Logan quick change gear boxes, School me please.

Yes, that's my understanding also. The second 48t gear is necessary only to be used in the stud gear position when cutting coarse threads, 4-7 tpi. I think we're both on the same page, just saying it a little different. God bless.
Jon In Tucson
 
My effort to use the parts catalog you uploaded to independently confirm your logic didn't work as the chart is apparently a generic list of gears that will fit, not what is normally fitted in the various locations. It covers several model series and doesn't differentiate by serial number or QCGB model. Although it gets there in a dfferent manner, assuming that your QC cuts 8 tpi and 4 tpi with the same lever settings, my Atlas also agrees with the 2:1 logic.
 
Robert,
Indeed, that is the way the lever settings are for 4 and 8 threads per inch. Left lever in A position, right lever in the first position. Only difference is the stud gear. God bless.
Jon In Tucson
 
Paraphrasing and old adage: "When in doubt, ask Logan..." I emailed Logan as to the proper gear train for the S/N of my lathe and they replied.

"For all Logan lathes with a Logan quick change gearbox, you need a 1:2
ratio for threads 8TPI and finer, and a 1:1 ratio for 4-7 TPI.

If the nameplate lists a 24 and 48 tooth stud gear, use a 48T on the
gearbox and either a 24 or 48T on the stud. This was used on 9", 10",
11" and 2900 series lathes prior to S/N 67839.

If the nameplate lists a 36 and 72 tooth stud gear, use a 72T on the
gearbox and either a 36 or 72T on the stud. This was used on 9", 10",
11" and 2900 series lathes after S/N 67839.

If the nameplate lists a 30 and 60 tooth stud gear, use a 60T on the
gearbox and either a 30 or 60T on the stud. This was only used on the
2500 series 12" and the 14" Logan lathes."

So another great mystery has been laid to rest in my quest of restoration of this lathe. I'm also a little closer to being able to cut threads.
Wa5cab, GarageGuy, Snag_one and all who offered help and assistance as I was rebuilding the gearbox as well as trying to figure out the gear train thanks for your patience and interest.:thumbzup3:

Since I have assembled the gear box and drive train, I have realized the left change lever will need bushings installed as it is sloppy. Might as well do both handles since I'll have it apart again... God bless.
Jon In Tucson
 
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