[starslayer]

Machinist is one of those skills where it becomes immensely more useful when the player has knowledge of what can be done with machineing.

I have used it to great effect on technical pcs both with and without gadgeteer.

Almost all of my technical pcs and any mage who has creation type abilities will have it.

Machinist in my mind has always been the symbol drawing of the crafint skills- it supports other skills but generally does not accomplish anything in an of itself.

I think it is not at all unreasonable as a quick rule to have a successful machinist used in support of another skill provide a +1 to other tasks (as per the custom fit modification for firearms) and/or to be able to negate penalties up to its MoS. If you have the option to machine your tools for a specific task that, almost by definition, means you have superior quality tools for that task (another +1/+2 - assuming that the craftsman in question did not already have superior quality tools).

Having the exact right tool/fit is one of those fantastic things that you don't appreciate until you have seen it done;
Real world example (from earlier this week):
I am about 2/3 through a reclaimed hardwood project.
Stage 1 was actually extracting the hardwood from the floor- there are multiple ways to do this, but I ultimately ended up developing a new method using an oscillating tool, and sliding that under the boards to cut the cleats, needing only lift them about 1cm. It was a process of experimentation, but using the oscillating tool with the metal cutting blade went at least 75% faster then any other method I had researched or attempted, it also radically reduced the learning curve on how to successfully extract boards without damaging them. Machinist would be the skill to adapt the blade on the oscilating tool to that new purpose (probably with a significant TDM, since it already does that.

Stage 2 is laying down the new flooring. Laying down flooring is generally done via a floor nailer/stapler, but the first two rows, and the last three rows of hardwood are too close to the wall to use the nailer. The traditional method is to drill a hole in the board and then hammer the cleat in by hand, finishing off by using a roberts screwdriver as a transfer punch (the roberts because you can rest the cleat on the shaft of the screwdriver paralleled to the head of the driver, thus giving you something to rest against). I spent about an hour modifying an air hammer chisel to have a slot that exactly fit a flooring cleat. Once I had the modified air hammer 'hand nailing' a cleat turned from a ~5 minute job per cleat to a ~15 second job per cleat (drill hole, place clean, use air hammer, done) that was far less finicky then the hand nailing method, and had far less room to accidentally bend the cleat- time savings ~40 minutes per row. Machinist would be the skill to build the hammer modification (Involved grinding, welding, and caliper use, so probably actually using straight machinist, but with a bonus for extra time, and multiple attempts before I got it right).