I might be able to help here. The early gearboxes were fed by a 12 tooth driver; the gearbox itself had a small side outrigger box on the tailstock side that provided the reduction drive to the leadscrew.

Those that were build later than serial no 2501, incorporating the through leadscrew, have a 1:2 reduction gear (26 drives 52) slim gear set just behind the gearbox proper. The 26T gear is hardened, the other equally slim gear is not. The arrangement for this gearbox and its working is shown and described in my book. At the time of writing that I was not aware of the difference in the drive arrangements in the early gearbox

Last but by no means least, the later gearbox is driven by the the more familiar 24T driver, hence the need for the reduction gears.

There was a long post exchange in the old forum pages started by Simon Williams who has the earlier machine. He was struggling to understand why he was getting half pitch threads using my book as the guide.

I hope this brief description helps

Brian

Well done Michael, I don’t think I would have been able to retrieve that.

It is that conversation and shows the side gearbox well, I didn’t trawl through it all as I have things I must do today, much as I would like to see where this goes now.

Brian

Hi all, thanks Brian for the acknowledgement.  There is the whole nine yards on this topic buried in the old archive but I’m not sure I know how to access it.

For the time being the salient points are that yes there is an older version of the Myford manufactured quick change gearbox which runs at half the speed of the later one.  This means that the Myford metric kit will fit onto the banjo but won’t give the results you’re expecting.  The banjo in question is not the same one as the normal one driving the QCGB with fixed centres, you have to take that off and substitute the slotted one which comes with the metric kit.

To make matters worse there are two metric kits; both of them are intended to operate the newer double speed QCGB not the older half speed GB.  I believe the associated banjo is common to both kits but one kit has one less gear than the other, though it seems to achieve the same results.

The older gearbox uses a 39/12 all in one compound gear as the input to the gear train whereas the newer one uses a 30/24 gear pair, the 24 gear is removeable and can be changed to other counts to give other TPI figures outside the published table.  Brian has written the definitive analysis of this and I recommend his book “Gearing of Lathes for Screw Cutting” which gives chapter and verse, albeit only in respect of the (much commoner) newer version of the QCGB.

I think it would be helpful if we could find the two or three threads where we have rehearsed this subject in the old forum.  I’m out for the afternoon but I’ll see if I can find the details this evening.

Last but not least if it is the older QCGB you have don’t go buying the 33 and 34 tooth change wheels which permit metric threads to be cut with the QCGB but only with the later version. They don’t fit on the banjo of the older gearbox so you can’t use them.   If we can establish beyond all doubt that the GB is the old one I have a set of the 30/17 and the 29/16 gears which are the correct metric adaptors in stock you can have for a moderate contribution to charity.  I’m not sure you can ping me a PM any longer, but we’ll fathom something out via the classifieds.

Hopefully more will follow later.  In the meanwhile the answer to the original question is that you can buy and fit the Myford metric conversion kit, but it won’t give the results you are expecting.

Rgds Simon

This is another one
Myford 33t and 34t gears for metric threads

Bill

On 7 June 2024 at 18:41 Brian Wood Said:

Peak4,

Sorry to point this out but Simon above has said that these gears will only work with the later versions of the gearbox. He has made the necessary gear pairs that suit the early gearbox, having done the work developing them in association with the late John Stevenson

I remember the exchanges back and forth to resolve the impossible 1/2 gear that is what the calculations suggested.

Regards  Brian

Edit  Michael G has very helpfully resurrected all that old thread material from the original forum some way back in this thread

Appreciate that Brian, but something odd has happened with my post(s). I put up links to several previous threads, at an earlier time, which have vanished from the post above.
I edited it a couple of times, added some words and links, which have now all vanished.
My intention was to pull several Myford gearbox metric thread posts all onto this topic, so if someone went looking again in the future, with different queries, they might come across them all in one place.
My bookmarks were to the old forum posts, so took a while to resolve the new locations via archive.org; no idea where it all went.

Bill

Re creating a ‘definitive’ thread on any subject on the web or even on this site is a forlorn hope – many pages and even sites disappear within months – the archive built up on the precursor to this site was wantonly thrown away – even now I find many images etc appear as 404 errors.

Bill

Further to Brian’s post:

I make no ‘pledge’ [what a topical word!] of success … but I’m happy to work with you on this, to the extent that I am able.

If you send me your archived bookmarks on the subject, let’s see whether another pair of eyes is any help.

MichaelG.

Brian

Fitting 33t/34t gears to a Big Bore Myford, I should provide a photograph of the problem but I lack the time and it is not on my list of priorities or even problems that may occur in the foreseeable future.

One day?

JA

(edit) Fitting an ELS. I am interested in the idea but I no longer have the time.

On 8 June 2024 at 09:56 Michael Gilligan Said:

Bill

Further to Brian’s post:

I make no ‘pledge’ [what a topical word!] of success … but I’m happy to work with you on this, to the extent that I am able.

If you send me your archived bookmarks on the subject, let’s see whether another pair of eyes is any help.

MichaelG.

Cheers, but I think I resolved the links I had bookmarked, some of which have now appeared on this thread anyway.
The others are probably not that relevant, though they themselves contained old links which are, but have now been updated here.
Essentially I just used archive.org on the old link, to see what actual thread it opened up, as it wasn’t always obvious from the title. I could then search for that thread on the new forum, either directly or via Google.
The difficulty is that when I click on an old link, the current forum auto forwards it to a 404 page, but the back button does not show the old link, pre-forwarding.
Hence needing to dive into the saved bookmarks folder.
It’s the vagaries of different browsers, I use opera, where I have the bookmarks stored, but there is no easy way to see the URL behind the bookmark title.
Backing up the Opera bookmarks folder (in HTML), and opening it in Pale Moon, allows me to, see & copy, the actual stored URL to plug into Archive.org.

Fiddly, but it works OK.

Bill