Constabulary

if you fear online tracking then use https://duckduckgo.com/

You have not found them? I just googled the part numbers / items description from the parts list. #94 - 267265 https://www.ronsew.com/lifting-lever-rod-267265-for-singer-212w/ #624 - 12361 https://www.ebay.com/itm/125637743697 #89 - Singer screw #175 https://www.sewingpartsonline.com/products/feed-fork-connection-screw-175 #90 - singer srew # 86 https://www.ebay.com/itm/265240279882 #93 - 508272 https://marfar.com.au/products/sin-508272-singer-link so the parts seem to be available - I would check with local industrial sewing machine dealers or with Toledo Industrial Sewing Machines https://www.tolindsewmach.com or maybe with Ralph´s Power Sewing https://powersew.com/parts I would guess an industrial sewing machine dealer can get most parts at once.

BTW - 12mm is pretty much the maximum this machine can sew - you may have reached it´s limits or you are close to it...

so the problem - I guess - is the foot cannot climb over the thick folded "bulge" right? There were feet (I say were cause they are barely available anymore) with a spring loaded foot sole this foot a easier climb over thick spots but there is no guarantee that it will work in your case. The only available foot for this kind of machine that may work comes from a Seiko SK-2 / Singer 132K. They also fit on Singer 45K and Adler 4 / 5 foot bar (machines w/o jump foot only) but the foot bar height may need some adjustment cause the Adler feet are a bit shorter than the Singer 45K feet. https://www.college-sewing.co.uk/170397661-presser-foot-seiko-singer-132k.html However you may need something something that "equals" the height difference too. In Germany we call it "Hebamme" (word has different meanings) and looks like this: https://schnittenliebe.com/shop/hoehenausgleich/ Check the pictures in the above linked offer so you will see what I mean. When talking about Adler 4 & 5 class machines and sewing over thick spots then the best would be a machine with jump foot (as mentioned above) on which you can adjust how high the foot lifts when sewing over thick spots. But I guess a new or different machine is no option for you, right?

Morning - sorry my bad. The Adler 5-6 is a machine w/o jump foot, I just checked my records and I was on the wrong track. The machine ex factory came with a roller foot! I mixed it up with the 5-8 which has a jump foot. The jump foot is a mechanism that enables the presser foot to feed the material along with the presser foot and it jumps back to its position when the feed dog descents at the end of the stitch cycle. The mechanism is not mechanically driven it works just with foot pressure and is pulled back to the front by spring. You can see it in this video at about minute 5:00 https://www.youtube.com/watch?v=QosP-IaqT_E How stick is the material (all layers together) you want to sew? Have you tried reducing the foot pressure?

This is what I´m using for resizing pictures: https://www.bricelam.net/ImageResizer/ super easy

Have you turned the jump foot mechanisms on or of? I guess you know what I mean. Due to the jump foot mechanism it would require removing parts from the foot bar to install a roller foot and make other adjustments as well - meaning the machine ex factory is not designed for mounting a roller foot. In what condition it the feed dog maybe the teeth are worn. Or maybe the feed dog is se too low.

I cannot see how good or bad the stitches are, pics are too small but when I sew NM 20 thread I´m using a larger needle size like NM 140.

BTW - this is how my singer 212 (double needle) look from the underside. Maybe it helps. Pic 2 show the junction point where bras tubes for the oil wicks come together a bit closer. How is it looking at your machine?

Have you checked in this Forum: https://www.naehmaschinentechnik-forum.de/

The subclass is not very common as it seems. I´d post post some pictures that may help finding answers.

Machine for sewing or generally? I`m a vintage machine guy and have a been bitten by the Singer bug but most likely it would be a Juki 341 or something in this class or a CB 3200 but I´d choose the 341 first I think.

a quick picture

Thats actually a restored Adler 30-15 (short arm) but it shares several parts with the Singer 29K. I can post a full view tomorrow.

Wiz, I think the bobbin thread belongs there. Thats what the gap in the bobbin retainer is for. Other machines have it this way or very similar too

I have not worked on machines with this type of hook for a loooong time. I guess its a thread take up lever or hook timing issue (or both).

I may have complete tension unit.... will check this weekend. But I´m in Germany.

Don´t know what N66 is but reg. needles - 135x17 and 135x16 have the same dimensions. 135x16 is a needle with a cutting tip for leather whereas 135x17 is for fabric but you can sew leather with it as well. The cutting tip depends on what stitch appearance you want to achieve. This brochure (direct download link) may give you more information reg. needle tips: https://www.groz-beckert.com/mm/media/en/web/pdf/Sewing_machine_needles_for_leather_and_technical_textiles.pdf

when I make turns my needle tip is still in the material the way that I see needle scarf - maybe worth giving it a try. BTW - have you opened your slide plate / hook cover and watched the thread when it slides around the hook? Maybe it keeps hanging somewhere maybe on the bobbin case opener or the hook needs some adjustment - just a guess.

Depends on how heavy you want to sew. Maybe the 45K1 can replace the Singer 7-10 beast and the 78-1 I guess is a good replacement of the Tiny 15K. Thats at least what I would choose.

No you cant but you can move the needle holder a bit sideways. Loosen the screw above the needle clamping screw and try to move the needle holder. It may be stuck if so try to remove it and clean it from oil, gunk and dirt and try again. Whe moving the needle holder make sure the tip of the shuttle hook does not touch the needle.

It was designed as garment / fabric sewing machine but if for sure can handle some light garment leather. But since the seller is your neighbor why don´t you go and test it with the materials you want to sew. Buy some leather needles if he has none and see what it does. Maybe you have to swap out the motor and buy a new servo motor this swill give you a better speed control.

I do not know the machine in particular but to me t looks like a drop feed + needle feed machine with roller foot. I´m not sure but it seems to be a short stitch machine (like 2-3mm or so) cause the slot in the needle plate is quite short. I think it is designed to sew shoe uppers and so forth. Not sure if it suits you needs but I would not pay 1100 for it.

Singer 29K1 or 29K4 manuals will work for the 29K3 as well. There is not a major difference. Maybe a side wheel or a wax pot but nothing really important when is comes to threading or sewing.

Please post pictures of your machine from the underside. I have a Singer 132K6 which is the predecessor of the SK-6. On my 132K6 there is a bushing for the hook drive shaft that is held in place by a set screw. I think when you loosen the set screw you can try to move (hammer) the bushing carefully to the right a little bit so you can move the hook a bit to the right as well. The set screw is probably covered by the bobbin case retainer assembly so you have to remove this first. If there is an adjustment ring on the right side of the bushing loosen its set screw first. I don´t know your machine but that's what I would try.