Dumb question about front mech

Will a 2x front mech work properly with 3x shifter, or is the amount of cable pull different?
I’m currently running xt front shifter and mech with the outer limit screwed in, for my slx double and bash
Will a saint front mech work?im building up a second bike out of parts and need a front mech so thought I may as well change the one on my main bike as apose to buying a cheap
9speed

Will a 2x front mech work properly with 3x shifter

Yes, in fact Shimano don’t make 2x shifters (unlike SRAM) so that’s your only choice. Although the newer 10sp shifters do have a 2x/3x mode switch.

But, the cable pull is different on the first shift versus the second, you have to pick the right one to operate your 2x FD.

All Shimano shifters, 9sp and 10sp, pull 11mm on the first shift (granny to middle) and 7mm on the second shift (middle to big).

If your FD is a 2x 9sp like the SLX M665/7 then its designed for an 11mm pull, so you need to use the first shift of your shifter. The newer 10sp 2x FDs like the SLX M675/6 and XT M785/6 are designed for a cable pull of 7mm so you need to use the second shift of your shifter. If fact, that’s all the 2x/3x mode switch does on the 10sp shifters, it forces you to use the second shift position, which has the right cable pull for the 10sp 2x FD. But – if you’re mixing a 9sp 2x FD with a 10sp shifter, which is fine, you have to set the 2x/3x mode switch to 3x and use the first shift position to get the right cable pull.

Will a saint front mech work?

Nothing to do with the shifter and cable pull, which is all fine, but IIRC the Saint had a different chainline and the FD was further outboard as a result, so you may find lining it up with your SLX double a problem!?!

Cheers Perth,
I had a feeling I’d read something about saint crainsets having different spacing a or something so this makes sense