Logan quick change gear boxes, School me please.

GG,

There must have been more to it than that. Note that in Jon's case, the banjo gear is compounded and the gearbox input gear is either flipped over or the spacer is put on before the gear (I can't quite tell whether the gear and spacer are one piece or two) so that the outer gear on the bottom of the tumbler drives the inner gear on the banjo and the outer gear on the banjo drives the gearbox gear. But in the photo that you posted, the small gear on the banjo is just a spacer. And the large gear is thus only an idler, like the FWD and REV tumbler gears.

GarageGuy said:
When I bought my machine, there was a 48 tooth gear here, and the thread pitch was off. I had to change it to a 72 tooth gear to get the thread pitch to match the plate on the QCGB. Doesn't that mean that the number of teeth on this gear does matter?

GG
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An "aha" moment... My problem is from the compounded banjo gear. By using a 48T gear on the gearbox input and using only the 72T gear on the banjo, I will have corrected the drive train to get the ratio right. Thanks for the insight. God bless.
Jon In Tucson
 
Jon,

I may be confusing you with another thread, but did you rebuild a gearbox that either came with your model lathe (please repeat the model number) or at least came from another machine of the same model? Or did the gearbox come from another model machine? If it's from the same model machine, you need to find that manual and it should tell you what gears are required. If it is from another model, you need to find that manual and also confirm that the lead screw pitch was the same on both machines. If you can't find the necessary manual, you will have to do it the hard way.

I have to go out of town later today for several days and may or may not have good internet access.

Jon In Tucson said:
Robert and Snag,
In the words of Forrest Gump, "I may not be a smart man Jenny, but I can count teeth on a gear.."
Let me tell you what I got and what I understand (less and less), because I'm becoming overwhelmed. A little history on the lathe: when we purchased the lathe, it had a gutted QCGB, no banjo assembly, no reverse idler assembly. Since April I have been acquiring the missing parts to be able to cut threads and have power feeds. Starting at the Spindle and proceeding to the lead screw drive this is what I have.
Spindle= 46T
Idlers (both of them)=34T
Reverse gear =46T
Stud gear=24T
Compound gear (running on the stud gear)=72T
Compound gear (outer powering GB)=64T
GB input gear =60T
lead screw gear=24T

If I understand you gentlemen correctly, I should be driving my gearbox with a 2:1 ratio to the stud gear. Which means my input to the gearbox should be 48T? Or am I totally turned around? In my pea brain I think a 72T gear installed on the input side of the gearbox will slow my speeds down to track with the threading plate. Thanks and God bless.
Jon In Tucson
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If I get some time, I will change the gears and read the input speed of the QCGB with an optical tachometer. Now I need to prove to myself that what happened really did happen. If I'm wrong, I'll admit it and check myself in to the Alzheimer's ward. Thanks for being patient.

GG
 
wa5cab said:
Jon,

I may be confusing you with another thread, but did you rebuild a gearbox that either came with your model lathe (please repeat the model number) or at least came from another machine of the same model? Or did the gearbox come from another model machine? If it's from the same model machine, you need to find that manual and it should tell you what gears are required. If it is from another model, you need to find that manual and also confirm that the lead screw pitch was the same on both machines. If you can't find the necessary manual, you will have to do it the hard way.

I have to go out of town later today for several days and may or may not have good internet access.
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Robert,
I did have to rebuild my gearbox. I bought one on eBay and then transferred all of the innards to my case. According to my correspondence with Logan sales, the only difference in my gearbox (LA-1240-1) and the one in the parts manual (LA-1240-2) is the threading tag. One denotes a 24/48 (1240-1, mine)and the other 36/72 (the one I bought) is the change gears. So in my way of thinking, I need to find a 48T gear for the input side of the gearbox to go with the 24T stud gear and then be golden... I 'spose I should look for a 24T gear also to be able to do the coarse threads as well as the fine. Thanks for making this gear science which is really just a lesson in ratios understandable to my pea brain.:allgood: God bless.
Jon In Tucson
 
Jon,

I could be wrong, as I have no extensive collection of Logan manuals as I do of Atlas ones. But my assumption is that the 24 and 48T alternatives shown on the threading chart plate visible in some of the posted photos refer to the outer gear on the compound stud (tumbler) gear (according to the parts list drawing called "Reverse Gear" by Logan). But not to the gearbox input gear. I.e., the 48T stud gear is used for the coarsest two rows selectable

