Can someone remind me how to cut a 1.5mm thread using an 8tpi lead screw. I don't have a metric conversion gear, but I have the normal steps of 5 up to 65 including many duplicates and a couple of 38 gears (which I have never used so maybe this is what they are for). I think its about 16.9tpi, so maybe 17tpi is good enough - but thats not in my thread chart either.
. . . . and an excellent piece of work it is too! . . . even though I have a 127 tooth wheel it has got me out of 'centre-distance' problems many times . . . if you have an extended set of wheels it will take account of those as well.
The lathe is a 1950s Winfield, it has a single banjo slot rather than the forked type you find on the Myfords (I bought a Myford banjo, but it is a completely different fitting, and have put it to one side for the moment). I vaguely remember looking at your excellent software, and I think I concluded that it was a bit Myford specific, or maybe it assumed I had gears that I didn't. That may have been a bit hasty on my part - although it can't give the gear layout, it clearly can give the ratios.
Can it be used for a single banjo like I have ? If the software allows you to insist that all the gears are on the single long slot, then that would work be perfect as the lengths are almost identical - its 4
3/4 inches between driver and leadscrew ! I sometimes have a real struggle getting the gear train right - and I am just off to the workshop to see how I can fit the ratios you have offered. I need to turn up a radiator plug to get my Land Rover on the road.
Hi Steve, it was build around the forked style of banjo rather than a parallel double or single.
However... I'll see if it's possible to fool the software into using a single, if not I can add an option to take the Myfordesque checks out so it will just concentrate on ratios rather than "will they fit".
It proved impossible to get the large gear combination on the single slot of the Winfield, but I downloaded your excellent program and was able to find 38/65 20/25 which I could manage and was (had to be) good enough for the task in hand (1.485mm instead of 1.5mm). Job done.
I'll think again about modifying the Myford banjo to fit, but I should be OK for now as I normally only have to cut imperial threads, and in a month or two my Cromwell lathe will be up and running so I will have a full thread cutting gearbox - at last.
On the ML7, you get 2 x 20t gears as standard, and also a 38t, which foxes many people.
The 38t is your best friend when it comes to metric pitches.
0.6, 0.7, 0.8, 1.0, 1.25 and 1.5 pitches can all be cut accurately with errors better than 0.02 leadscrew revolutions using the 38t somewhere in the chain.
If anyone wants the chart I have prepared with all the ratios and pitches, just PM or email me.
A 100/127 gear will work the magic on any Imperial lathe that can accept it, because 127 is half of 254, and there are 25.4mm in 1". The trouble is that some smaller lathes simply don't have sufficient space for such a large gear. Unfortunately, 127 is a prime number, so anything smaller has to be a compromise between accuracy and usability. A 38t gear does just that.
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