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)

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.

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.

Dc31k –

It’s not as arithmetically complicated as you make out; but there are serious mechanical difficulties.

The question is specific to Myford lathes that have 8TPI leadscrews and on the ML7s fitted with either of two patterns of Norton-type gearbox – the pattern may be important but mechanically rather than mathematically.

The gearbox is driven by a set of change-wheels on a banjo differing from that used for change-wheel only operation, in that the default version has fixed studs and the only adjustment is rotary about the gearbox input axis.

In standard trim the earlier Type 1 gearbox box uses a 24 + (flimsy)12 Teeth pair engaging the reverse tumbler, thence a reversible pair that gives threads / fine-feed choice, to a double-width gear forming the gearbox input.(I do not know if this is also true for the later Type 2 Gearbox.

We do not need change the wheels for inch-based threads given directly by the gearbox.

So we can cut those threads up to the limit set by the gearbox; 56T.P.I, I think from memory.

We can not cut threads not listed on the gearbox’s settings plate, save only that if you use a 24 + 24T pinion pair you need set the gearbox to indicate twice the wanted t.p.i. (Hence the two ME threads need that 12T initial pinion to reach the 32 and 40 TPI.) This gives only the advantage of a more robust driving pinion; but does double the pitch of a fine-feed. You need adjust the banjo’s angular position for this change.

Now we come to the difficult bit.

Metric and other non-inch threads.

The Manual for fitting and operating these gearboxes devotes two pages to Diametral and Module pitches (for worms?) and BA threads. For these you need change all those wheels on that fixed-stud banjo to ones from an assortment of odd-count wheels indeed.

The next page covers Metric threads, and here we need change the banjo as well, for one with studs adjustable along slots; and as with the DP, Module and BA threads set the gearbox controls to positions not TPI numbers.

Now, the book tabulates all the requisite intermediate change-wheels, the appropriate banjo, and the control settings, for the ML7 and ML Super 7 lathes, but it’s not easy.

Indeed, you may well wonder why even fit one of these gearboxes if you intend to cut many non-inch threads, because that still needs swapping gears around!

(For BA and smaller metric pitches, a die may be more appropriate anyway.)

The only way you can use one of these inch-pitch gearboxes with its own standard input banjo to cut metric threads, seems to be replace the 12+24T driving pinion with one calculated to change the entire ratio downstream of it. This is based on the fact that swapping from 12 to 24t pinions means you need select the twice-TPI count; so for mm threads the swap is to some other number.

These two gears are cut on a single piece of steel, so the replacement without replacing any other components would be a 12 or 24T wheel paired with the appropriate translation wheel of modest tooth count (in range 16 – 40t perhaps?), the two keyed together; and the mesh set by rotating the entire banjo.

I have not investigated this on my own lathe.

Macolm –

How the thread is described does not matter. You can define any thread by both turns-per-unit and pitch.

The difficulty is firstly, that the two systems of measurements are not compatible.

Secondly, the Myford lathe has an inch-based leadscrew (8TPI or 0.125″pitch) and the gearbox gives threads based only on the various inch-based series. So with its supplied input gears it can not cut BA threads (millimetric, geometrical progression), ISO pitches (millimetric, no numerical progression!) and worms (inch or mm, circular pitches).

You can cut a good range of standard metric threads to close accuracy on a Myford lathe using the standard change-wheels (without gearbox). The tables in the lathe manual and on a plate inside the cover, tell you which. Myford also stocks a 127T wheel to improve this selection. You might also be able to cut worms, selecting the change-wheels by pitch rather than TPI ratios.

So what Phil – and I and any other ML7 owner asking – need know is:

– can we select the primary-drive pinion between the spindle and the gearbox, to alter the entire gearbox ratio to give the wanted mm-pitch.

– and by using the existing banjo, which may or may not depend on which pattern of gearbox.

Phil, here are some more links to forum posts relating to the Myford Mk2 gearbox and metric threads,  you have only one gear to change and select the correct gearbox setting,  I use this method and it works well for all practical purposes.

You can see there are some very minor pitch errors so if you happen to need “perfect” thread pitches then you need to use the Myford metric conversion kit with a special slotted quadrant.

https://www.model-engineer.co.uk/forums/topic/myford-33t-and-34t-gears-for-metric-threads/

https://www.model-engineer.co.uk/forums/topic/myford-metric-lathe-leadscrew/

https://www.model-engineer.co.uk/forums/topic/availability-of-a-t33-t34-myford-change-gears/page/2/

Phot from another post showing the only gear you need to change when using the table in the move posts or in peak4’s post — hope this helps John

Peak4, JohnF –

Thankyou very much.

I’ll have a look on my ML7.

Myford’s own manual for the gearbox does not even mention this possibility!