# Question about threading on a lathe



## PHPaul (Dec 14, 2018)

I have watched a few videos and believe I understand the basics of threading on a lathe.

My Grizzly mini-lathe has a threading dial and change gears so I'm pretty sure I'm ready to try to actually cut some threads on it.  I understand the difference between watching a video and actually making chips and I fully expect to deal with a learning curve.

My question, however, is about my Seneca Star 30 lathe.  It has a threading chart on an embossed plate and what appears to be a full set of change gears and I get how all that works.  What has me scratching my head is the fact that there is no threading dial on the apron.  This leaves me with three questions.  I suspect I know the answers as unhappy as that makes me:

1.  Is there a way to cut threads without a threading dial?   (I suspect not.)

2.  Is it likely that the lathe came with a threading dial and it has been removed at some point?  (I suspect so.)

3.  If I'm correct about Number 2, what are the chances that I can find a threading dial that will work on my lathe?  (Slim and none would be my suspicion.)


----------



## middle.road (Dec 14, 2018)

1.) Please post some picts, that'll give those of us who don't know a Seneca Star 30 from our Logan 210 a chance to help.
2.) I have spotted folks doing up the body, shaft, and the dial face via 3D Printing. 
3.) Then all we need to do is figure out the Spur gear.
4.) Perhaps someone here has one that we can reference.
5.) and we need to find out what they look like. Shouldn't be too hard to come up with a replacement for you. (famous last words.)
6.) May need to start another thread with a title something like "Threading Dial for Seneca Star 30". . .


----------



## Bob Korves (Dec 14, 2018)

Is the lead screw metric or imperial?  What is the pitch of the lead screw?  That is the only information needed...
This group has already been there...
https://www.hobby-machinist.com/threads/seneca-falls-star-30-lathe-resto-mod.68221/


----------



## T Bredehoft (Dec 14, 2018)

PHPaul said:


> 1. Is there a way to cut threads without a threading dial?



10. Position your tool for the start of the first cut. 
20. With the lathe running (slowly), engage the half nut.
30. when you've threaded far enough, turn off the lathe
40. Back the tool out.
50. Reverse the lathe, let the tool  run back beyond the start. 
60.Turn off the lathe
65, engage forward.
70. Run the tool in just a bit more. 
80. goto 20
Repeat until you've reached depth of cut.

I haven't written code for 18 years. it feels good.


----------



## RJSakowski (Dec 14, 2018)

T Bredehoft said:


> 10. Position your tool for the start of the first cut.
> 20. With the lathe running (slowly), engage the half nut.
> 30. when you've threaded far enough, turn off the lathe
> 40. Back the tool out.
> ...


The implication of line 80 is that the half nut has been disengaged.  Once the threading has been started , the half nut should not be disengaged until the thread is complete.    Basically, the procedure is that followed for metric threading on an Imperial lathe or vice versa.


----------



## P. Waller (Dec 14, 2018)

The only thing that a threading dial does is gear the spindle to the lead screw, absent a thread dial just retract the tool and run the tool back with the lead screw engaged. This is slow and tedious but you are a hobbyist not a production shop correct?

If indeed you require speed skip the whole half nut manual thing and buy a NC lathe that threads, it is way faster and easier to use.


----------



## PHPaul (Dec 15, 2018)

Thanks for replies!

I'd seen that restoration but had forgotten that he built a thread dial for it.  At the moment (and for the foreseeable future) 3D printing and gear hobbing is beyond my skill set and equipment availability.

I will get pictures of the overall lathe, apron and lead screw later this morning.

How does one tell if the lead screw is Imperial or metric?  I _assume _it's Imperial, but you know how that works.  I don't have an Acme pitch gauge if such a thing even exists.


----------



## ttabbal (Dec 15, 2018)

If you can get some STL files, I would print parts for you. I suspect that you still need to know the leadscrew specs though. What machine is it?


----------



## RJSakowski (Dec 15, 2018)

You can tell from the number of threads per inch.  An Imperial lead screw will have a nice round number of threads per inch; 8, 12, or 16.  If it's metricthere will be a number of threads plus a fraction in an inch.  Not having used a metric lathe, I don't know what the common pitches for their  lead screws are but most likely some multiple of .5mm.


----------



## P. Waller (Dec 15, 2018)

PHPaul said:


> How does one tell if the lead screw is Imperial or metric?  I _assume _it's Imperial, but you know how that works.  I don't have an Acme pitch gauge if such a thing even exists.


You measure the lead which may be done with a dial indicator.
The distance the thread travels per revolution is the lead, as an example a thread that advances .050" per revolution is 1"/.050 = 20 TPI. Inch thread systems are often specified in Threads Per Inch rather then lead.

