Lathe HELP

[RafaelMarujo]

You mention a gearbox change lever. So does this have a way to dial in the desired cutting gear pitch? If so, then don't you just need to have a gear to connect from the spindle to the gearbox? If your spindle has 25 teeth and the gearbox has 100, then this will effect a 25/100 = 1/4 speed change.

KT

Thats whay i firsy thought, just a simple idle gear, but theres a banjo (broken also, but easy to make) , that makes me think there should be a compound gear reduction

 

[RafaelMarujo]

Thats whay i firsy thought, just a simple idle gear, but theres a banjo (broken also, but easy to make) , that makes me think there should be a compound gear reduction

As you can see here

 

[Lo-Fi]

Compound gear reductions are often used to keep the physical size of the gear train down when cutting finer pitches. Doesn't have to be one way or the other, though. The banjos are used just as much for making trains of idlers. Looks like you've got plenty of room to take up there!

 

[brino]

Isn't there a way to calculate the gear ratio by the already existing gears? If anyone knows the formulas we could just bruce force it

Great idea, but unfortunately there are a few other complications......

The math itself is not difficult, it's really just a string of fractions with "driving gear tooth count" on top (numerator) and the "driven gear tooth count" on the bottom (denominator).

The complications are:

1) how many intermediate gears? Without knowing the size and shape of the original banjo it's hard to guess the number of terms in the equation. Should the formula include 3 fractions? or 4 or 5? Some banjos are Y-shaped with slot for multiple gear axles.

2) down-stream gear box: you posted above a picture of a lathe identical to yours. It has a gear box with feed-change levers.
This will end-up being a "black box" on the output of your calculations. However, since you own this lathe you can look inside and count teeth on every gear. I did that on my lathes, really just to understand everything about them. I wiped off the gear and used a paint pen to mark the tooth where I started counting. This required a flashlight and mirror as well, to look thru the open bottom of my quick-change gear box (Southbend 9"). Of course I had the advantage of being able to verify them in a manual.

3) lead screw: Your picture shows that the lead screw looks very close to 4 tpi, but if this lathe was made in Spain, then it likely is metric, and
@T Bredehoft may be correct that it is in fact 6mm. Knowing this is required to work out how far the carriage moves linearly for each rotation of the lead-screw. Perhaps a screw thread gauge can help you to tell the difference.

4) gears that are pinned together need to be calculated a little differently. These may appear as two gears with key ways that together run on a small bushing also with a key. With a pinned pair of gears the "input" gear is only a driven gear NOT a driving gear, therefore its tooth count appears only in a denominator. Similarly, the "output" gear of the pinned pair is only a driving gear and so its tooth count appears only in a numerator.

5) gear spacing; what is there physically room for? for the given gear module (or diametral pitch), can you fit a 50 tooth gear, 64 tooth? 84 tooth?
It is hard to know what options we are allowed to plug into the equation.


Please know that I am NOT trying to discourage you!!!
You CAN figure this out and we will always try to help!

One other idea is to look at other lathe manuals for a "similar" arrangement. Look for one that also has a 25-tooth gear on the spindle and the same lead-screw pitch; you might be able to use those threading/feed charts exactly as they are (depending on what gears fit your banjo). But also look for any others with a 50-tooth gear on the spindle....that would just require a driven gear with twice the teeth later in the gear chain.

Please don't give up. That looks like an amazing lathe.

-brino

 

[DavidR8]

Is an Electronic Lead Screw an option here?

 

[RafaelMarujo]

Compound gear reductions are often used to keep the physical size of the gear train down when cutting finer pitches. Doesn't have to be one way or the other, though. The banjos are used just as much for making trains of idlers. Looks like you've got plenty of room to take up there!

With the 6mm pitch leadscrew,, would 25/100 make the correct pitches?
I dont know because the lathe doesn't have any charts, they're e all missing

Great idea, but unfortunately there are a few other complications......

The math itself is not difficult, it's really just a string of fractions with "driving gear tooth count" on top (numerator) and the "driven gear tooth count" on the bottom (denominator).

The complications are:

1) how many intermediate gears? Without knowing the size and shape of the original banjo it's hard to guess the number of terms in the equation. Should the formula include 3 fractions? or 4 or 5? Some banjos are Y-shaped with slot for multiple gear axles.

2) down-stream gear box: you posted above a picture of a lathe identical to yours. It has a gear box with feed-change levers.
This will end-up being a "black box" on the output of your calculations. However, since you own this lathe you can look inside and count teeth on every gear. I did that on my lathes, really just to understand everything about them. I wiped off the gear and used a paint pen to mark the tooth where I started counting. This required a flashlight and mirror as well, to look thru the open bottom of my quick-change gear box (Southbend 9"). Of course I had the advantage of being able to verify them in a manual.

3) lead screw: Your picture shows that the lead screw looks very close to 4 tpi, but if this lathe was made in Spain, then it likely is metric, and
@T Bredehoft may be correct that it is in fact 6mm. Knowing this is required to work out how far the carriage moves linearly for each rotation of the lead-screw. Perhaps a screw thread gauge can help you to tell the difference.

4) gears that are pinned together need to be calculated a little differently. These may appear as two gears with key ways that together run on a small bushing also with a key. With a pinned pair of gears the "input" gear is only a driven gear NOT a driving gear, therefore its tooth count appears only in a denominator. Similarly, the "output" gear of the pinned pair is only a driving gear and so its tooth count appears only in a numerator.

