Threading intimidation.

[Tb1988]

new member here. I’ve got an old south bend 9 model c. I’ve used a fair amount. I’ve always been intimidated to thread with it. Most threads need to make are very common so I have just used a tap or die as needed. And honestly will most likely continue to do so as it’s more than likely faster than adding and removing change out gears etc. however I have decided I would like to give it a shot and try to become familiar with it in the event I need to thread something that I don’t have a tap or die for or it’s not cost effective to purchase for a one off type job. I’ve done a lot of research on the subject. According to the diagram I’m supposed to run an 80 tooth idler gear. My lathe did not come with an 80 tooth, it’s an 81 tooth. I think I have most if not all the other gears. Except this one. This is where I need the help. I’ve gotten conflicting info, some say the number of idler teeth doesn’t matter as long as the stud gear and the screw gear are correct. I’ve also read if the diagram calls for 80 teeth it has to be 80 teeth. I don’t have a problem ordering a gear if I have to but if the 81 is close enough to work and still give me a proper thread then I’ll just use what I have.. thanks in advance.

 

[Jim F]

Re-count the teeth, SB did not make an 81 tooth gear.
Idlers just fill in space, stud and screw gears are the ones that matter.

 

[GeneT45]

Easy enough to verify. Set it up for your intended thread pitch, chuck up some round stock and make a scratch (very light) pass. Then check the pitch with a ruler or pitch gauge. Once you've made a scratch pass at the correct pitch, you're half-way there!

GsT

 

[Jim F]

Also, changing gears is not hard or time consuming.
I can change my C in about 3 min.

 

[GT-6 Racer]

If you are concerned about threading towards the chuck, check out Joe Pie’s video on threading with the tool upside running lathe in reverse. Works great especially threading to a tight shoulder.

 

[RJSakowski]

An idler gear doesn't figure into the thread pitch. Any gear that isn't keyed to another gear that is in the drive train or on an input or output shaft is immaterial. so switching They are used to obtain clearance between other gears or to reverse lead screw rotation relative to the spindle.

I dealt with having to change gears for threading on my Atlas/Craftsman 6x18 and my Grizzly G0602. To make matters worse, the lead screw was used for both power feed and threading which made for gear changes so switching between power feed and threading became a bother and like you, I tended to avoid single point threading. However, single point threading has the distinct advantage of creating a thread which is concentric with the work. It also offers the advantage of being in control of thread fit.

The answer to my dilemma was to replace the change gears with an electronic lead screw. Now I can change between power feed and threading, left or right hand threads, and various thread pitches or feed rates at the press of a few buttons. Single point threading has become a joy rather than something to be avoided.

 

[Jake M]

new member here. I’ve got an old south bend 9 model c. I’ve used a fair amount. I’ve always been intimidated to thread with it. Most threads need to make are very common so I have just used a tap or die as needed. And honestly will most likely continue to do so as it’s more than likely faster than adding and removing change out gears etc. however I have decided I would like to give it a shot and try to become familiar with it in the event I need to thread something that I don’t have a tap or die for or it’s not cost effective to purchase for a one off type job.

There's nothing wrong with that approach, and you're right, it's often much more efficient to use a tap and/or die. On the other hand, as you say, it could be cumbersome at best to own "every" tap and die... And sometimes you just need that teeny tiny little bet of accuracy that comes from making the threads on the same spindle, and the same setup as the rest of the part. That's not an every day thing of course, but somehow I find that cutting threads, watching them come to be, is very satisfying...

Quick tossout, changing gears is a thing that must be done on a C model. But I can assure you, after the first couple of times, you know which gear(s) are getting swapped, you know where they're going when you shift them into mesh, it gets much better. You still have to do it, but the pain factor drops tremendously.

I’ve done a lot of research on the subject. According to the diagram I’m supposed to run an 80 tooth idler gear. My lathe did not come with an 80 tooth, it’s an 81 tooth.

