[Newbie] Gear configuration on Chinese lathe

[jcmullis2]

I recently bought a wm210v extended 8x31 Chinese lathe. They said it would cut imperial threads but the chart is useless. I want to single point 16tpi and don’t understand how to arrange the gears to get the 16tpi. The spindle has 56t and the lead screw is 2mm. The banjo has 3 pairs of gears. The top and middle pairs are gears and the bottom is a gear and a spacer. The top pair of gears on the banjo meshes to the spindle and the bottom gear turns the lead screw. I have the following gears 30,40,45,50,56,60,66,80,80, and 84. I tried the little machine shops gear program but it only shows 4 gears. I’m totally lost at this point and was hoping someone might be able to help me out with this.

 

[Lo-Fi]

The little machine shop calc will do what you want. You need to select "other lathe" and input your available gears and leadscrew pitch. Ignore the four min/max size boxes if you want. I've just run it; looks like you can hit that with an error of 0.0001" per inch with about 10 setups to choose from. Which you choose will be dictated by size restraints and what actually fits.

 

[jcmullis2]

The little machine shop calc will do what you want. You need to select "other lathe" and input your available gears and leadscrew pitch. Ignore the four min/max size boxes if you want. I've just run it; looks like you can hit that with an error of 0.0001" per inch with about 10 setups to choose from. Which you choose will be dictated by size restraints and what actually fits.

I appreciate you responding. I did all that before posting my SOS and it’s only giving me 4 gears A,B,C,and D. The lathe that’s pictured has A gear by itself at the top and B & C in the middle and D on the lead screw. Should I call my small gear on the top of my banjo B and forget about the large gear that touches off the spindle? Thank you for your help. It got the best of me yesterday. The gears are very tight and don’t separate easily. I look forward to hearing from you
Here’s what mine looks like.

 

[jcmullis2]

If I call the inside small gear on the top Pair A gear then which gear is B in the middle set? Is B gear now The large inside gear that turns from the would be A gear?

 

[Lo-Fi]

Ah, I think I see where your confusion is coming from.

The pic on little machine shop showing the positions differs from your setup by having a resersing mechanism and idler. The ider is driven either through two of the smaller white gears, or just a single one, giving a reverse rotation in one configuration. The idler and spindle gears are the same number of teeth. The idler then drives the first gear in the change gear train exactly like it would if you geared directly onto the spindle.

To make things single, your setup ought to have the 56 tooth gear meshing with the spindle. It then becomes the same as the LMS pic, just without the reserse idlers. Whatever gear you key to that 56 tooth then becomes A and hopefully it all falls into place. A is that first gear that you key to the 56 tooth. B is a gear that meshes with A. C is keyed to B and drives D on the leadscrew.

You can, of course, use a different gear other than the 56 to mesh with the spindle, but then you'll have to calculate with that ratio in the equation as well.

Hope that makes sense? We've all been there

And a warm welcome aboard, by the way!

EDIT: Hopefully I've not over explained that, just wanted to be super clear! Also, there's actually a better calc here:

https://bilar.co.uk/cgi-bin/change-gear-calculator.pl

 

[jcmullis2]

Ah, I think I see where your confusion is coming from.

The pic on little machine shop showing the positions differs from your setup by having a resersing mechanism and idler. The ider is driven either through two of the smaller white gears, or just a single one, giving a reverse rotation in one configuration. The idler and spindle gears are the same number of teeth. The idler then drives the first gear in the change gear train exactly like it would if you geared directly onto the spindle.

To make things single, your setup ought to have the 56 tooth gear meshing with the spindle. It then becomes the same as the LMS pic, just without the reserse idlers. Whatever gear you key to that 56 tooth then becomes A and hopefully it all falls into place. A is that first gear that you key to the 56 tooth. B is a gear that meshes with A. C is keyed to B and drives D on the leadscrew.

You can, of course, use a different gear other than the 56 to mesh with the spindle, but then you'll have to calculate with that ratio in the equation as well.

Hope that makes sense? We've all been there

And a warm welcome aboard, by the way!