5) gear spacing; what is there physically room for? for the given gear module (or diametral pitch), can you fit a 50 tooth gear, 64 tooth? 84 tooth?
It is hard to know what options we are allowed to plug into the equation.


Please know that I am NOT trying to discourage you!!!
You CAN figure this out and we will always try to help!

One other idea is to look at other lathe manuals for a "similar" arrangement. Look for one that also has a 25-tooth gear on the spindle and the same lead-screw pitch; you might be able to use those threading/feed charts exactly as they are (depending on what gears fit your banjo). But also look for any others with a 50-tooth gear on the spindle....that would just require a driven gear with twice the teeth later in the gear chain.

Please don't give up. That looks like an amazing lathe.

-brino

Omg brino thank you so much, i agree with everything you said, and i have lookes for similar lathes with 25 teeth gear spindle, but the 50 tooth gear is a genious idea and i will try to search tomorrow!
Either way I'm going to count every gears in between and try to make a schematic of all the existing gears and see if i you guys can help. Thanks so much!!!

 

[Blair]

Hey guys, so i bought this lathe a couple of days ago, and im in the process pf restoring it. I knew it had some problems and most of them I already adressed, except for one, every change gear is missing, and since im relatively new to machining, i dont knows how to make the calculations to figure out what i need.
Can anyone help me out? Or better yet, teach me? Ive seen tens of videos about it, and still i get more and more confused
Anyway thanks for any help you can give
The spindle gear is: 25 teeth
The final gear is :70 teeth
Im only cutting metric threads, i will attatch pictures

Check this guy out, he has helped me out alot and he has a program called Ride the gear train, he will set you up and teach you about gear ratios

 

[brino]

@RafaelMarujo

I am almost finished an excel chart for your lathe....it already covers 14 of the 15 most common metric threads.

I have come up with gear ratios to allow it all to work, however, there will still be some figuring on your end.
To fully detail it, I'd need to build a model of your lathe (either real or in CAD) with the shaft spacing, banjo, and gear sizes all mocked-up.
That would allow me to check exactly what gears actually physically fit on your lathe.
However, that's easier for you to do on your end......"sweat equity" if you will...

Still for me to do:
i) finish the last 1 of 15 (0.35 mm pitch),
ii) I need to double-check the entire thing,
iii) I came up with one more question.....

Actually, two outstanding questions for you......

1) are you okay with me publishing the schematic you PM'ed me for your gear layout?
I'd like this posted so maybe it can help others, either by working thru it as an example, or for those with a similar lathe.

2) Are the existing 25-tooth gear on the spindle and 100-tooth gear on the gear-box input perfectly in line?
If you placed a straight edge against the side of the 100-tooth gear does it also perfectly contact the side of the 25-tooth gear?
Your 100-tooth gear seems to be on a key (see below).
Can that 100-tooth gear be placed in different positions on the shaft (ie. to the left or to the right)?

Thanks,
-brino

 

[RafaelMarujo]

@RafaelMarujo

I am almost finished an excel chart for your lathe....it already covers 14 of the 15 most common metric threads.

I have come up with gear ratios to allow it all to work, however, there will still be some figuring on your end.
To fully detail it, I'd need to build a model of your lathe (either real or in CAD) with the shaft spacing, banjo, and gear sizes all mocked-up.
That would allow me to check exactly what gears actually physically fit on your lathe.
However, that's easier for you to do on your end......"sweat equity" if you will...

Still for me to do:
i) finish the last 1 of 15 (0.35 mm pitch),
ii) I need to double-check the entire thing,
iii) I came up with one more question.....

Actually, two outstanding questions for you......

1) are you okay with me publishing the schematic you PM'ed me for your gear layout?
I'd like this posted so maybe it can help others, either by working thru it as an example, or for those with a similar lathe.

2) Are the existing 25-tooth gear on the spindle and 100-tooth gear on the gear-box input perfectly in line?
If you placed a straight edge against the side of the 100-tooth gear does it also perfectly contact the side of the 25-tooth gear?
Your 100-tooth gear seems to be on a key (see below).
Can that 100-tooth gear be placed in different positions on the shaft (ie. to the left or to the right)?

Thanks,
-brino


View attachment 358325

Hello brian, im so sorry for the late response, i have been super busy at work and barely come here anymore, and somehow i stopped receiving email notifications somehow?
Anyway, to answer your questions yes you can use anything i sent to help others, i just wanna be able to help people in need, just like you!
To answer the alignment question, is cant remember but as soon as i get home i will check and send some pictures, and ill know for sure...
Everything about the lathe as been restored, the only thing im missing is the banjo and the gears, and i cant wait to have them! Once again thank you so much for your time and help, and i hope everything is good with you and your family in these troubled times...
Thank you Brian!
Rafael Marujo

 

[brino]

im so sorry for the late response, i have been super busy at work and barely come here anymore, and somehow i stopped receiving email notifications somehow?

No worries.

Anyway, to answer your questions yes you can use anything i sent to help others, i just wanna be able to help people in need, just like you!

Great. I'll be back with some more info for anyone following along.

Everything about the lathe as been restored, the only thing im missing is the banjo and the gears

Nice, congratulations.
What have you turned so far?

thank you so much for your time and help

I am very glad to help.
Reviewing this info every few years helps keep it in my brain.

-brino