# Logan quick change gear boxes, School me please.



## Jon In Tucson

I recently acquired a Logan 1957 lathe, S/N 64747, that has had the QCGB gutted and a direct drive DC gear motor used in place.  In an effort to bring it back to a place where I can use for threading operations I have been in the search for gearboxes and the drive train to power it.  I bought a complete gearbox from a Logan 816 as well as the banjo bracket.  I also have the reverse drive assembly in route but haven't received it yet.  There are still some other parts to fill in the gaps to complete the project that I have yet to lay my hands on.  My quandary is:  There are some differences in the two gearbox castings, size wise as well as diameters for shafts, some are bushed, some are not.  

1.  My 1957 gearbox is a LA-1201 casting, the 816 is not.  
2.  When I lay out all the gear train for the lead screw speeds I have a .5 inch gap in the 1957 that I don't in the 816.  

The selector levers will fit and the shaft lines up as it should.  Edit:Upon further investigation I'm not so sure...  

Bottom line,  Am I going to get this to work or did I buy the wrong gear box?  Thanks for your help in advance and God bless.
Jon In Tucson


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## gjmontll

Hi Jon,

You didn't say which model Logan you have, but looking in my Logan 820 Parts List, I see the QCGB with two different variants. My 1944 model 820 is pre-S/N 46561, and its casting is a LA-475. Post S/N 46561, the casting is an LA-1241. I don't know what the differences them might be.

But perhaps my thread in this forum may help you. See "Greg's Logan 820 Restoration", in particular, the postings dated in September thru November 2013 as I struggled through teardown, repair/replacement/renewal, and reassembly of the gearbox. There are a bunch of photos that might help in your issue. 

My lathe is about a week away from reassembly, and the QCGB is quietly sleeping on the carpet in my study. Let me know if I can take some measurements or additional photos that might help you.

Greg


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## Jon In Tucson

gjmontll said:


> Hi Jon,
> 
> You didn't say which model Logan you have, but looking in my Logan 820 Parts List, I see the QCGB with two different variants. My 1944 model 820 is pre-S/N 46561, and its casting is a LA-475. Post S/N 46561, the casting is an LA-1241. I don't know what the differences them might be.
> 
> But perhaps my thread in this forum may help you. See "Greg's Logan 820 Restoration", in particular, the postings dated in September thru November 2013 as I struggled through teardown, repair/replacement/renewal, and reassembly of the gearbox. There are a bunch of photos that might help in your issue.
> 
> My lathe is about a week away from reassembly, and the QCGB is quietly sleeping on the carpet in my study. Let me know if I can take some measurements or additional photos that might help you.
> 
> Greg



Thanks for the reply Greg.  My Logan is a model 1957, S/N 64747, I know that it was produced after April of 1953 as it has a V belt drive rather than the flat belt.  It appears that all of the shafts and gears will fit into my casting, LA-1201,  However some are bushed on the donor box and not on mine. I will add some photos to clear up my questions.  Just to let you all know, I was told that a clean work bench was an indicator of a deranged mind.  So just saying...  

The 816 gearbox is taller than mine, but not as long as my gearbox.  My gearbox is longer, uses 2 drift pins rather than the one on the 816.  Both use 48/24 stud gear and the threading charts are the same.  The bolt spacing is not the same either.  I want to make my casting work with the "innards" of the 816, or have I bit off more than I can chew.  God bless.
Jon In Tucson


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## Tool-in-the-Box

I didn't read threw it all but this might help:


http://lathe.com/ll-group-archive/adapting_a_qc_gearbox.html


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## Jon In Tucson

Tool-in-the-Box said:


> I didn't read threw it all but this might help:
> 
> 
> http://lathe.com/ll-group-archive/adapting_a_qc_gearbox.html



