[pseudogod]

Hello.

I'm trying to figure when does the G42 compensation actually "turns on" when using G71 turning cycle.

for example:
G0 X52. Z2.
G71 U2. R0.5
G71 P10 Q20 U1. W0.1 S200 F0.2
N10 G0 G42 X36.
G1 Z1.
X40. Z-1.
Z-10.
X52.
N20 G0 G40 X54.

Does the tool compensation turn on when moving from x52 to x36? (so it's not actually x36.) OR does it turn on when moving from x36 to z1?

[sinha_nsit]

There is no definite answer, because it is not properly documented.
G71 may or may not use compensation depending on controls/parameters.
You need to experiment and analyse the result.
I have seen most people commanding G42 before G71 block. If you have it within P and Q blocks, then, I believe, G71 may (not sure) ignore this; G70 would, of course, use it (when the tool moves to Z1, in your example).