Interchangeable gears on 7 x 12 King Canada lathe

[Robert Gallagher]

Hi,

I just purchased a Mini lathe.

I have never understood how to install the différent gear for thread shaping. Exemple: I need to make 3/8-24 thread; the label indicate that you need a 40T on the A spindle and a 60T on the D spindle. My understandind is no gears are needed on spindle B and C. When I go that route, gears A and D cannot engage.

what am I doing wrong here?
Thank you in advance.

 

[DPittman]

So you know some gears move on the "banjo" assembly themselves and the banjo assembly also moves?

 

[RobinHood]

The “stud gear“ is gear A in your chart (red circle). For 24 TPI, according to the chart, it needs to be 40 T. Gear D (blue circle) is 60 T. You already have that. Put any size, single gear in the middle ( ”B”, green circle - like the top gear train diagram shows [A-B-D]) to close the gap using the slot in the banjo and the banjo angular adjustment. All gear B does in this case is change direction of rotation of the output D. So you will need to use your feed direction lever to get the lead screw to turn the correct way.

Edit: when both the lead screw and the lathe spindle turn in the SAME direction, you will produce RH threads; when the lead screw and the lathe spindle turn in OPPOSITE direction to each other, you will get LH threads.



Let us know how that worked out.

 

[Robert Gallagher]

The “stud gear“ is gear A in your chart (red circle). For 24 TPI, according to the chart, it needs to be 40 T. Gear D (blue circle) is 60 T. You already have that. Put any size, single gear in the middle ( ”B”, green circle - like the top gear train diagram shows [A-B-D]) to close the gap using the slot in the banjo and the banjo angular adjustment. All gear B does in this case is change direction of rotation of the output D. So you will need to use your feed direction lever to get the lead screw to turn the correct way.

Edit: when both the lead screw and the lathe spindle turn in the SAME direction, you will produce RH threads; when the lead screw and the lathe spindle turn in OPPOSITE direction to each other, you will get LH threads.

View attachment 13891

Let us know how that worked out.

Hi Robinhood,

your answer has been a tremendous help understanding the gear change. Knowing that the B and C gears has effect on the ratio for thread cutting is the secret here. Yesterday night, after I purchased some tools from an old man close to home, I have been able to fabricate a piece. I will try to make the thread today.
Thank you very much.

 

[Robert Gallagher]

Hi folks,

after some noodling on the minilathe, I have yet to find the way to slow down the carriage speed. I though of installing the gear for 52 TPI, but it has no effect the carriage speed. So once again, I hit the wall.

Can someone chim in?

Thank you very much.

 

[DavidR8]

This may be useful to you. Pretty much all of the mini lathes have the same gearing arrangement.

 

[YYCHM]

Slow the carriage speed? What is it you are attempting to do?

 

[Robert Gallagher]

Slow the carriage speed? What is it you are attempting to do?

Hi, I am merely trying to make a pass using the carriage engaging thing? ( don't know the exact word........)

 

[DavidR8]

Hi folks,

after some noodling on the minilathe, I have yet to find the way to slow down the carriage speed. I though of installing the gear for 52 TPI, but it has no effect the carriage speed. So once again, I hit the wall.

Can someone chim in?

Thank you very much.

When threading, the carriage speed is related to the spindle speed.
For example if you are cutting a fine thread, say 32 tpi, the carriage will feed slower than cutting an 8 tpi thread.

 

[Robert Gallagher]

This may be useful to you. Pretty much all of the mini lathes have the same gearing arrangement.

Thank you very much David.

 

[DavidR8]

Thank you very much David.

For what it's worth, when I owned a mini lathe I ordered a set of 3D printed change gears because even with the largest gear the carriage feed was too fast. I'll see if I can find the link.

 

[YYCHM]

Hi, I am merely trying to make a pass using the carriage engaging thing? ( don't know the exact word........)

I think you're talking the half nut. That's actually more for threading than anything else. When I had my mini I just used the default gearing (feed rate) and jockeyed the spindle speed to achieve the finish I was looking for.

 

[DavidR8]

I think you're talking the half nut. That's actually more for threading than anything else. When I had my mini I just used the default gearing (feed rate) and jockeyed the spindle speed to achieve the finish I was looking for.

On the mini lathe the half nut is the only way to power feed the carriage.

 

[YYCHM]

On the mini lathe the half nut is the only way to power feed the carriage.

Yup, I realize that and the default feed rate is a pretty good compromised for most things. I was just asking what he was attempting to accomplish. If he uses threading gearing to control the carriage feed rate he will be cutting a thread.

 

[JReimer]

Just found this as I was trying to figure out the gears for my 7x12 lathe. But i need 11.5 this... which isn't on the chart. Anyone know any resources on how to figure out what I need?

 

[combustable herbage]

If you have a 3d printer the files for the gears are on thingverse.

C2 Mini lathe gear set (complete) by blue-v

The complete gear set for C2 mini lathe aka Sieg, Rotwerk, RC6120,... The gear set includes metric and inch gears. Also I made a 127 tooth gear, which is not part of sold sets, because it will not fit into the machine,unless you modify the gear train. Only the 127 tooth gear allows to cut "real"...

www.thingiverse.com

 

[VicHobbyGuy]

A few thoughts- I use a 7x lathe:
1- The spacer on the leadscrew needs to be moved if using only 3 gears in the change gear combination. Usually, I have to use a small gear as a 'filler' on the middle gear (the one with the keyed sleeve). BTW, be sure to keep that steel on steel 'bearing' oiled.
2-The 'stock' gear combination for turning is usually: 20-80-20-80 - this gets the leadscrew speed about as low as it will go with the stock gears. For better surface finish a 'slow gear' set is useful. Little Machine shop re-sells the PETG printed gears from 'Kwick' Aronson and you can order them directly from him, too. https://www.mmandls.com/product/mini-lathe-7x-slow-feed-gear-set-15-80-90t/ Steve Aylor (contact via Facebook) also prints and sells 7x lathe accessories from time to time.

3- Besides being the "go-to" source for parts and other stuff for 7x lathes and mini- mills, Little Machine Shop (a.k.a. LMS in online forums) has a lot of good resources available. They have a good generic 'User manual' for the 7x lathe. Also, a gear combination calculator which is useful: https://littlemachineshop.com/Reference/change_gears.php For 11.5 TPI:


4- There are a couple of spots online with good answers for 7x lathe questons (in my experience). If you use Facebook, the "7x mini lathe" group is very active and has a number of expert participants including Ted Hansen and Peter Brush + many inexpert folks like me who are willing to help. The groups.io "7x12Minilathe" group is also reasonably active. And of course, folks here are always willing to help but most suffer from a coddled life with bigger lathes and mills.

 

[JReimer]

Thank you, this is exactly what I was trying to find

a gear combination calculator