I think Jim is right, you wanna recheck the gear teeth. I'll bet that is an 80 tooth gear that you have.

I think I have most if not all the other gears. Except this one. This is where I need the help. I’ve gotten conflicting info, some say the number of idler teeth doesn’t matter as long as the stud gear and the screw gear are correct. I’ve also read if the diagram calls for 80 teeth it has to be 80 teeth. I don’t have a problem ordering a gear if I have to but if the 81 is close enough to work and still give me a proper thread then I’ll just use what I have.. thanks in advance.

Here's how you know- Yeah, you could get an answer, but working through this in your head for a minute will sort out every gear train you see in your life...

In a PLAIN gear train, only the drive and driven gear matter. (The input and the output). Each and every idler in between has it's own gear ratio, but because they are driven on one side, and drive on the other side, they cancel out as one to one in the math, so they can be ignored. Any tooth count for an IDLER will be fine.
You have a "fancier" gear train though. The stud gear, that's a "compound gear", because it "inputs" a different number of teeth than it "outputs". So the "driven" number does not match the drive number, so those must be correct. Yes, they're separate gears, but they're keyed together, and act as one. That WILL change the ratios, and therefore the tooth count on BOTH gear teeth of the compound gear will matter.
In this case, the spindle gear is a given, anything between the stud gear and the spindle (reversing gears) are idlers, and could have any tooth count. The stud gear (both gears) need the correct count. The 80 tooth gear is as large as it is for space and fitment. Any tooth count would work. And the last gear, the screw gear, that one needs an accurate count.

So in the context and constraints of this, the 80 tooth gear would not matter if it was 81 teeth, or 29 teeth, or 256 teeth, as long as the banjo has the physical space to make it all mesh together.


And aside from all of that...

You'll hear that you can thread with the compound, and you'll hear that you can plunge straight in... Both are right, but on a 9 inch south bend, you'll find limits... I strongly recommend using the compound to feed in. You also will hear to set it at 30 degrees 29 degrees, 29.5 degrees... They're all correct, and here's the trick- 30 degrees is the magic number, but you MUST be at or under. Under by a little won't bother anything. Over by ANY amount will bugger stuff up. The answer is "as close as you can get to 30 degrees WITHOUT risk of going over. 30 degrees. You'll want to leave a bigger window until you can sort out the accuracy of the scale on your compound.
And the catch with some lathes. Your lathe is (I believe, mine is) labeled "opposite" of lathes that are most common today. The difference is whether zero degrees is parallel to the spindle axis, or parallel to the cross slide axis. So when you hear 30, you're going to looking for 60 degrees on the compound. (That's thirty degrees away from 90, not 30 degrees away from zero as many lathes are). So you would dial in 60 degrees, 60.5 degrees, 61degrees.

And the Joe Pie way, threading upside down- A very nice method, but there are couple of issues with that in this specific case. First, the carriage is not all that heavy, and the front side is not "tied down" all that tight. You'll be into some chatter and carrying on before you know it. And second, it's got a threaded chuck. Turning in reverse needs to be very much respected, as all the cutting force (and the hammering from chatter and other carrying on IF that occurs) are all working to unscrew the chuck. You wanna be on a REAL HIGH confidence level before you consider that. Once that starts to happen, you WON'T have a chance to stop it.
I highly recommend the "conventional" way, with the tool bit right side up on this particular lathe.

 

[Tb1988]

Re-count the teeth, SB did not make an 81 tooth gear.
Idlers just fill in space, stud and screw gears are the ones that matter.

I counted it 4 times came up with 81 each time. I’ve got an 80 tooth gear but it’s keyed not an idler. I set the 80 on top of the 81 and the 80 tooth is slightly smaller in diameter. Also matched the teeth to one another and visually followed it round and the teeth become no longer aligned. So im certain its an 81

 

[Tb1988]

Easy enough to verify. Set it up for your intended thread pitch, chuck up some round stock and make a scratch (very light) pass. Then check the pitch with a ruler or pitch gauge. Once you've made a scratch pass at the correct pitch, you're half-way there!

