I never really gave it any thought until quite recently.
A few weeks ago I was testing out a Singer 401A prior to listing it for sale and the darn thing WOULD NOT sew leather. The thread would fuzz up every few stitches and then it would break. I tried everything I could think of. I changed needles, I changed thread, I changed leather. I cursed and swore and kicked the trash can. (Not really, but it makes for a better story!)
Finally I took a deep breath and watched what was happening when the needle was going up and down through the leather. I noticed that the presser foot was "hopping" up and down with each stitch, which created a sawing effect on the thread.
That's when I discovered the importance of this little knob. It's the pressure adjustment for the presser foot. On the machine in question the pressure was too light and the presser foot wasn't holding the leather firmly enough to allow the needle to travel cleanly through.
So I gave the knob a little turn to the right and it was better. A little fine tuning and it was perfect.
500A pressure adjustment
Of course the pressure will need to be backed off to sew lighter fabrics but that's the beauty of adjustable pressure!
On most vintage Singer machines (and Class 15 clones) the pressure adjustment can be found at the top of the machine directly above the presser foot lever.
Turning the knob clockwise increases pressure, turning it counter-clockwise reduces pressure. You should be able to feel increased or decreased resistance when you lift the presser foot lever.
The pressure adjustment looks a little different on the 500A, 503A and 600-series Touch and Sew models. It's located inside the end cover and looks like a wheel with numbered settings. The higher the number, the greater the pressure. So now you know...that little knob is the key to even greater creative expression and control!
Happy Sewing! Barbara OldSewinGear...dedicated to helping you get the most out of your old sewing gear.
OldSewinGear is the collaborative effort of retired repairman Gary and daughter Barbara. We love old sewing gear and enjoy sharing what we've learned in our vintage sewing machine adventures. We are located in Roseburg, Oregon.