Needle Timing And A Singer 31-15

[Wizcrafts]

This is just a thought, but, test a stitch without any material under the pressor foot, using the hand wheel. As the loop is picked off the eye of the needle (just as the needle begins its ascent), rotate a quarter, or half turn more and see if the top thread pulls easily around the bobbin case. If the top thread is being pinched by inadequate clearance inside the bobbin case/shuttle, the knots will form under the work, rather than in it.

[jfhspike]

This is just a thought, but, test a stitch without any material under the pressor foot, using the hand wheel. As the loop is picked off the eye of the needle (just as the needle begins its ascent), rotate a quarter, or half turn more and see if the top thread pulls easily around the bobbin case. If the top thread is being pinched by inadequate clearance inside the bobbin case/shuttle, the knots will form under the work, rather than in it.

Oooh! I really liked this idea, and ran downstairs to test it...but alas, no joy: the top thread slides around the bobbin smooth as can be. (Sigh).

--John

[jfhspike]

John;

If at all possible, could you take some close up photos showing your thread path, from the spool to the needle and a snap or two with the take-up lever and slack spring in various positions and the needle itself?

Are you using the same size thread top and bottom? Is this a #18 needle/#69 thread setup?

If you can't make any more headway on your own, consider sending in to Bob Kovar, owner of Toledo Industrial Sewing Machines. It might be out of time on the top end and he will know that and get everything back into the proper sequence.

OK. The first sequence shows the thread path. Pardon my cone-holder; the one in the real sewing table is a little more sophisticated. I put some brown sunbrella behind things to make the thread path easier to read.

Second sequence shows 8 equal steps in the operation of the machine, seen from the end. In about step 5, you can see the top-thread coming off the bobbin that it's just passed around.

Third sequence shows the tension spring and thread-take-up-lever in a similar 8-step sequence. Sorry about the bright highlight; I was trying to get things well-lit for this sequence.

--John

[catskin]

I am NOT an expert as some are BUT I just fixed the same problem on one of my machines today. Make SURE the presser foot is pressing down hard enough. On mine the pressr foot was not going down far enough. it was worn so it was holding the leather down enough to feed good but would let the leather lift a few THOUSANTHS of an inch thus the top thread was not pulled far enough back. Its worth a try. Or change feet to see if that makes a difference. Or if some thing is keeping the foot from going down the last couple 1/000ths.

After studying the pics again I am wondering if the hole or slot in the foot might be to big/wide. and the material is lifting into the hole or slot slightly ( think 1/000ths of an inch) as the thread is being pulled tight. Or the bottom of the foot is not flat and allows the material to lift at the stitch even though it holds it tight behind where the stitch is being formed. All of these can cause what you describe.

Edited November 15, 2010 by catskin

[jfhspike]

I am NOT an expert as some are BUT I just fixed the same problem on one of my machines today. Make SURE the presser foot is pressing down hard enough. On mine the pressr foot was not going down far enough. it was worn so it was holding the leather down enough to feed good but would let the leather lift a few THOUSANTHS of an inch thus the top thread was not pulled far enough back. Its worth a try. Or change feet to see if that makes a difference. Or if some thing is keeping the foot from going down the last couple 1/000ths.

After studying the pics again I am wondering if the hole or slot in the foot might be to big/wide. and the material is lifting into the hole or slot slightly ( think 1/000ths of an inch) as the thread is being pulled tight. Or the bottom of the foot is not flat and allows the material to lift at the stitch even though it holds it tight behind where the stitch is being formed. All of these can cause what you describe.

Thanks for the ideas, catskin. I think you're partly on to something. The material isn't lifting, but the shiny coated dacron sailcloth IS very slippery. And when the take-up lever is at the very top, tugging on both the upper thread at the workpiece and the thread coming through the tension disks, there's a moment when it actually manages to pull the workpiece BACK towards me a tiny bit. That sure suggests that there's plenty of tension there. What I can't figure out is why it's not managing to pull the bobbin thread UP as it should. Unfortunately, even when I hold the work and move it along with the feed dogs so that the backsliding DOESn't happen, I still get the little loops.

