Help with Myford metric gear setup

[john beattieParticipant @johnbeattie99677]

Hello

I’ve just joined your forum as I have a small problem and need some help.
I have a Myford ML7 with gear box (imperial machine) and have just bought the metric conversion gear set with quadrant. No 1481/1
I installed the 60T/63T and the 50T/45T as the diagram shows and put a 60T on the leadscrew.
The thread I was wanting to cut was a 1.0 pitch. The gearbox manual says to put the 30T on the tumbler the selector on 6 and the lever on A but this gave me a 2.0 pitch.
I also have a metric chart inside the gear cover on the lathe which is different to the on in the book Following this chart I put the 40T on the tumbler set the selector to 1 and the lever to B but again got a 2.0 pitch thread.

I'm not sure how to attach photos of the charts but I'm sure everyone is familiar with them

The chart in the lathe cover has two sides one for using the 60T left side the other for using the 30T right side. Looking down the right hand side using the 40T 60T 1 B would be correct if using the 30T on the leadscrew but I’m using the 60T.
Am I missing something and put this together wrong ?

The only thing I’m thinking may be wrong is the gear set I bought was advertised for a Super 7 not the ML7 but as far as I know it should be fine. Or does it have something to do with the two small gears on the reverse lever being different on the Super 7 ?
Any help would be much appreciated.
Thank you
John

[john beattieParticipant @johnbeattie99677]

[DC31kParticipant @dc31k]

Someone will be along soon to advise the exact answer, but with a bit of thinking you might be able to solve the problem yourself.

For imperial threads, the numbered selector changes the tpi and the ABC lever multiplies or divides those tpi by a factor of 2 (if you take B as the starting position).

Since your required 1mm thread is coming out as 2mm, you need to do something to the ABC lever that would increase the tpi of an imperial thread by a factor of 2.

There are only three possible positions for the ABC lever and you have posted what happens in one of those for two cases. Try the other two positions in each case and report your findings. If it does not solve the problem, it is data that will contribute to solving it.

Having a problem that is exactly twice what it should be is easy to solve. Think how lucky you are that the thread did not come out as 1.87mm pitch – that really would require some thinking.

To save wasting metal, tie a marker pen to the toolpost with an elastic band and use that to draw on the stock as it rotates.

[Simon Williams 3Participant @simonwilliams3]

Can we have a picture of the right hand end of the QCGB please. Also a second pic' of the gear train between the spindle and the broad 72 T input gear to the gearbox.

There is a possibility that you have the old Mk1 gearbox which runs at half the speed of the Mk2. This would give you the fault (double the pitch) you describe. It is recognisable by the shape of the die cast cover over the right hand end of the g'box where the leadscrew comes out.

If it is the case that the old gearbox is confusing things there is plenty of previous to help herein, but to save starting that hare running unnecessarily let's check what we've got first. We can catalogue some links to the relevant info once we know which g'box you've got.

You'll need the instructions to put pic's as jpg's up. Essentially you initialise an album, then upload pic's to the album. Now you can call them into your post on the forum. There is a sticky post with detailed instructions, somebody please add a link cos' I can't find it just now.

More anon Simon

[john beattieParticipant @johnbeattie99677]

Thank for your reply.

40-60 1A gives me 4.0 pitch

40-60 1 B gives me 2.0 pitch

40-60 1 C gives me 1.0 pitch

The chart in the lathe cover says

40-60 1 A should give me 2.0 pitch or 4.0 pitch if 40-30 1 A

40-60 1 B should give me 1.0 pitch or 2.0 pitch if 30-40 1 B

40-60 1 C should give me .5 pitch or 1.0 pitch if 30-40 1 C

The chart in the gearbox manual only give one pitch using the 40-60 1 A which it says 2.0 pitch other pitches you need to either change the 40T or move the selector higher than 3 for example 40-30 1A gives 4.0 pitch or 40-60 4 A gives 1.60 pitch

I know I can get the pitch I'm looking for I just wanted to know why my machine doesn't match up with the charts

I'm guessing if I replaced the 60T on the leadscrew with a 120T it would half the speed and things would match. If no one comes up with the answer I may just draw up my own charts.

I know what your saying about it being lucky it's just half or double. if it had been anything more than that it would have been a die nut.

Thank you for your input.

[Howard LewisParticipant @howardlewis46836]

Cou;ld you run 20:60 instead of 40:60? If you could, the chart on the cover would then deliver the pitches that you want, with the A – B – C settings as per the chart.

As already suggested, it might be that you have a Mk1 gearbox, so what you seek is half of what the set up delivers.

Howard

[john beattieParticipant @johnbeattie99677]

Thanks guys I will take some photos tomorrow and look to get them posted up then you can see what I have.

John

[john beattieParticipant @johnbeattie99677]

Here are some photos. I found a serial number on the back of the bed but can't see one on the gearbox as the Myford manual shows. The manual I got with the lathe has the same number on the front in biro along with two other numbers K25915 and R9960 maybe one of these is for the gearbox ?

