"Off centered" threaded parts.. Help?

JerryK said:
The tap follower is great, but how did you guide
the die with the chuck ?
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I just pushed the Jacobs chuck into the back of the die/handle.

4ssss said:
The minor dia. of the 5/16-24 is .280. If I'm reading this right you then only have a .060 wall (.400-.280) With the harder steel, I'll guarantee you that it's heating up and crushing. I never cared for Tap Magic, it was either dark cutting oil or Kool Tool for me.

http://www.engineershandbook.com/Tables/threadlimits.htm
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Well, that's part of my problem sounds like.

I also turned it to the MAJOR diameter of 0.3125", which is another place I messed up.

Where are you picking up the minor diameter as .280? I see .260" as minor diameter. Are you using "pitch diameter minimum?" I'm not being confrontational, just trying to learn. LOL

This link has the minor diameter listed as .2614"

I guess I need to sort out a different place to thread these two parts together. I'd like for the final OD of the pen to be 0.335″.

I'll pick up some Kool Tool and give it a shot, I guess I aught to grab a machinist book as well.
 
BellyUpFish said:
3 jaw chuck.

No, I didn't indicate the work. Should have, clearly. I'm a YouTube taught, and still learning, obviously.

Turned both pieces down to 0.40" on the dot, but the center hole is off..
Click to expand...
It may be runout in the three jaw chuck. Put an indicator on the chucked workpiece and check before turning the work. If necessary, go to a 4 jaw chuck or a collet system to get more accurate results. Another option is to turn the entire length of the workpiece you will be using at the start so it will be concentric. After turning it, leave it in place until completely finished with the lathe operations. It will stay concentric that way.
 
In my experience, a thread produced with a die will often run off center. For a thread concentric with the shaft, single point threading will produce a superior thread. Even partially threading by single point, followed with a die will produce a better thread.
 
Bob Korves said:
It may be runout in the three jaw chuck. Put an indicator on the chucked workpiece and check before turning the work. If necessary, go to a 4 jaw chuck or a collet system to get more accurate results. Another option is to turn the entire length of the workpiece you will be using at the start so it will be concentric. After turning it, leave it in place until completely finished with the lathe operations. It will stay concentric that way.
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I'll give that a shot and see what happens. It would be nice to be able to leave the piece chucked up. I did quite a bit of taking it out and putting it back in, so there's bound to be some error there.

RJSakowski said:
In my experience, a thread produced with a die will often run off center. For a thread concentric with the shaft, single point threading will produce a superior thread. Even partially threading by single point, followed with a die will produce a better thread.
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I really need to get more experience single point threading..

JerryK said:
Die nuts usually start crooked without proper guidance.
Best guess from far away, that's the problem
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May very well be. I've just bought an MT2 arbor from Neil's Niche, I want to make a tool using it.
 
Fish, I see a number of issues with your set up that are or may be contributing to your problems.
1. You're using a 3 jaw so if you remove the work piece then you won't get it realigned again unless you have a set-tru chuck or collet system.
2. Stainless generally needs a larger hole to tap well. If you go with the charts the tap will often bind up. When working on thin walled pieces like this, it is usually better to bore it and then screw cut it.
3. Dies do not produce accurate threads. They will cut a class 2 okay but in thin wall work, the chances of distorting the tube are high and this goes for almost any material, not just stainless. A tailstock die holder might help with alignment but it won't help with the distortion. Again, your best chance is to screw cut the thread. You will need to pay attention to thread tolerances because the thin wall doesn't give you much room for error.

A pen seems like a simple project but due to the thin walls, deep holes and the need for precise alignment of at least two parts it is not that simple. I've done multiple projects on thin walled work pieces before and I know that using a die doesn't work well. Tapping a hollow work piece can also be difficult because you can't clamp down hard enough on the hollow work piece without distorting it. The best results I got came from screw cutting the threads.

Just my 0.02.
 
mikey said:
Fish, I see a number of issues with your set up that are or may be contributing to your problems.
1. You're using a 3 jaw so if you remove the work piece then you won't get it realigned again unless you have a set-tru chuck or collet system.
2. Stainless generally needs a larger hole to tap well. If you go with the charts the tap will often bind up. When working on thin walled pieces like this, it is usually better to bore it and then screw cut it.
3. Dies do not produce accurate threads. They will cut a class 2 okay but in thin wall work, the chances of distorting the tube are high and this goes for almost any material, not just stainless. A tailstock die holder might help with alignment but it won't help with the distortion. Again, your best chance is to screw cut the thread. You will need to pay attention to thread tolerances because the thin wall doesn't give you much room for error.

A pen seems like a simple project but due to the thin walls, deep holes and the need for precise alignment of at least two parts it is not that simple. I've done multiple projects on thin walled work pieces before and I know that using a die doesn't work well. Tapping a hollow work piece can also be difficult because you can't clamp down hard enough on the hollow work piece without distorting it. The best results I got came from screw cutting the threads.

Just my 0.02.
Click to expand...

I appreciate the reply and the advice.

I am still learning, but everything you said makes perfect sense and is showing up in real life for me.

I've spent the last couple hours rethinking how I'm going to tackle this project and I think I can do so without too much heart ache.

I'll let you guys know how i get along.
 
Here is an input from a rookie.

Align your lathe to the best of your ability with tools you have.

Cut your pieces a little longer, thread the pieces applying techniques as others suggested.

Screw the 2 pieces together, put a couple of drops of purple Locktite just for insurance. Hopefully the shoulders meet flush.

With the 2 screwed together turn them down as one piece. If you turn between centers I would not trust the center drill by itself. Initial drill, then with small boring bar, bore it with the compound set at 30 degrees. Sweep a dead center with an indicator, adjust compound till you have no indicator movement as you sweep the cone. You have a fairly new lathe, most likely your TS alignment is true the length of the bedways. My lathes are old, TS alignment varies from end to end of the travel.

With the 2 pieces turned together, you should have a seamless mating. Finish the rest of your steps, but do as much as you can with the 2 together.

To separate the 2, small amount of heat should allow you to unscrew them.
 
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