Change Gear Question

Jmanb13

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I've been researching (for several months) a change gear setup for my 1946 Leblond. Due to the obvious lack of old random translation gears for a 70 year old lathe, I am contemplating replacing all of the gears with a newer matching set of stocked boston gears.

The stock setup from leblond is 3 gears for connecting the spindle to the quick change box.

32 tooth -> 120 tooth -> 32 tooth. The oem way to do metric threads was a 120/127 compound gear. in place of the 120 gear. These gears however are a weird 14 pitch gear.

The stock boston gears that have a 127 tooth option are 16 pitch so it is smaller. The issue i'm running into is that the adjustment mechanism for the gears is maxed out with the stock 14 pitch gear, so it would not be able to move any further for the smaller gear.

Would there be any issue running a higher tooth count gear (aka bigger) in place of the 32 tooth gears to make up the distance?

Something like
40 -> 120 -> 40
and
40 -> 120/127 -> 40 for metric threading.

In my limited understanding of gears, it shouldn't make any difference as long as the spindle and quick change gears are exactly the same tooth count.
 
40 - 120 - 40 is commonly used. It should cause no issues. It will, however invalidate any charts on the lathe if the 40 tooth gear is used with the tooth counts called out in the charts.
 
Maybe i'm misunderstanding this. Since the driving gear and the quick change gear box gear have the same tooth count, are they not the same gear ratio and would be turning at the same speed regardless of having 10 teeth or 100 teeth. The spindle turns 1 time and the quick change box turns 1 time.

This is what the gears look like (except the 2 small gears are identical on my lathe)

maxresdefault.jpg
 
The threading charts will often call for different "change" gears, especially at the QCGB input. If you do that, and also have a 40 tooth spindle gear, which the charts do not, then you will have problems. If you get a complete set of change gears with tooth counts same as the lathe came with, then you should be OK as long as gear spacing does not become a problem. As long as the ratios from the spindle to the QCGB matches the ones on the threading charts, it should work fine.
 
I think I get you. Some lathes QCGB have different input gear sets to match the threading charts. On my lathe the QCGB does not rely on different gears, it is all handled internally in the QCGB. In this case I should be ok swapping out the spindle gear and the QCGB gear as long as they match. If it matters, this is my threading chart. Kind of hard to see since its worn down.

full
 
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