Fix For Thread-Cutting Bobbin

by Mike McGuire

Inexpensive bobbins will with use start to cut thread because of wear around the mouth. Some of them are that way new.I have never had much luck grinding or filing it to fix it. Here's a fix that has worked well for me.

The fix is to fasten a glass bead in the mouth with heat shrink tubing. The mouth of the bobbin is bell shaped. For this revised version, I have come to the conclusion that two layers of heat shrink tubing are needed to keep the bead from coming loose with use.

The inner tubing layer should be just large enough to slip over the outside of the bell. For bobbins I have fixed, 1/16 inch a.k.a 0.063 inch or 1.5 mm is about the right diameter unshrunk. The outer layer is 3/32 inch, a.k.a 0.093 inch or about 2.25 mm in the unshrunk condition In a previous version of this, I formed a socket with heat shrink tubing and glued the bead in it. This eventually failed, but this two layer method seems to hold up. The bead should be a glass seed bead with a barrel-shaped cross-section. There are straight sided beads that won't work very well.

1. Slip a length of 1/16" shrink tubing over the mouth and neck of the bobbin, leaving enough tubing beyond the mouth to cover the bead that will be put there.
2. Skewer the bead on the toothpick.
3. Push the bead into the shrink tubing up against the mouth.
4. Slip the 3/32" tubing over all of this.
5. Shrink the tubing with heat. I use a paint stripper / heat gun. The burner on top of an electric stove also works well.
6. Using a razor blade, trim the tubing off exactly flush with the bead so most of the end surface of the bead is exposed.

You may find that you need to use a threader to thread the bobbin. I use a loop of light copper wire. A piece of tape over the ends of the loop makes it easy to find on the bench.