[Newbie] Gear configuration on Chinese lathe

[Lo-Fi]

OK, this should work:


You have these options:

A	B	C	D
50	80	56	66
56	80	50	66
50	66	56	80
56	66	50	80

Doesn't matter which you choose, but you might find some don't fit within size/clearance/banjo constraints.

To explain:

84/56 is 1.5. This is a nice neat ratio. So mesh the 84 with the 56 on the spindle. The spindle will turn 1.5 times for every time the 84 gear makes a complete rotation.

Now, to calculate. This might seem a little roundabout, but bear with me.... There's no way to tell the calculators online (either the LMS or one I posted) that we've got a fixed pair of gears ahead of what it's going to calculate. Essentially, whatever we put downstream of that 56/84 wil turn 1.5 times fewer times than the calculator is expecting. But we can fool it by lying to it about the pitch of the leadscrew to compensate for that 1.5 ratio. A leadscrew that moves 1.5 times less than a 2mm screw for every rotation is 3mm. Nice and easy So bung that into the calc with everything as normal, but telling it you have a 3mm leadscrew and the table above pops out.

If you don't get it immediately, it doesn't matter. It'll work for any pitch you want, just keep that 84 tooth in that position and tell the calc you've got a 3mm pitch leadcrew.

I *could* have stuffed up some maths somewhere and bozo'd it, but I think that's right. Set the lathe up and see what you get. I like using a sharpie marker in the tool holder when playing with stuff like this. You can't get an exact 16tpi with the gears you have, but the calc shows those options to be within about 0.2%

Keep us posted!!

 

[jcmullis2]

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

I can’t honestly say I totally understand everything you just said but like I mentioned earlier I can substitute the positions of their ABCand D gears for my gears.
I appreciate your patience and understanding. Guys like you have always amazed me. You probably see machinery and stuff like this and instantly understand it. Guys like myself could spend their natural life and never comprehend it.
I really can’t thank you enough and I’ll definitely be tearing back into my gears when I get off work in a few hours. I’ll post the outcome so others will know incase they have the same lathe or gear setup.

 

[Lo-Fi]

Honestly, I have to work hard at it too. I used to look at people who had a shed full of machine tools and knowledge to use the them to their potential, and think "I want to be like that when I grow up". Now I'm well on the way, I'd like to think, but it wasn't so long ago I found stuff like this completely confounding! I suspect almost everyone here would say the same, but thanks none-the-less. Let's hope my rambling gets you going!

 

[markba633csi]

This is one thing I would look closely at if I was looking at buying an import lathe; does the threading chart in the manual match the chart on the front of the machine and are all the gears included
I have seen at least one case here on the forum where the manual and the machine chart didn't match- it was as if they were from two different machines
-M
ps I believe it's a bit easier to convert an imperial machine to do metric than the other way round

 

[atunguyd]

OK, this should work:
View attachment 346107

!!

If gear A is meshing with gear C then A is just an idler here and does not come into the equation. Treat the ratio as spindle to C and then work from the. Doesn't matter how many turns A does relative to the spindle, for every tooth that the spindle moves gear C will move one tooth.

Sent from my SM-N975F using Tapatalk

 

[Lo-Fi]

If gear A is meshing with gear C then A is just an idler here and does not come into the equation. Treat the ratio as spindle to C and then work from the. Doesn't matter how many turns A does relative to the spindle, for every tooth that the spindle moves gear C will move one tooth.

Sent from my SM-N975F using Tapatalk

Agreed, but that's not the setup in the pic or that we're discussing. It's not possible to get very close to 16tpi with a simple gear train. I think about 15.8 is the closest, if I recall correctly.

 

[jcmullis2]

Agreed, but that's not the setup in the pic or that we're discussing. It's not possible to get very close to 16tpi with a simple gear train. I think about 15.8 is the closest, if I recall correctly.

My manual had nothing in it for imperial gears. The chart on it didn’t match the metric in the manual. The seller on amazon represented it did metric and imperial threads. Chinese instructions for you.
however I can’t blame it all on that. The absence of information on the internet surprised me.
I disassembled the change gears and went to your message with the explanation and realized a couple of things. The first thing being the 84t gear being meshed to the 56t spindle eliminates it from being used in any one of the ABC or D positions.That is if I understand you correctly.
Next I realized I had gears listed earlier that I don’t actually have. They were listed in the manual but not included. I actually have the following gears 20, 30,40,45,50,56,60,66,80,80. I didn’t include the 84t when I re-entered the gears in the LMS gear calculator. Those numbers show a .215% error or .0021” or 15.966tpi. I stopped there and wanted to ask you if that was a significant error. I also ordered a 42t gear from LMS. I’ll have to do some fitting but if it corrects the error then it’s money well spent.
Was I wrong in removing the 84t from the calculations?

 

[jcmullis2]

Lack of sleep has me over thinking things. I just read your instructions again and we’re on the same page. I actually confused myself. In looking at my choices of possible configurations it appears the only one that’ll work is the A=56 B=80 C=50 and D=66. The others would have the 84t meshed with the spindle and C gear. Hopefully nothing interferes with my only possible gear configuration for 16tpi. Maybe I can get some rest since you solved this puzzle. Thank you again for everything

 

[Lo-Fi]

Nice one, fingers crossed it all slots into place

What are you working on?

 

[jcmullis2]

Ultimately I want to learn how to thread and chamber my own rifle barrels. I’ve always been drawn to machining and thought why not. I know this sounds crazy but I wanna make a small gasoline engine. However first things first and I have to make tools. My first real project is a spider for my spindle. That requires internal threading but for that I had to learn how to set my gears up. Next I must learn external threading so I bought some round bar and tubing to start practicing.
I’m excited about learning how to do these things and wish they had a course or two offered locally. However the community college doesn’t have anything so I thought a place like this would be full of practical knowledge and tons of real hands on experience. At this point I have nothing to contribute but hopefully in several months I’ll be able to share what I’ve learned with others. My journey has begun and all because of your assistance. I’ll post my results after I actually cut some threads but I’m confident you’ve put me on the right path. I appreciate all of your help and I can’t thank you enough. I’m probably rambling a bit so I’m gonna stop here. Thanks again and happy holidays to you and yours