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[Ted B]

I have a Thompson Mini-Walker walking foot machine. Lately in zigzag mode, after several inches of perfect stitches, there are several with an huge excess thread loop on the bottom. I'm sewing 2-4 layers of Sunbrella 9 oz. canvas. And there is always a dark grease/oil stain visible on the thread on that stitch. And the top thread at those points are pulled over way too tightly.

One top side photo and two bottom side photos are attached.

Machine is in good repair and is oiled correctly. I wiped ALL of the oil off the shuttle area and the problem persists. There are no nicks on the gib hook or cap spring. The gib hook rotation timing and side clearance from hook to needle are in spec.

What could cause the top side thread mark? And what is wrong?

Thanks for any advice.

[Ted B]

Some additional comments

The middle photo is the top surface. Others are the bottom.

It is perfect in straight and narrow (1.5mm setting or 1/8") zigzag modes.

The dark stain at every loose bottom stitch is ON or immediately at the beginning of the next stitch. SOMEHING MUST BE CATCHING AND DRAGGING THE EXRA BOBBIN THREAD.

CLean: I think it's clean. Shuttle, bobbin, and tension assemblies disassembled and cleaned. No jammed threads or lint.

Top tension control: am very familiar with its cleaning, setup, and adjustment. I know it's an obvious thread tension problem, but as it's perfect in straight stitch- how could it be a top thread tension problem. Bobbin is set at minimum. It is threaded correctly.

Shuttle parts: I just showed my shuttle retaining ring, gib hook and bobbin to a local sewing repair guy. He thought they looked undamaged and clean. He couldn't explain the dark thread stain exactly where there was a big loose bottom thread. If you look carefully at the first photo, you can see the bottom dark stain at the loose thread- distinct from the thread shadow close to it.


Thread: the repair guy also mentioned it could be bad thread. Mine is the best Sailrite V92 polyester thread. He said he has seen a bad section within a large spool cause loose loops. So I put brand new Sailrite pre-wound bobbin thread on top and bottom. Same problem.


Feed dog: The feed dog underside side was not oily but has a flat blackened finish, not paint. The clearance between the bottom of the feed dog and the shuttle retaining ring cap spring during a stitch is VERY close. Maybe 1/32". Question: as the thread goes around the Class 15 bobbin to make a locked stitch- does the THREAD go ANYWHERE near the bottom of the feed dog?

Much appreciation for comments.

[John]

Any time you have thread tension inconsistencies that are that drastic 90% of the time something is threaded wrong on your machine. Take a look at your manual and make 100% sure you routed everything correctly. Sometimes the manuals can be hard to understand if they have bad pictures.

[BigRig]

I agree and can never get my machine set proper, no manual for it.