How Modern Quick Change Lathe's Change/Convert internally from Inch to Metric Threads

I think I am misreading your question, but here goes:

As long as each meshing gear pair has the same DP you can do anything you like. You can never mesh two gears of differing DPs together. it will result in excessive wear and rough running.
 
The answer really is that it depends what you're meshing either 40t gear with...

This is a superb primer on everything gear related and will explain far better than I can:

ciechanow.ski

Gears – Bartosz Ciechanowski

Interactive article explaining how mechanical gears work.
ciechanow.ski ciechanow.ski
 
Every lathe that I have seen that does both Imperial and metric threads has a compound gear with one of them being a 127 tooth gear. That makes both the Imperial and the metric pitches exact.
 
Dabbler said:
I think I am misreading your question, but here goes:

As long as each meshing gear pair has the same DP you can do anything you like. You can never mesh two gears of differing DPs together. it will result in excessive wear and rough running.
Click to expand...
Yes you are miss reading
I know you can't run different DP's together, But if you want to use a different DP in a gear train you have to use a conversion gear at the point you want to use a different DP
So in my case i want to make the change at a 40T 8DP Idler gear, So I want to bolt or attach a 40T 10DP gear to the side of the 40T 8DP gear, it would be like a compound gear, but it would be changing the DP of the gear train and not the Ratio
Now what im not sure of is will it change the ratio? The 40T 8DP gear outside diameter is 5.250 and the 40T 10DP gear will have a 4.200 outside diameter, But they both have 40 Teeth so there should not be a change in Ratio even though there is a difference in diameters.

Am I correct in this deduction?

I am limited in room for gearing, so I want to use a smaller DP so I can get gears with more teeth in a smaller area. This is the only way I can see being able to do this with out changing the whole gear train which is not possible
I want to get a 127T gear in this limited area so i need to use a smaller DP to get this done

Thanks for your advice
Blair
 
My metrication pair is MUCH finer pitch than my other change gears. A bit more fiddly to set the backlash, but worth it to cut the size by about 4!

Sent from my SM-G892A using Tapatalk
 
An interesting coincidence as I was watching Quinn (BlondieHacks) for an unconventional threading technique and then happen across this entry. It seems her machine, make unknown but Chinese, uses a 64 tooth gear in the train for metric conversion. With appropriate gearing, I suppose a 32 tooth would give the same results.

Accept up front, the conversion factor is 1.27, the smallest whole number is 127, a prime number. It cannot be reduced any further. Supposedly, 1.28, or 128 gives close enough for a dozen or so pitches. 128 divided by 2 is 64, by 2 again is 32. This gives not quite true metric conversion but is apparently close enough for fasteners.

It would be up to the individual whether or not 1.28 was close enough to be usable. I have two lathes. One has a 127/120 gear set, the other has a home made plastic 127 tooth conversion gear. The matter doesn't concern me but I don't use my lathe as a machinist would. When I have any work that has to be that precise, I use the Taiwanese machine which has true metric conversion. But it is a detail to be kept in the deep, dark recesses of my memory. Useful to someone some day.

EDIT : the Atlas (and Craftsman) lathes use a 52 and 44 pair, which gives a conversion factor of 1.181818 ad infinitum.

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@Blair changing the DP will change the radius for the same number of teeth. When you mesh it with the next gear, you will see the benefit by being able to put a different radius gear in the same space. I hope this helps. Also, sorry for misunderstanding your post.
 
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