Myford ML7 gearbox and how it affects metric change wheels.

[philml7Participant @philml7]

Hi,

I have a Myford ML7 with gearbox type II. I have bought a metric set of change gears and am wanting to cut an external 8mm x 0.75 thread. I have used lathes occasionally for many years and have done some thread cutting before. I know which gear wheels to use am wondering how the gearbox affects it. Presumably, after fitting the correct gears, I need the gearbox to only have a ratio of 1:1. Is this correct and if so then how do I do that?

Cheers,

Phil

[BazyleParticipant @bazyle]

see this thread/

https://www.model-engineer.co.uk/forums/topic/metric-threads-on-a-myford-super-7-with-quick-

change-gearbox/

You still need to select the appropriate gearbox setting for the thread. You might also clarify what ‘metric gear set’ you actually have as there may be more than one option (I’m not a Myford user so can’t help directly)

[Nigel Graham 2Participant @nigelgraham2]

It won’t give a 1:1 ratio but I’d start the calculations by using a simple binary ratio gearbox setting such as 16 or 32TPI, as those are half and quarter the leadscrew pitch.

The secret seems in changing the 12 or 24T primary pinion after the reverse tumbler, so the drive ratio is altered by (12 or 24) / New.

For example, if the gearbox could be set to 1:1 overall with a 12T pinion, to give 8tpi; the cut pitch would = 0.125″ = 3.175mm. Rather cruel to the lathe of course. Use the 24T wheel and set the gearbox to 16TPI gives the same result- a point that baffled me for a while until I studied both machine and handbook more carefully.

So swapping that primary wheel and applying its ratio with the substitute, we now need determine what substitute tooth-count to use in place of the 24 or 12 tooth wheels, for a given gearbox setting.

 

I have just spent some time trying to do that but it pushes my numeracy to the limit and I do not believe my answers. Luckily others have already done these calculations and published them!

 

It’s something I would like to know too, as the Myford literature seems to advise it needs a special banjo; which of course Myford no longer stocks now that more users of these elderly lathes are using metric screws more often.

The thread Bazyle suggests is for a Myford Super 7, and there may be important detail differences between that, your ML7 with Type II gearbox, and mine with Type 1. For a start, the gear-studs on my lathe’s banjo are on fixed centres so any other than 12 and 24T pinions may not be possible. I don’t know if the original, fully-slotted banjo could be used instead, but it would be a faff.

 

I asked in a different way a couple of weeks ago, and the upshot of a lengthy thread (!) was keep the gearbox now I’ve fitted it, and use dies for the metric threads I’m ever likely to cut. Useful if most of your threads are inch-based as mine are, and the intended mm threads all small diameter; not so useful if needing screw-cut the metric ones.

[philml7]

On 6 October 2026 at 15:43 philml7 Said:

I have a Myford ML7 with gearbox type II. I have bought a metric set of change gears

When you state your problem in this way, you are somewhat limiting the pool of potential helpers, and the brain power at your disposal.

Any person answering needs to know what a type II gearbox is as well the tooth count of the gears you have purchased.

If you could write down the gear on the lathe’s mandrel, all gears in the train forming the input to the gearbox, the internal ratios of the gearbox, and the leadscrew pitch, it is at least initially a purely mathematical exercise that anyone could attempt. At this point the problem is entirely generic and not Myford-specific.

Once you have some numbers, and only at that point, does the specific machine become important. The importance arises from the need to fit a calculated input train into the space available. That can be trial and error and also be done using cardboard discs of the correct diameter if an actual gear is not available.

[Grindstone CowboyParticipant @grindstonecowboy]

I’ve mentioned it before, but this site https://www.ridethegeartrain.com/ is well worth a look. I don’t have a gearbox on my lathe, but I believe there are options for that in the calculations.

Rob

[MacolmParticipant @macolm]

Perhaps to point out that the reason things are so complicated is that Imperial thread series are defined as simple ratios of threads per inch, whereas thread pitch is used for the Metric thread series. One is the reciprocal of the other.

Thus the available thread series on an imperial box will not provide a useful series of metric threads. Different change wheels together with a suitable gearbox setting will therefore need to be chosen for each individual thread.

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