Uwe

The bird's nesting may be due to operator error. On these vertical axis hook machines you have to hold both threads for the first few stitches, otherwise the loose thread may get pulled into the works and create a bird's nest underneath, even on a perfectly adjusted machine.

That's helpful info, and yes, obviously within topic. My recommendation is to get BOTH machines. Give the good one as a gift and use the second head to learn sewing machine maintenance on. Being able to fix the gifted machine when it has issues will be the true gift that keeps on giving.

Sometimes apparent tensions issues are easy to fix, sometimes they're just the tip of the iceberg of a machine's real problems. I don't recommend gifting a machine with known issues. Try to keep this topic focused on the Seiko. It's okay to start a new topic with questions not related to this machine. We have quite enough runaway my-personal-journey-of-considering-a-dozen-machines type topics.

Looks like the machine is in very nice condition, actually. Price seems reasonable, but obviously it varies across the globe. I've paid less for machines, but then I spent better part of a week making them work. This must be the Seiko model that was sold under the Consew brand as a 226 model here in the US. Parts are cheap and everywhere. These are great starter machines and they're reliable workhorses at the same time. The motor may be on the fast side, but the motor pulley itself looks just about as small as they come. If the clutch works well, it may not be a bad starting point for upholstery. The best way to find out is to just try it out. Swapping out the motor with a modern servo motor is relatively simple and you can spend as little or as much on a servo motor as you like.

That locking lever is actually a very cool solution. Thanks for posting the details!

The rear presser foot bar itself is just about the only that can stay in place. But frankly, you might as well take the whole thing apart and inspect/clean all the parts. I'm curious as to why you want to replace the thread take-up lever at all. Is it actually broken? Can you post some pictures of your machine?

Looks like that #1 part in your photo is Singer Part No. 14768 (according to the Singer 11-24 Parts list) . It turns out I have one of those monsters hiding under my shelves, too, and that part is missing on mine (along with the various tension units). It also seems like your thread path is not quite right. I'm picturing something like this, but I haven't seen an actual owner's manual yet: There's no shortage of thread guiding items in the parts diagram. I suspect that Part 11471 is the actual check spring, although I'm not sure exactly where it would go.

The closest thing I know of is this section of a US Army service manual ( https://archive.org/details/TM10-3530-202-24 Pages 122/123) that describes the procedure on a Singer 111W155 (a relative of the Juki LU-562 in certain design elements):

I've done it and I wouldn't describe it as a trivial undertaking. I'm not aware of a simple set of instructions or a video showing the procedure, sorry. You basically have to disassemble everything in front of the take-up lever inside the head of the machine.

When I decided to do some 3D CAD design work, I researched a few options and I ended up settling on Autodesk Fusion 360. The learning curve with any powerful 3D CAD programs is steep and painful, so I only wanted to do it once. I don't regret my decision. Fusion 360 is one of the very few, very powerful 3D CAD programs you can use for free. In fact, I don't know of another 3D CAD program that's as powerful AND free. The importance of the CAM (Computer Aided Manufacturing) end of the 3D CAD program is not to be underestimated - I've used Fusion 360 to design CAD parts and generate CAM G-Code files for Tormach CNC mills, ShopBot CNC wood routers, as well as export files for use with my Cetus 3D printer. I learned most of what I needed to know from watching videos made by NYC-CNC on YouTube. The "cloud" aspect hasn't interfered with my work. Fusion 360 is a program installed and run on your computer, not just some web browser interface to a program that runs remotely. I've used Fusion 360 with and without an internet connection on my Mac laptop. I occasionally use the Windows computers at my MakerSpace to just log into my Fusion 360 account and have access to all my designs for quick little tweaks. For simple 2D CAD design work, other options like SketchUp etc. may be fine, but the topic question was about 3D CAD design programs.

Pfaff 141 is a bottom+needle feed machine, the Pfaff 145 is a bottom+needle+upper feed machine. Here's a Pfaff 141 in action. It'll give you an idea how well the machine can sew vinyl and leather material:

The adjustment screw won't work unless it has something inside that hollow main shaft to press against. You'll have to slide a suitable rod inside the shaft AND find an adjustment screw. Screw sizes on old sewing machines are notoriously difficult to determine (especially if the screw is missing) and often impossible to find in a store. I'd be tempted to try and replace the shoulder bolt+nut that goes through both parts (just above the "0" marks) with a regular bolt+nut. A suitable regular bolt+nut may allow you to clamp the two parts together and fix them in various positions to change stitch length. Cumbersome, but workable.

Here's a video I made some time ago when the same question had come up on another Singer 153 machine that had a non-functional stitch length knob.

Telling us what YOU found out about that machine in terms of pictures, documentation, specs, is a great way to get the ball rolling. Specific questions help, too. We occasionally suffer from let-me-google-that-for-you fatigue.