That may be my problem.:banghead:  I have no idea of the S/N of the donor gear box.  My lathe defiantly is of the "new style" gear box.  The 816 is a 10" lathe, and my 1957 is an 11" lathe, however, will it be possible to utilize the parts in my newer style gearbox?  Does anyone have pictures of the later gearbox so I can see any differences?  God bless.
Jon In Tucson


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## gjmontll

Jon

Okay on the Model 1957, I am not familiar with that one and I thought that was the year. I now see that it is an 11" and apparently a somewhat different gearbox than on my 10". BTW, my QCGB does have two pins. About that extra half inch width, here are a few photos of mine after finishing the overhaul. In the first shot, notice how the wider gear is inserted - I think you have yours in backwards. You say the gears all shift okay, so maybe you just need to make a 1/2" spacer.





You mentioned differences in the bushings. According to the Parts Catalog, I had noted that some of the gearbox steel shafts bear against cast iron, without any bushings. Maybe some prior owner bored it out and added bushings? In my restoration, I had to make a new slider shaft and a new gear cluster shaft because of bad wear. To prevent future selector shaft wear, I added bushings onto the selector arms. (And as my thread details, I had all sorts of self-induced problems doing so!). 
Hope this helped, good luck to you
     Greg




Jon In Tucson said:


> Thanks for the reply Greg.  My Logan is a model 1957, S/N 64747, I know that it was produced after April of 1953 as it has a V belt drive rather than the flat belt.  It appears that all of the shafts and gears will fit into my casting, LA-1201,  However some are bushed on the donor box and not on mine. I will add some photos to clear up my questions.  Just to let you all know, I was told that a clean work bench was an indicator of a deranged mind.  So just saying...
> 
> The 816 gearbox is taller than mine, but not as long as my gearbox.  My gearbox is longer, uses 2 drift pins rather than the one on the 816.  Both use 48/24 stud gear and the threading charts are the same.  The bolt spacing is not the same either.  I want to make my casting work with the "innards" of the 816, or have I bit off more than I can chew.  God bless.
> Jon In Tucson


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## Jon In Tucson

Greg,
Thanks for the reply.  I had been stripping the gear box down for a transplant and used a 3/8" tee bar to check fit and had the gear with the setscrew stacked wrong.  upon further examination my change levers may not swap over either.  I concur with your thought as to why some shafts are bushed and some are not. I'm going set back and study this awhile.  I may be in the market for another gearbox and put this one up for sale.  God bless.
Jon In Tucson


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## Jon In Tucson

Jon In Tucson said:


> Greg,
> Thanks for the reply.  I had been stripping the gear box down for a transplant and used a 3/8" tee bar to check fit and had the gear with the setscrew stacked wrong.  upon further examination my change levers may not swap over either.  I concur with your thought as to why some shafts are bushed and some are not. I'm going set back and study this awhile.  I may be in the market for another gearbox and put this one up for sale.  God bless.
> Jon In Tucson



After a email to Logan company I find that I have a LB-1240-1 gearbox.  However, My parts manual lists a LA-1240-2 gearbox...  By the way what does (20 D.P.) and (16 D.P.) mean in reference to the parts manual for gearboxes?  I know that I don't know much about this lathe.  God bless.
Jon In Tucson


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## gjmontll

Jon,
  D.P. is "diametral pitch" - the ratio of the number of teeth to the pitch diameter. Gears with the same D.P. will properly mesh together (assuming they have the same pressure angle. For the Logan, I think the P.A. is 14.5 degrees
   Greg



Jon In Tucson said:


> After a email to Logan company I find that I have a LB-1240-1 gearbox.  However, My parts manual lists a LA-1240-2 gearbox...  By the way what does (20 D.P.) and (16 D.P.) mean in reference to the parts manual for gearboxes?  I know that I don't know much about this lathe.  God bless.
> Jon In Tucson


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## Jon In Tucson

Jon In Tucson said:


> After a email to Logan company I find that I have a LB-1240-1 gearbox.  However, My parts manual lists a LA-1240-2 gearbox...  By the way what does (20 D.P.) and (16 D.P.) mean in reference to the parts manual for gearboxes?  I know that I don't know much about this lathe.  God bless.
> Jon In Tucson



I have learned that the difference in the LA-1240-1 and LA-1240-2 gearboxes is: "*The only difference in the 1240-1 and -2 assemblies is the nameplate **(and this results in using different change gears on the end)."


