friquant

Can you post an up-close slow motion video of the hook area as this is happening? My usual approach to preventing the hook from catching on the thread when the hook comes around the second time is to retard the hook. It's quite predictable on the two machines I've tried this: Advance the timing and the hook grabs the loop of thread on the second time around. Retard the timing and the loop of thread is too far out in front of the hook point to be grabbed. Rather than follow factory timing on those two machines, I found my own timing specification that is advanced enough that the thread can be pulled around the bobbin case without too much tightness, but retarded enough that the hook does not grab the thread on its second time around. See this post for some background: https://leatherworker.net/forum/topic/131646-new-way-to-measure-and-visualize-hook-timing/

I don't have a double needle machine (yet!) but what an interesting challenge. 🤔 This excerpt (from the 112W139 manual, I presume) actually says to use left twist thread for both needles. @DMH This photo you posted shows both left and right threads having about the same twist when they land in the fabric. It's also skipping several of the first ten stitches in the seam (no time for thread unwind to happen). What I'm saying is the left side may be skipping due to other issues. @nylonRigging What machine are you using? I was hoping someone would show a photo like this...at the end of a seam so we could see the two sides.

In general, you may be able to sew with bigger thread than what a manufacturer states. But be prepared to accommodate the machine! 1. The needle + top thread needs to fit through the needle plate. (You can adapt the size of the hole as long as you polish it after.) 2. At some point, you will max out the tension adjuster for the needle thread. To get a balanced stitch with such limitation, you may need a bigger needle (makes a bigger hole, which is easier to pull the thread through when locking the stitch.) Also lessen the bobbin case thread tension to accommodate. (Thicker thread gives more bobbin tension for the same adjustment.) Let us know what you discover!

Looks like you have the left side more or less stitching I might thread one side of it and work to get that one side dialed in, then move to the other side. By "dialed in" I mean not skipping (check forward, reverse, short stitches, long stitches, thick material, thin material). And smooth action as the thread goes around the hook (no popping sounds, no broken thread.) By the way, you can slide one of the bobbin case covers open and watch the hook as you stitch slowly. This can help you to understand the cause of your occasional skips. Using a narrow piece of fabric (or just moved to one side) makes visibility easier. Someday I'll get to use a double needle 🤩

UPDATE: Since becoming more acquainted with domestic sewing machines and their low-power plain-bushing motors, I have started choosing belt tension that optimizes for best top speed. That is, looser belt tension than before. (This is 5mm PU belt for reference.) Top speed of the machine head is now 750rpm with no bobbin case, no thread, and presser foot up. Also fun to watch it spool up, as the belt shape becomes asymmetrical. This photo taken right after stepping on the pedal. Here's a demonstration of varying belt tension with a domestic motor and how it changes top speed. (Listen to the hum of the machine head to judge speed) Ah, well 😊

Yes. The cad files are here: https://leatherworker.net/forum/topic/125148-replacement-pulley-for-tapered-shaft/page/3/#findComment-790324

Wow, not much of a manual, is it? Maybe a sales brochure? This page says your machine takes a 135x7 needle: https://ismacs.net/singer_sewing_machine_company/model-list/classes-100-199.html This page shows 135x5 and 135x7 as being interchangeable: https://ismacs.net/needle_and_shank/pdfs/NeedleXRef9-30-23.pdf So I expect the needles from the first photo you showed (Organ 135x5) to work fine. (No need to purchase special order needles...135x5 is a fairly common system so needles are straightforward to find) But next up is you need to get the needle bar height (and possibly other timing issues) set correctly. This video by Uwe covers the basics of setting needle bar height: Possible reasons for the hook point to be striking the needle: Incorrect gauge set installed (this sets the spacing between the two needles) Needle is not oriented correctly. (Scarf of each needle must face its respective hook) Hook point is striking needle either above or below the scarf (hook point should enter scarf) Hook is too close to needle (hook to needle distance is adjustable) Needle guard not adjusted out far enough Needle is bent toward hook (Always set timing with a fresh new needle of correct system) Needle with 1.6mm shank being used in a machine that is built for 2mm needle shank (Again, always set timing with a fresh new needle of correct system) Axial play in the needle bar rock frame rock shaft, causing erratic left-to-right positioning of the needles. (Press the parts on both ends of the shaft towards each other while tightening the ends.)

Looks like your outer toe is not touching down. I'm not sure how to adjust that on the 341. Is the foot lift hung up on something? Are those the correct presser feet for the machine?

What makes you say the threads are damaged? If they will still tighten up, I would clean the threads and reassemble using medium strength threadlocker. (Coarse threads like this are likely to back out without threadlocker)

I've heard chain stitch is used as a decorative topstitch, but I haven't seen that in the clothes I wear. With the two-thread chain stitch I've used, the top side of the fabric looked just like a lockstitch seam. But the bottom looked fatter, because of the chain pattern. In the jeans I buy and wear, they put the chain pattern on the inside where it's not visible. There is an additional "gotcha" in making a chain stitch: Too-low tension (for a given material) will give skipped stitches. At least it did with the Baby Lock EA-605 that I repaired and used briefly.

Can you post or link your manual here?

Oh I get it...you were pouring oil in waiting for the oil to reach the sight glass.. The float pin on my industrial overlock (Union Lockstitch 39500) came with a red painted tip, so it's high visibiliity.

I bought this one and it was fine: https://www.amazon.com/dp/B0D3V2SB9N (Complete hook and bobbin case assembly)

Are you changing needle systems? The photo you have above shows needle system 135x5, in size 20 / 125. Then you have a photo showing two needles of different length (definitely two different needle systems in that photo). You don't need to change needle systems in order to use a thicker or thinner needle. A cursory glance at the internet did not tell me what needle system this model is supposed to take. Sometimes people do use a different needle system than called for, either because the called-for needle system is hard to find, or because they need/want more clearance under the needle. But unless you have one of these reasons to do so, I would either: Use the factory called-for needle system, or Use the needle system the machine is already set up to use. (Needle bar height is what you would change to swap between systems.)

Not sure how similar this will be to your machine, but here is a video with some close-up slow-motion of loopers in action.It took me a long time to figure out how this one was supposed to work, and there are SO many adjustments. I finally did get a service manual.