My ford quick change gearbox

[DAVID WildboreParticipant @davidwildbore26734]

Can anyone advise what the difference is between the early qcg and the later qcg on the my ford lathe. The metric screw cutting kit I bought doesn't give the threads it is supposed to. My gearbox has the three external gears on the right and I have been told it has a different output ratio.

David

[DAVID WildboreParticipant @davidwildbore26734]

[Simon Williams 3Participant @simonwilliams3]

 

Later model QCG's have a 2:1 step down gear at the output. The earlier model doesn't so the input gear train steps the speed down externally to the g'box. This means that the mandrel gear is halved.

The gear boxes are superficially the same, the difference is under a cover on the RHS of the gearbox. On the newer g'box there is a pair of gears which reduce the output by 2:1, on the older gearbox there is still a pair of gears at the output but they are 1:1.

In terms of pictures there is quite a bit of history buried in the forum of one against the other

Here's one such:

https://www.model-engineer.co.uk/forums/postings.asp?th=125630

And another:

**LINK**

I know there is a much older article on this which is quoted in one of the links above but I haven't found the url link yet.

If this is the explanation for the problems you have been seeing, then you are probably cutting half the pitch you meant to. Would you like to describe what input gears you have set up on the banjo and what pitch you have actually found. We can then determine if the explanation fits the evidence.

HTH Simon

Edited By Simon Williams 3 on 10/01/2019 09:04:37

[Simon Williams 3Participant @simonwilliams3]

Here's another thread which contains some more direct comparison stuff :

**LINK**

This includes pictures of the label inside the gearbox cover which should (if the right cover is fitted!) explain the difference in set up.

HTH Simon

[Brian WoodParticipant @brianwood45127]

Hello David,

The necessary 1:2 reduction gearing was made at the start of the gear chain in the older gearboxes with a 12 tooth driver in the place of the 24 tooth version in the later gearboxes. The other changes made with the newer gearboxes were to incorporate hardened dog clutches and gears; those in your gearbox will be unhardened.

I don't agree with Simon though, without that reduction I would expect you to be cutting threads of twice the pitch, eg coarser

You could perhaps compensate on your set up by deliberately setting the gearbox to cut half the pitch you intend. Before cutting metal though, I would do a practice run with a Sharpie marker instead of the cutting tool to see if the outcome is what it should be

I hope this helps you make progress

Regards

Brian

Edited By Brian Wood on 10/01/2019 09:48:59

[JasonBModerator @jasonb]

Depends on the drive train if using a 12T driver into the box with the reduction gear you would get the finer threads.

David has not actually said what he is getting compared to what is selected so don't know if fine or coarse

As Simon said what is the full gear train you are using and what is the pitch being produced from your chosen pitch?

Edited By JasonB on 10/01/2019 09:53:06

[Simon Williams 3Participant @simonwilliams3]

Thank you Brian, I don't disagree with you though I couldn't decide whether to expect twice or half the intended pitch on the basis of what we know so far. Hopefully it'll be one or the other, in which case we know why it's doing it and how to fix it.

David we also need to know what TPI setting the gearbox is set for as well as the gear train tooth counts and the pitch actually being cut on the workpiece.

Best rgds to all Simon

[DAVID WildboreParticipant @davidwildbore26734]

Many thanks Brian and Simon. The setup on the chart for 1mm pitch actually produces 2mm pitch. I'll set it up again and try halving the pitch on the gearbox.

Thanks agai

[DAVID WildboreParticipant @davidwildbore26734]

I have set it up again on the metric banjo with 30t on the stud, 60 and 63t on the 1st driven and driver, 45t and 50t on the second diver and driven and 60t on the gearbox input shaft. The box was set on position 6 and the selector on position A. This was supposed to cut. 1mm pitch thread but actually cut a 2mm pitch thread. I moved the selector to position b and it worked. It cut a perfect 1mm pitch thread. I can now work out the gearbox setting to cut other threads.

Is there a way I can change the external gears to give the 2:1 output?

