[cdspk]

In reality, to what accuracy can lathes commonly keep a long thread pitch length?

We have a 'dumbbell' shaped component - 28" long with a 5" long, 1 1/4" dia. 11tpi thread on each end.

The threads must be 'in pitch' - the same thread - like a piece of studded rod with the mid section turned down.

We need the pitch over the 28" to be within 0.002" but the CNC guys with have contacted say they would struggle to produce that accuracy?

Cheers, Sean

[carlos1970]

In reality, to what accuracy can lathes commonly keep a long thread pitch length?

We have a 'dumbbell' shaped component - 28" long with a 5" long, 1 1/4" dia. 11tpi thread on each end.

The threads must be 'in pitch' - the same thread - like a piece of studded rod with the mid section turned down.

We need the pitch over the 28" to be within 0.002" but the CNC guys with have contacted say they would struggle to produce that accuracy?

Cheers, Sean

Yeah that's a long thread if machine has feedback scales it could be very possible...

[Chipper5783]

Hi, new here, long time on manual machines. Hope to start playing with CNC.
Your project sounds pretty straight forward on a manual machine (put the follower rest on and away you go). I recently completed a lead screw for an antique meat slicer: 15.75" thread, 3/4-10. You would laugh at me for how long it took, but my pitch diameter was within the tolerance you have requested, with a much more flexable set up.

I assume you will need tailstock support. With CNC, could you not simply cut it as a straight thread, then measure the thread - determine how much tool push there is, then tell it to cut that much of a taper in the thread?

[Eldon_Joh]

is the material aluminum or steel?

on the surface it sounds easy, 2 thousanths is the same as 2 tenths at 2.8 inches.. but you will probably need to make one piece.. measure it, and then adjust the machine, or the code to produce the next one correctly...