Needle Timing And A Singer 31-15

[jfhspike]

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.

Sorry -- I wasn't clear. I meant that I cranked the PRESSURE down, by screwing counterclockwise.

Anyhow, here are the results of tonight's experiments:

1. I looked around for another foot, and found the only other one in the drawer appears to be a 1/4" welting foot (I'm only guessing from the shape, of course). The key thing is that there's this big "tunnel" down the middle, hence nothing to pinch the upper thread. Result: Joy! Beautiful stitches. Upper tension something like 3 turns away from "cranked all the way down".

2. Swapped back to regular foot...no joy. Loops prolapsing from the bottom of the material.

3. Changed back to regular needle plate and feed dog (and then spent time messing with adjusting the feed-dog position, because it has to be reset for the different dogs). Set up machine with regular presser foot. Took a few stitches (and inch or two) that looked OK for knot-position, but with the bobbin thread kind of slack. Tried again and...ran out of bobbin thread.

4. Wound a new bobbin. Found that with regular foot and regular plate and dog, at 16 stitches per inch, things look OK. By the time I'm down to 12 per inch, I get loops.

Overall: the test with the welting foot convinces me that the upper thread's getting pinched under the foot, and even very modest presser-foot pressure is enough to cause a problem. Once the stitch-length is great enough with the regular foot, the trapping of the upper thread under the foot starts.

I think that when the stitch-length is too great, the workpiece moves, and it moves back BEYOND the slot in the presser foot -- maybe 1mm beyond. So maybe I need a presser-foot with a deeper slot between the two toes, or need to go with a shorter stitch-length, or...who knows. But with all your help, I feel as if I'm definitely on the right track now.

Thanks again, everyone.

--John

PS: I just noticed that the presser foot I'm using is the most basic possible: it's a single casting, with no "ankle joint" of the kind I'm used to seeing on my Pfaff. I doubt that this is a major cause of problems, but perhaps it's worth considering.

Edited November 16, 2010 by jfhspike

[Wizcrafts]

Call Bob Kover, at Toledo Industrial Sewing Machines: 866-362-7397. He has parts and accessories for most Singer machines and other major brands. No doubt he has various pressor feet that will fit your machine.

[jfhspike]

SUCCESS!

After careful side-by-side comparison of the 31-15 and my Pfaff 140, I decided that the timing of the feed dogs really WAS wrong on the Singer. Basically, the material was done feeding by the time the thread-take-up lever reached the top. That meant that the stitch I was trying to tighten was already "buried" under the presser-foot, and things just weren't working. By contrast, on the Pfaff the feed dogs were at top dead center just about the time the take-up lever reached its top position.

So, after carefully marking the current position of the feed-dog cam (which was pretty easy: the grease on the main shaft was a perfect medium in which to draw a "line" with a small awl), I went ahead and retarded the feed by about 30-40 degrees. Result? Perfection! The stitches look like real stitches, I can reduce the tension by about 2 turns from where it had been, and I can even tighten up the bobbin tension a little without any adverse effects. And when I stitch that sailcloth, it looks like a sailmaker did it rather than a bozo

Part of my reason for being willing to mess with the feed timing is that it was clear that it had been messed with relatively recently (less accumulated grease there than on other nearby areas of the machine, and a slightly bunged-up screw-slot was a further clue. I would not, in general, recommend that anyone with a machine that's worth real $$$ try this. I only did it because my machine cost just $50, and I figured I didn't have much to lose.

Thanks again to everyone for helping talk me through this. You guys helped me figure out that if I just reasoned about it hard enough, I'd get somewhere.

--John

[Wizcrafts]

So, I was right when I mentioned that the top end was out of time with the bottom end. This is what I meant.

[jfhspike]

So, I was right when I mentioned that the top end was out of time with the bottom end. This is what I meant.

Exactly -- it was that comment that got me thinking, and I looked around and couldn't find any information about how to adjust this "top end timing," so I went with the "maybe it should work like other machines" approach. Thanks again for steering me right.

-John

[suzelle]

jfhspike,

Thanks so much for sharing your experience here!!! Thanks to all who answered the questions too!

My new sewing machine is a 1937 (?) Singer 31-15, and I have to get her up and running. So wish me luck! This is my first post here, I just joined and am excited to be part of this group!

Have a great day!

-Suze

Edited December 3, 2012 by suzelle

[Merlyn616]

John, I have had this se problem with mine and found it can be as simple as missing one of the lower thread guides as the cause. Don't overlook the possibility of needing to use a different type of needle. I've also found that rotating the tension spring up to about a 70 degree angle (or higher if need be) instead of the 40 to 45 degrees they are usually at makes a world of difference in eliminating bottom loops. The fact that your material is slipping back toward you is definitely a presser foot issue as well as a contributing factor. I do a lot of historical costuming as well as leatherwork and deal with similar issues on most of my machines frequently. Try sewing silk and satin over buckram and heavy canvas to make a 17 th century dress mess jacket if you want headaches. Don't get me started on hats.....