Metric thread systems are often specified by lead, as an example M12 1.5 has a lead of 1.5MM per revolution and a nominal major diameter of 12MM.
This is a far more intuitive method of describing a thread feature, Major Diameter and Lead.

A 1/2"-13 TPI single start thread has a lead of 1/13 or .07692".
A 1.5MM single start thread has a lead of 1.5MM
Which of the above numbers is easier to understand?

Also do not confuse TPI and lead, every thread has a lead but the TPI is a different animal.
I turned ball screw ends this week, they were 1"-4 TPI threads with 4 starts giving them a lead of .250" X 4 for a total lead of 1.000" or 1 TPI/4
Like so



As you can see it has 4 starts.


----------



## T Bredehoft (Dec 15, 2018)

RJSakowski said:


> The implication of line 80 is that the half nut has been disengaged.



Good catch, I guess 18 years is too long. I should have spent more time de-bugging the "program."


----------



## P. Waller (Dec 15, 2018)

RJSakowski said:


> The implication of line 80 is that the half nut has been disengaged.  Once the threading has been started , the half nut should not be disengaged until the thread is complete.    Basically, the procedure is that followed for metric threading on an Imperial lathe or vice versa.


What programmable NC lathes employed 1/2 nuts if they are only 25 years old?
This is programming a thread cycle on a lathe made in 1996, simple as can be.


----------



## middle.road (Dec 15, 2018)

P. Waller said:


> What programmable NC lathes employed 1/2 nuts if they are only 25 years old?
> This is programming a thread cycle on a lathe made in 1996, simple as can be.


That's a plum fancy screen compared to the old 5" green/orange on black ones...


----------



## RJSakowski (Dec 15, 2018)

P. Waller said:


> What programmable NC lathes employed 1/2 nuts if they are only 25 years old?
> This is programming a thread cycle on a lathe made in 1996, simple as can be.


Here is a post about the same model lathe.  No CNC involved.
https://www.hobby-machinist.com/threads/seneca-falls-star-30-lathe-resto-mod.68221/


----------



## middle.road (Dec 15, 2018)

*@PHPaul, *Post some picts. Since the Seneca's were mfg'd in NY, and given the vintage of the one Bob linked, might we not assume that it is Imperial?


----------



## T Bredehoft (Dec 15, 2018)

The program I wrote is for MNC, Manual Numeric Control, Not CNC.


----------



## PHPaul (Dec 15, 2018)

The lathe.






The apron from the front.  Power crossfeed!






The apron from the side.  No evidence that I can see of a thread dial ever being present.






The lead screw.  Appears to be a 10TPI Imperial, yes?


----------



## middle.road (Dec 15, 2018)

Picture is too low of resolution to determine, but it almost looks like there is a round plugged hole above the handle, maybe. . .
Comparing it to the SF30 it's in the right place.


----------



## PHPaul (Dec 15, 2018)

In this area?  Not seeing it.


----------



## Bob Korves (Dec 15, 2018)

middle.road said:


> *@PHPaul, *Post some picts. Since the Seneca's were mfg'd in NY, and given the vintage of the one Bob linked, might we not assume that it is Imperial?


I completely understood that the lathe was US made when I posted, and understood the approximate vintage of the lathe.  That SUGGESTS that the lathe is imperial, but does not make it so.  Don't guess, prove!  

PHPaul's measurement appears to show 9 TPI.  Which could also be 2.82mm pitch, or maybe even 3.0 mm.  Definitely not 10 TPI per the photo.


----------



## benmychree (Dec 15, 2018)

If the thread to be cut is a factor of the lead screw, you can open the half nuts and restart the thread at any point where the half nuts will close; as an example, if you had a 4 TPI lead screw, you can cut 4,8,16, & 32 TPI without having a thread dial, otherwise you can simply back up the tool by engaging reverse back to the starting point, OR you can stop at the end of the thread, disengage the half nuts and measure back in full 1" distances and reengage the half nuts before starting the lathe spindle, that is what the thread dial does.


----------



## RJSakowski (Dec 15, 2018)

Bob Korves said:


> I completely understood that the lathe was US made when I posted, and understood the approximate vintage of the lathe.  That SUGGESTS that the lathe is imperial, but does not make it so.  Don't guess, prove!
> 
> PHPaul's measurement appears to show 9 TPI.  Which could also be 2.82mm pitch, or maybe even 3.0 mm.  Definitely not 10 TPI per the photo.


