I took a new job this week as an operator only to find out that the previous fella that ran this machine wiped all the programs out of the machine. I need help writing a program to cut 12 tpi I’m assuming that I’ll have to use the G32 code? I’ve never programmed a lathe before and am pretty lost. They are internal threads 1.125” deep inside of a 5.410 inside diameter. Just an example program would help a bunch. Thank you in advance for any help.
Hello Cec330,
Your control can use a Multi-repetitive Threading Cycle G76 in the following format:
G76 X_ _ Z_ _ K_ _ D_ _ F_ _ A_ _ P_ _
Where:
X = X Coordinate of Minor Dia. when cutting and External Thread. Major Diameter when cutting an Internal Thread.
Z = Z Finish Coordinate
K = Thread Height (Radius Value)
D = DOC for the first Threading Pass (Radius Value)
F = Lead of Thread
A = Included Angel of Thread Form (Included Angel of Threading Insert)
P = Cutting Pattern (P1 to P4)
The Cutting Pattern most commonly used is specified by P1 (Constant Cutting Amount - Single Cutting Edge). If the "P" address is omitted, P1 is assumed by the control.
When cutting an Internal Thread, the Major Diameter is specified by the X address and the Thread Height by the K address. Given these two values, the control calculates the coordinate of the Minor Diameter, with the First Pass and all subsequent DOC being applied from that calculated diameter.
In your example, you have specified the Minor Diameter and Thread Pitch (Lead). On the assumption that it a 60deg. Thread Form, the Major Diameter is 5.5".
To cut an External Thread, you initially park the Threading Tool at a diameter larger than the Major Diameter, and for an Internal Thread, at a diameter smaller than Minor Diameter of the Thread. Provided the X and K values have been correctly specified, the control determines whether an Internal or External Thread is being cut by comparing the specified X value in the G76 Cycle and the current position of the Threading Tool in X.
Constant RPM spindle speed should be specified and not Constant Surface Speed. If a not too difficult to cut steel is the material being used, a reasonable starting CSS would be circa 490SFM and at a Major Diameter of 5.5", that equates to 340RMP.
Because the tool must accelerate from Zero to a Z axis Slide Velocity equaling the Thread Lead x Spindle RPM, each time a Threading Pass is Started, the tool should be parked at a Z coordinate far enough away form the start of the Thread, so that the correct Slide Velocity is reached before starting to cut. If not, then the lead of the first part of the Thread will be incorrect. The greater the Slide Velocity, the greater distance required for the correct Slide Velocity to be reached. There is a formula for calculating the minimum distance required, but with a Spindle Speed of 340 RPM and a Thread Lead of 0.0833" a 0.25" standoff in Z will be plenty.
So, putting all the above together, a G76 Block something like the following will get you close:
G76 X5.5 Z1.125 K0.0496 D0200 F0.08333 A60 P1
Incorporated into the program, it may look something like the following for your control:
N2 G28 U0.0
G28 W0.0
T0100 G97 S340 M03
G00 Z0.25 T0101 M08
G00 X5.3
G76 X5.5 Z1.125 K0.0496 D0200 F0.08333 A60 P1 (P1 could be omitted)
G28 U0.0 M09
G28 W0.0
M01
Regards,
Bill