Explain Thread Whirling?

[BiPolarMoment]

I have a vague knowledge of thread whirling but nothing I've found online really describes it adequately to me. I'm aware that it can cut an entire thread in one go but it's hard to visualize how. For my purposes, I'll use this custom thread as an example for my questions:

Dimensions to describe this thread: Constant OD (7mm), Tapering Minor Diameter (deg), Constant Root Width (1.7 mm), Constant Tooth Angle (35 deg), Constant Pitch (2.5 mm)

Now, if given a particular tool set to create this thread, which of those dimensions can or cannot change on the part being made (or how are they related to the tool)?

Thanks in advance.

 

[MikeHalloran]

If you look straight at the transverse profile of the part, you'll see that you could, e.g., mill a thin template of the projected shape with a cutter having teeth like an Acme thread.

So you buy a milling cutter that looks grossly like a bunch of stacked Woodruff keyseat cutters, except with the pseudo-Acme profile.

You spin it about an axis parallel to your cylindrical blank's axis, and feed it radially into the blank, so your workpiece now has a neat row of Woodruff keyseats, with tapered sides, facing the wrong way. Keep the cutter spinning and simultaneously orbit it around the workpiece and advance it (helically) by one pitch of the finished thread. Then you can withdraw it radially and then axially, and you're done.



Mike Halloran
Pembroke Pines, FL, USA

 

[BiPolarMoment]

Thanks mike, but I was under the impression that there was more than one cutting "point"(a number I've once heard is three) per tool set. Would your example still apply except with 3 milling cutters? What would this look like and how would each tool differ from each other?

Using your example it seems that everything except the helix dimensions are concrete per tool, is this correct? If there are three cutting bits it would seem this would also make the pitch a non-variable as well as they'd have to be arranged into a shape reflecting the pitch already.

 

[MikeHalloran]

Nope; one tool.

The tools for whirling an internal pipe thread, for example, look a lot like a pipe thread gage, with two differences:
- There are axial gashes, of course, to produce cutting edges.
- The teeth are not helical, they are circumferential.

The big advantage of thread whirling over tapping is that you don't stop and reverse the spindle; you spin it as fast as the material will allow.

In your case, for whirling an external thread, the tool's od would be tapered to complement your thread's minor diameter, and the tool itself could be arbitrarily large.

For such a long, slender external thread as you have illustrated, you might have to use a fine feedrate, but I can't see a need for multiple tools.




Mike Halloran
Pembroke Pines, FL, USA

 

[Decker78]

If this is to be done on a CNC lathe, then the OD would have to be established prior to threading. The OD is your major dia. The Thread pitch and minor dia. will be adjusted equally if the cutting tool is ground correctly. The depth of the tool will control the pitch and minor at the same time. the thread major is controled by the OD. If the threads are long, then a tailstock will be in order. This is my first post. I hope i am some help.