Myford Gearbox and Metric/BA

Hello Thomas

I am most happy to do that. You need to send me a personal message (message member) and tell me what your email address is, then I can email you the spreadsheet as an attachment.

Norm

In 50 years of model engineering I have screw cut many types of thread but never a BA one. Apart from perhaps 0BA they are all too small to screw cut easily. I have made lots of male BA threaded parts of all lengths using good quality dies in a tailstock die holder. The main advantage of this is that a true profile thread is cut very quickly without resorting to complicated change wheel set-ups that at best only give a close approximation of the desired thread both in form and pitch. Same basic reasoning for any small metric thread (or imperial for that matter other than the pitch will be OK)

I am sure others have gone to the trouble of successfully screw cutting down 12 or 14 BA but life is too short to bother when the use of a dies produces an excellent result.

Eric

Norman, did you find you had to buy a slotted quadrant/banjo with moveable studs in order to create enough space in the train to accommodate the 34T gear when swappping the existing 24T for it? Or can you lengthen the bottom slot of the "Normal Quadrant" enough by milling it out, so that the 34 T can be squeezed in? Many thanks, Adam

Hello Adam,

Look in the digital issues for MEW 212 and 213. There is a two part article of mine that will give you the chance to fit mandrel drivers all the way up to 75T and open up a treasure trove of non standard pitches as a result.

The simple mod in MEW 212 replaces the standard clamp stud with a drop arm you can make in about 2-3 hours, it is really that easy.

If you want pdf versions of the 8 tables of pitches send me a PM.

Regards

Brian

Hi Adam

Just to be clear, this thread about swapping the tumbler gear refers to use with the Myford gearbox. You will not need to change the quadrant that supports the gears driving the gearbox. From the attached picture you can see the locknut at the bottom that secures it. With a 24T standard tumbler gear fitted and there is about 3/8" movement left in the slot. It seems that most people can fit the 34T tumbler and there is just enough slack in that slot to adjust for that largest gear. If there is not, then you can simply hand file a little more length to the slot.

I have had quite a few enquiries for my spreadsheet so this tumbler gear swap, to quickly obtain Metric and BA threads from the Imperial gearbox, is still popular.

Best wishes

Norm

Hi Norm, that is very odd. I have the same standard setup with the 24T tumbler stud gear and the slot is fully used up as it is with no residual length available at all.I have never changed the standard gearbox setup gears and believe the previous owner since 1972 never changed it either. It is a Mk1 Super 7 if that makes any difference. I do think your 2nd stud may be set a bit lower than mine and looking at your photo , extrapolation from the slot to the 1st stud does not appear to be a straight line edge to the casting unlike as seen in the diagram on page 3 of the manual (publication 712E).... Adam

I'm sorry that I cannot offer much more help. The only clue is that other people also seem to get the 34T gear to fit and slot space runs out around 35T. Are the two intermediate gear pairs 57/19 T? Perhaps you can post a photo of your lathe end as I have done and we see if a Myford guru can spot the difference? Norm.

here we go - photos of my gear train with the 24T and then with the non-fitting 33T. You can see how with the 24T all the available slack is already taken. Maybe I have an especially early quadrant ....

I think my slot is shorter than yours perhaps, which is very odd! Adam

Norm I am off to count the teeth, but it does look as if there is good room to mill the slot longer, but whether enough room is another question. Adam

Yes both 2nd and 3rd studs have 57/19 gears. The slot is exactly 1.2 inches long. Adam

Hi Brian, many thanks for the advice and offer but I am very happy with the standard British 48 threads as is with the gearbox, plus a handful of Metric M6, M8, M10, M12, M16 that I can get with just the 33T and 34T tumbler gear swap. It looks like I can simply lengthen the existing slot to accommodate the 33T and 34T though goodness knows why my slot is shorter than Norm's!

Oh, the joys of having converted to cnc and being able to dial in whatever thread you need...

(ducks again!)