Designs like the SInger 111W drive the feed dog motion from the lower shaft, so in that case the upper and lower shaft need to be synchronized. That's where you'll find those shaft synchronization marks. The Adler 67 design drives feed dog motions (lift and feed) directly from the upper shaft, so no synchronization between upper and lower shaft is required. The lower shaft only drives the hook (and optional thread cutting cam). The hook itself can be freely adjusted on its own. The cone/bevel gears on the other hand usually do have factory marks on them that indicate which teeth should mesh. Watch out for them if separate the cone/bevel gears. The gears may still work but may be noisy and wear more quickly if they're not properly meshed.

You have my sympathies dealing with this abomination of a user interface on a servo motor. Here's the manual for the two-digit display model - good luck: http://www.consew.com/Files/112347/InstructionManuals/CSM1000.pdf 500 RPM may well be the slowest this motor can spin. The initial running-on syndrome may have to do with the position sensor - especially if the actual position sensor is missing. The controller logic will keep spinning the motor after the pedal is released to wait for the signal that the handwheel is in the right position. If there is no signal (because the sensor is missing) the controller logic will give up after a few turns, and perhaps record the position sensor as missing, so it won't try again until you cycle power. There's usually a setting that tells the controller whether the position sensor is installed or not - make sure that setting reflects reality. Installing a speed reducer pulley may also cause problems on some motors if the reduction is too strong. Some control logic systems only allow for certain number of motor revolutions to reach the desired handwheel position. The controller may give up before that position is reached, even if the position sensor is installed correctly.

Post some picture before you start taking things apart. If you're unsure whether you have a clutch motor or a servo motor, I'd recommend taking a step back and evaluate before you start digging in. General rule: don't turn a screw unless you know what it does (unless you can afford the machine to be down for a week or two while you figure out what went wrong.)

You can move the speed reducer pulley toward the back. There's a bit of science/geometry to installing motors and speed reducers. Tilting back of the machine is part of it. When installed just right the tilting works like it does without the speed reducer. Essentially, when you draw an imaginary line through the hand wheel and the hinge pivot, the center of the connecting pulley (speed reducer or motor) needs to be slightly towards the back of that line. Otherwise you have to overcome increased tension at first when tilting the machine back. There's nothing you can do about the position of the hand wheel and hinge pivot, so the only thing you can adjust is the position of the pulley. Here's a quick diagram that hopefully illustrates the concept. Green pulley (or motor) position is good, red position is trouble when tilting the machine back. The graphic exaggerates a little. Pulley on that line or slightly behind is fine. In the red pulley position the distance between hand wheel and pulley (and thus belt tension) increases at first, then decreases as you tilt the machine back. In the green position, the distance between hand wheel and pulley only decreases (reducing belt tension) as you tilt the machine back.

When you manually back-tack you slightly raise the feet to turn the material around 180˚. What they mean is that thread tension should not release when you lift the feet only slightly for that purpose. Some chain stitch designs are technically incapable of sewing in reverse (and it's not a question of reversing material transport like with lockstitch machines.)This has to do with how the thread loops/triangles underneath are formed. On some chains stitch designs the chain can only form if the material moves in one direction.

Yes, "441" is shorthand for a class of machines that includes the original Juki TSC-441 and the many copies, clones, and close variations of that design.

That flatbed table sure is bigger than mine! Seiko makes good machines. A good used original (Juki,Seiko,Adler,Pfaff,etc.) is worth as much as a new clone - and will likely hold its value better, at least in my book. The 441 is the more popular design, more people have experience with it, and you may have an easier time finding help, parts, and accessories for it. Most people cannot tell if a stitch line was made on an original or a clone, but some people find working with originals more enjoyable and rewarding.

I recommend ordering bobbins by part number. Don't trust the "Fits XYZ machines" statements (your bobbins "fit" but they're not right.) Get some original Juki bobbins to do your machine justice - how much can they cost, really?

Sounds like your bobbin basket got forcefully rotated out of position and jammed up pretty well. If the bobbin basket rotates out of position, the needle will surely find an early demise. Normally that bobbin basket will only properly lock into place in exactly one position. If it's not inserted properly and the latch key that keeps the basket from rotating is not properly engaged in the matching cutout, the basket may spin out of place and bind up. I made a video that hopefully will illustrate what I'm trying to say:

The phenolic plywood does not lend itself to glueing because nothing sticks to that slick coating. So screws it is, and lots of them. Makes for a very solid table top, though.

I built a table for a sunken 5-thread Juki MO-816 serger for a client. Not precisely a leather machine, but a rather challenging table to build. The tabletop and suspended shelf are made of two layers of 3/4" plywood, phenolic and baltic birch plywood, screwed together. The black laser-cut acrylic rings on the suspended shelf keep the machine's rubber feet in place to keep the machine from wandering as you sew.