Bobbin Tension Adjustment:
1. Do you have a genuine Bernina bobbin casing and not an Oriental copy? If yes, proceed as follows:
2. To set the bobbin tension, wind a genuine Bernina bobbin with Metrosene thread, type 1161 white thread as your "gaging thread". Load the bobbin case so that the bobbin turns CW. Attach the bobbin case to the hook body from the machine. Wind a couple of revolutions of thread around your index finger with the assembled bobbin case and hook body dangling about 6" to 12" below your finger. Gently and rapidly move your finger back and forth in a "sideways" motion about 1/4" to create a gentle vibration on the bobbin assembly. (Do not shake the bobbin assembly up and down). When the tension is right, the bobbin assembly should fall slowly and as you stop the movement, the assembly should stop.
The adjustment is found on the small screw, holding the flat tension spring against the bobbin case. If the tension is too tight, one must loosen the screw (past) the desired location and always make the adjustment by tightening to the correct position.
There are other checks for tension imbalance and associated problems on the bobbin case that I won't go into here. For further information I can help you later on.
Top Tension Adjustment:
1. The top tension rarely changes and can be depended on throughout the life of that machine providing that tension assembly is maintained occasionally. This can be done by blowing out the tension disks with the presser bar lever in the up position. One can also drag or pull a piece of sized percale or muslin through the disks with the presser bar lever in a down position. Perhaps both methods can be employed.
2. Load the top of the machine with Metrosene 1161 thread in a dissimilar color. I prefer to use a pastel color so as not to create an optical illusion of imbalanced tension.
3. Sew a satin stitch (.25 on the Nova 900) in sized cotton muslin with a thin piece of paper between two plys of fabric. The width should not exceed 4.5mm (standard width on the 900 Nova), however the newer machines have wider stitch widths so one must adjust as specified. The result will be a slight amount of top thread in symmetric lines on both the right and left sides of the satin stitch.
Typically, the top tension will not need adjusting. If the Nova 900 needs adjustment, please ask for additional help.
Sep 11, 2008 |