# G4003g: 91 and 86 End Gears



## Splat (May 11, 2019)

So tonight I was planning on my first cut threads, metric 1.25mm. All other threads I've done I've used a die or tap on the lathe. So I go to change my G4003g's   F and G gears and I notice the 91 and 86 tooth gears aren't right. The 91 is on the outside and 86 on inside. This is opposite of what the manual shows. Can anyone please verify the position of their 91 and 86 gears on their G4003g?   Thanks.

Ps, don't know if it matters but my lathe is from 2010.


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## epanzella (May 12, 2019)

It's been a while since I cut metric threads on my G4003G but I remember I had to do some finagling to get the power thru the right gears.  You can't do much with the position of the F gear but you have a lot of options with the rest of the gear train by flipping gears and changing spacers. My gears were all tight fits on their shafts requiring a gear puller so I bored them out a thousandth or two for a slip fit. It's easy to figure out once you get into it but at least on my machine the solution was more than just follow the manual.  BTW, if you need 27TPI you can use 40/any/60 and set the QC at C2.


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## Splat (May 12, 2019)

Yes, my gears are definitely not slip fit. I too used a puller. Good to know about 27tpi. Thanks!


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## Splat (May 12, 2019)

Finally found a thread about the end gears in the 12x36 import lathe Yahoo group. I also found a few older G4003G manuals. My 2010 manual incorrectly identifies the 86T and 91T gears. The 2011 version does show and indicate the gears in the stock setup, which is the 86T being the inner gear. That's how mine is. Interestingly, the latest manual on the Grizzly site shows the 91T being the inner gear! WTH? So which one is right? I think I'll leave mine as-is and resort back to using my 1.25mm thread die in a TS die holder.


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## Superburban (May 12, 2019)

How do they show the spindle gear driving the  combination gear? Everything I quickly looked at, show the spindle gear driving the larger (91 tooth in this case). My 2011 vintage lathe, I can set either the spindle, or the final gear in the inner, or outer position. So the 86/91 gear can be in either position, it just depends on what position the other two gears are set in. Looking at some random G4003G  pics in the google search, it looks like the spindle gear on many cannot be reversed to be bale to drive the outer position of the change gear.


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## hman (May 12, 2019)

Splat said:


> Finally found a thread about the end gears in the 12x36 import lathe Yahoo group. I also found a few older G4003G manuals. My 2010 manual incorrectly identifies the 86T and 91T gears. The 2011 version does show and indicate the gears in the stock setup, which is the 86T being the inner gear. That's how mine is. Interestingly, the latest manual on the Grizzly site shows the 91T being the inner gear! WTH?


I think this is a case of Grizzly buying their lathes from different manufacturers over the years.  

My own Grizzly 12x24 (Taiwan, 1990s) was badged DF1224G, but came with a G1003 manual and is very similar to the later G4002, 4003 and other 12x24 and 12x36 lathes, including the Enco 411-0105.  I have several old manuals that illustrate various similarities and differences.

By the way, my lathe uses the 127/120 gear cluster, so I unfortunately don't have any insight into how yours should be set up.


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## Mitch Alsup (May 12, 2019)

The 88/91 gears perform the conversion from inch to metric.
Since the lathe is inherently an inch lathe (the leadscrew is inch), 
AND since the <Norton> gearbox has lots of finely spaced selections,
.....factors of 2 on one handle, 8 selections between powers of 2 on the other;
When one puts power into the 88/91 and take it off the same gear; one is using the lathe in inch configuration. 
When you put power into the 88 gear and take it out of the 91 gear you are turning the inch lead screw at metric rates.

This is because there are 25.4 mm in an inch.
A big lathe might actually use a 254 tooth gear and match it with a 240 tooth gear.
Many lathes use 120/127 since 25.4/.2 = 127 and 120 is a convenient size when the other size is 127.
Our smaller 12×36 use 88/91 and 88/91 is 0.19% different than 120/127 which is identical to 240/256.


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## westerner (May 12, 2019)

Mitch Alsup said:


> Since the lathe is inherently an inch lathe (the leadscrew is inch),


This is the key, yes? The crux of the biscuit, so to speak. Since the leadscrew is the very last gear in the train, then it has the final say. That is how my poor little brain sees it, anyway. I love math, even though I ain't much good at it.


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## Splat (May 13, 2019)

Thanks guys. Manuals from different years show different inside gear, 91T or 86T. What's wierd is in my manual it shows "ANY" all down the middle of the list for metric threads. Not so with other year manuals and not so with the actual placard on my lathe's end gear cover. I've got it straightened out now. I have my 86T on the inner side and meshing with both 40T gears, as it was from the factory. I used the 1.25mm die and all went well. I will definitely try cutting threads with thread tool or boring bar but not at this moment. Too many other things on the back burner.


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## epanzella (May 13, 2019)

The 86/91 gear can be flipped with either the 91 0r the 86 on the inside. Mine came with the 91 in but I've used it both ways depending on the thread.


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## Splat (May 13, 2019)

epanzella said:


> The 86/91 gear can be flipped with either the 91 0r the 86 on the inside. Mine came with the 91 in but I've used it both ways depending on the thread.



So I understand you correctly here, are you saying you can cut metric with either gear on the inside? Not talking about feeding, only threading. It was my understanding it had to be the 91T on the inside to cut metric. Thanks.


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## epanzella (May 13, 2019)

Splat said:


> So I understand you correctly here, are you saying you can cut metric with either gear on the inside? Not talking about feeding, only threading. It was my understanding it had to be the 91T on the inside to cut metric. Thanks.


What I'm say is that you need to mesh the gears that the chart calls for to do a particular thread and how the gears were when you got the machine doesn't matter. If you can't make it work one way flip the gear over and do it the other way.


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## Splat (May 13, 2019)

epanzella said:


> What I'm say is that you need to mesh the gears that the chart calls for to do a particular thread and how the gears were when you got the machine doesn't matter. If you can't make it work one way flip the gear over and do it the other way.



Yes, I understand that.  I thought you meant it didn't matter re: the middle gears. That's actually what one would believe if they read the crappy manual I got with the machine. They corrected many errors in the next, 2010, edition, btw.


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## Superburban (May 13, 2019)

Yea, my lathe also says "any" in the chart, but the diagram to the left shows the spindle gear "F", mating with the 91 tooth gear, and the QCGB gear "G" mating with the 86 tooth side.


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## epanzella (May 13, 2019)

Splat said:


> Yes, I understand that.  I thought you meant it didn't matter re: the middle gears. That's actually what one would believe if they read the crappy manual I got with the machine. They corrected many errors in the next, 2010, edition, btw.


When ever you use one gear as the middle gear it doesn't matter how many teeth it is as it changes nothing.  eg; 40/91/60 is the same as 40/86/60 or 40/25/60. That's why the top section of my chart shows "any".  The bottom four parts of my chart also shows "any" which is incorrect. The picture in the far left column correctly shows the F gear meshed to the 91T and the G gear meshed with the 86T. That's definitely not "any".


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## Splat (May 13, 2019)

epanzella said:


> When ever you use one gear as the middle gear it doesn't matter how many teeth it is as it changes nothing.  eg; 40/91/60 is the same as 40/86/60 or 40/25/60. That's why the top section of my chart shows "any".  The bottom four parts of my chart also shows "any" which is incorrect. The picture in the far left column correctly shows the F gear meshed to the 91T and the G gear meshed with the 86T. That's definitely not "any".



I see. I'm not too up on gearing so didn't figure about the middle gear not mattering if both F and G gears mesh with it. Thank you.


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