Good luck and Ihope you get this solved.

[jfhspike]

Thanks for the suggestion, Merlyn616. As it turned out, it was a top-end timing problem for me, but there's probably someday going to be someone else reading this thread of postings for whom your answer is exactly what's needed. I'll keep in mind the idea of adjusting the tension rotation as a possible fix for future problems. --J

[blue99]

The same thing happen to my Singer 31-15 when I decided to change the feed dogs to the heavier style........Loops on the bottom side of the fabric. I am using a 18 needle with 69 bonded thread sewing two layers of cotton ticking. I have the thread tension set almost to the maximum, would that be correct? that is the only way I get a good stitch with a long stitch. I have timed the dogs and the needle to the shuttle and even compaired the 31-15 strokes to a 15-91 they seem to be identical. The thread tension is so high that it doesn't seem right. I pulled the tensioner all apart and cleaned everything........I don't understand what John did the 30-40 degrees......I've done everything by the manuals..... this is an old tailoring machine, so why the high tension? Thanks for any help, Sincerely, blue99, John.

[jfhspike]

Hi, blue99. Look really closely at what happens during stitch formation. There are two things going on. (OK, there are a million things going on, but let's concetrate on two of them).

(1) The needle is plunging down through the material, pulling up a bit to form a bulge, which the "hook" is catching and wrapping over the bobbin, forming the "knot", and then rising up to pull the knot -- both the "top" and "bobbin" halves of the knot -- up into the midpoint of the material (at least if you've got things set up right).

(2) The cloth is being advanced by the feed dogs, so that the knot you've just formed is now pressed between the feed dogs and the plate beneath it. That holds tension on the "already sewn" part of the two threads so that the needle/tension and bobbin/tension assemblies can get the right tension in the next knot.

Imagine if part 2 happens too early -- before the needle and the up-and-down-arm that's above it have pulled the knot into the cloth, the material has already advanced. You end up with a loop of top-thread dangling below the cloth, and pinched between the foot and plate. The arm rises up but cannot pull that loop back up tight, and instead pulls more thread through the upper tension assembly.

If you think about this, you'd expect the problem to be worst with long stitches. With short stitches, the previous knot isn't really all the way under the presser foot as described in item 2 above. (This is what I found on MY machine; if you don't have these symptoms, then I doubt my solution is the one to follow!)

So I'd try the following: back off on the stitch length until you're making quite small stitches and see if the loops still appear on the bottom side. If not, then with small cloth-advance, you're good, but with large cloth-advance, you're getting the pinching I described. You might even want to try the small cloth advance and see whether you can adjust the tension to something reasonable in that situation.

What you need to do, IN THIS CASE ONLY -- i.e., only if the "small stitches" situation doesn't make loops and lets you use more reasonable tension, but long stitches make you get loops -- is to adjust the timing of the feed-advance vs the needle/hook operation.

How do you do that? None of the manuals I found described that, so I'll make an attempt here. Look at page 4 of http://parts.singerco.com/IPinstManuals/31-20.pdf; there's a cover plate marked "F" in Figure 3. If you look behind that cover plate, you'll see that the main crankshaft of the machine is visible. Two things are driven by that crankshaft at that end, and ONE of them drives the feed-dog assembly. Look at the diagrams at

http://parts.singerco.com/IPpartCharts/31-15.pdf

Find the page saying 22303-1/3 at the right. There's a screw marked 446AL; if you loosen that, the feed eccentric (127152) can be rotated on the crankshaft by a few degrees, adjusting the timing of the feed. Which way do you rotate to advance or retard the feed? I have no idea. I did it by trial and error.

I want to be clear here: adjusting this is what I did to make my machine work, but I'm NOT a sewing machine service person -- just an amateur kind of mechanically inclined guy. It's pretty clear to me that adjusting this eccentric too far can really screw things up, and trying to make the adjustment through that cover-plate hole isn't easy. If I were you, I'd be very certain to mark the initial position of the eccentric so that you can put it back to its former state, and try adjusting it by only quite small amounts to see if you can improve matters. The fact that adjusting this eccentric is not included in the general manuals suggests to me, at least, that you're messing with the Dark Arts, and are more likely to screw things up than fix them. I'd never have done it to mine if it weren't essentially a machine that I could afford to destroy (I only paid $50 for it).

Anyhow, with that caveat, and with a clear understanding of what I've written above, you could try what I'd described, and it if works for you, let us know.

Or you could take the safer route and have a professional adjust it for you.

By the way, when you adjust that screw, make sure to use a screwdriver that fits really well -- wide enough for the slot, thick enough to fill the slot but not so thick that it won't go in --- and make sure to snug it up decently when you're done. You'd hate to have the feed adjust itself during your later sewing.