Double start acme threads

[D Ford]

I have a customer request to cut 1-1/2" double start acme nut.

I haven't done this before.

Looking to do this on CNC lathe

Any suggestion on programming.

[Guest MTB Technical Services]

Since it's a 2-Start thread, you need to change the lead to 2 x Pitch.

When both starts are cut you get the correct pitch between starts.

 

The rule of thumb I use with any kind of ACME or API thread is at least 4 x Lead for the run-in distance

to assure that the spindle is properly synchronized.

This is especially true for larger workpieces.

 

You want to write two separate thread cycle lines that have the same end point.

However, one of those cycles will have a start point that is adjusted by 180 degrees in Z.

 

This means that your second cycle line should have its start point adjusted away from the chuck

by a distance of 1/2 the lead (180 degrees).

Mastercam handles this by simply entering the number of starts.

 

FYI, always verify the output as you can get inconsistent results if you establish all your settings

from a library thread and simply change the number of starts.

I've seen it where the IPR feedrate and Z doesn't get changed to account for the number of starts.

[D Ford]

Thanks

[Guest MTB Technical Services]

Here's some sample FANUC code

 

 

(1-1/2 - 4 ACME 2-START NUT)
G00 X1.15 Z2.0
G76 P020060 Q36 R0.0036
G76 X1.52 Z-2.5 P1350 Q170 F0.5
G00 X1.15 Z2.25
G76 P020060 Q36 R0.0036
G76 X1.52 Z-2.5 P1350 Q170 F0.5
G00 X1.15 Z2.25