My wife started sewing patches onto our leather motorcycle vests in 2001, with a JC Penney 7057 (1980s machine), using Coats Dual Duty Plus thread and a size 11 Singer Universal needle. We haven’t had a patch come loose yet. She tried leather needles for home machines, but they broke more often than the small ones.
In 2006, she started using a Singer 401A with the same thread and needle size.
By 2007, I had picked up a Consew 225 and a Singer 29K70 (industrial walking foot machines) that we use most of the time now with #92 Ultra Dee UV-resistant thread and size 20 needles to sew most of the patches onto leather vests at our shop. But, she still sews one on every now and then with the Singer 401A and the small thread and needle. Haven’t had any problems.
CD in Oklahoma