Myford gearbox and leadscrew

[Adam HarrisParticipant @adamharris13683]

I have come across a knackered early Myford Super7 with a functioning quick change gearbox (the later version where the leadscrew goes through the whole gearbox to the changewheel side) but the leadscrew itself has a badly worn thread where the carriage is busy. Of course I fancy putting this gearbox onto my nice Super 7 and wonder if I can adapt my existing nice leadscrew to use with this gearbox. Is it an impossible, difficult , or straightforward job (requiring just a long keyway cut?)? Any advice would be very much appreciated. Thanks, Adam

Edited By Adam Harris on 09/03/2014 12:58:58

[Adam HarrisParticipant @adamharris13683]

Leadscrew for Myford Quck Change Gearbox

[John Stevenson 1Participant @johnstevenson1]

Cut the worn leadscrew off just past the gear box.

Cut your screw off to match the part cut off and then join the two with a sleeve and two brass pins about 3/32" or 2.5 mm diameter to act as shear pins.

Like this.

With a bit of luck this will save your tufnol tumbler gears in the even of a crash.

The early ML7's had this arrangement and i don't know why it was dropped on later designs ?

Perhaps to help the sale of tumbler gears ?

[Andrew Moyes 1Participant @andrewmoyes1]

The Super 7 has a 3/4" leadscrew which is the same diameter as the hole through the gearbox. No need to fit a sleeve as shown on John's ML7 photo

The arrangement for the ML7 is different and the reason for the sleeve is to join the 5/8" diameter ML7 leadscrew to the 3/4" shaft in the gearbox. It would be worthwhile reading the Myford instructions for fitting a gearbox and I think you will find them on the Myford Yahoo Group, which is worth joining.

Andrew M

[Adam HarrisParticipant @adamharris13683]

Hi John, thanks for a quick reply and a simple and very elegant solution! Makes me feel rather foolish…Many thanks, Adam. Should I assume that the internal gear wheels of the gearbox are likewise knackered despiote working or are the gears made of harder wearing material than the leadscrew?

[Adam HarrisParticipant @adamharris13683]

Thanks Andrew – so you would advise it is possible to use the standard leadscrew (with simply keyways cut to take the internal gears and the external wide 72T gear)? Adam

[Andrew Moyes 1Participant @andrewmoyes1]

PS

I've just checked the Myford Yahoo site for the gearbox installation instructions and they are under 'Files' s7gbox2.pdf

Andrew M

[Adam HarrisParticipant @adamharris13683]

Sorry Andrew I see that the fat 72T external gear sits on a different shaft altogether!

[Andrew Moyes 1Participant @andrewmoyes1]

Posted by Adam Harris on 09/03/2014 13:25:09:

Thanks Andrew – so you would advise it is possible to use the standard leadscrew (with simply keyways cut to take the internal gears and the external wide 72T gear)? Adam

Yes, use the standard leadscrew but you will need to shorten it as per instructions. No need to cut a keyway and there are no internal keys on this shaft; it passes straight through the gearbox to pick up on the external gear on the left.

Andrew M

[Adam HarrisParticipant @adamharris13683]

Thar is great Andrew, I have found that file with a google search without being a yahoo mail member and am reading it now. Many thanks, Adam

[Brian WoodParticipant @brianwood45127]

Hello Adam,

I just wonder if John Stevenson's suggestion is still less effort than fitting your leadscrew through the box to replace what is currently fitted. The gears in the box should be hardened, only the early ML7 gearboxes had soft gears and in any case it isn't difficult to establish what you will have.

The outer gears meshing to the leadscrew are 26 T from the gearbox layshaft and 52 T on the leadscrew to provide the final step-down ratio for the box to deliver what it is built for.

Enjoy the freedom it brings

Brian

[Adam HarrisParticipant @adamharris13683]

Hi Brian, Thanks for your input. The file Andrew directed to me (a pdf of the installation and operation manual for the quick change gearbox) lays out the instructions clearly and it is very simple to use my existing leadscrew and just shorten it a bit. Adam

[Brian WoodParticipant @brianwood45127]

Hello Adam,

You will learn more about the gearbox construction that way.

When you come to fit the gearbox to your own lathe, may I suggest one minor modification that will help future servicing of the lathe immeasurably? The upper mounting face covers one of the headstock alignment adjusting screws completely, the one nearer the chuck end is still accessible. If I had the choice I would make an access hole through the gearbox to flange so that it remains accessible after fitting.

And, for my own assistance, would it be too much trouble to ask you to make the centre to centre distance of those adjusters available to help me do an in-situ access on my own gearbox? It came with the lathe as a factory fit.

I've also sent you a PM on a related matter.

Regards

Brian

[Adam HarrisParticipant @adamharris13683]

Hi Brian, am away from the workshop until next week, but will let you know next week about the distance. Thanks for your advice and help. Adam

[Brian WoodParticipant @brianwood45127]

Hello Adam,

Thank you, it will be very helpful

Brian

Edited By Brian Wood on 12/03/2014 10:33:48

[Adam HarrisParticipant @adamharris13683]

Thanks

Edited By Adam Harris on 12/03/2014 10:35:47

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