[norfolker]

Hi all

I need to cut a left hand external thread (M30 x 2)

Is it possible to machine this thread with a right hand tool, using G76, coming away from the spindle.

We dont want to buy a left hand tool, as its a repair job for a test rig, & we probably wont need to machine left hand threads again.

Here is my program for the RH version (fanuc Oi TD) its up to a 36mm diameter shoulder with a 3mm undercut


(M30 X 2 THREAD)
N7T0707
G97S300M3
G00G99X150.Z4.
G00G40G99X32.M8
G76P020060Q40R0.04
G76X27.55Z-41.R0.P1300Q300F2.
G00X40
G28U0M9
G28W0
M05
M01


Could I just reverse the Z figures?

Any help appreciated

Thanks, Dave

[txcncman]

Not exactly. You will be plunging into the material with the threading tool and will need to have an appropriate thread relief groove. Also, you may run into a lead problem at the start (Z minus) side of the thread due to acceleration issues. Recommend tool lead in for Fanuc is 3 times pitch to give the Z axis acceleration time to stabilize before entering the thread. Given this, the first 3 threads would be suspect in your scenario.

[fordav11]

also, depending on the tool type cutting in the opposite direction can cause the insert to be pulled out of the tool.
A more accurate formula to calculate lead acceleration/deceleration clearance is Pitch X RPM / 500 for the start and Pitch X RPM / 1500 for the end point.
If you go slow enough a small groove at the back of the part is enough, assuming a groove at the back is acceptable to your quality control people.

[Heavy_Metal]

Hi Dave,

If you have a (right hand) tool for internal thread, pitch 2MM, you can use that for (outside) external thread.
Only setup the GEOM. OFFSET for the tool and you can use it with M03.

Heavy_Metal
The Netherlands.

[fordav11]

sure, if you are desperate and also at the expense of rigidity :-)

[Heavy_Metal]

Hi,

When you don't have a left-hand external tool but you have a internal right-hand tool it works great at 30mm OD x +/-50mm lenght.
There is a small difference between internal and external thread hight but that can be solved.
A left-hand external insert on a internal right-hand tool would be a good solution for the correct tolerance.

Heavy_Metal
The Netherlands.

[norfolker]

Thanks guys for your input,
Very helpful as usual, its not a production job, just a replacement for a damaged part on one of our test rigs, I can increase the undercut width, so will try that for starters, interesting suggestion about the inverted threading bar, I hadn't thought of that, its also an option.
Will experiment on some scrap bar first,

Thanks again,
Dave

[norfolker]

Just to update, I increased the undercut width to 4mm & ran the above program with the Z figures reversed, it worked really well. a duller finish than the right hand version, but more than good enough for its intended use.

Thanks again,

Dave