Sewing machine performance is often measured by the quality of stitches it produces. If the tension are messed up, the quality will be poor. In this case, it does not matter whether the sewing machine was a $99 special or a $12,000 Bernina. Perfect tension is a must.
If extreme cases, you may need to see your professional sewing machine repair technician. You may even want to take a sewing machine repair course or a series of sewing machine repair courses. The more you understand sewing machine tensions, the easier sewing will be.
Like two teams playing tug of war, rope is stretched across a stream (or line). Each team pulls on their end of the rope. One team pulls harder than the other. Them the other team pulls harder. Back and forth the teams pull against each other. Eventually, the reach a stalemate. The pull of each team is offset by the pull of the other team.
Like a playground teetertaughter, one person straddles the board on each end. First one pushes off and up they go. The other comes down, and pushes off. Up they go. Up and down. Down and up. Then the two kids work to position them self just right. They push off so gently and easily that the board comes to balance with the two kids both half way up.
Sewing machine tensions are just like these two examples. Tension is by definition the amount of pull, drag, or resistance the thread has as it flows through the sewing motion.
Along the top of the sewing machine, is the upper thread that passes through the tension discs, the tension spring, the take up lever, and eventually the eye of the needle.
On the bottom is the bobbin. It rides secluded inside its bobbin carrier, with its thread neatly flowing under the bobbin tension spring.
The top thread is drawn down into the sewing machine as the needle drops through the needle plate. However, the thread has resistance on it as it moves. The thread tightens as it moves down, and then looses as it moves back up. The sewing machine take up lever lists the thread to maintain drag even as the needle rises.
The thread from the bobbin is also under resistance. It is draw up by a overlapping loop with the upper thread. As the needle rises, the bobbin thread rises. However, the bobbin tension also pull back creating drag on the thread.
As we saw in our two illustrations, there is a tendancy for upper and lower threads to pull against the other. If the upper thread pulls harder than the lower thread, you will see puckers of excess thread collect across the top of the seam. If the lower thread pulls harder, you will see a nice looking top seam. But when you look under the fabric, you will see gobs of excess theads collected.
Perfect sewing machine tensions are achieved when the upper and lower thread drag is equalized. The thread knot forms in the center of the fabric. You see no excess on top of the seam or under the fabric.
In our next post, we will explore how to insure perfect tensions every time. If you would like a free sewing machine repair course, check out our 7 Steps To Peak Performance For Your Sewing Machine at http://www.fixsewingmachines.com.