How to cut a thread on a manual lathe (Intermediate method ideal for home workshop & hobby engineer)

How to cut threads on a lathe is a fundamental skill of any machine operator. This is an intermediate method that is ideal for most applications and lends itself perfectly to the home workshop and hobby engineer. Cutting threads on the lathe this way is both fast and low risk. The basic way to cut threads on a lathe is very slow. The more advanced way to cut threads on the lathe is a little more risky and you are more likely to make a mistake. It's not hard and i'm sure you are more than capable, there is just more to do and therefore more opportunities to make a mistake. I think this method of cutting threads on the lathe is a good compromise between the two. The beauty of cutting threads on a lathe using this method is it is very versatile. If you need to stop thread cutting and do another operation you can just come back to it and the tool with pick up where you left off. You can't to this with the basic method...

I was asked to make a new motorbike axle for a friends flat track motorbike. The axle is turned from S275 which is a steel with a yield strength of 275 MPa. It machines nicely and has good shock loading properties making it ideal for this application. The Axle consists of three diameters with an M14x1.5 thread on one end for a nut.

Here is a recap of the order of operations for cutting a thread on the lathe using this method.

First set up your part, tool, speeds and feeds.
Colour in the area you want to thread and do a scratch pass.
Check the scratch pass with a thread gauge.
Cut your threads.
Clean up with a file, emery paper, and scotchbrite.

For the actual thread cutting:
1) Wait for your number on the thread dial indicator
2) Then your number lines up, engage the half nuts.
3) The thread is cutting.
4) At the end of the thread, dis-engage the half nuts.
5) Withdraw the tool in the -X Direction. (+X if threading internally)
6) Move back in Z direction to your start point.
7) Put on your next cut and repeat until down to size.

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Cheers,

Rob
- Handmade Extreme -

Disclaimer: This video is meant for educational and entertainment purposes only. It is in no way meant to be a set of instructions and therefore no attempt should be made by any party to recreate what has been seen in this video. Any attempt to do so is done completely at your own risk.

[nathanhastings]

It is more imortant that you are taking the time to show someone how to do something . Good on ya mate

[andymodeller]

Nicely done sir. In the early 80's I was fortunate enough to have my employer fund a full 5 year mechanical engineering apprenticeship. This Brough back happy memories. Excellently and precisely explained.

[crystalgreco]

This is the method I have learned on the manual lathes. and always used. I used to make spindles for axles on semi tractors and stuff. Then I went to school for CNC and was smitten. Thank you for explaining this so well

[jaspreetmatharu]

My father used to do a 14 feet long shaft with ease.
I was about 11 or 12 years old maybe. He was a great turner. Passed away in 2012.
Wish he was alive to teach me all this stuff.

[guyloren]

Superb video mate, & demystified manual threading massively for me- been having to use retention screws instead of threaded parts on my hobby project due to lack of time to get trained up, & this has given me a mental grounding in the process to get started threading future builds.Brilliantly clear explanation- much obliged, sir!

[brianjohnson]

That was a brilliant lesson on thread cutting. I'm a very keen hobbyist and self taught. Your lesson has taken away most of the scary stuff for me. Thank you very much

[BLECHHAUS]

That's how I learned it during my apprenticeship but we also rotate the toolpost. Very good tutorial!

[tmcmellon]

Flip the tool upside down, and start the tool from the chuck side and feed toward the tailstock and run the lathe in reverse. Learned this from the best toolmaker I have ever know who was from Germany. Many advantages, the most important is that the chips fall down out of the groove instead of bouncing around in the groove and ruining the finish. Running off the part at the end is more forgiving and gives you more time to disengage the half nut, therefore you can run the rpm higher for smaller diameters. And no, you won't cut a left hand thread this way.

[zhiweima]

When I started my apprenticeship, I was taught how to calculate the thread depth (using simple mathematics). The second thing I learned is that when you did the final cut and the nut fits perfectly, NEVER to use a file on the thread or "scotch brite". The thread should be smooth and shiny. In this video, you can see on the "chip" that there is chatter. However, a good tutorial for a beginner !

[yeseniajulloa]

This is the method I learned in school, great job at making info more accessible.

