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BOXFORD Metric Threads on Imperial Model A

How to set it up

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Martyn Bannister14/06/2011 12:51:25
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Hi all,
 
Forgive a newbie his first question.......
 
I have searched high and low on t'internet and cannot find a definitive answer to my question. I hope someone here can help because SURELY it's a problem solved by many over the years...............
 
I have just purchased a Boxford Model A lathe. It has the Imperial screw cutting quick change box and 8TPI lead screw. It has the standard imperial setup of change gears between the tumbler reverse (AKA spindle) and the gearbox input shaft i.e 20T, 80T idler, 56T (with 40T on same shaft but not engaged).
 
With my lathe came the gears which many sites (incuding lathes.co.uk) specifiy are required to enable this machine to cut metric threads.
i.e. 24, 26, 28, 32, 36, 44, 48 and the all important 127/100 compound gear.
 
What no web site that I can find does explain is HOW are these gears used?
 
I have found mention of how to set up a LOGAN lathe (which apparently has the same box?) and that specifies MM Pitch = (40/Box Setting) * (spindle gear/gearbox gear). From this I deduce that if I put a 24T on the spindle driving the 127T compound and then drive a 48T on the gearbox from the 100T of the compound I should set the gearbox to its 20TPI setting and this should give a 1mm pitch.
 
Unfortunarely it DOESN'T!!!!!
 
Has anyone got the definitive low down on how this should alll work for a Boxford Model A? Instructions need to be clear for a dummy like me!!!!
 
Thanks in advance.

/\/\artyn Bannister
John Stevenson14/06/2011 13:12:18
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5068 forum posts
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You should have this thread chart inside your end cover.
 
 

John S.
_Paul_14/06/2011 13:24:32
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543 forum posts
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Martyn,
 
Try the Boxford "Know your Lathe" Manual my 1988 copy has the chart you need on page 75.
Same page shows the banjo setup.
 
The pic isn't that great however if you need a clearer one i'll take a photo of mine.
 
I think I had the manual from one of the Yahoo groups.
 
 
Paul

Martyn Bannister14/06/2011 13:35:46
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4 forum posts
Paul, John, many thanks. Nope, I don't have that chart on the inside of the change gear cover. I also avoided buying the "Know your lathe" manual, since I came across quite a few posts which mentioned that it DIDN'T have the chart in it !!!!!
 
Thanks very much for your help. It is extremely clear, once you know. I shall make up a spreadsheet, print it off and laminate it and put it inside my cover.
 
Many thanks again for your rapid and helpful response
 
Martyn Bannister14/06/2011 13:41:42
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4 forum posts
And, for all those who are curious, it would appear that the correct formula is......
 
MM Pitch = (56/Box Setting) * (spindle gear/gearbox gear)
 

ady14/06/2011 15:23:36
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50 photos
I vaguely recall someone posting about a British producer putting imperial leadscrews into "metric" lathes which were going to be sold to educational places, schools etc because no-one was ever going to notice or care if they were metric or not.
 
...until they got sold onto the second hand market that is.
 
It might be worth your while having a closer look at some of your critical parts, they may even have been deliberately swapped over by a previous owner so it could do "metric stuff more easily".
 

Edited By ady on 14/06/2011 15:32:49

Martyn Bannister14/06/2011 16:53:09
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That will probably be this page under "Metric & English Screwcutting"

I have checked all the relevent parts and they are indeed standard imperial parts. It was the lack of the "metric thread chart" which was my problem. I now have the spreadsheet and, should anyone wish to use it, it's HERE.
Roderick Jenkins14/06/2011 19:31:01
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2376 forum posts
800 photos
Ady,
 
Metric Myford S7s are (and as far as I am aware only ever have been) sold with an 8TPI leadscrew. Does anybody know how many divisions there are on a "metric" leadscrew handwheel?
 
Rod

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