Single point thread tools

[Neale]

Do you need two different inserts? Surely the only difference between cutting LH and RH threads is the movement in the Z axis?

[magicniner]

Do you need two different inserts? Surely the only difference between cutting LH and RH threads is the movement in the Z axis?

That's correct, thread milling tools cut left or right handed threads.

[Lloyd Barnes]

That was my logic too but the inserts still seem to be available in left or right handed versions which makes no sense to me.

I need to spend some time browsing the links provided earlier in this thread at the weekend.

[magicniner]

That was my logic too but the inserts still seem to be available in left or right handed versions which makes no sense to me.

You mean for the tools that can be used both for turning & milling like the one I linked to?
It's because you do need left and right hand inserts for some turning operations, I always thread away from a shoulder and from the bottom of a hole outwards and it's handy to have both LH & RH threading inserts.

[m_c]

The LH/RH in that respect is to do with the physical position of the cutting edge, not the type of thread.

There are holders/inserts available for turning that require angled shims, to ensure the insert is cutting at the correct angle for the required diameter, and ensure the correct thread form is produced. Larger diameters for a given pitch, have a less angled thread, so to ensure a 100% correct thread form, the cutter has to be angled to compensate for the thread angle, however if you need that level of accuracy in your threads, you probably won't even be considering thread milling.

[magicniner]

Larger diameters for a given pitch, have a less angled thread, so to ensure a 100% correct thread form, the cutter has to be angled to compensate for the thread angle, however if you need that level of accuracy in your threads, you probably won't even be considering thread milling.

If you need a full thread right to the bottom of a flat bottomed blind hole you probably won't even be considering anything other than thread milling.
If you need a thread with specific start/finish points for alignment of two mating parts you probably won't even be considering anything other than thread milling.
If you want one tool in your drawer that will get you a working part covering a huge range of threads you probably won't even be considering anything other than thread milling.

Job specific threadmills can produce perfectly accurate thread forms and full forms too, not partial, what you have to understand is that the form of the tooth on the tool differs not just for different thread angles but also for different diameters of tool, outside threads versus inside threads and different ranges of Major Diameter, knowing these the manufacturer designs a cutter profile which when swept through the work and following a helical path generates the correct thread form.
Single point inserted thread milling tools are a great thing to have around, they are specifically produced because they allow a wider range of threads to be cut, albeit with reduced accuracy, but in this situation it is clearly incumbent on the programmer/operator to ensure the resulting thread is close enough to spec to be acceptable.
If you need a higher level of accuracy in your threads you probably won't even be considering not buying the correct threadmill for the job. ;-)

- Nick

[m_c]

If you need a full thread right to the bottom of a flat bottomed blind hole you probably won't even be considering anything other than thread milling.

Is that to go with the 90 degree hole the designer wants drilled at the bottom of the blind hole?

If you need a thread with specific start/finish points for alignment of two mating parts you probably won't even be considering anything other than thread milling.

Rigid tapping? Plus any good lathe will able to control the exact thread start point.

If you want one tool in your drawer that will get you a working part covering a huge range of threads you probably won't even be considering anything other than thread milling

Job specific threadmills can produce perfectly accurate thread forms and full forms too, not partial, what you have to understand is that the form of the tooth on the tool differs not just for different thread angles but also for different diameters of tool, outside threads versus inside threads and different ranges of Major Diameter, knowing these the manufacturer designs a cutter profile which when swept through the work and following a helical path generates the correct thread form.
Single point inserted thread milling tools are a great thing to have around, they are specifically produced because they allow a wider range of threads to be cut, albeit with reduced accuracy, but in this situation it is clearly incumbent on the programmer/operator to ensure the resulting thread is close enough to spec to be acceptable.
If you need a higher level of accuracy in your threads you probably won't even be considering not buying the correct threadmill for the job. ;-)

To give you a comparison to think about, why do gear hobs have to be offset at an angle from what they're cutting so accurately?
You could cut a gear keeping everything perfectly inline, and you'd still get a gear with the correct number of teeth, but would the tooth form be correct?

For over 99.9% of uses, a thread mill will produce a perfectly acceptable thread. I was just highlighting where it might not be acceptable, but the fact is, very few people would be able to test the difference. For those of us posting on here, we're far more likely to have problems with a milled thread not being perfectly round, let alone having problems with the correct thread form.