**So, I'm going to be on the lookout for another gearbox, change gears as well as reverse assembly for an 11" lathe.  God bless.
**Jon In Tucson

**
*


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## Jon In Tucson

*Re: Logan quick change gear boxes, repair time...*

It looks like I have purchased the correct QCGB for my Logan.  It came from a 1940-2H Logan, which was a turret lathe.  Not sure what the "H" stands for though.  The gears appear to be good shape, but I have to replace a couple of shafts and a handful of bushings.  The shift lever cross shaft, what the shifters travel back and forth on, has about .010 of wear in one end.  Also the left hand shifter, large gear idler shaft and bushing, are "wore plum out".  That's a technical term...  So making the shafts shouldn't be too big of a deal, but I have a question for you vastly more experienced and knowledgeable folk  out there beyond my laptop screen:  How do you go about buying bushings for the repair of this gear box?  Straight from Logan or an industrial supply house like McMaster Carr?    God bless.
Jon In Tucson


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## AR1911

Either source works. If Logan is reasonable I'd buy there. But the bushings are usually standard sizes, available even at hardware stores.  But you may need a reamer or two in the correct sizes.


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## mjhenks

I got my bushings from McMaster Carr and had to ream them in place to get things to fit right.  That was a challenge as I could not finding a reamer that long for one of the shafts.  I indicated both sides in and reamed from each side.

Jigging the housing was a real treat as there are not many flat surfaces to grab onto.

http://www.hobby-machinist.com/showthread.php?t=21634&page=2&p=193218&viewfull=1#post193218  Post #48

I also had to re-make the selector shaft.  Post #45 & #48

Have fun.

Matthew


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## Jon In Tucson

mjhenks said:


> I got my bushings from McMaster Carr and had to ream them in place to get things to fit right.  That was a challenge as I could not finding a reamer that long for one of the shafts.  I indicated both sides in and reamed from each side.
> 
> Jigging the housing was a real treat as there are not many flat surfaces to grab onto.
> 
> http://www.hobby-machinist.com/showthread.php?t=21634&page=2&p=193218&viewfull=1#post193218  Post #48
> 
> I also had to re-make the selector shaft.  Post #45 & #48
> 
> Have fun.
> 
> Matthew



I have purchased bushings from the local Ace hardware, McMaster Carr, and from Logan.  
1.  The two bushings on the power input side of the gearbox I was able to find at Ace as well as a long sleeve bushing that I cut up for the 40T handle gears. 

2.  From McMaster Carr I ordered the stack shaft bushings and a new shaft for the slider shaft assembly. I will get to learn how to cut a key way in the aforementioned shaft. 

3.  From Logan I ordered the third bushing or inboard bushing for the input power.  This is the one with a 3/4" OD and a 7/16" ID.  Couldn't seem to source it out of anyone else.  Also ordered a "pin" that secures the 40 T gear in the left handle as the old one was worn down about 1/16th of an inch.   

I'm starting to get excited about the possibility of completing the gearbox and actually having a power feed on the saddle and compound.  God bless. 
Jon In Tucson


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## Jon In Tucson

Received my order from McMaster Carr in less than 24 hours, wow!  Ordered about 5 pm on Monday, got it about 1:30 pm Tuesday afternoon.  Shipping charges were nominal in my estimation for that kind of service. Still waiting on my order from Logan.  Hope to get the key way milled on the slider shaft this weekend, if my machinist friend's shop is available. Just like the movie "What about Bob?", "Baby steps, Bob, baby steps."  God bless.
Jon In Tucson