I took a photo of both the imperial and metric gear set up just to make sure I have it correct, the two small gears on the 60T leadscrew are just used for spacers.

Have a good weekend

John

[Simon Williams 3Participant @simonwilliams3]

OK, and congratulations for figuring out the niceties of the routine for uploading photos.

The last but one of your photo's shows the cover plate of the older Mk1 gearbox. The newer Mk 2 gearbox also has a cover, but it has a 2:1 step down gear pair hidden behind it. The import of this is that Myford decided to run the internals of the gearbox at twice the speed of the original design. I would imagine this was a ruse to reduce the torque transmitted by the gears as at that stage of its development the internal gears of the QCGB weren't hardened. Eventually Myford built these gearboxes with hardened gears inside, but that's another story.

Further evidence of this being the old Mk1 slow speed gearbox is in photo 3, which shows that the mandrel gear is 12 teeth. This gear is 24 teeth when driving the Mk2 g'box. I'm assuming that the set-up with the two 51/17 gears between the mandrel and the broad 72 T g'box input gear cuts TPI's as detailed on the g'box top label – i.e. the imperial settings all work out, it's just the metric conversion kit which has screwed things up.

Unfortunately it seems that Myford only ever made a metric kit for the Mk2 g'box, though there were undoubtedly two versions of this kit and so there are two different label diagrams with the accompanying table of gears to use. This appears to have been a cost cutting exercise – that later kit has one less gear in it. AFAIK you can use the banjo with either selection of gears.

If you can fathom out a way of reducing the input speed of the g'box by half I think you will have solved the problem you have encountered with cutting threads of twice the pitch expected. A 120T gear on the leadscrew would do it, but I'm not sure it'll fit in the space available.

There is another solution, for which you don't need the metric kit at all, just a different gear mounted on the mandrel. This is the subject of a whole slew of correspondence on the forum, and if you would like to read up on it this is a good place to start. There is some more related stuff here where the OP was trying to cut imperial threads and finding he was cutting an apparently arbitrary TPI.

If you decide you want to experiment with the idea of changing the tooth count of the mandrel gear let me know, but DON'T buy the 33T and a 34T gears mentioned in the posts I have tagged, they are no use to you and will give you the same problem you presently have. I will explain further in due course though the details are in the threads referenced above.

Hope this helps, in due course do please let us know how you get on.

Best rgds Simon

P.S. This is also relevant, more of the same.

edited for post script

Edited By Simon Williams 3 on 09/09/2023 14:26:05

[Simon Williams 3Participant @simonwilliams3]

My bad, but I ought to not let it pass into archive.

My last post (para 3) refers to the reversible gear pair of the "normal" drive train as a 51/17 pair. Afficionados of the art t will know this wrong, and the tooth count is 57:19.

My apologies.

Simon

[john beattieParticipant @johnbeattie99677]

Hi Simon and Many thanks for getting back. The sticky for uploading photos by Neil was a god send and easy to follow.

I forgot to add the gear sizes from the top in my last post they are 25T then the two on the revers lever are 20T Left and 18T right 25T-12T cluster then 57T-19T and reversible 19T-57T then to the 72T

I've not checked to see if the imperial side is fine but will give it a try and see what I get.

When I started looking into metric cutting I found some forum chat about the 33-34T gears but don't think I had the correct gears on the studs so went looking, it was at this point I found the metric set and thought that's a better way to go. using a 120T did cross my mind but wasn't sure if you could get one or if it would put the lathe under any unwanted stress and as you say may not fit. If i find one for sale that's not going to cost the earth I will give that a go but think for now I will draw up a new chart and work with that. I could just remember to set the gear for half what I want but brain not being as it use to be I need all the help I can get so a new chart will keep me straight.

Thank you to everyone who has chipped in with this your help has been much appreciated.

Take care

John

[noel shelleyParticipant @noelshelley55608]

Though no expert, on seeing the pictures The box does not look like mine which I knew was the later one, so it must be the ealier version with unhardened gears. I must also thank Simon for the long explanation, I had not realised that the later box had a 2:1 ratio in it . 51/17 sounds like the back gear ratio ? Though I have never tried to use it I do have a 127T change wheel for metric threads, came in a box of bits – not sure it would fit ? The cover would not close ! Noel

[john beattieParticipant @johnbeattie99677]

Hi Noel. Thanks for that, I'm guessing if the 127T won't allow for the door to close then the 120T isn't going to either, that said looking at the chart on the inside of my door I should be able to cut from 1.0 to 4.0 with the gears I have using the 30T side of the chart which will do me just fine as I can't see me ever needing to cut something smaller.

The main thing is I now know why the machine cuts twice the pitch when using the chart set out in the cover and that's what was bugging me not knowing if I'd set it up wrong and I now know the gearbox is a mk1 which is good to know.

Take care

John

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