How to Thread Without the Thread Dial by Jim B.

[HMF]

TO THREAD WITHOUT A THREAD DIAL by Jim B.

Start by setting up as you normally would, you can use back gear but that's a matter of how fast you are and how course the thread is.

Your part should have a thread relief.

Set the compound at 29 degrees (Standard 60 degree Vee thread, US or Metric)

Zero the compound, taking out the play in the in direction. (make sure you have enough travel in the "in" direction.)

Bring your tool in a just touch the work, zero the cross slide.

Back the cross feed out 1 full turn.

Back the carriage about ¼" past the start of the work.

Return the cross slide to zero. Advance 0.005 on the compound.

(NO THREAD DIAL)

Engage the half-nuts. NEVER DISSENGAGE THEM AGAIN UNTIL THE THREAD IS FINISHED!!!!!!!!!

When the tool enters the relief, shut the motor off. In back gear the spindle will stop within ¼ turn.

Back out the cross feed one full turn.

REVERSE THE MOTOR and back the carriage under power to a point ¼" past the start of the threads.

Shut the motor off.

Return the cross slide to zero. Move the compound in another 0.005. (0.010 total at this point)

Start the motor in forward.

When the tool enters the relief shut the motor off

Back the cross slide out one full turn.

Reverse the motor and back the carriage out ¼" past the start of the threads.

Every third pass is a spring pass.

Depending on the thread pitch after 0.010 to 0.015 reduce the depth of cut to 0.0025.

After about 0.040 to 0.060 reduce the depth of cut to 0.001.

When you are within 0.003 of the calculated depth start testing for fit on a "standard" nut!

When the nut starts to feel like it might be there, tight but does not screw in all the way. Start taking 0.001 at a time on your cross feed.

You can calculate the double depth in the following way.

(32/TPI)*0.040 = DD Or just remember that the Double Depth of a 32 TPI thread is 0.040 “

Your in feed is(of course) ½ the double depth.

This works well for short threads. For long threads its slow.

Unless you have a special metric thread dial with multiple gears it is the only way you can cut metric threads with an Imperial lead screw.

 

[SamIAm]

TO THREAD WITHOUT A THREAD DIAL by Jim B.

Every third pass is a spring pass.

Whats a spring pass?

Sam

 

[Tony Wells]

A spring pass is a pass with no depth of cut increase by dialing in. When you are taking a cut on a lathe, whether threading, turning, boring, or whatever, you normally get "push-off", a little movement of the material, the tool, or usually both. This deflection results in the actual cut being less than dialed. If you take another pass at the same dial setting, the forces that cause this deflection are much less, and the "spring" of the material and/or tool is allowed to relax and cut a bit closer to what was actually dialed. This is more pronounced on long, thin work while turning, or deep bores where the bar is extended a great deal. It's just a step to make the cut more true. Also, at the chuck, and at the center(if used) the deflection is less due to the support they give. You will see a barrel shaped cut in this case, because the force pushes the part away easier in the middle.

 

[SamIAm]

ahh I see excellent. When I tried my first threading I noticed the Pushing and did some clean up passes(what I called them). Now, I know what to call them!

Thanks!