How to cut threads on a lathe

[kvom]

My 13 inch Sheldon with an 8TPI leadscrew will pick up a 10 TPI thread just fine when I open the half nuts, crank the apron back, and close the half nuts on any of the marks on my thread dial.

You are correct. Brain fart when posting above. :hDe:

 

[kuhncw]

No problem, KVOM. I was just puzzled by the comment. Those brain farts happen to me as well.

Regards,

Chuck

 

[vascon2196]

A decent pdf of the SB HTRAL

http://www.scribd.com/doc/62662262/South-Bend-How-to-Run-a-Metal-Lathe

Here is a 60 guide to lathe threading it was written for Mach 3 cnc but a lot of the considerations are common with manual threading.


http://www.machsupport.com/docs/Mach3_Threading.pdf

Tin

Thank you Tin...I love that SouthBend book!!!

 

[vascon2196]

I just spent about 4 hours slowly turning the first part for my Quadricycle and attempted to turn a 5/8"-11 thread in the process.

Everything was going great until the 5/8"-11 nut that I have did not fit. I grabbed a thread guage and sure enough it was off....it does not even match anything??????

Here is a picture of the sticker on the lathe....for an 11 it looks as if lever "B" and "D" need to be selected and "1" "V" for the other two knobs. I then set up my dials and chose the #1 on the spinning dial. I then proceeded to use the same number, #1, for the entire process.

Can anyone see what I am doing wrong?

The first couple of threads seem okay but then it goes to hell.

50" long piece of stock is now scrap.

 

[sssfox]

Do you have the 60 and 66 tooth gears installed at positions A and B on the banjo?

You know you don't need to turn the entire thread before you check the pitch? If you just put a "scratch" on the stock, you can make sure it's correct before you ruin something.

 

[vascon2196]

Do you have the 60 and 66 tooth gears installed at positions A and B on the banjo?

You know you don't need to turn the entire thread before you check the pitch? If you just put a "scratch" on the stock, you can make sure it's correct before you ruin something.

Unfortunately I am unfamiliar with the "banjo" and I do not know anything about installing gears. I thought the levers took care of that.

I made a 1/2"-13 thread the other day without a problem and now having difficulty with the 5/8"-11?

Do I have to take the gearbox cover off to change gears?

 

[sssfox]

If you look at the lever diagram you attached, in the upper left-hand corner, it shows three circles that represent gears: A, B and 120t. If you look at the chart, it shows that you need A= 60 and B= 78 for 13tpi. Look at the top of the 11 and it shows A= 60 and B= 66. Those gears are on an adjustable bracket called a banjo. With your current settings, you should still be getting 13tpi.

The gears should be behind the cover where the chart is. You should have some extra gears that came with the lathe.

 

[sssfox]

Chris,

Your shaft isn't necessarily trash. You can make a nut that fits the threads that you put on there. I guess 5/8-13?

 

[vascon2196]

Ahhhhhh!!!

Thank you for pointing this out!

I took the platic guard to the left of the headstock nad staring me in the face were the change gears! I then looked in the bottom drawer of our toolbox and there was a pile of spur gears that have been kicking around for years. Now I know what to do with them!

Oh boy....you learn something new everyday.

Thanks again to everyone for all of your help.

 

[vascon2196]

:wall::wall::wall::wall::wall::wall::wall:

Now I cannot locate the 66 Tooth spur gear to make the 5/8"-11 thread!

Looking through the Supermax manual the gear is MOD1.25x66T

I cannot find anyone who stocks metric gears and the supplier is no longer in business. So without this gear I cannot make a 5/8"-11 thread on the lathe!:rant::rant::rant:

 

[sssfox]

Chris, sorry to hear that. It always seems to work out that way, doesn't it?

Sounds like a good time to learn to make your own. It really isn't that difficult. There are a lot of places on the web that describe the process. All you need are a mill with a flycutter and some type of dividing head/rotary table. Make the single point cutter to fit the 60t gear and it will work fine.

It doesn't need to look perfect, it just needs to fit. I've made several for my old Atlas lathe from PVC plate.

 

[sssfox]

Chris

Here is a PDF of what I believe the gear should look like. According to Gearotic Motion, it should be 85mm outside diameter (3.35"). I didn't know what the shaft diameter was, so I used 5mm. If you print this file full size, it should be exactly that and the tooth profile should match.

If nothing else, you know what you are working with.

Hope this helps,
Steve Fox

View attachment 66tMod1.25.pdf

 

[Bastelmike]

I just spent about 4 hours slowly turning the first part for my Quadricycle and attempted to turn a 5/8"-11 thread in the process.

Everything was going great until the 5/8"-11 nut that I have did not fit. I grabbed a thread guage and sure enough it was off....it does not even match anything??????

Here is a picture of the sticker on the lathe....for an 11 it looks as if lever "B" and "D" need to be selected and "1" "V" for the other two knobs. I then set up my dials and chose the #1 on the spinning dial. I then proceeded to use the same number, #1, for the entire process.