Jon In Tucson said:
Robert,
I did have to rebuild my gearbox. I bought one on eBay and then transferred all of the innards to my case. According to my correspondence with Logan sales, the only difference in my gearbox (LA-1240-1) and the one in the parts manual (LA-1240-2) is the threading tag. One denotes a 24/48 (1240-1, mine)and the other 36/72 (the one I bought) is the change gears. So in my way of thinking, I need to find a 48T gear for the input side of the gearbox to go with the 24T stud gear and then be golden... I 'spose I should look for a 24T gear also to be able to do the coarse threads as well as the fine. Thanks for making this gear science which is really just a lesson in ratios understandable to my pea brain.:allgood: God bless.
Jon In Tucson
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Jon,

I could be wrong, as I have no extensive collection of Logan manuals as I do of Atlas ones. But my assumption is that the 24 and 48T alternatives shown on the threading chart plate visible in some of the posted photos refer to the outer gear on the compound stud (tumbler) gear (according to the parts list drawing called "Reverse Gear" by Logan). But not to the gearbox input gear. I.e., the 48T stud gear is used for the coarsest two rows selectable.

Robert,
In my Logan operators and parts manual is a picture of the later stud and change gear configuration. The photo shows a 36 tooth gear in the stud gear position driving a 72 tooth idler that is compounded with a 64 tooth in the spacer position. That 72 tooth gear drives the 72 tooth "screw gear" or what I call the gear box input gear. The explanation of the power feeds,

" For threads from 4 to 7 per inch move the 72 tooth idler gear to the stud gear position. Place the inactive 64 tooth gear in idler position and put the 36 tooth gear you removed in the inactive position."

So by substituting 24 for 36 and 48 for 72, I can make the jump that I will need 2-48 tooth gears to get my ratios back on track. One to be used as a stud gear and the other to be used as the screw gear. Worst case is with only one gear I will not be able to cut the coarsest threads of 4 to 7 threads per inch.

The good news is that Logan used the same 16 DP gear in all of the small lathes like mine. Ebay has lots of gears for sale. Thanks again and God bless.
Jon In Tucson
 
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Jon (In Tucson),

I think that I understand your logic for concluding that you need a 24T stud gear and a 48T idler but how did you conclude that the gearbox input gear is also a 48T?

If you will say what model number, serial number and swing your specific lathe is, I might be able to take the all-models consolidated parts catalog and turn it into a single model parts list.

Jon In Tucson said:
Jon,

Robert,
In my Logan operators and parts manual is a picture of the later stud and change gear configuration. The photo shows a 36 tooth gear in the stud gear position driving a 72 tooth idler that is compounded with a 64 tooth in the spacer position. That 72 tooth gear drives the 72 tooth "screw gear" or what I call the gear box input gear. The explanation of the power feeds,

" For threads from 4 to 7 per inch move the 72 tooth idler gear to the stud gear position. Place the inactive 64 tooth gear in idler position and put the 36 tooth gear you removed in the inactive position."

So by substituting 24 for 36 and 48 for 72, I can make the jump that I will need 2-48 tooth gears to get my ratios back on track. One to be used as a stud gear and the other to be used as the screw gear. Worst case is with only one gear I will not be able to cut the coarsest threads of 4 to 7 threads per inch.

Jon In Tucson
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Robert,
In post #1 I listed the model and s/n, but to reinterate, its a model 1957, 11" swing, s/n 64747 made after April 15, 1953.
My logic is as follows: using Logan's operating manual verbiage regarding power feeds. Logan's picture identifies the components in the power train as a 72 t screw gear and a 72t stud gear to obtain 4 to 7 threads, or coarse threads. That I take to be a 1:1 ratio of rotation. Using the 36t stud gear and the 72t in the idler makes the 2:1 ratio that another gent mentioned.
In my case having a 48t screw gear with my 24t stud gear will give the proper 2:1 ratio on my Logan and then the threading chart "should" be accurate. Whatever idler gear is in the middle should not matter. As least that is how I understand it... God bless.
Jon In Tucson.
 
I can't do anything else until I get back to Houston as a needed program isn't on this machine.

I'm sure it's just a typo but the 48T idler doesn't set the 2:1 ratio. It's the 24T stud and the 48T gearbox input.
 
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