Change Gears for Jet 920N

Dbingen

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I purchased the lathe and found that 7 of the 9 change gears are missing. It doesn’t have the QCGB, but instead uses change gears on a banjo. Jet Machinery wants a small fortune for the gears, $45-$70, depending on the tooth count. Does anyone have an idea where I could source these gears? I am not adverse to using 3D printed gears, if I could find someone who could do that for me at a fair price. Thanks for any help you might offer.

....David
 
Good evening, Sir;

I realize this isn't going to help much, but here it is. Perhaps you can take this a little further and get a good fit-up.

The gears are(should be) Metric modulus one(1), 20 degree pressure angle, and an eight(8) MM face with a 12 MM bore. There is one pair, 127 and 120 teeth, that are basically an idler and metric/SAE conversion set. Although it is always in one or the other configuration, it can be changed, giving you other (unlisted) threads.

My machine has a QC gear box, so I can't reliably speculate on the tooth count you need. Both Grizzly and Harbor Freight are possible sources. Likely cheaper, but may need touching up a little. The given size is fairly common. You might try other sources, especially as sets, once you know what you need. They are used on many(if not most) of the lathes that size. The Grizzly model is G-4000(currently). The HF model I don't remember. But they're the same machine. There are many others, I just happen to remember those two.

There is one plastic gear that operates as a "safety valve". That one you need. The rest are steel. I wouldn't recommend printed synthetic gears, although they will work. They just won't last as long.

Your threading/cutting cherts should reveal the tooth counts you need. Keep in mind too, any "mis-fits" will change the threading. Often not that you can see, but it will be incorrect. If the chart calls for a 43 tooth, a 42 or 44 will fit well enough, but won't be quite right.

I realize this won't help a lot, but should get you started on the right path. I do have a related project that you may be interested in. http://www.hudsontelcom.com/9X20Gear.html It will give a little insight into your machine.

Bill Hudson​
 
Good evening, Sir;

I realize this isn't going to help much, but here it is. Perhaps you can take this a little further and get a good fit-up.

The gears are(should be) Metric modulus one(1), 20 degree pressure angle, and an eight(8) MM face with a 12 MM bore. There is one pair, 127 and 120 teeth, that are basically an idler and metric/SAE conversion set. Although it is always in one or the other configuration, it can be changed, giving you other (unlisted) threads.

My machine has a QC gear box, so I can't reliably speculate on the tooth count you need. Both Grizzly and Harbor Freight are possible sources. Likely cheaper, but may need touching up a little. The given size is fairly common. You might try other sources, especially as sets, once you know what you need. They are used on many(if not most) of the lathes that size. The Grizzly model is G-4000(currently). The HF model I don't remember. But they're the same machine. There are many others, I just happen to remember those two.

There is one plastic gear that operates as a "safety valve". That one you need. The rest are steel. I wouldn't recommend printed synthetic gears, although they will work. They just won't last as long.

Your threading/cutting cherts should reveal the tooth counts you need. Keep in mind too, any "mis-fits" will change the threading. Often not that you can see, but it will be incorrect. If the chart calls for a 43 tooth, a 42 or 44 will fit well enough, but won't be quite right.

I realize this won't help a lot, but should get you started on the right path. I do have a related project that you may be interested in. http://www.hudsontelcom.com/9X20Gear.html It will give a little insight into your machine.

Bill Hudson​
Thanks for the quick reply, Bill. I have a list of the change gears needed. It is out in the shop. I was looking for a source to purchase the ones I need. I appreciate the information on the geometry. I haven’t measured the gears I have. I have been told the bore is 14 mm. I will have to verify. I have 2 other lathes, a Harbor Freight 7X14 and an 11x48 Sheldon. I wanted a little larger lathe than the 7x14. Plus one that would do metric threads. I can do imperial threads with either one that I have. I will probably just purchase the gears that I need for metric threading, once I find a source.

...David
 
Can you still get the same gears from Grizzly? Might be cheaper than from Jet?
 
I will try them in the morning. I just found out the equivalent Grizzly lathe. I believe it’s a 1550.

..David
 
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