over more than perhaps 10 or 20 turns.
A tip when setting the change-wheels in mesh. To avoid undue stress and wear they should not be tight together. Put a strip of ordinary, thin printing paper between them as a spacer; hold the assembly together while tightening the banjo screws then manually rotate the lathe to wind the paper out. This gives a clearance of typically 0.003″.
I see your lathe does have its thread dial indicator. That should be put into mesh with the leadscrew only for screw-cutting. Otherwise swing it back a little clear of the screw.
I have a note pinned up behind the lathe to remind me how to use that indicator for given TPI multiples!
….
There may be plenty who will come here advocating replacing change-wheels or gearboxes on even the simplest lathes with electronic leadscrews, but unless your lathe has neither of these it would seem a drastic solution to a simple problem. Unless you spend every day cutting umpteen screws of all sorts of different pitches – or are converting the lathe to CNC operation anyway!
A friend told me he reverted his gearbox-fitted Myford ML7 to change-wheels because it gives him wider range of pitches, particularly allowing metric as well as inch-based ones. He said he does not find it any less convenient to use change-wheels instead of gear-box.