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## Jon In Tucson

Made some progress lately, although September 1 is the beginning of dove season here in AZ, I did go out a few times and attempt bag a few of those small feathered rockets.  All of you guys who have been restoring their lathes gave me the urge to do some restoration as well as the refurbishment that is necessary.  My color scheme is Rust-oleum smoke gray, Sunrise red, and gloss black.  The gear box casting gray, Logan logo red as well as the shift levers, and the thread chart black.  I learned that even with spray cans you can put too much pain on the the surface.  Did some judicious scraping with a straight edge and steel wool buffing and the results are tolerable, but much easier to read.  The last of the bushings arrived today and now the re-assembly will commence.  Still need to get the key way cut on the replacement slider shaft.  Here are a few photos. Little by little...  God bless.
Jon In Tucson


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## Jon In Tucson

Another step forward.  I was able to go to my friend's place of employment and we, (I use that term loosely) mostly Ken, made the new slider shaft for the QCGB.  After assembling and test fitting, I made a few chips.)  Now I will have to locate a LA-517 bracket to secure my banjo drive train before I start getting too crazy. I also need to test thread stock to see if the stud and change gears are correct for this gear box.  I have: 34T idler and reverse gears,  36T stud gear,  72T/64T change gears and a 60T input gear on the QCGB.  My thread chart shows stud gears of 48/24.  

Question:  Can any one tell me if I have the proper combination of gears to transmit power from the spindle to the QCGB?  Here are a couple photo's of the current progress.  God bless.
Jon In Tucson


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## CNCMAN

looks good.)


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## GarageGuy

I bought a replacement gear for my QCGB on my Logan 820 built in 1945 from a very knowledgeable gentleman in California.  When the gear arrived, it was too small.  I called him, and he said I have the older model QCGB that uses a different DP gear.  There is a certain serial number (can't remember it, of course) where Logan changed to a smaller DP gear set.  He makes both styles, so we exchanged gears, and I learned something.

GG


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## Jon In Tucson

GarageGuy said:


> I bought a replacement gear for my QCGB on my Logan 820 built in 1945 from a very knowledgeable gentleman in California.  When the gear arrived, it was too small.  I called him, and he said I have the older model QCGB that uses a different DP gear.  There is a certain serial number (can't remember it, of course) where Logan changed to a smaller DP gear set.  He makes both styles, so we exchanged gears, and I learned something.
> 
> GG


GG,
Thanks for the info.  I wonder if it is the same vendor that makes the replacement bracket (LA-517)for securing the banjo assembly?  I suspect that I may need another 72T gear to put on the input side of the QCGB.  And it is possible other things are wrong also...:think1:When I tried to run a 10tpi threading speed on a piece of scrap, I was nowhere near 10, more like 28...  So, I got to slow it down some.  

CNCman, Thank for the compliment!  God bless.
Jon In Tucson


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## GarageGuy

Jon In Tucson said:


> GG,
> Thanks for the info.  I wonder if it is the same vendor that makes the replacement bracket (LA-517)for securing the banjo assembly?  I suspect that I may need another 72T gear to put on the input side of the QCGB.  And it is possible other things are wrong also...:think1:When I tried to run a 10tpi threading speed on a piece of scrap, I was nowhere near 10, more like 28...  So, I got to slow it down some.



It's possible.  His eBay name is "trikerdad".  Here is a link to his store:  http://stores.ebay.com/raybillscustomoptions/

It looks like he has a banjo for sale, but I don't know if he makes them or not.  He has a lot of Logan parts.

Mine had a 48 tooth gear on the banjo when I bought it, and the lead screw was spinning *very* fast.  The motor couldn't even spin up to speed when on the "A" range on the QCGB.  I attempted to cut some threads, and my 8 TPI threading attempt came out at something like 16 TPI.  I was confused, did some reading, and found out that it should have the 72 tooth gear installed.  I changed the banjo gear to the 72 tooth, and threads came out like they were supposed to.  I'm not sure why you would want to use the 48 tooth gear if it throws everything off, but it was in there.  It sounds like yours may be the same.