David

[JasonBModerator @jasonb]

What gear have you got on the tumble, a 24T will be giving twice the pitch of a 12T

[DAVID WildboreParticipant @davidwildbore26734]

It’s the 30 tooth on the tumbler using the metric banjo but it’s a 12t on normal use

[Brian WoodParticipant @brianwood45127]

David,

You could swap the 50 T in the banjo for a 25, that would also do.

You might run into meshing clashes with 45 T gear fouling the collar adjacent to the final 60 T gear into the gearbox, in which case setting the gearbox up as I suggested earlier is I think the better alternative

Regards

Brian

[DAVID WildboreParticipant @davidwildbore26734]

Simon

Thank you for you kind help. I will try both methods tomorrow, I think each method may have it's merits dependant on pitch to cut.

I now feel very confident about cutting metric threads now thanks to you and Brian

My kindest regards and grateful thanks

David

[Simon Williams 3Participant @simonwilliams3]

Hi David, good evening and thank you for the warm feedback and news that we've been of help. It's always nice to close the circle.

While changing gears inside the gear train will give the 2:1 step down, it's not always straightforward to assemble something which will actually mesh correctly. Brian's last post alludes to this. I side-stepped this problem by making special gears for the input (mandrel) gear as below. The one shown is for use with the alternative method of achieving metric pitches – keeping the standard gear train of the QCGB and altering the input gear (mandrel gear) That's what the above correspondence threads to which I linked examine. I see no reason why you couldn't do a mix and match of both approaches, in which case the mandrel gear needs to be 15 tooth.

The gear cluster on the left is the standard Myford QCGB 30/12T mandrel gear which you will recognise, and the right hand one is an adaptation of the same idea with the same 30T one end and a 17T the other. So one with a 30T and 15T would look very similar.

To the best of my knowledge such a thing isn't commercially available. If you want to pursue the same idea send me a PM and we can discuss further.

Someone will point out – perfectly correctly (so it might as well be me) – that this is a complicated way of achieving a simple outcome, and it would be more straightforward to ditch the metric kit completely and go for the special input (mandrel) gear option, as per the threads above. If you had the later style gearbox that would be a no brainer, but with the older gearbox there are pro's and con's of both methods. If you want use your metric banjo as Mr Myford intended we can make this work by using a 30/15T cluster. Depends I guess how much resources you want to devote to being able to cut metric threads.

One thing further – Brian am I right in thinking the ML7 uses a different mandrel cluster from a S7? I've got an idea that the 30T gear is peculiar to the S7 but I might be imagining things. If so we just need to confirm from David that he is working on an S7.

Best rgds Simon

[JasonBModerator @jasonb]

So is the Myford chart that shows the metric banjo only intended for the later gearbox or was there one for the old box? Would not be too hard just to rewrite the chart to give what is available and just refer to that though you obviously won't get the very fine pitches but they are more likely to be cut with a die anyway.

Having a set of gears that are half the number of teeth shown on the chart would be the other alternative like the 15T shown

[DAVID WildboreParticipant @davidwildbore26734]

My lathe is an ml7. It would appear that the metric banjo is for the later gearbox as there is only the one chart.

My thoughts are that for now I'll experiment with the mandrel gear and the gearbox and produce a chart that I can rely on. I can cut gears easily enough and I can 3D print them to experiment with. I do need to cut finer threads for my telescope is M40 which is a 0.7 pitch thread which is my main reason for needing to cut metric threads.

Regards

David

[Brian WoodParticipant @brianwood45127]

Hello David and Simon,

Simon's alternative gear cluster will work just fine, being bespoke it will of course need making. Simon also raises an interesting but important point, the answer is I don't know for sure whether the large gears on the ML7 are cut for 25 T or 30 T. I have a feeling it is the smaller size.

David I think is the best to advise on that. My own lathe is an ML7R which has the S7 headstock with 30 tooth gearing through the tumblers

Hopefully this now clears a path for the way ahead for David, a good outcome

To answer Jason's question.The banjo for the gearbox is unchanged between the gearbox models, the first driver gear for the chain was of 12 teeth which then produced the pitch results that the gearbox was built for. The later boxes had a reduction gear [26/52] built in to drive the leadscrew which was brought right through the gearbox on the later design. For that arrangement, a 24 tooth driver was then the standard first gear in the chain outside the gearbox.