Apparently, Seneca Falls did use a 9 tpi lead screw. https://www.hobby-machinist.com/threads/change-gear-chart-for-9-tpi-lead-screw.52432/


----------



## middle.road (Dec 16, 2018)

RJSakowski said:


> Apparently, Seneca Falls did use a 9 tpi lead screw. https://www.hobby-machinist.com/threads/change-gear-chart-for-9-tpi-lead-screw.52432/


(8) I get, (10) I understand, but who in the heck would have thought that (9) was a good idea?
Facilitate the change gears? I'm trying to wrap my head around that one, and failing.


----------



## benmychree (Dec 16, 2018)

Weird ----- !


----------



## RJSakowski (Dec 16, 2018)

middle.road said:


> (8) I get, (10) I understand, but who in the heck would have thought that (9) was a good idea?
> Facilitate the change gears? I'm trying to wrap my head around that one, and failing.


My Grizzly 602 has a 12 tpi lead screw.  There are 48 teeth on the thread dial gear so it travels 4 inches for one complete rotation of the thread dial.   The dial has 12 divisions and any thread where the tpi is divisible by 3 can be engaged on any mark.  All other integer tpi are engaged on every third mark. and odd half integers on every sixth mark.
A similar setup should be possible for a 9 tpi lead screw but it's to close to midnight to try to work it out.


----------



## Bob Korves (Dec 16, 2018)

They only had one pair of master gears at the factory...


----------



## middle.road (Dec 16, 2018)

RJSakowski said:


> My Grizzly 602 has a 12 tpi lead screw.  There are 48 teeth on the thread dial gear so it travels 4 inches for one complete rotation of the thread dial.   The dial has 12 divisions and any thread where the tpi is divisible by 3 can be engaged on any mark.  All other integer tpi are engaged on every third mark. and odd half integers on every sixth mark.
> A similar setup should be possible for a 9 tpi lead screw but it's to close to midnight to try to work it out.


Heck, I'm trying to work out the 48/12/3, cause 3 doesn't go into 48... I don't think I have any gray matter to spare if we start discussing 9TPI...


----------



## Bob Korves (Dec 16, 2018)

middle.road said:


> Heck, I'm trying to work out the 48/12/3, cause 3 doesn't go into 48... I don't think I have any gray matter to spare if we start discussing 9TPI...


How about 3 times 16?


----------



## middle.road (Dec 16, 2018)

Bob Korves said:


> How about 3 times 16?


/me thimks it's time for bed...   duh!


----------



## P. Waller (Dec 16, 2018)

middle.road said:


> That's a plum fancy screen compared to the old 5" green/orange on black ones...


A <$100.00 Dell 16" monitor simply plugged in to the output that was used by the original 5" X 5" monochrome display which would cost >$750.00 to replace. Works a charm and is far easier on the old eyeballs.


----------



## middle.road (Dec 16, 2018)

P. Waller said:


> A <$100.00 Dell 16" monitor simply plugged in to the output that was used by the original 5" X 5" monochrome display which would cost >$750.00 to replace. Works a charm and is far easier on the old eyeballs.


performed that modification a few times over the years.
One of the first times around I remember the CRT (clunky 14") going crazy when we powered it up. One of the maintenance guys who knew electronics ran off to the Shack and picked up the parts to make a filter and another one of the guys made up a copper mesh 'box' for it and then it was fine. Too much noise in that old plant I guess.
Oh, and the cool aluminum mount they made for it was nice.
Wish that digital cameras were prevalent back then, It would be neat to have picts of that kind of stuff.


----------



## P. Waller (Dec 16, 2018)

middle.road said:


> (8) I get, (10) I understand, but who in the heck would have thought that (9) was a good idea?
> Facilitate the change gears? I'm trying to wrap my head around that one, and failing.


Because you can, there is nothing to stop a manufacturer from producing a 61/64 - 4 11/32  TPI thread  if they choose to do so.

I have made slightly off threads in the past as a joke on someone in the future (I do not dislike younger generations, keep them on their toes however), 3/8-15 1/2 TPI for example, these will drive someone trying to repair something at home 20 years from now completely batty.

Endless entertainment


----------



## Hoss (Jan 2, 2019)

Use the Joe pi method see Joe piezinsky on YouTube. He shows how to thread without fear


----------



## Firstram (Jan 2, 2019)

P. Waller said:


> Endless entertainment



Priceless


----------



## P. Waller (Jan 2, 2019)

Firstram said:


> Priceless


Unfortunately you never get to actually see the result of such subterfuge so it is a hollow joke, it does give me solace however that 20 years from now some poor bugger is going to be in his garage shop measuring these threads, scratching his head and proclaiming WTF.


----------