GsT

I will do this thanks for the ide

 

[GT-6 Racer]

There's nothing wrong with that approach, and you're right, it's often much more efficient to use a tap and/or die. On the other hand, as you say, it could be cumbersome at best to own "every" tap and die... And sometimes you just need that teeny tiny little bet of accuracy that comes from making the threads on the same spindle, and the same setup as the rest of the part. That's not an every day thing of course, but somehow I find that cutting threads, watching them come to be, is very satisfying...

Quick tossout, changing gears is a thing that must be done on a C model. But I can assure you, after the first couple of times, you know which gear(s) are getting swapped, you know where they're going when you shift them into mesh, it gets much better. You still have to do it, but the pain factor drops tremendously.



I think Jim is right, you wanna recheck the gear teeth. I'll bet that is an 80 tooth gear that you have.



Here's how you know- Yeah, you could get an answer, but working through this in your head for a minute will sort out every gear train you see in your life...

In a PLAIN gear train, only the drive and driven gear matter. (The input and the output). Each and every idler in between has it's own gear ratio, but because they are driven on one side, and drive on the other side, they cancel out as one to one in the math, so they can be ignored. Any tooth count for an IDLER will be fine.
You have a "fancier" gear train though. The stud gear, that's a "compound gear", because it "inputs" a different number of teeth than it "outputs". So the "driven" number does not match the drive number, so those must be correct. Yes, they're separate gears, but they're keyed together, and act as one. That WILL change the ratios, and therefore the tooth count on BOTH gear teeth of the compound gear will matter.
In this case, the spindle gear is a given, anything between the stud gear and the spindle (reversing gears) are idlers, and could have any tooth count. The stud gear (both gears) need the correct count. The 80 tooth gear is as large as it is for space and fitment. Any tooth count would work. And the last gear, the screw gear, that one needs an accurate count.

So in the context and constraints of this, the 80 tooth gear would not matter if it was 81 teeth, or 29 teeth, or 256 teeth, as long as the banjo has the physical space to make it all mesh together.


And aside from all of that...

You'll hear that you can thread with the compound, and you'll hear that you can plunge straight in... Both are right, but on a 9 inch south bend, you'll find limits... I strongly recommend using the compound to feed in. You also will hear to set it at 30 degrees 29 degrees, 29.5 degrees... They're all correct, and here's the trick- 30 degrees is the magic number, but you MUST be at or under. Under by a little won't bother anything. Over by ANY amount will bugger stuff up. The answer is "as close as you can get to 30 degrees WITHOUT risk of going over. 30 degrees. You'll want to leave a bigger window until you can sort out the accuracy of the scale on your compound.
And the catch with some lathes. Your lathe is (I believe, mine is) labeled "opposite" of lathes that are most common today. The difference is whether zero degrees is parallel to the spindle axis, or parallel to the cross slide axis. So when you hear 30, you're going to looking for 60 degrees on the compound. (That's thirty degrees away from 90, not 30 degrees away from zero as many lathes are). So you would dial in 60 degrees, 60.5 degrees, 61degrees.

And the Joe Pie way, threading upside down- A very nice method, but there are couple of issues with that in this specific case. First, the carriage is not all that heavy, and the front side is not "tied down" all that tight. You'll be into some chatter and carrying on before you know it. And second, it's got a threaded chuck. Turning in reverse needs to be very much respected, as all the cutting force (and the hammering from chatter and other carrying on IF that occurs) are all working to unscrew the chuck. You wanna be on a REAL HIGH confidence level before you consider that. Once that starts to happen, you WON'T have a chance to stop it.
I highly recommend the "conventional" way, with the tool bit right side up on this particular lathe.

Good cautions on the Joe Pie method. I am on industrial lathes with camlock spindles and massive carriages. Didn’t consider translating this procedure to small lathes. Please reconsider using that method on your machine. Thanks for the correction and cautions Jake.