After years of quilting, and then moving on to sewing chap leather, I decided I wanted to start working more with tooling leather, making holsters, portfolios, and bags. I am not ready to invest in an industrial machine. I did, however, find a Singer 15K88 to use, and after cleaning it up, it sews like a dream. Using a 110/18 leather needle, it sews right through up to 3 layers of tooling leather, no problem. Honestly, I don't know how heavy the leather is, but basically, whatever I can fit under the needle, the machine will sew through. The problem I'm having is with the thread. I started out using Coats & Clark upholstery thread (nylon) and the machine liked that thread just fine. But it didn't really have that nice looking stitch line on the leather because the thread was too thin. So I tried two other thread weights including Dual Duty Heavy and Dual Duty Button & Carpet threads. However, because the thread is heavier, I can't seem to get the tension adjusted correctly. The machine is pulling the top thread down to the bottom, and even after loosening the bobbin tension as much as possible and tightening the tension on top as far as it would go, I can't get the tension right. Is there any way to modify the machine to take the heavier thread? Or some other trick? Or a different thread I should be using? Any advice?