[taxicamel]

This is a good, thorough, tutorial covering ALL steps in setting up the machine. I would offer to immediate improvements to ending up with a better thread. The first being a faster spindle RPM. It appeared the RPM chosen was simply the slowest ...which is fine. But the problem is this cutting speed is in fact very slow ....on purpose.

1) A faster CS would automatically provide a better finish on the thread form. But this is up to the operator and their comfort zone with operating the half-nut disengagement only, for this one example. As determined and explained, for this thread pitch, any of the 8 engagements on the thread dial indicator will keep the pitch ...so there is no challenge factor in engaging ....and this engagement can be as far away from the thread start point aw the operator chooses. It is the "disengagement" that is the critical point ....but this is also dependent on how wide the relief is. Nothing wrong with practicing this technique. It just requires concentration.

2) The depth of cut chosen was very deep on the second pass. Considering the extremely low RPM, this resulted in extremely poor surface finish because the metal was literally tearing off the parent material ....and the surface finish looked awful. The depth extreme depth of cut can be taken, but it need NOT be that deep. As the final thread depth of cut is approached, the actual cutting depth should be reduced, simply because there is more material being removed at the deeper cuts.

3) And lastly, it is very common practice to run at least one "extra" pass after the last finish depth has been reached. Even though this bar is supported on a center, the bar material still deflects. There was a lot of tool pressure still on the last cut. A "cleanup" cut just makes sense to perform. It will literally always improve the thread surface finish as well is what the female thread is going to be running on.

There wasn't very much offered about "fitting" the thread and the testing of the nut did not reveal very much either nor was there any mention about the fit/class considering this was only a tutorial using the cross-slide, ....enough said.

[Rubbernecker]

Excellent video!! I have seen dozens and dozens of videos of thread cutting. This one is by far the best and most well explained!

[CaptainSwoop]

Excellent, concise and honest presentation. No verbal diarrhea ... just tell it as it is. Well done ... thanks.

[lumpyzx]

So THATS the part I forgot to do, been a while since I've run a lathe and I was running some practice passes a bit ago on some plastic and a few times I cut right through the high side of my threads, wasn't sure why, now I know, I got certified as a machinist when I was 16 and I'm 22 now so I've forgot quite a bit, tryina get back into it and you just solved my issue, I knew it had to be something simple, I just forgot to wait for the number to come around before I engaged the feed

[Barrybushski-gekf]

My two cents worth……..engaging and disengaging the half nut lever is only done when you are cutting very long threads. With most typical threads such as this you simply withdraw the tool quickly at the end of cut and put the machine into reverse to get back to your start.

[tonybetts]

Great video .. in my school days we did so much theory on how lathes worked and then never got to use one.. now I'm at an age I can maybe buy my own and learn.

[martinS-vnwy]

I was taught to turn tool upside down, run lathe in reverse, and cut from chuck towards tailstock. This reduces the risk of a crash into the shoulder, and no need for a large undercut. I always cut threads this way, and have done for last forty-five years, unless using an Ainjest attachment.

[graemewhite]

Just found your channel as I've upgraded to an M300 from a Myford and liked your RPC video.
If you're just doing a simple "plunge cut" threading job and you have the nut handy for sizing, advance the top slide a couple of thou every cut, this mimics the angled top slide method and let's the tool cut primarily on its leading edge, reducing tip loading and generally provides a smoother finish to the threads.

[PiefacePete]

Many of your viewers (me, for instance), have less rigid lathes. If I try to plunge-cut a 1.5mm thread on my seventy year old Myford Super 7, I will end up with a lifetime supply of chatter marks!
For lesser beings like us, the 29.5 degree compound slide method is our saviour! Sadly for me, my lathe is also short of its thread-cutting dial... My father bought the lathe when I was five years old, and gave it to me thirty years later, so I know it did not ever have a dial... might be a project for me. 😜
Great video, thank you. It did drive me la-la though; your voice is very familiar, but I could not figure out why! 🥴
As an afterthought... because the Myford has a clutch, I can make a cutting pass, disengage the clutch and withdraw the tool, then wind the carriage back using the handwheel on the leadscrew. This is actually a very quick process, and works great with the 29.5 degree compound, and no threading dial... it's also pretty foolproof. 😛

[manin]

I got 11 cars and several motorbikes. I bought a lathe for this kind of projects.
I remember the first time I cut a perfect thread. It was like I'd mastered witchcraft!