Gunsmithing Need help with threading on lathe (UPDATE)

[JBoomhauer]

Try threading without disengaging the half nut. Shut the lathe off when you reach the undercut. Back out. Start the lathe in Reverse direction to past the start point. Dial back in and cut forwards to the shoulder again.

 

[FCrifles]

If everything is how you state, try threading a piece of aluminum or steel with just plunging in with your crosslide, you can take .002" passes to ease tool pressure. Make sure you compound is tight and locked down.

Since you were feeding in with your compound the first time, check your gibs and make sure they don't need adjustment. If they are real loose, this could change your profile under load.

 

[Rubicon Precision]

If something was moving, the thread form would still be correct on both sides, just the angle would be off.

A worn leadscrew would have no effect on the thread form. Once the screw catches, the weight/friction of the carriage keeps the screw loaded the same every pass.

 

[Gunfighter14e2]

I've not threaded much, but it looks to me that the bit angle is off?

 

[Danny1788]

Interested to hear what he finds out. Those look way off and he looks like he is setting it up correctly.

 

[Easy_E]

It's hard to tell with the picture are you just cutting threads or are you shooting for a 1/2-28 fit ? What diameter are you starting with before threading ? It kinda looks like your thread is going good then starts the angle cut at the end ?

 

[cattleman99]

It's hard to tell with the picture are you just cutting threads or are you shooting for a 1/2-28 fit ? What diameter are you starting with before threading ? It kinda looks like your thread is going good then starts the angle cut at the end ?

Starting at .498, cutting 28 TPI

 

[cattleman99]

I was thinking and I decided to check to see if the insert was tightened down at a goofy angle in the tool bar, so I pulled the insert and put a new one in, making sure it was square in its spot. This is the result -

Still not perfect, but much better. Everything else was the same, feeding in the with compound at 29.5. Any tips on how to clean up the threads and make them more uniform?

 

[smoooth1]

I was thinking and I decided to check to see if the insert was tightened down at a goofy angle in the tool bar, so I pulled the insert and put a new one in, making sure it was square in its spot. This is the result -

View attachment 7116076

Still not perfect, but much better. Everything else was the same, feeding in the with compound at 29.5. Any tips on how to clean up the threads and make them more uniform?

On the last couple passes, run the cross slide in a couple thousandths , should clean them up.

Wire brush and a file works wonders too.

 

[Gunfighter14e2]

Start at 24.20 an listen to what he says about tool angle as he makes the final cuts.

 

[cattleman99]

Start at 24.20 an listen to what he says about tool angle as he makes the final cuts.

Very helpful. Thank you

 

[Easy_E]

Are you threading some bar stock or actual barrel ? I was beating myself up trying to get cold roll threads to look good picked up some barrel and it threads much nicer.

 

[cattleman99]

Are you threading some bar stock or actual barrel ? I was beating myself up trying to get cold roll threads to look good picked up some barrel and it threads much nicer.

Barrel

 

[cattleman99]

This is the result of the above method of feeding in with the cross slide and a couple clean up passes -

 

[JBoomhauer]

Getting better. Now increase RPM and flood with cutting fluid.

 

[DukeGSP]

looks good!