For what is my Logan 200's 66T 66 tooth gear used?

Good question. It's not for converting to metric threading since the gears Logan sells for that purpose are different.
Let us know when you find out. :) You could always ask Logan.
 
I'll email them if I can't figure it out.

If anyone has their gears out and it's convenient, would you mind measuring the OD on the 60T gear? I'll need to print one to have available until I can find a real metal replacement for the missing 60T. And would like to verify I get it right by comparing OD. Not super critical, I can gage off the close gear sizes as a sanity check if needed.

Thanks!
 
My 60 tooth has an OD of 3.875.

Ebay is a good place to look for Logan change gears.
 
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Looks like its used (with the metric transposing gear) to cut at least 2 metric thread pitches.

While not surprising, I didn't consider the possibility that I'd need MORE additional gears beyond the transposing gears to cut metric threads. .... although that looks like it may only apply to lathes with quick change gearbox?


Given this is the USA, I hope I don't have to cut many metric threads... but nice to be prepared.
 
The table is a bit unclear, but it looks as though you would need that gear for 1.25, 2.5 and 5.0 mm pitches.
The 66 tooth gear shows up in that table as well. Interesting that you have the gear, but no transposing gears
to make it useful. Well, at least you have answer to your original question.
 
The only other possible use for the 66 tooth gear could be to produce a feed rate of very close to 0.0050 inches traveled per revolution. However, I don't know of any particular reason to need to produce exactly that feed rate. The thread and feed chart for the 200 Series shows 0.0046" and 0.0052". So the metric guess is probably the correct one.
 
If I'm reading the chart on the Logan site correctly, for the Model 200 (manual change gears), the two middle columns should be disregarded. The ratio in the right-hand column is what matters. They show a 2.00mm pitch using the 32T stud gear, and a 40T screw gear, which corresponds to the 0.80 ratio listed for that thread pitch.

The math seems to follow.... as you add more teeth to the screw gear, lowering the ratio (of stud/screw), it takes more revs of the headstock to traverse the carriage, so the thread pitch becomes finer.

So I guess the chart that would be most helpful, is one that has calculated the right stud gear, screw gear, and intermediate gear train (if applicable) for each thread pitch.
 
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