hello friends,
i am a beginner to mach 3 threading. i am using g76 thread cycle to cut 0.750 inch long thread 1/4 bsf type.
Internet says that the pitch for the thread is 0.039 inch. But when i began to cut thread, 0.052 pitch matches the taps i have of 1/4 bsf thread.
i am running the spindle at 900rpm.

The problem begins after a couple of hours of run when the spindle looses some rpms due to thermal expansion. it reads 890 now and the pitch of the thread changes.
Whrere is the problem? a friend at cnczone said that it is longitude gain problem and i should use cut/rev mode. But i am already using it in the beginning of the program.
ex:
t0101m6
gox1 zo
g95
m3s900
g76 x0.950 z-1 blah blah blah

where could be the problem?
I am scraping a lot of parts that i make after an hour of run of the machine.
thanks hood in advance for the previous and future help.

jasminder

it is longitude gain problem
don't know exactly what is meant by that....

Any change in rpm will change the pitch, it's just a matter of degree. 1% is not a lot and normaly should provide an acceptable thread, but...not sure what tolerance you are trying to achieve. If mach sees a change in rpm, after the first thread pass, planning is done to provide a correction to the next pass so the pitch is mantained.

Later , got to go,
RICH

dear rich,
longitude gain means: feed not changing with the change of rpms.
Do you thread on mach?
if yes then please post an example code
g76 then what after and before?

i didn't get an example any where.
thanks for help,
jasminder singh

G32 Code for a 1/4-20-1" long on a 1" shaft @ 400 rpm from the wizard.

For  G76 parameters see the Threading on the Lathe Manual in members docs.

RICH