Can anyone see what I am doing wrong?

The first couple of threads seem okay but then it goes to hell.

50" long piece of stock is now scrap.

Hi Chris,just had a quick look at Your gearbox setup. If I'm not mistaken, Your 1-2-3-4 Lever should be in the 1 position. In the pic it seems to be 2 !Another point: You need a transition 60:66, if You would write the teeth number of all gears You have, maybe there's another gear combination that will do this.Mike

 

[vascon2196]

Chris

Here is a PDF of what I believe the gear should look like. According to Gearotic Motion, it should be 85mm outside diameter (3.35"). I didn't know what the shaft diameter was, so I used 5mm. If you print this file full size, it should be exactly that and the tooth profile should match.

If nothing else, you know what you are working with.

Hope this helps,
Steve Fox

Steve..that does help. When I get back to work on Monday I will check the tooth form against what I currently have. I finally got in contact with a supplier in California regarding spare parts...I am waiting to hear back from them on stock and lead-time.

Thank you for your advice Steve.

 

[vascon2196]

Hi Chris,just had a quick look at Your gearbox setup. If I'm not mistaken, Your 1-2-3-4 Lever should be in the 1 position. In the pic it seems to be 2 !Another point: You need a transition 60:66, if You would write the teeth number of all gears You have, maybe there's another gear combination that will do this.Mike

Thank you Mike. A huge part of me goofing all of this up is that I never had basic machine shop training. If I was not so damn busy I would love to start right at the beginning....layout work, lathe work, mill work, fixturing, tooling, and everything related to machining. This issue has taught me a lot though. I now know more about threading in this past week than ever before!

I will sort through the gears I found to see if other combinations will work.

Thanks again.

 

[peterw51]

Hi all, I have been following this thread, and with some help from DR jo, I have just turned my first 1mm pitch thread & it looked good against the thread gauge. Thanks vascon for starting the thread & all the members who took the time to help others.

 

[vascon2196]

You can learn SO MUCH from everyone here....I use the forumn almost weekly in my Manufacturing Processes class when teaching. Whenever I get stumped, this is the first place I go to when I need the answer.

 

[Jtrain]

I found this, so I c&p it here, it seems like a good expanation in most parts to me, hope it helps others.
John


The lead screw is the part of the lathe that determines the pitch or number of threads per inch that are being cut. Machines that have inch dials and gear boxes will have a lead screw with an even number of threads per inch and will range from two threads per inch to perhaps 16 threads per inch with small bench lathes having 8 TPI or 16 TPI.
If you cut 8 threads per inch with an 8 thread lead screw then the spindle and the lead screw are rotating at the same speed so the half nuts can be closed in any position on the threading dial. You will pick up the thread in the work you are cutting when you close the half nuts. If you wish to cut 16 TPI then the lead screw will be turning at half the speed of the spindle and 12 TPI will be three quarters of the spindle speed or 3 revolutions for every 4 revolutions of the spindle.
If a machine does not have a device to tell you when the lead screw and spindle have come into synchronization then you would have to close the half nuts when starting to cut your thread and not open them again until the thread is complete. This can only be done by stopping the spindle retracting the tool and reversing the rotation until the carriage returns to a point where you can take another cut. This operation is repeated until the thread is finished. Needless to say this can be a very tedious and nerve wracking exercise.
Fortunately thread cutting dials are available that allow the half nuts to be opened and the carriage moved back to the start without losing control over the relationship of the screw and spindle. The dial reads directly from the lead screw using a gear that fits the screw. The gear on the dial will usually have a gear with 4 times the number of teeth as the pitch of the screw. For example an eight pitch screw will mesh with a thirty two tooth gear giving you four positions on the dial where the screw is synchronized with the dial.
The dial will be divided into usually 8 divisions that are numbered one to eight. Each lathe will have a chart that relates to the dial, listing the different pitches to be cut and the positions on the dial where the half nuts can be closed. For example there may be a group of pitches listed and the chart will say you can close the nuts at any number on the dial. You will see another group of pitches listed and the chart will say you can close the nuts only on one, three, five and seven.
You will probably find other pitches where the chart will say that you can only close the nuts at the same number each time. Thread cutting with the dial will become second nature to you with a little practice

 

[jerryc]

If you have an old machinist's handbook, such as Machinery's or Audel's from the 30's/40's from when lathes and mills had gears that you manually changed, you will be able to use the direct gear chain computations. I only know this stuff because I went through an apprenticeship with a couple of old world Germans who showed me how to do it. ...and got cussed at in English and German if I did it wrong!

 

[Tin Falcon]

the last couple of issues of home shop machinist have articles by Randolph on lathe threading. my NOv/december issue came today with part 2.
as far as older machinery handbooks I have links here for out of copyright ones.
IIRC top of the link section as well as the getting started in model enginebuilding thread.
Tin