LordHoot

Quick follow up: thanks for the help, I managed to find a hook timing setting that made a little stronger stitches ( 1.6 mm instead of 2mm on the needle bar after BDC ) works well for 2 layers of webbing, but tension setting is very finicky. Reduced take up spring tension a bit, but corners remain hard to adjust. I also tried a size 20 needle and it works with 8 layers. I had to adjust the knee lifter motion range to lift the needle foot high enough to turn. I'll finish what I started and probably look into purchasing a lighter machine. Do you guys have any recommendation on light/medium duty machines for nylon webbing/fabric?

All previous tests were done with 2 layers of webbing, which is roughly 2-2.4 mm thick. I did a test run with 4 layers which is around 4 to 5 mm and it definitely made better stitches, had to adjust tension to have the knot in the middle and then loops disappeared, stitches were tight. I tried 8 layers but it was too much for the machine, it seemed like the needle deflected and hook didn't always catch the thread. What I usually sew with this machine is 2-4 layers of webbing, sometimes with other fabrics. I need it to sew 2 layers perfectly as it's used for pocket flaps and loops would be very visible. Could it be like you described, the machine is not suitable for this kind of work? Is there a way to adjust the timing so that it would handle lighter fabrics? Edit: How does this machine compare to an Adler 267 in terms of sewing light/medium fabric? Do you guys have recommendations on sewing machines for that type of work?

My bad I forgot to write the current setup I use in the first post. Setup: Bonded nylon thread, #69 (A&E) both top and bottom, usually all black but using green to help see the problem, 135x17 DP17 110/18 round point needle. Sewing mainly 1000D, 400D nylon and various width of nylon webbing. Yes this is the screw I'm talking about. Usually it's not set like that, I set the bobbin tension so I can feel a little resistance when pulling it, just enough to keep it tense but nothing crazy. If I tighten it further, I do get increased tension until it bottoms out and the bobbin tension is way too high. Tension feels tight when pulling the bobbin thread before sewing, but even at max tension and proper balance between bobbin and top thread, stitches are still weak. Once I get a chance I'll disassemble it and verify if there's any grooves or catches along the thread path. Looking closely at this video which shows how the lockstitch is made on the same model (older but still close enough) I see the same behavior, upper thread drags the previous stitch thread, but then lower thread tension seems to pull it hard enough to form the stitch properly. I'll also keep investigating the lower thread tension while sewing to see if that could explain the problem.

Doesn't seem like it, started at 6mm, then reduced the stitch length a few times while checking tension and it remained the same. Random loops and weak stitches occurred in all settings.

Good idea, I checked the bobbin case and currently there are some wear marks both on the case and the spring, but no grooves. Machine came with a spare, unbranded bobbin case with spring, no marks on it, replaced the Pfaff one with it, tightened the adjustment bolt to the max, it was harder to pull then before for sure. Then swapped the top thread tension spring since it was not strong enough to pull the lower thread through. Once I got a decent setting I still managed to the get the issue a few times, and there is still a lack of tension. No knee lifter interference either unfortunately. Unfortunately that did not help either. I tried a few positions, even something like 7 o'clock and the problem persisted after adjusting tension. Also tried a range of tension on the take up spring, from very weak to very strong and it did not improve the stitch strength and looping problem. For fun I used a screwdriver to pull stitch after stitch to tighten them, and over 20 stitches I had maybe 1" of leftover thread, so it seems there's really a tension problem somewhere. Here's a picture after adjusting the take up string stop down and increased tension.

Hey guys, I've been using this site for a while for information on industrial sewing machines, especially how to set up an Adler 69 for binding, which was really helpful. Decided to join and ask for help regarding a problem with a Pfaff 1245. Problem: Randomly, the upper thread forms a loop when sewing nylon webbing (2+ layers). Issue is more visible with 6mm stitch length, but occurs at any length, I usually sew at 3 to 4 mm. Bobbin thread looks fine. See linked videos for details on the issue. I managed to get a high speed capture of the problem occurring, and it seems that after making the stitch, the needle comes out, then the threads coming out of the hole in the fabric sticks with the existing upper thread from the previous stitch and pulls it out, then it never gets set back down properly. When it’s less dramatic, the stitch feels weak. I’ve tried many combinations of lower thread/upper thread tension, more tension makes the issue less frequent, but at some point the bobbin thread pops up and the issue still occurs. For comparison, the same needle, fabric and thread combination on an Adler 69 has no problem sewing this fabric in the same fashion. The thread never pulls up the previous stitch and they are very strong. - I re-timed the machine according to the manual, then checked it over multiple times, adjusted feet motion, needle position, hook timing, take up string and so on. Manual says 2mm after BDC, tried 1.8 and 3mm, but no change. - I’ve tried modifying the tension on the take up spring, changed the tension disc, and bought new thread, but the problem still occurs. - Tried a much larger needle with no success. I’ve seen a similar issue discussed here: https://leatherworker.net/forum/topic/67986-random-loose-top-thread-consew-289rb-1/ But with no solution, it’s unclear what fixed the problem. I did try lubricating the thread by spraying it with silicone lube, but it had no impact on the problem. I’ve reached a point where I’m considering selling it and getting another machine because it doesn’t produce quality stitches. It's a bummer because I bought it used and it seemed in good condition. Do you guys have any idea what could cause this problem?