Regards Brian.

[JasonBModerator @jasonb]

Brian, I understand that but my query was did Myford not make a plate or publish a chart for metric threads with the early gearbox?

Looking a fig6 and fig7 of the gearbox instructions they show a 12T in fig7 (early) yet the chart in fig 6 uses the larger gears around the 30T sizes in place of the 24T which you say will only work on a late gearbox.

Edited By JasonB on 11/01/2019 08:51:34

[JasonBModerator @jasonb]

Further to above I see further down the instructions where they describe fitting the box they say to fit a 24T. So it would seem these instructions are for a later gearbox.

Anyone got instructions for an old style box which will hopefully show how to get metric pitches that match the plate/chart. Or had Myford not caught up with metric at the time of making the early boxes

[Simon Williams 3Participant @simonwilliams3]

Jason – good morning,

My series 1 gearbox has got this label inside the gear cover.

To the best of my knowledge this simply uses the same banjo as the (later) metric adaptor kit, but alters the selection of change wheels. I worked it out once long ago, and came to the conclusion that the gears shown on this table gave metric pitches as shown, so they allow for the 2:1 factor. I think!

Brian will maybe correct me if I'm wrong.

Much of this is examined in the links above to earlier threads, with John S's input 'cause he knew the history of how this developed.

I'd be interested to know if it is this early label in the cover on David's g'box, and we haven't bottomed out the issue of the size of the spindle gear on an ML7 and whether it is 30T or possibly 25T. My picture of a home brew mandrel cluster gear (the bronze one) assumes that the spindle gear driving the tumbler gears is 30T. But David seems to have a handle on the answer to his original question, so all of this is a bit academic. It's just nice to have these things sorted out and recorded in the archives.

Best rgds Simon

Edited for minor typo which had a disproportionate affect on the logic!

Edited By Simon Williams 3 on 11/01/2019 09:30:15

[JasonBModerator @jasonb]

That would seem to be David's better option to use the chart for his gearbox not the later chart combined with an early box.

Still won't give his 0.7mm pitch which is a bit odd for metric as 0.75 is the more commonly used fine pitch but should be able to work out a gear train which combined with the box ratios will give 0.7.

Easiest train looks to be the one for 0.35mm on the later chart which would come out at 0.7mm if using the 28T shown which is an easier gear to obtain and fit than a 14T and use the 0.35mm setting

[DAVID WildboreParticipant @davidwildbore26734]

Hi folks

I didn't have that chart in my machine when I purchased it Simon. I did however 3D print the 44 and 52 teeth gears and tried out the setup and table as shown. It worked perfectly with no issues so you are correct in assuming that the 2:1 ratio is taken into account. I purchased the gearbox data pack (£30 ouch) pointed to by one of the links above and "screw cutting in the lathe". I intend to continue my researches spurred on by the grateful help I have received on the forum. The 0.7 pitch was a typo and should have read 0.75 Jason but I shall try your setup and see if it produces the 0.7 pitch.

Thanks again guys

David

[Simon Williams 3Participant @simonwilliams3]

Hi David, good evening, I was wondering how you were getting on.

That seems like an excellent outcome, and many thanks for the update. It's good to know that the original question has been put to bed.

Best rgds Simon

[Brian WoodParticipant @brianwood45127]

Hello David,

Thank you for the feedback, it is always helpful to close the loops. Having the ability to print your gears will be a real help in experimenting.

I note you plan to continue with the research, presumably for other ratios, metric or otherwise. I would be happy to help if you feel you need it, send me a PM

Regards

Brian

[Antony PriceParticipant @antonyprice56876]

Hi David

I would another reference book along side “Screw cutting in the lathe” . For Christmas, I was given “The Gearing of lathes for Screwcutting “ (Crowood Metalworking Guides). It has two chapters “The Myford ML7 and Variants” and “The Myford ML7 with the David Machin Gearbox”. It has lots of detail and, in my opinion well worth the purchase price

Tony

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