The Singer 3810 we traded for has a plastic shell on it. Under that a cast light weight aluminum frame and inside of that all the workings.
All the drive gears are plastic
Many of the stitch controls, levers, nobs, gears, sliders, are plastic.
Some of the parts in the needle area are plastic.
The stitch length parts are plastic.
The bobbin carrier is plastic.
It has just enough metal to hold it together and function and I'm sure if they could figure out how to make that out of plastic they'd do it.
This machines only saving grace is that it stitches very nicely.
Joe