I can confirm that the material isn't lifting any more than the sunbrella was lifting -- probably less -- and that the foot tension is quite high -- higher than on my Pfaff 140, for instance, by a substantial amount.

Boy, I'm getting to know this process WAY better than I ever intended to.

--John

[Wizcrafts]

Aw hell; toss in that #20 needle, with #69 thread and see what happens. A bigger hole may help pull the knot up.

For slippery material you may want to consider using a roller foot. That could be just the foot, with little rollers inside, or an entire roller attachment conversion kit. Start with just the pressor foot and see if that helps feed the slippery material better.

If the top thread is pulling the material back towards you, there is too much top tension. Back off some. Loosen the bobbin some more to compensate.

[jfhspike]

Aw hell; toss in that #20 needle, with #69 thread and see what happens. A bigger hole may help pull the knot up.

For slippery material you may want to consider using a roller foot. That could be just the foot, with little rollers inside, or an entire roller attachment conversion kit. Start with just the pressor foot and see if that helps feed the slippery material better.

If the top thread is pulling the material back towards you, there is too much top tension. Back off some. Loosen the bobbin some more to compensate.

Brilliant! You guys are awesome (esp. you, Wizcrafts). You pointed me towards the problem, which I should have seen about 10 posts ago.

My thought was "if there's so much tension that it's pulling the piece back, SURELY that's enough to pull the knot up through the material. UNLESS the tension on the upper thread is coming from the pinch between the foot and the material and the throat-plate..." So I tried removing the throat-plate and sewing a couple of inches. The result? Not very pretty stitches, but with the knots on TOP (as you'd expect with too-high top tension).

In fact, the throat-plate I removed was my new one -- a "heavy duty" model that was needed to use a heavy duty feed dog, which seemed like a good idea for working on big canvas (think of a cover for a 35 foot boat -- it weighs about 100 lbs!). That heavy duty plate actually is THICKER than the normal one -- perhaps 1.5mm thicker -- which probably increases the effective presser-foot pressure (and means that the knot would have to get pulled up about 1.5mm more, too!); it probably all conspires to just screw things up (to use the technical term).

I'm betting that a swap back to the old dogs and plate may resolve all my problems; we'll have to see this evening when I'm back from work. But I'm definitely on the right track now. Thanks!

-John

Edited November 15, 2010 by jfhspike

[Wizcrafts]

It appears that your problem is too much tension presented by the raised throat plate and pressor foot. Have you tried reducing the pressure on the foot? ?? ?????

[jfhspike]

It appears that your problem is too much tension presented by the raised throat plate and pressor foot. Have you tried reducing the pressure on the foot? ?? ?????

Yep. I cranked it pretty far down, with no real improvement. But I'll try going down further before I swap the feed dogs and throat plate. I was also considering the possibility of filing a small groove in the middle of one of my spare presser-feet, just wide/deep enough to let the thread slide in it. But I'll only go that route if other things don't work first. (If I were making short stitches, this would all be no problem, I expect. But 1/10" stitches are actually pretty short for the sort of canvas work I'm doing, and after 1/10" feed, the hole is firmly buried under the presser foot.

--John

[Wizcrafts]

Yep. I cranked it pretty far down, with no real improvement. But I'll try going down further before I swap the feed dogs and throat plate. I was also considering the possibility of filing a small groove in the middle of one of my spare presser-feet, just wide/deep enough to let the thread slide in it. But I'll only go that route if other things don't work first. (If I were making short stitches, this would all be no problem, I expect. But 1/10" stitches are actually pretty short for the sort of canvas work I'm doing, and after 1/10" feed, the hole is firmly buried under the presser foot.

--John

If you cranked the pressure spring adjuster "down," you just increased the pressure! Turn it counterclockwise/up. Only apply enough pressure to secure the work between stitches and keep the material from lifting with the needle. A roller foot may be your secret friend in this application.