# I cut metric threads on my lathe today.



## n4zou (Feb 7, 2012)

I purchased my 12X36 import lathe new way back in 1988. I purchased it because it had English and Metric dials and change gears for cutting metric threads. Today is the first time I have ever used it for turning and threading metric parts. I made a new BXA T-bolt and and T-nut for an Atlas 12" Lathe. The Compound T slot is 5/8" and the bolt that attaches to the supplied BXA T-bolt is 15mm with a thread pitch of 1.5. The person that brought the Atlas lathe in wanted me to make a new T-nut and modify the supplied bolt to 1/2-20 on the T-bolt end because he was worried about the tight fit. I agreed with him except for turning down and threading 1/2-20 threads on that BXA bolt. I made the new T-nut and drilled and taped a 1/2-20 hole in it on my mill. That was easy. I then turned down a 5/8 cold rolled steel shaft to 15mm. that was only a .005 cut. I then turned it down and threaded it 1/2-20 to fit the T-nut. A test fit in the compound slot turned out nice. He was happy so far. This is when I discovered my lathe was not metric thread cutting ready. The manufacturer skipped putting a 1/4-20 threaded hole and set screw in the change gear that needed one and the bracket that holds the idle gear would not allow sliding the shaft in the slot where the idle gear would properly engage the other two gears. After 24 years it's a little late to complain to the dealer about the problems I had (LOL). I took it all apart and found the idle gear bracket slot needed a 1/2 end mill run through it to clean it up and I drilled and tapped the gear for a set screw. My friend was worried about the time it was taking me to fix my lathe. I told him not to worry as I was going to do this job for free. He got really happy at that point. After getting the lathe fixed and set up to cut 1.5 pitch threads I started cutting the threads to fit the 15X1.5mm nut that came with the BXA tool post. It was sort of weird using the forward-stop-reverse lever instead of the half-nut lever. I still used the cross slide handle to pull the tool out of the work. I got the hang of it after a couple of passes and started dialing in the compound for the next cut while reversing the carriage with the motor. The thread cutting went faster than I expected by doing that. When I started checking the progress by test fitting the nut on the threads I noticed the thread pitch was not quite perfect. The nut went on smoothly for about a 1/2" and then it got tight. I dialed in another .002 on the compound and cut another pass. The nut spun on smoothly and my friend was happy with the fit of the nut on the bolt. I told him it was close enough for government work as I retired from the military. He had a good laugh at that. We fitted his new BXA tool post to the Atlas compound and it fit perfectly. He took me out to dinner at an all you can eat joint which was just fine by me. I wonder if I'll still be alive when I need to cut another metric thread after another 24 years.


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## rake60 (Feb 7, 2012)

I have cut a few metric threads on my import lathe.

The forward / reverse thing isn't something I like, but it works.

Some of the "Old School Boys" will tell you that using the half nut is a 
poke and hope method of threading even an imperial thread.
They will insist on ALWAYS leaving the machine in a locked in lead while
they scrap, rip and tear the thread open at 14 RPM.

I had better quit at that.
I can see the hate mail coming already!  

Congrats on the successful metric threading n4zou! Thm:

Rick


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## tel (Feb 8, 2012)

No probs if you build Boggy's pop up threading tool holder - works like a charm!


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## Blogwitch (Feb 8, 2012)

Rick,

Threading is like every other machining operation, use whatever works for you.

As with most things, you can read all the books about the subject, but when you actually come to do it on your machinery using those read words of wisdom, it is a totally different kettle of fish. You tend to bugger up everything until you find what works for you.

Most of what you read in books is the theoretical perfect way or someones thoughts on how to do it. Getting YOUR machines to do it that way is another matter.

That is why on most of my posts that I have done about making something, I invariably use the words 'this is how I do it', purely because unless someone has EXACTLY the same equipment, that is set up EXACTLY the same as mine, then the results could come out completely differently.

So definitely no hate mail from this side. You have found your way, everyone else has to do the same.

We can only guide, not enforce.


John


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## mygrizzly1022 (Feb 8, 2012)

HI All

John.. Could not say it any better than you. Your post is bang on, Karma for you.
Bert


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## n4zou (Feb 8, 2012)

tel  said:
			
		

> No probs if you build Boggy's pop up threading tool holder - works like a charm!


That would not work on my Lathe. The spindle does not stop immediately when the forward-stop-reverse lever is switched from forward to stop. I did use my new cross slide stop which made returning the cross slide dial to zero a lot faster. It was also easier to build and cheap to make.
http://www.homemodelenginemachinist.com/index.php?topic=17467.0


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