We have had the opportunity to work on many different brands and models of all metal vintage sewing machines. The reason we do is because the quality in these machines is not matched by any but the most expensive sewing machines on the market today.
I have talked about superior materials, precision tolerances, quality of finish, the stitch quality, durability, reliability, and more. I will continue to do so. Nothing drove my point home more to me than when I noticed this…

This is the presser foot bar lifter. It attaches to the lift lever, and clamps to the presser foot bar. See that little screw? its tiny… why is it there?
Here is another picture of it…

This is the assembly it mates with… by the way, this happens to be a Singer model 201-2 made in 1952…

Have you guessed why it is there? Well, its purpose is to adjust the side to side clearance of the presser foot bar to the presser foot lift lever. This is to ensure that the presser bar foot doesn’t wiggle side to side when the machine is sewing. Tightening this screw wedges the “wing” wider so there is no movement… its an adjustment.
Why did they do that? They probably didn’t have to, and I don’t think anyone would notice if they didn’t. They did it because in those days, details mattered. These machines were made to that level of detail. They were not the only manufacturer that cared about details like this, but as an example, it is is the level of detail Singer put into their engineering and manufacture, and you can see similar examples of this just about everywhere you look on these machines. Adjustments for wear, adjustments for timing, adjustments for needle transportation, darn near an adjustment for everything that the machine does to make a stitch.
Its no wonder that these things will last lifetimes with a little cleaning, oiling, and adjusting. So, if you need another reason to consider before getting (or keeping) a vintage all metal sewing machine, this is it.
By the way, does your sewing machine have this adjustment built into the design?
Let me know what you think!