GG


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## Jon In Tucson

GarageGuy said:


> It's possible.  His eBay name is "trikerdad".  Here is a link to his store:  http://stores.ebay.com/raybillscustomoptions/
> 
> It looks like he has a banjo for sale, but I don't know if he makes them or not.  He has a lot of Logan parts.
> 
> Mine had a 48 tooth gear on the banjo when I bought it, and the lead screw was spinning *very* fast.  The motor couldn't even spin up to speed when on the "A" range on the QCGB.  I attempted to cut some threads, and my 8 TPI threading attempt came out at something like 16 TPI.  I was confused, did some reading, and found out that it should have the 72 tooth gear installed.  I changed the banjo gear to the 72 tooth, and threads came out like they were supposed to.  I'm not sure why you would want to use the 48 tooth gear if it throws everything off, but it was in there.  It sounds like yours may be the same.
> 
> GG



Yup, that's the guy I was thinking of, sure enough.  According to my parts manual, I "should have" a 72T gear on the input side of the gearbox in a safety gear assembly.  I have never seen one offered for sale.  So I suppose that a regular 72T gear with a 5/8" keyed shaft is the alternative.  More searching...  God bless.
Jon In Tucson


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## Snag_one

Jon In Tucson said:


> Yup, that's the guy I was thinking of, sure enough.  According to my parts manual, I "should have" a 72T gear on the input side of the gearbox in a safety gear assembly.  I have never seen one offered for sale.  So I suppose that a regular 72T gear with a 5/8" keyed shaft is the alternative.  More searching...  God bless.
> Jon In Tucson



  I'm pretty sure your machine is the same as mine , in that the proper stud:QCGB ratio should be 2:1 for most work - one exception is for very coarse threads , where you'll want 1:1 . The number of teeth on the gear on the banjo is unimportant <in most cases> and will have no effect on the final ratio . I don't recall what gears you have , but if you have say a 36 and a 72 , you'd be good to go . Since my Wards 94TLC2136 has a plain apron <half-nuts only> , I sometimes gear my QCGB input to 4:1 or even lower to get a better finish .


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## wa5cab

I'll add emphasis to Snag's "unimportant" comment by saying that if you have a spur gear train made up of spindle gear, screw gear (the gear on the lead screw) or gear box input gear, and n gears in between, and all gears are in the same plane, then the only requirement on the n gears in between is that they are all large enough for the teeth to mesh.  The only two that matter are the spindle gear and the screw gear.  Only if one or more of the gears is a compound gear do their tooth counts matter (compound gear being defined as two gears on the same axis with different tooth counts, one driven and one driving, and keyed, pinned or otherwise made together).  It took me a while to get my head around that concept so that I didn't have to think about it.


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## Jon In Tucson

wa5cab said:


> I'll add emphasis to Snag's "unimportant" comment by saying that if you have a spur gear train made up of spindle gear, screw gear (the gear on the lead screw) or gear box input gear, and n gears in between, and all gears are in the same plane, then the only requirement on the n gears in between is that they are all large enough for the teeth to mesh.  The only two that matter are the spindle gear and the screw gear.  Only if one or more of the gears is a compound gear do their tooth counts matter (compound gear being defined as two gears on the same axis with different tooth counts, one driven and one driving, and keyed, pinned or otherwise made together).  It took me a while to get my head around that concept so that I didn't have to think about it.



