# Gear Ratio for QCGB



## Lumps (Jul 23, 2021)

So i tried cutting a 20 tpi part today.  I ended up with 23 or 24 threads per inch.  So if i understand correctly the bull gear should be 24 tooth unless doing course threads.  after reading through the manual i am a bit confused as to which gear is the "bull" gear.  Obviously there is something wrong here,  but i am not sure what exactly or if it is multiple problems.  I do have what i believe to be a full set of change gears.  Would anyone be so kind as to walk me through fixing this? 
Logan ward15tlc-2130 lathe, 74tlc-2138 qcgb.  10" swing.


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## Lumps (Jul 23, 2021)

this might help with communication.


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## markba633csi (Jul 23, 2021)

I'm guessing your manual is for a change gear version of the machine- you have a quick change version.  But then, we don't see any 24 tooth or 48 tooth gears in your gear train as mentioned on the qc gearbox; looks like your machine was converted- incorrectly, or incompletely
Bull gear usually refers to the large spindle backgear which has nothing to do with the outboard gears per se

I think the input gear to the gearbox is the wrong size (too large)  that would explain the leadscrew turning too slow which would give more tpi than desired, but that doesn't fully explain the 24/48 tooth mystery
-Mark


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## markba633csi (Jul 23, 2021)

Probably need to wait for another Logan owner to chime in on what the correct gearing for a qc equipped model should look like
I'm sure that will clear up the confusion- my guess is someone wanted to avoid buying the additional gears so the conversion was incomplete
-M


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## Campfire (Jul 23, 2021)

My Logan 820 has he QCGB, and the standard gearing on it that always worked great when I got it was...
24 tooth stud gear (top on the drive/main shaft)
60 tooth idler with a 48 tooth as a spacer
48 tooth screw gear

Hope this helps, I'm looking for pictures I have somewhere.


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## markba633csi (Jul 23, 2021)

Here is a picture I found of another member's (T.J.) Power Kraft which also is a conversion: 
I can see two differences; the gearbox input gear and the dual gear on the tumbler lever.
You might want to contact him and ask about it: here is the thread where I saw it








						'new' Powr-kraft 10" Lathe And Some Questions.
					

Well, after owning my first lathe (Craftsman/Atlas 6") for only a few months, I'm already 'upgrading'!  Over the weekend, I picked up a Powr-Kraft (Logan) model 15TLC-2136 while traveling to visit family.  I wasn't really shopping, but here on the high plains, this stuff is scarce and you better...




					www.hobby-machinist.com


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## benmychree (Jul 23, 2021)

The 72 tooth gear would seem to be the culprit, it would give an odd ratio.


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## Campfire (Jul 23, 2021)

Found two of my old “guide diagrams “ in my Logan manual. 
	

	
	
		
		

		
			










Hope this helps. 


Sent from my iPhone using Tapatalk


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## benmychree (Jul 23, 2021)

exchange the 64 tooth and 72 tooth and it should work.  With 32 stud gear and 64 screw gear, you get the same ratio as 24/48 as above. disregard all the other gears in the train, they are only serving as idlers to connect the stud and screw gears.


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## markba633csi (Jul 23, 2021)

Spindle gear is 30- will that still work?


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## benmychree (Jul 23, 2021)

If the stud gear is 30, then the screw gear should be 60, or any other combination that gives a 2:1 ratio. correction! it is not the spindle gear that counts, it is the STUD gear that counts, everything that is in between the spindle and stud gear and between the stud gear and the screw gear are considered idlers and do not enter into the overall ratio (I think).


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## benmychree (Jul 23, 2021)

the stud gear is "E", the screw gear is "F", could be 32 and 64 teeth respectively or any other combination that gives a 2:1 ratio


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## markba633csi (Jul 23, 2021)

Yes, I've seen two different versions of this qc Logan and they both have a 2:1 ratio in there


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## T. J. (Jul 25, 2021)

I’m a little late to the party here, but I’ll help if I can. On my lathe (same model as OP’s), the gears are set up as in Campfire’s photo (post #8). 

That being said, I would follow benmychree’s recommendation of using the gears you have to get the 1:2 ratio.


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