Starting a thread on the lathe with a die

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RSG
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Starting a thread on the lathe with a die

Post by RSG » Sun Dec 31, 2017 1:05 pm

I'm about to thread some 303 stainless with a 5/16-18 die and find it difficult to start the thread. I am using a die holder I made and so far the only way I've found to start the thread is to put pressure on the die with the tail stock but even then it's tough. Any suggestion would be appreciated.

Ron
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Mr Ron
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Re: Starting a thread on the lathe with a die

Post by Mr Ron » Sun Dec 31, 2017 1:30 pm

You need to put a chamfer on the end of the rod so the die can get a grab. Some pressure is also needed to get the die started. After it is started, the die will self feed.
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BigDumbDinosaur
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Re: Starting a thread on the lathe with a die

Post by BigDumbDinosaur » Sun Dec 31, 2017 3:32 pm

RSG wrote:I'm about to thread some 303 stainless with a 5/16-18 die and find it difficult to start the thread. I am using a die holder I made and so far the only way I've found to start the thread is to put pressure on the die with the tail stock but even then it's tough. Any suggestion would be appreciated.

Ron
As said above, some pressure is required to get the die started, which is no different than when manually cutting threads. A gentle chamfer assists in getting the die started and also helps to center the die so you don't get askew threads. Once the die has cut three or four threads it will self-feed.

Although 303's chemistry makes it less difficult to machine than other austenitic stainless alloys (e.g., 304 and 316), you must flood the die and workpiece with cutting lubricant as you are threading. Also, run your lathe very slowly to minimize heating. Inadequate lubricant and/or excessive speed will likely result in a raggedy thread and die damage. My go-to lubricant for any stainless machining, including thread cutting, is a mixture of mineral spirits and petroleum-based cutting oil, 10 percent mineral spirits and 90 percent oil.
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liveaboard
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Re: Starting a thread on the lathe with a die

Post by liveaboard » Sun Dec 31, 2017 4:44 pm

Cut stainless with a die?
It never worked for me, but maybe you have better dies than I ever did.

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RSG
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Re: Starting a thread on the lathe with a die

Post by RSG » Sun Dec 31, 2017 5:49 pm

Thanks for the replies, the chamfer idea is good but I guess I should have been more clear to begin with. There is an internal thread as well that is 12-24 and the face of the thread lip is important to have a flat on it so the internal threaded component can snug up to it. Here's a picture of what I'm doing. Either way what you are saying is I do need some pressure on the die to get it started, which is what I was doing, so thanks for confirming that.

Image
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RSG
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Re: Starting a thread on the lathe with a die

Post by RSG » Sun Dec 31, 2017 5:50 pm

Oh, and BDD, thanks for the lube recipe. I'll give it a try.
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GlennW
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Re: Starting a thread on the lathe with a die

Post by GlennW » Sun Dec 31, 2017 5:56 pm

I'd single point it if you want a nice thread that is concentric with the shaft.
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Re: Starting a thread on the lathe with a die

Post by John Hasler » Sun Dec 31, 2017 6:56 pm

RSG wrote:Thanks for the replies, the chamfer idea is good but I guess I should have been more clear to begin with. There is an internal thread as well that is 12-24 and the face of the thread lip is important to have a flat on it so the internal threaded component can snug up to it. Here's a picture of what I'm doing. Either way what you are saying is I do need some pressure on the die to get it started, which is what I was doing, so thanks for confirming that.

Image
Face off the chamfer after all the threading and tapping is done. I'd single-point it, though.

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Re: Starting a thread on the lathe with a die

Post by spro » Mon Jan 01, 2018 3:33 am

So the 5/16 X 18 is already internally threaded with 12 X24. What sort of set screw or pilot are you using inside? I've had to use something, especially when using a die.

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Re: Starting a thread on the lathe with a die

Post by tornitore45 » Mon Jan 01, 2018 8:20 am

When machining a part from scratch, if the thread is too delicate or too large that requires a lot of starting pressure I turn a little undersized spigot for about a 10-20% thread, it help start centered and feed. Then is turned off and chamfered.
Mauro Gaetano
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Re: Starting a thread on the lathe with a die

Post by RSG » Mon Jan 01, 2018 9:35 am

Glenn, I thought about doing it on the lathe but I'm not well versed on threading up to a shoulder that small and I have about 14 to do as well. I wish I could do it, it's one skill I've avoided perfecting.

I do like John and Mauros ideas and will give them a try today.

Thanks for the input guys and Happy New Year to the board!
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Re: Starting a thread on the lathe with a die

Post by John Hasler » Mon Jan 01, 2018 10:01 am

I like the idea of a spigot turned to the minor diameter rather than just a chamfer. If it's about as long as the die the die will be perfectly aligned when it starts cutting the first thread.

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