Excellent information, thanks. Now if we can get Roger to get very specific on the rasant types/model / name.
Peter, thanks, I think I'm seeing/discovering exactly what you are saying, leave it to me to find the limits of the tools or methods, then bang my head a while, then return to what works. That's tragically typical for me.
So to be clear, and for anyone else who comes across this thread, which is a virtual certainty, here's the actual threads being discussed, correct any errors:
standard gutermann, ie, what all the outdoor fabric shops sell. Not the heavy polyester stuff, at 33 yards a standard spool, but the 110 yard stuff, or larger spools. This is what is being referred to as thin thread. I think.
I'm not able to connect this with any tex number, is this the tex 40/mara 70?
Rasant threads, specifics not known, haven't seen this in fabric stores so have to order it online I guess. Would require thread id numbers for let's say black to actually know the specific types Roger suggest are very good for thin nylons like silnylon, unless I'm missing the point.
Mettler, check out metrocene plus, see how that thickness is.
All thick threads, like the heavy duty gutterman, the c and c heavy, and the nylon upholstery threads, are a wash, avoid them and save your money until you get a real industrial machine and go into actual production. If I get it right. So stack those somewhere and enjoy their nice shapes. Or colors, whatever.
Needles, use larger and thicker as the materials get thicker, but use the same thread if your machine can't handle the thicker stuff. Mine can actually sew with up to 18, 19 is a touch too thick, but because tensioner can't create tension enough to pull the knot up into fabrics that are densely woven, like nylons, dimension polyants etc, the heavy thread doesn't really work. Needs industrial machine, this fits with what I see in my industrially created packs re sewing.
I'm not taking the machine to a sewing shop, that's way too expensive, plus the thing weighs 50 pounds, tough carry on a bike, did it once, that was enough, but I have dismantled it in parts to fix things already, and am familiar with the tensioner innards, it's quite simple system mechanically, pressure plate pushes against disk that creates tension. Uses a spring, so there is a chance the spring wears out over time and fails to fully tension, but I'm going to go with the experiences here, and just give up on the heavy threads, the motor analogy is good, that's the same method you use when creating software too, start with the basics you k now works, then move out from there.
It's obvious that with the bigger needles and thicker materials, the smaller knots of the standard gutterman type thread, or the mettler, I'll check that out, will have no trouble moving up into the fabric layers, so that's how I 'll do it.
I stopped at the shoulder strap attachment points, was the first thing, so it's not a lot of material lost.
If there are further specifics you feel will help others avoid errors, or if I made errors in my summary, please feel free to correct them.
I really like the kenmore, that's a tough, powerful, old school machine, hard to understand how they could get 50 pounds of steel into that small space, but they did. But it looks like I found it's upper limit, also found its lower, it doesn't like silnylon much, but it likes everything else.
Thanks very much for the great input and feedback, there is / was a definite weakness in online documentation / myog how to s in this area, I think this helps clear everything up, or at least bring light to the question.
Peter, your words resonate, might be my tools, but I think what you say is what I should do in general, thanks..