ML7 Leadscrew Handwheel Bafflement

[Nigel Graham 2Participant @nigelgraham2]

I have a fitted and a spare, hand-wheels for my ML7's 8TPI lead-screw, although to be honest I don't use it very often.

'

Wheel 1

Graduated 0 = 125 in 10s then 5.

One revolution moves the carriage 1/8" = 0.125".

So one minor graduation = 0.125 / 125 = 0.001.

So far so good. The engraving is even deep enough to be filled for contrast.

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Wheel 2

(That presently fitted) 0 = 160, all in 10s.

I've not right good at sums but trying to work out what those are supposed to be, gives strange answers.

I thought first, "direct" equivalents for binary fractions. 20 on the scale gives 1/64", but still demands quite a lot of arithmetic for such use. For that I'd rather have a scale divided into just 8, numbered by the vulgar fractions, not tens.

Using the same arithmetic:

0.125 / 160 = 0.000781

Eh?

A thought….

Does anyone know the lead on a metric Myford lathe? The nearest to 1/8" is 3mm but 3mm / 160 gives 0.019mm per minor division. ( 0.02mm steps would need 150 divisions.)

So meaningless for 3mm lead, but 4mm lead gives one mark = 0.025mm.

So is this hand-wheel really for a metric lead-screw of 4mm lead?

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Why two wheels, one with strange graduations?

I had bought a hand-wheel only to find some while later, that it would not fit as the driving slot was too far off-centre; so I failed to spot this strange scale The kind lady on the Myford stand at one of the shows replaced it with the true Imperial-scale one, but didn't keep the faulty one.

Subsequently, when fitting a screw-cutting gearbox, I made a new lead-screw, from ACME bar-stock, to preserve the original screw lest it is needed again. I gave the new screw a slightly over-size metric roll-pin for the hand-wheel: lots in stock, and I could enlarge and partially centre the faulty hand-wheel's off-centre slot to suit.

The other would need the pin changing.

[Nigel Graham 2Participant @nigelgraham2]

[JasonBModerator @jasonb]

Makes it very close to 0.02mm (0.0198) per division for an approx metric read out on an imperial screw

[egaParticipant @ega]

Posted by Nigel Graham 2 on 13/07/2022 09:56:06:

I have a fitted and a spare, hand-wheels for my ML7's 8TPI lead-screw, although to be honest I don't use it very often.

I use mine all the time – an advantage of the standard length bed.

[Nigel Graham 2Participant @nigelgraham2]

Jason –

Thank you for that tip. I'd not spotted that. Obviously it gives a cumulative error but useful over quite long short distances. (1.98mm short of 100mm)

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EGA –

Not sure why the bed length matters – the lead-screw is of constant pitch however long.

I tend to work to a rule mark with the top-slide for fine adjustment, instead; or for short distances, make an initial top-slide cut. For both starts, then using the manual rack or the self-acting, feed to that mark.

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When fitting the gear-box, I arranged for moving the lead-screws' driving pinion out of mesh, to facilitate using the hand-wheel by avoiding dragging all that extra machinery round with it. Although I have not gone that step further I did allow for fitting the pinion with a proper control, better than faffing with Allen keys.

I have though also pondered making an equivalent hand-wheel for my Harrison L5, and on that, it might be possible to arrange driving the powered cross-feed for generating tapers longer than the top-slide can give. This is to exploit the lead-screw and feed-shaft being geared together, with only one axis or neither engaged; but I don't if it would work..

[HopperParticipant @hopper]

Posted by Nigel Graham 2 on 13/07/2022 11:59:05:

EGA –

Not sure why the bed length matters – the lead-screw is of constant pitch however long.

You need arms like a gibbon to reach the handle on a long bed.

[SandgrounderParticipant @sandgrounder]

Does anyone know the lead on a metric Myford lathe? The nearest to 1/8" is 3mm but 3mm / 160 gives 0.019mm per minor division. ( 0.02mm steps would need 150 divisions.)

They've certainly made a ML7 bed with metric lead-screw and calibrated hand wheel, I have one with a 3mm pitch screw and handwheel, it was bought from them about 30 years ago by the company I worked for use as an optical bench, I bought it from them when it was no longer needed, it was a 1-off special so I've no idea what is currently available.

John

This is the link to a post of mine on here,

https://www.model-engineer.co.uk/wp-content/uploads/sites/4/images/member_albums/152997/650608.jpg

[V8EngParticipant @v8eng]

I think Myford currently list spare imperial and metric hand wheels for the ML7 you could check for matches to yours.

[JasonBModerator @jasonb]

The current metric handwheel for the 3mm pich screw has 150div of 0.02 and numbered 0 – 3mm

Error of he 160 div is not 1.98/100mm its

Handwheel reading 160 x 0.02mm per turn =3.2mm so 31.25turns would be 100mm.

Actual is 31.25 turns of 3.175mm = 99.219mm

Therefor error of 0.781mm per 100mm

[Howard LewisParticipant @howardlewis46836]

If your lathe has a 8 tpi Leadscrew, ,presumably the other Leadscrews and handwheels are also Imperial.

The rest of the machine will be Imperial.

So, when using an Imperial machine, why saddle yourself with using a calculator to work in metric, rather than directly in Imperial units?

Since you have a Handwheel with 125 divisions, use that and consign the one with 160 divisions to "Come in handy, one day" box.

Howard

[egaParticipant @ega]

Posted by Hopper on 13/07/2022 12:04:18:

Posted by Nigel Graham 2 on 13/07/2022 11:59:05:

EGA –

Not sure why the bed length matters – the lead-screw is of constant pitch however long.

You need arms like a gibbon to reach the handle on a long bed.

That was precisely what I had in mind.

Incidentally, I missed the hand wheel when using my Willson and contrived a hand wheel from an old pulley:

This has the added advantage that when the leadscrew is engaged that fact and the direction of rotation are apparent (as standard the lead and feed screws are hidden by the cover seen in the photo).

A refinement, of course, would be a re-settable dial.

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