There seems to be some bad information out in the world, having to do with where and how often to oil the hook assembly on Bernina’s with a “C-B” hook. This is the hook design that oscillates back and forth, rather than simply rotates.
To check to see if your machine is one of these, open the bobbin door and rotate the hand wheel while watching the hook move around the bobbin. If it makes a half revolution and then returns to its resting place rather than just rotating, it’s a “C-B” hook. The other way to tell is if the zig-zag width is 5.5 millimeters or less, it’s an oscillating (C-B) hook. This type of hook never incorporates scissors, which may help with the identifying process; however, not all rotary hook machines have scissors.
What does “C-B” stand for? Have to ask the Swiss, but I think it means “Come Back.” This design creates a very nice stitch, and has been around for a long time. Here’s the service process you can (and should) perform in the privacy of your own sewing room:
1- Open the bobbin door, remove the bobbin and release the bobbin cage latch at the upper left side of the bobbin door opening. The bobbin cage will swing out towards you.
2- Gently remove the hook assembly (it looks a little like a half-moon) and check the hook point for burrs or roughness. If any of those appear, bring the hook into the shop and we’ll take care of it for you. Burred hooks cause lots of unpleasantness, such as loose top thread on the underside of your work, thread breakage, etc.
3- While you’re in there, pick the lint, pieces of thread, broken needles, etc. out with tweezers. Don’t blow it out; it will end up inside the machine, where it will be an even worse offender. Grab a Q-Tip and wipe out the hook race. Inside the hook race, there is a small groove; use a toothpick to get the junk out of the groove. Be sure to clean the lint away from the feed dogs. When the hook race is clean, put a drop of oil in the groove, where the hook will reside when you put it back in, and then replace the hook. Be careful to get the hook seated properly in the race.
4- Put a very small bit of oil on the black bobbin cage where it will rub on the hook and rock it back into position. Make sure the latch is fully engaged; it takes a second firm push to click into place properly.
5- This little chore should be done every 6 to 8 bobbins worth of sewing. If you forgot to count bobbins, the machine will tell you it’s time by making unpleasant noises. It’s called “hook clatter”
6- Remember to sew a bit on a scrap of fabric to get rid of any excess oil on the hook when you’re done.
I hope the above (which is an excerpt from our service seminar) will be helpful.
If you’d like to see a demonstration of the above technique, bring your baby into the store, and we’ll gladly give you a hands-on lesson.