Myford used the same 8 tpi leadscrew on both imperial and metric lathes, only the cross and topslide screws are metric pitch on the metric version. Myford's screw cutting chart is therefore the same for both the imperial and metric lathes. The metric pitches are not precise in the mathematical sense but are very close approximations, way beyond the accuracy that the machine is capable of.

Rod

Is it a metric Super 7, or just an Imperial Super 7 with a metric screwcutting chart? Seems odd for a metric lathe to list imperial threads first, metric second.

Are the cross slide and top slide collars graduated in metric or imperial?

You can always check the pitch of the Leadscrew, by measuring the travel for ten turns of the Leadscrew.

If it is an 8 tpi Imperial, the travel will be 1.25 inches (31.75 mm).

If it is Metric Leadscxrew, the travel will be ten times the pitch, (So 15, 20 or 30 mm, as examples )

Lots of Myford 7 Series owners on here to help with details.

More general questions can be answered by lots of other model engineers.

Find and join a local model engineerinbg society for face to face contact, and advice from like minded folk.

Don't be surprised if some of the advice is conflicting!

Different ships, different splices. What works for one, may not work for another!,

Howard

The 20 driver and 20 leadscrew with idlers between giving a 0.125" pitch is a good indication of it being an imperial 8tpi leadscrew. as that is a 1:1 gear train

Any of the common metric leadscrew pitches need a far more complex gear train so not likely to be a metric leadscrew.

Edited By JasonB on 28/12/2022 19:09:53

It's not just the backlash, you would lose the indexing between the gears in the drive chain.
As far as I'm aware, Myford never made a S7 with a metric leadscrew; all are 8TPI
The cross and top slides had metric screws, with the appropriately marked thimbles.
On the end of the leadscrew, you might have a hand wheel; on an imperial lathe it has 125 divisions, whereas on a metric one, it will have a different number. (I'm not sure what off the top).

When screwcutting metric threads on the Myford, it's convention to run the lathe motor backwards, after withdrawing the tool a bit, to return for a fresh cut.
If you don't give the tool clearance, by withdrawing it a bit, that's when you strip the previously cut thread pass, due to backlash.
Don't disengage the feed, or the tumbler.

Bill

That's a clever little trick and a good way of doing it if you are machining up to a shoulder. Othewise, it is just as easy to wind the tool out a turn and hit the stop switch then reverse switch without disengaging the half nuts.

If you don't have reversing on your lathe motor, a hand crank in the spindle is very good for most hobby screwcutting jobs. They are usually short and you want to go slowly anyhow. Easy enough to make a hand crank that slides inside the far end of the spindle and grips via a tapered plug on the the end of a bolt that expands the split end, like a concrete anchor bolt in principal. Also a fantastic aid when cutting threads with a tap or die. Soooo much easier than wrestling the chuck or the tap handle etc. I love mine. Best thing since sliced bread. Along with the resettable cross and top slide dials it is the best accessory I have made for my lathe. The shown tailstock die and tap holders are gold too.

Can't see the motor but there are switches, most notably dewhurst or santon but also others . the change in the wiring is (or should be ) easy. BUT when reversing, the motor MUST have stopped turning before reversal and keep an eye on the temperature of the motor as repeated starting of a single phase motor will in time cook it. If you can post the motor diagram then help will be forthcoming . I'm assuming that you have a single phase motor not 3Ph and VFD. Noel.

I am wondering if you grind all your dies specially. None of the ones I have will thread up to a shoulder, even if used from both directions, due to the lead/chamfer that is on them from the factory.

In Martin Cleeve's little book Screwcutting in the Lathe (highly recommended) there is a discussion of how to pick up threads accurately by calculating the "synchronous distance". IIRC you can use this to just cut your thread in the usual way, disengaging the leadscrew at the end of the cut and winding the carriage back, and being able to find a position for starting the next pass which will re-engage with the thread exactly. I think it involves marking the spindle so you can put it in a known rotational position and possibly having a carriage "back stop". It seems it may not be practical for all threads but it might mean that you can avoid having to reverse the spindle in many cases.

Some, mostly older and higher quality brands, dies have a tapered end and a flush end where the threads come full to the face of the die with just a small chamfer on the very first tooth.

But I did notice using a borrowed set of CEI dies yesterday that they have the long lead-in taper on both ends. Possibly to spread wear on cheaper carbon steel dies by sharing the work between two ends over time?

Myford-metric or name it imperial-metric is accurate enough for model enginering but it is not metric. Niko.