Logan quick change gear boxes, School me please.

[GarageGuy]

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

 

[Jon In Tucson]

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

 

[Snag_one]

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 .

 

[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.

 

[Jon In Tucson]

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

 

[Snag_one]

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>

 

[GarageGuy]

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

 

[John Hasler]

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.

 

[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

 

[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.

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