They are well made, but only "heavy duty" compared to modern machines, that can struggle going through a few layers of denim, and don't even consider canvas.
At the time the old machines were made, the companies also made true industrial "heavy duty" machines, and on Singer's info, it clearly states that the non-industrial were for "family use". Singer did make some mid range machines designated as "for light industrial" too.
If you only have small project, it won't hurt the machine to try it. Either it will or it won't. If you are going to be doing production work, you will wear it out.
The worst you'll do is usually knock it out of timing, and that's not a hard thing to fix.