Myford Gearbox and Metric/BA

[Norman LortonParticipant @normanlorton75928]

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

[Adam HarrisParticipant @adamharris13683]

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

[Norman LortonParticipant @normanlorton75928]

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.

[Adam HarrisParticipant @adamharris13683]

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 ….

[Adam HarrisParticipant @adamharris13683]

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

[Adam HarrisParticipant @adamharris13683]

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

[Adam HarrisParticipant @adamharris13683]

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

[Adam HarrisParticipant @adamharris13683]

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!

[John HaineParticipant @johnhaine32865]

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

(ducks again!)

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