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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## Snag_one

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




  OK , the spindle/idlers/reversing gear form a 1:1 train , because the in and output gears have the same count . OK , you're going to need to buy some gears . You can get a 36 to pair with the 72 , and get a 48 to pair with the 24 . I see you have 2 24t gears{?} , that'll get you the coarsest range of threads . Use the 24/whatever fits/48 set to drive the QCGB <all in the same plane , no compounding> your thread count should be correct as set on the box - same with the 36/intermediate/72 set . You can compound the 2 pairs and get 4:1 reduction , that will give you twice the thread count of the setting . <was that clear? set for 16 tpi gives 32 tpi>


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## GarageGuy

wa5cab said:


> I'll add emphasis to Snag's "unimportant" comment by saying that if you have a spur gear train made up of spindle gear, screw gear (the gear on the lead screw) or gear box input gear, and n gears in between, and all gears are in the same plane, then the only requirement on the n gears in between is that they are all large enough for the teeth to mesh.  The only two that matter are the spindle gear and the screw gear.  Only if one or more of the gears is a compound gear do their tooth counts matter (compound gear being defined as two gears on the same axis with different tooth counts, one driven and one driving, and keyed, pinned or otherwise made together).  It took me a while to get my head around that concept so that I didn't have to think about it.



I'm confused too... according to your post, this gear:




can be *any* number of teeth and the speed of the lead screw won't change?  This is the banjo gear I thought we were talking about.

GG


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## John Hasler

GarageGuy said:


> I'm confused too... according to your post, this gear:
> 
> 
> can be *any* number of teeth and the speed of the lead screw won't change?  This is the banjo gear I thought we were talking about.
> 
> GG



Visualize an arrangement where the stud gear (the top one) has 32 teeth and the leadscrew gear 64.  Then when the stud gear turns one revolution the idler (middle gear) must rotate 32 teeth.  This in turn requires that the leadscrew gear rotate 32 teeth as well.  That's half a turn, which is exactly what it would have turned had it been directly in contact with the stud gear.  The number of teeth on the idler does not figure in the calculation at all.  All it does is makes the stud and leadscrew gears turn in the same direction.  Thus it can have however many teeth you find convenient.


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## GarageGuy

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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## wa5cab

GG,

That is correct.  I'm somewhat handicapped by not being very familiar with Logan lathes and by not having but one maintenance or parts manual (on the 200 series) to look at.  And I'm therefore not certain what some of the various gears are commonly called in the Logan world.  But the diameter or tooth count of the larger gear that you circled (the smaller one is just a spacer) that is mounted on the banjo is immaterial.  The only requirement on it is that it be large enough to bridge between the two gears it connects.  This is easy to prove.  I don't know for certain the tooth count on the three gears involved but they look to be around 20T, 60T and 40T.  If the speed (RPM) of the 20T is say 1000 then the equation for calculating the RPM (x) of the assumed 40T gear is 

x = 1000(20/60 * 60/40) = 500.  

If you change the banjo gear (maybe that's what it's commonly called if there is only one) to 72T, the equation becomes:

x = 1000(20/72 * 72/40) = 500.

This applies for any number of spur gears in series so long as they are all in the same plane (not compounded).  Suppose that with the same 20T and 40T input and output gears, it was physically possible to put a 42 tooth gear on the left end of the banjo and a 36T between it and the gearbox gear.  The equation would be:

x = 1000(20/42 * 42/36 * 36/40) = 500.

Regardless of how many gears are in the train, so long as they are all in the same plane, the only two that matter are the input and output gears.

If any of the gears in the train are compound gears, then the tooth count of both gears plus the input and output gears matters. 




GarageGuy said:


> I'm confused too... according to your post, this gear:
> 
> View attachment 84016
> 
> 
> can be *any* number of teeth and the speed of the lead screw won't change?  This is the banjo gear I thought we were talking about.
> 
> GG


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## wa5cab

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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## Jon In Tucson

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


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## wa5cab

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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## GarageGuy

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


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## Jon In Tucson

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.



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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## wa5cab

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 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. 

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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## wa5cab

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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## Jon In Tucson

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.


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## wa5cab

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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## Jon In Tucson

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


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## wa5cab

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.


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## Jon In Tucson

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


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## 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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