Myford ML10 spindle crank trouble

My old Myford ML10 is quite long in the tooth, holding tolerances that are just the other side of 'intolerant'. But having nothing better at the moment and being loathe to part with the amount of money for a worthwhile replacement I continue to use the lathe for what it will do... adding to the tooling along the way.

I have the extended set of gears for metric threads, but on this old girl when cutting metric threads one must engage the half nuts on the leadscrew, not releasing them until the threading operation is finished. Therefore, on fussy little parts (or when turning up to a shoulder), it is better to use a hand crank for precise control.

Having no spindle crank, I finally decided to get around to making one. The design I'm using is to be found online at 'Instructables Workshop', created by qthurtle. The photos and design plans of same are to be found at this link: ML10 Lathe Spindle Handle

Well, the project was coming along swimmingly, although the threading of the end for the 12mm nut was a bit of a fuss. I mean, I didn't have the lathe spindle handle that would have made my life easier here, so I ended up grabbing and turning the chuck back and forth by hand (like a rat on a treadmill) for every pass (ouch!).

Here is the finished shaft of the spindle crank, just ready for slitting...

...and I was just about to do that when I had a sudden inspiration to try slipping the finished shaft into the rear end of the main spindle for a test fit. And that's when it hit me...

... It wouldn't work!!

The reason should be obvious from the photo below.

The ML10 does not enjoy a built-in tumble reverse arrangement like the larger lathes made by Myford. As such, the gears on the banjo engage the spindle gear directly and - as should be obvious - in those configurations where the outboard driver gear on the first group is larger than the driven gear of that same group, the teeth of that driver gear can intrude into the space of the spindle through hole. This is almost never the case with the gear arrangements for cutting imperial threads, but for metric... OH BOY!

What you see in the photo above is the first stage gear arrangement for cutting the 1.75 mm stepping for a 12mm thread. The 25-tooth gear on the main spindle drives a 50-tooth gear which is paired with a 63-tooth gear to drive the next group. That 63-tooth gear intrudes almost 2mm into the spindle shaft opening... exactly where the shaft of that spindle crank would be.

Fully 21 out of the possible 27 metric threading gear arrangements for the ML10 use exactly that same 50/63 gear group on the first stage. Like, OUCH!!!

What this means is that the spindle crank as designed won't work for cutting metric threads. Why nobody has ever seen or mentioned this before is beyond me.

However, I have already hit on a solution.

In this photo you can see the alteration to the basic spindle shaft design. I turned a very small 45° shoulder to serve to locate and stop the shaft of the crank in the rear of the main lathe spindle. Behind that the shaft is turned down to a diameter of 12mm to allow it to clear the teeth of that 63-tooth driver gear.

And here a snapshot of the altered crank design in position. It clears that 63-tooth gear quite nicely.

The only other problem is that when using metric threading arrangements with this crank design one must (A) first insert the spindle crank and lock it in place and only then (B) engage the gear train on the banjo and lock it into position. Because of this it will be impossible to have the protective gear cover in place. I don't see this as a major safety issue since the lathe will never be plugged in and under motor power when using the spindle crank.

I'll report further on this when the project is finished. If anyone is interested I can post a measured drawing of the altered spindle.

Does it matter if the 63T gear is meshed further down the train? If NO, move it and fit the Mandrel Handle as originally intended.

But Good on yer for making a mandrel Handle. A useful accessory. Save a lot of broken tools when cutting upto a shoulder, as well as thread cutting!

Howard

Thanks for the suggestion. The Myford ML10 handbook doesn't seem to imply that the gears can be switched around on the banjo. However, it... might... be possible for some of the pitches. Guess I would have to play around with it and see.

On some lathes, the 63T can be placed further down the train.

Brian Woods Book on "Gearing Lathes for Screwcutting" suggests some set ups for Metric threads, using a 63T gear, A lot for the mini lathe with a 16 tpi Leadscew do start with a 63T as the first driver, after the tumbler reverse, which your ML10 lacks ) Table 1, for the ML7 WITH A GEARBOX, gives the various changewheel set ups, for Metric pitches with a 8 tpi Leadscrew, without using a 63T gear.

Martin Cleeve's book"Screwcutting in the Lathe" ( Workshop Practice Series No. 3 ) on Page 54 gives tables for Metric pitches on a lathe with an 8 tpi Leadfscrew, using gears 20-20-75, incrementing in fives, plus one 38T, which may be of help.

Howard

If I may just add a word.

It is often helpful to get large diameter wheels as low down in the gear train as space to fit them permits. That allows room to get the smaller toothed wheels in position early on where the space for fitting is a bit more limited.

The gearing calculation doesn't make any distinction as to where in the calculation the numbers are used, just as long as they divide or multiply as required.

Regards Brian

That suggestion to place the larger gears further on down the train sounded so good to me, but...

...sadly, this doesn't work on the ML10. The quadrant just isn't long enough to accommodate the gears if the ordering is changed.

Elegant solution to a knotty problem there by necking down the spindle.

I would not worry about exposed gears etc either. Of far greater danger is the crank handle spinning around if it is left in situ and the lathe motor started up. And the guard makes no difference to that. I have seen some lathes in industry with a solid handwheel or disc used in place of the hand crank which is quite nice to use and can be left in situ while the lathe is run under power. I've been meaning to make one for my Myford for years. One day...

Ignatz,

Myford published metric gearing tables for the ML7 and later derivatives such as the Super 7 which avoided the use of a 63 tooth translation gear; they used 21 tooth gears instead. I thought you owned one at one time.

You can download that information ( I am not clever enough to find and add a link to get you there quickly) but that is another route you may care to explore.

Your stepped spindle is elegant but as you have pointed out, there is a fiddle-faddle involved in fitting things in the right order

Regards Brian

Bravo.

Hi Don't know if its possible, but if your ML10 is on raising blocks you could fit a 127T gear on the leadscrew and save all the 63 - 63 etc set up I'll try find the chart I had and add it here.

There could still be a problem with the space needed to get a pukka translation gear of 127 teeth in place on the leadscrew, it is only a shade under 6.5 inches in diameter.

Brian.

Martin Cleeve got round this problem by using a 127 of 30DP: see page 44 of WPS3.

Just found this pic of an ML10 fitted with a reversing tumbler that moves the gears right out of the way of the main spindle. No idea if it is a Myford accessory or aftermarket. It looks to be a professional casting rather than home shopmade. Has the name Noble cast into it. But the principle is simple and could be easily replicated out of a piece of aluminium flat plate about 20mm thick or so and maybe using ML7 tumbler gears?

PS

Might have known. Previous ME forum thread with drawings etc on the very topic https://www.model-engineer.co.uk/forums/postings.asp?th=109904

Edited By Hopper on 30/09/2019 11:43:41

Wow! That is a nice looking add-on.

Might be a future project (?)

In the short term I'm going to finish up my spindle crank.

Just finished up the spindle crank.

This is going to make threading work on the lathe a whole lot easier for me.

I use a similar crank on my Speed 10 lathe and find I use it for almost all the threads I cut. Even at the low speeds obtained with the crank, carbide threading inserts work very well. It is a good idea to switch the lathe off at the mains when using the crank in case you accidentally turn the machine on with the crank still in place (yes I have done it but fortunately I use a three phase inverter with a ramped start speed and my quick reactions ! )

Doug

Edited By Douglas Johnston on 05/10/2019 15:36:58