EDIT: Hopefully I've not over explained that, just wanted to be super clear! Also, there's actually a better calc here:

https://bilar.co.uk/cgi-bin/change-gear-calculator.pl

I can’t thank you enough for your help. You obviously have a good understanding of how the gears work together.
I misspoke, I don’t actually have a 56t gear, it’s the spindle that’s the 56t. I’ve been looking at the banjo gears as 3 sets. A top set, a middle set and bottom set with gear and spacer.
The large gear on the Top of the banjo, that touches the 56t spindle is gear A. The gear that’s attached to A with the bushing, and not visible in the picture is B gear. The small outside gear in the middle section of the banjo is C and the larger inside gear on the same bushing is D gear. The bottom gear on the banjo that drives the lead screw is either E gear or F gear depending on where the spacer is located.
I’m seeing gears in my sleep. I never was good with math. I’m totally lost man.
I think If you could tell me what gears go in my A B C D E/F from any of the combinations from the little machine shop calculator I’ll be able to get my head around it. The first combination on the little machine shop list shows A=40 B=30 C=50 and D=84. Where would they go using my A,B,C,D,E/F.
I really appreciate your help with this.

 

[Lo-Fi]

No worries, it's why we're all here this place is like a giant "pay it forward". The great thing with conversations and learning experiences like this being on a public forum is that countless other people will no doubt benefit from it, even if we don't see it directly.

I'll try and figure out why they've chosen a 56 tooth wheel for the spindle. It seems an odd choice, but closer inspection of the pic you posted shows that setup having a first driven gear that's larger diameter. There's probably a cunning reason for it that's not immediately obvious. I'll do some calcs and get back to you. Don't sweat that it's hard - compound gear trains are not simple to calculate. Figuring what rate to turn the leadscrew in relation to the spindle is trivial, but working out how and if you can do that with certain gear combinations is not.

Rather than just figuring out how to get this particular 16tpi setup, it'll be more useful to understand how it's arrived at, so I'll do my best to do that.

 

[jcmullis2]

I can’t thank you enough for your help. You obviously have a good understanding of how the gears work together.
I misspoke, I don’t actually have a 56t gear, it’s the spindle that’s the 56t. I’ve been looking at the banjo gears as 3 sets. A top set, a middle set and bottom set with gear and spacer.
The large gear on the Top of the banjo, that touches the 56t spindle is gear A. The gear that’s attached to A with the bushing, and not visible in the picture is B gear. The small outside gear in the middle section of the banjo is C and the larger inside gear on the same bushing is D gear. The bottom gear on the banjo that drives the lead screw is either E gear or F gear depending on where the spacer is located.
I’m seeing gears in my sleep. I never was good with math. I’m totally lost man. If you could tell me what gears go in my A B C D E/F from the any of the combinations from the little machine shop calculator I’ll be able to get my head around it.

No worries, it's why we're all here this place is like a giant "pay it forward". The great thing with conversations and learning experiences like this being on a public forum is that countless other people will no doubt benefit from it, even if we don't see it directly.

I'll try and figure out why they've chosen a 56 tooth wheel for the spindle. It seems an odd choice, but closer inspection of the pic you posted shows that setup having a first driven gear that's larger diameter. There's probably a cunning reason for it that's not immediately obvious. I'll do some calcs and get back to you. Don't sweat that it's hard - compound gear trains are not simple to calculate. Figuring what rate to turn the leadscrew in relation to the spindle is trivial, but working out how and if you can do that with certain gear combinations is not.

Rather than just figuring out how to get this particular 16tpi setup, it'll be more useful to understand how it's arrived at, so I'll do my best to do that.

I would love to understand how it’s arrived at, however I don’t know if I have the capacity. I’m just being honest with you. I’m good at monkey see monkey do. That’s why I was asking about associating the Little machine shops ABCand D with my ABCDEand F. I figured once I learn where their A B C and D gears are on my setup I can use their calculator. Thank you for taking a look at this and walking me through it. There’s nothing out there explaining this lathes gear setup and several people have had issues as well. I look forward to hearing from you

 

[jcmullis2]

It just occurred to me the reason for them having 56t on the spindle. The spindle bore diameter on these lathes is 38mm so they probably went with 56t because they couldn’t use anything smaller.

 

[markba633csi]

Looks like your lathe may not natively cut 16 tpi, I found a Bolton manual for a similar lathe and it only listed 14 and 18 tpi. I tried to upload it but the file was too large- here is the link:
-Mark

https://boltontool.com/pdf/BT210V.pdf