ok, if you need an example project, see the attached test design.
This is as VERY simplified version of a design I was working on recently. The pulley system for the corner of a corexy printer.
What I have (crudely) modelled here is the corner of a frame with stepper, stepper standoff mounts, a toothed pulley on the stepper and two idler pulleys.
If you look at the sketch, you will see the stepper is constrained to slide in the x direction but fixed by the "steppertoframe" dimension.
The belts are not actually modelled but the path is shown by the x and y construction lines.
Lets assume the y belt is a fixed distance from the side of the rail ("beltclearance") but other stuff is driving the x belt position ("topbeltvariableclearance").
Lets say that ideally I want the stepper to be touching the frame in x and y. However if the x belt moves up (lets say topbeltvariableclearance is 10mm) then I have to make steppertoframe something like 15mm for the belt to clear the standoff.
If I manage to move the belt down (say topbeltvariableclearance becomes 25mm) then the stepper can move in x to touch the side rail.
In reality I spent a good hour moving stuff around to get the stepper where I wanted it. I could have left it unconstrained in x but that caused other issues elsewhere that were hard to spot so I got in a mess. Hence wanting to keep it fixed when working elsewhere.
I practice I just set the position to 0.01mm to simulate zero. That sort of works but then I am in danger of forgetting and leaving it as such, causing small errors in the final design which then need chasing down.
I hope that makes sense, feel free to tell me there is a better way of doing this! 😉