As a sewing machine repair technician, it is essential to be able to tell the difference between real sewing machine or mechanical problems, and user error.
While it is probably not a good idea to tell a sewer they made a mistake, often what they see as a mechanical problem is simply a case of user error.
This is especially true when a customer attempts to use knit or stretchy fabrics without changing their needle. Even the best sewing machine will produce skipped stitches and poor quality stitching when the user fails to use the proper thread, needle, and fabric combination.
Needles today are made with very specific applications in mind. Some have very sharp points to penetrate tightly woven fabrics. Some needles have rounded or ball point tips to slide through knit fabrics without pricking or catching the knit fibers. It is essential that you use the right needle for the application at hand.
Recently, I had a customer bring her sewing machine in for sewing machine tune up. She complained that all of sudden it just started skipping stitches. I asked her about her project. While she had sewn for many years, she did not realize that a special needle was needed for knit fabrics. Most of her sewing had been on woven cottons, but she just wanted to do this one project using a very stretchy fabric. The result was frustration.
As a sewing machine repair technician, I believe it is our duty to explain to our customers the simple solutions to their frustrations. Simply stated, if you sew woven fabrics use a sharp or universal needle. If you sew on stretchy fabric, use a ball point of stretch needle. It saves loads of frustration and possibly even a sewing machine repair bill.