Why are threads cut at slow speed?

[flosi]

I always assumed it was to have time to stop before you ran into something with disastrous results. Is there any reason to do it slowly when using CNC?

[DaveH]

Hi Flosi,

Correct on both parts No reason to do it slowly when using CNC. Just hope your nerves can take it   
 
DaveH

[doubleboost]

It has a great deal to do with the size of ones balls

[EdK]

(03-22-2015, 05:27 PM)doubleboost Wrote: It has a great deal to do with the size of ones balls

[flosi]

No balls involved. My Sherline cnc ready lathe has just ordinary screws and nuts.

[PixMan]

Hello Flosi,

The only limiting factors in threading with CNC is the tooling (need carbide) and the processing speed of the control. The second is the key to what speeds you can run because of the timing required to position the slides, execute the coordinated motion of Z axis with spindle rotation to get the right lead, retract X at the end of the cut, return in Z to the start point, lather , rinse, repeat.

When I first started using NC machines (paper tape Numerical Control) the threading speeds were "a few hundred rpm". Any faster would have the threading tool not in X position before the Z motion started and pulling out before Z axis had reached the programmed position. The CNC machines of a 1/2 dozen years ago could thread at 2000 to 2500 rpm successfully. New CNC machines (commercial, full blown CNC not a Sherline) can thread at twice those speeds.

You can find the limits of your individual machine by experimentation "in air" by just watching the position readouts. If the X axis starts retracting before the programmed Z position is reached, you must slow down the process.

Good luck,

Ken

[flosi]

Thanks for that. I will refer back to this tread when my CNC ready lathe gets the motors it's waiting for.

[f350ca]

My manual Hardinge with automatic kick out recommends not threading above 1000 rpm. On small threads say under 3/8 I cut at 6-800 rpm, first couple of times was scary though.

[TomG]

(03-22-2015, 07:07 PM)f350ca Wrote: My manual Hardinge with automatic kick out recommends not threading above 1000 rpm. On small threads say under 3/8 I cut at 6-800 rpm, first couple of times was scary though.

Yup, scary as hell. Especially when threading to a shoulder or to the bottom of a blind hole.

Tom

[Vinny]

And "disasters are always better in slow motion." -- Mert Baker 7x list