Need change gear help with a Vevor model YS-1835-A mini lathe!

Regarding the indicator dial, here is a short clip from Blondihacks tutorial on threading. She specifically says the indicator stops turning when the half nut is engaged.
 

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VicHobbyGuy said:
For regular turning (not thread cutting) I either remove the threading dial or swivel it so the gear teeth aren't engaged with the leadscrew. No point putting a lot of wear on it when it isn't being used, IMO.
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Good idea
 
VicHobbyGuy said:
In your original post, you said : "The manual and the label on the case say the gear setup needs to be a 40-tooth on A, a 65-tooth at B, nothing a C (?), and a 55-tooth at D. There are no 65 or 55 tooth gears in the set or even on the lathe."

The 65 tooth is just an idler; you could have used any gear that fits in that space (with adjustment). No matter; the 55 tooth may come in handy some day. It took a while before I understood how change gears worked - it's just arithmetic (ratio between the spindle and leadscrew rotations), but it can be confusing. :)
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Well….here’s a vid of my setup running. The printed 65T gear meshes with the 50T that is on the lead screw shaft. Maybe that combo is different on a different model?
 

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6Sally5 said:
Well….here’s a vid of my setup running. The printed 65T gear meshes with the 50T that is on the lead screw shaft. Maybe that combo is different on a different model?
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Yes, every time the 40T moves by one tooth, the 50T also moves by one tooth. It doesn't matter whether it's a 65T, a 60T, or a 63T in between-it's an idler. As long as you can adjust the banjo to get the idler to mesh with the other gears, you can use any size you like. I think you had 40T,50T,60T in your stock set of change gears?
 
Oh geez…just when I thought I might be understanding it! ‍. I guess I’d better get educated on gear ratios and the like! Yes, I have those in addition to a 30T, 35T, and 45T.
 
6Sally5 said:
Oh geez…just when I thought I might be understanding it! ‍. I guess I’d better get educated on gear ratios and the like! Yes, I have those in addition to a 30T, 35T, and 45T.
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It took me a while to have things start making sense. At the beginning I just 'followed instructions blindly' - which worked OK, mostly. :)
For more detail than you probably need or want, 'Screwcutting in the Lathe for Home Machinists' by Martin Cleeve is a good book.
There's a lot of arithmetic, but it isn't as bad as it seems at first glance.
Just playing with some of those gears on a tabletop, with marks to help count rotations, helped me.
Also, realizing that with a 16TPI leadscrew, setting the gears to make the leadscrew turn at the same speed as the spindle would produce a 16TPI thread was a 'slap forehead' moment. After that it was all ratios. As I said, I didn't find it very obvious at first! :)
Your 20TPI thread with a 16TPI leadscrew needed a 20:16 ratio, or 5:4 - thus the 50T and 40T gears, with the idler connecting them.
 
B2 said:
the manual for your lathe. I found it and according to the manual,
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I am still confused. That manual states that the lathe has a metric (1.5mm pitch) leadscrew. If that's true (and I have always assumed that all the Vevor lathes had 1.5mm leadscrews) I don't see how @6Sally5 could have cut an accurate 20 TPI thread using a 40 and 50 change gear combination. 20 TPI is a thread pitch of .050" A 40/50 gear set with a 1.5mm pitch leadscrew will produce a thread with a pitch of 1.2mm or .047"
That's a pretty big error (about 6%?). It would be interesting to see a close-up picture of that lathe-cut thread held up to a regular 1/4-20 bolt or threaded rod.
Or, take a piece of 3/8-16 threaded rod and hold it up to the leadscrew to check that pitch?
On a different Vevor lathe, MatthiasWandel found that the threading chart was full of errors, and apparently Vevor hired him to correct the charts.
Matthias said: "After much investigation, I realized the included threading table was very inaccurate, to the point of being practically useless for imperial threads."

So, perhaps the saga continues? :)
 
Here's the threading table from the manual that @B2 posted:
Vevor threading chart.JPG


Looking at the metric section, you can see that for a 1.5mm thread pitch, there's a 1:1; ratio between the spindle and leadscrew (40T and 40T gears with a 60T idler) - so that seems to confirm that the tables are calculated for a 1.5mm leadscrew.
Moving down to the Imperial thread section: For 24TPI, the recommended gears are 40T and 60T. (Ratio is 2:3 or .67) This will produce a thread with a pitch of 1mm or .039". 24TPI is about .042". so a pretty big error. The LittleMachineShop threading calculator suggests something like a 50T-60T/55T-65T gear combination - for a ratio closer to .70- to produce a 24TPI thread with very small (.06%) error.
https://littlemachineshop.com/reference/change_gears.php
For the 20TPI thread that @6Sally5 wanted, a better gear combination would have been 55T-any idler-65T, I think.
 
I would have thought the Vevor is all metric. I'd remeasure the lead screw over 32 threads. If an imperial 16 TPI, that would be 2.000". If metric 1.5mm, then 32 threads would be 48mm, not 50.8. 48mm is about 1.889", which would be easier to discern. If the OP has a 123 block, he can use it as a precise gauge. Just line up the 2" section to the lead screw and check that there's an exact line up with threads. Any discrepancy, then it's not an imperial thread. One needs to compare the same portions of the thread, pick a feature, like the leading edge.

For the new guys (saying this in general, not pointed at anyone) it's important to measure over many threads to get a good measurement. Measure over many threads, greater than 10, let's say N threads, and divide the result by N. This gives a significantly lower error than a single thread measurement.

Something else that is handy to have are thread pitch gauges. They can be purchased quite inexpensively and have saved me many a time. Buy both an imperial and metric set, you'll need them. With a pitch gauge, it's pretty easy to see if you achieved the correct pitch. I always check my scratch pass when threading to ensure it's right. Just something one learns to do. If it's the wrong pitch, you can fix it then. Later, you're stuck with the wrong thread.
 
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