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I'm sure many of you know this but I just figured out how to alleviate the dreaded railroad tracks on my machine (2009 Millie, L size bobbin).

The two little "arms" on the bobbin spring were bent up too far causing more drag on the bobbin.

I couldn't figure out why my bobbin thread pulled so hard once I brought it up thru the quilt sandwich.  I set the bobbin thread tension with the spider test and all seemed fine.  After trying many different things on both top and bottom thread, even bringing the bobbin thread up thru a different combination of quilt sandwich, I wondered if it wasn't those two little arms.

This may not be the culprit on others' machines, but it sure worked for mine.  

BTW, I've been using So Fine on top and BL on the bottom.


Hope this helps someone else having the same problem.

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So great that you found the culprit! It's so wonderful when we can figure these problems out! 


The drop test works great for finding the tension of the thread through the slot and hole in the bobbin case. What it doesn't take into account is the pressure on the bobbin when it's inserted into the machine. With the backlash spring fingers extended out too far, the bobbin is pushed extra hard against the back of the bobbin assembly, and will require more force for the thread to be pulled through.

That's why you'll see many recommendations for the Towa Gauge. It measures the force with the bobbin seated as it would be in the machine and is a huge time-saver.

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