Change gear help

bpimm

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I thought I had a full set of change gears... I was trying to cut a 1mm thread pitch and was setting up the gears, it called for a 40 tooth and 127 tooth, I put the 127 on and went through the stack and no 40... How do I tell if the gears are Metric or Imperial? The lathe is a JET but it came from URPE in Spain in the early 80's.

I'm leaning toward Metric, OD is 4.25" or 108mm, Shaft size is 22.22mm or .875" but the key slot is what I'm basing my assumption on as it's 6mm or .236" not .250

If it's metric the module comes out to 1.5, the gear I'm measuring is a 70 tooth.

Also what else do I need to know to find a replacement gear

Thanks
 
Is there a differnece between metric and Imperial gears? teeth are teeth, diameter of gear is dependent upon number of teeth. The only thing to be metric would be the center hole.
 
A 127 tooth gear is commonly used on an imperial lathe for the ratio change needed to cut metric threads. Is your lead screw
in inches? Imperial gears use diametral pitch and metric gears use a system called module and the two do not fit together. Your gears
are all imperial or all metric. Machinery's handbook has life size diametral pitch gear tooth drawings that you can compare to your gears
as a way to determine what they are. By the way, where in the gear train is this 127 tooth gear?
 
Diametral Pitch = Number of teeth / Outside diameter.
In your case 4.25 / 70 = 16.4706 which isn't Imperial
 
Not sure what Jet Lathe model you have, but if it is a 1024 or 1236 model, here's the manual for the Grizzly Branded Version (It's the most thorough I've found) https://cdn0.grizzly.com/manuals/g9249_m.pdf

If my memory serves me, the 40 tooth Gears should already be installed, as they are part of the imperial threading.

For Metric Threading one of the 40 tooth gears is repositioned, such that one is engaged with the 120 tooth gear and the other 40 tooth gear is engaged with the 127 tooth gear of the 120/127 gear set.

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For Imperial Threading the 40 tooth gears drive the 120/127 gear one to one. Though this image show the two 40 tooth gears engaging with the 127 tooth gear, it would also work if they were both were engaging the 120 tooth gear, unlike for Metric Threading where the ratio of driving through the 120/127 gear is needed to convert from imperial to metric.


289803

Hope this helps.
 
It just occurred to me that you said this is a Jet lathe. I have a Jet 1340. I can check gear dimensions in a bit if you'd like.
 
Is there a differnece between metric and Imperial gears? teeth are teeth, diameter of gear is dependent upon number of teeth. The only thing to be metric would be the center hole.
There is a difference Inch gears measure diametral pitch whereas metric gears measure mod (modulus or module). The relationship between diametral pitch and mod is diametral pitch = 25.4/mod, the 25.4 being the number of mm in 1 inch. There will always be a difference in tooth spacing between metric and inch gears. For example, my Grizzly 602 has a mod 1.5 spindle gear. A B & S timing gear from a lawn mower engine has a diametral pitch of 16. Converting the latter to mod, the modulus would be 25.4/16 or 1.5875. It is close enough to mesh the two gears but the mesh would be imperfect and the gears would wear rapidly.
Diametral Pitch = Number of teeth / Outside diameter.
In your case 4.25 / 70 = 16.4706 which isn't Imperial
Actually, diametral pitch = number of teeth/pitch diameter. Diametral pitch = (number of teeth + 2)/ outside diameter which, as I recall, is exact. The diametral pitch would be 72/4.25=16.94 and the mod would be 25.4/16.94 = 1.502. The gear is a metric mod 1.5.
 
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Correct. Thanks for clearing up my mistake.


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A 127 tooth gear is commonly used on an imperial lathe for the ratio change needed to cut metric threads. Is your lead screw
in inches? Imperial gears use diametral pitch and metric gears use a system called module and the two do not fit together. Your gears
are all imperial or all metric. Machinery's handbook has life size diametral pitch gear tooth drawings that you can compare to your gears
as a way to determine what they are. By the way, where in the gear train is this 127 tooth gear?
The 127 tooth is the driven gear, I need to get a copy of the Machinery's handbook...
Here is a picture of the controls.
289818
and closeups of the charts.
289819
289820
Now after I look at these charts on screen, not down on a knee wanting to stand up as quick as I can, I'm seeing the possibility that I have 3 different combinations to get a 1mm thread pitch, Am I reading this right I could use a 40 and 127 with II-X selected or an 80 and 127 with II-XI selected or in the Mod section (I don't even know what that section is about) I could use 48 and 97 with I-X selected, if that's the case I can cut the thread.
The lead screw is in inches at 4TPI.
 
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It just occurred to me that you said this is a Jet lathe. I have a Jet 1340. I can check gear dimensions in a bit if you'd like.
It's a 1440 but it doesn't seem to correlate to any other jet lathes I have seen. Thanks for the offer.
 
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