Gymnast

This is from a manual of a Household Janome HD9 straight stitch sewing machine. I think it is a relative new type of sewing machine - perhaps 10 years old, but is still being sold. The only specifications I can find regarding how heavy thread or fabrics it may be able to handle is this table on page 32. Do you know what kind of threads these are?

Is it always the case? I guess this would be the case, if the hooks are spinning in opposite directions for drop in bobbin machines. If you look this part of video, you see that the hooks spin in same direction, and therefore the hooks pass the two needles in the same geometrically way. Therefore I should think it would require the same kind of thread for both needles and bobbins.

I normally call the thread S-twisted and Z-twisted. Almost all thread is Z-twisted unless otherwise specified and can as default be used on all sewing machines except for the situation Wizcrafts points out. We had a thread about 2½ years ago about twisting of thread:

Hello Jonas Amann Serafil thread got good quality, and I have used it a lot, and it is easy to buy in Denmark. It is a polyester thread. On the Amann website you can find the recommended needle sizes for it. Nylon thread is a bit thicker and almost the same thickness as the polyester thread for the same weight, because the density of polyester is a bit higher than nylon. https://www.amann.com/products/product/serafil/ I think the link proposed by kgg to Toledo provides a good table to you as to the thread size specifications most used on this website. But there is more systems to define thread sizes than that, and some of them can be quite difficult to figure out. /Viggo

I think it will be a good idea for you to sew something easy first until you may have fixed some more serious issues. It could be 2-3 layers of canvas and a Tex 70 thread or something similar. Then I suggest, that you show us a video while you sew very very slow by hand, and with the sliding plate open so we can see the thread over shuttle. One stitch should take about 20 seconds in video. We shall be able to see take-up lever and check spring too. When the take-up lever go down, the hook is supposed to pull the thread around the bobbin case. I do not know if this video can help you. It is a video of one stitch on another sewing machine, but it do also have a rotating hook. You see one stitch explained over 17 minutes:

I lately made a study of presser foot pressure and made a little video about the result. I have noticed, that the range of foot pressure, that you can set on a sewing machine, is normally not a public specification by the manufacturer. So I measured the foot pressure, presser bar friction and the stiffness of the presser bar spring on seven vintage household sewing machines. I know, that I need about 25-30 Newton (5-6 lbs.) foot pressure when I sew some heavy vinyl or webbing on my drop feed machines. And a low pressure about 5 Newton on soft fabrics with thin thread. I noticed that some of my machines are not able to provide that as it seems like they were made from factory. But some of them can get modified. I guess most Leatherworkers do not need to know the figures of foot pressure of a machine, and you will always be able to set it as you need by some test sewing. But perhaps some of you like to see some reference to measured foot pressures and how machines can vary in this regard. It is easy to measure foot pressure. I studied some previous threads on Leatherworker about this subject, and I think this one do provide some extra good information: https://leatherworker.net/forum/topic/78816-cowboy-cb-4500-waliking-foot-pressure

Uwe made a video about timing of this class of machines. It may help you: EDIT: I just noticed, that you wrote Singer 112 and not Singer 111. Singer 112 got quite many different versions, so I guess you need to specify it a bit more for us.

I just want you to be aware, that the center of the needle vary with size of needle, because the side of the needle facing the hook needs to be fixed in position. This picture illustrates this:

Interesting and very decorative piping. 9:47 Cechaflo show two synchronized seams quite close. Can you figure out how he managed to sew that? Normally double needle machines got higher distance between seams, and I guess, that it is not sewn with double front loaded needles.

I think, that you should be able to adjust the needle thread tension up to about 10 Newton (=36 oz) in a reliable way. I guess about 7 N is needed here. I do not know this machine in detail, but I guess the bobbin thread tension should be about 0.4 N. You may find some way to measure it or evaluate it. Perhaps this video can help: https://youtu.be/kINRgj42GnI

I just saw two beginners having problems with thread tension in this forum. And it can be hard to help them when many things can be wrong. But thread tension can be quite easy to measure for a beginner and then this problem will be almost fixed. All the old guys in this business can just feel that the thread tension is right and adjust it according to that. Lately I did a video about ways to adjust bobbin thread tension:

You need to look for more numbers on the needle pack or needle. 135x16 identifies the needle system. Each needle system got many sizes of needles. It is important, that you got the right needle size for your thread size. I would prefer it to be size 22/140 for this thread.

I have seen a problem like yours with some servo motors discussed back in 2012. Perhaps it is the problem you have got. This is a video about it: I think there were more threads on leatherworker about it. This is one of them:

Now I start to wonder why the original design of the needle plate got the hole so much wider than this new design?

This is a mathematician with some interesting points about these Reuleaux Triangles - so if you like to see this for fun:

I agree that a solution like that would be good. I think the problem is, that the market for slow speed servo motors for sewing machines is too small and may have too many variations in shaft diameters and so. A lot of gear motors for industrial use is mass produced and I am sure the cost is quite low this way. Small reduction gears are also used in tools like drills, circular saws etc. But if you can find a mass produced gear for some other purpose, that may fit, I guess you could get them quite cheap.

Thanks for the replies. I agree, that most leatherworkers would look for a solution with a speed reducer. But perhaps a few would like the extra range of speed (from minimum to max speed) that a machine could get with such a motor, because it could add some more flexibility for some machines. But I should like to know, if someone have tried to use the motor with such low speed and how it actually perform. The price level is indeed very high for these Efka motors. However you may find one second hand on a machine. If you got a machine on factory floor for mass production, I guess you look for many bells and whistles to increase production rate and then the high price can be justified. I tried to look for a specification for minimum speed for the Reliable brand, but could not find it.

Slow speed and slow speed control of sewing machines have quite often been discussed in this forum. Many leatherworkers like to have the possibility of very slow speed control. I just read some specifications for a Dürkopp Adler brushless servo motor, and it is possible to set the lowest speed to be 10 RPM. Most brushless servo motors I have studied got a minimum speed of 100 RPM and perhaps more. I think Dürkopp Adler uses motors from EFKA, but I am not sure. On the EFKA home page I do not find specifications on that low speed yet. For a specific Dürkopp-Adler machine, they reference EFKA DC1550 DA321G drive at https://www.efka.net/en/ You find a parameter of minimum speed to be set down to 10 RPM according to page 15 in this parameters manual: https://www.duerkopp-adler.com/commons/download/public/525i/0791_523901.pdf The default setting is 150 RPM. Do you have any experience in using this kind of servomotor down to this very low speed of 10 RPM?

I have read about the Singer 20U, that it characterized as a 3/4 size machine. So I guess the harp area right of needle is less than a Pfaff 138. I Know that the Pfaff 130 got about 205 mm right of needle as a full size domestic sewing machine. I saw a sailor forum with a guy, that had got a used Dürkopp Adler 525i for about $1500. https://www.duerkopp-adler.com/en/main/products/shoes_FB_ZZ/525i-811.html https://www.duerkopp-adler.com/commons/download/public/525i/B_52Xi_EN.pdf It can be configured 1:1 with motor, and then the speed is 3500 stitches/min. But 1:2 with motor is also possible to half speed and more torque, and I guess this will be most applicable here. It got a harp area of 265 mm. So I guess this machine is both for high speed and somewhat heavier work. I am impressed by the possible very low speed of the servo motor of only 10 RPM. It is excellent. Normally I have seen the minimum speed of brushless servo motors to be at least 100 RPM, but Dürkopp Adler may have an extra low speed feature here, and as far as I can see, it is a brushless type motor. The speed specification can be found at page 15 here: https://www.duerkopp-adler.com/commons/download/public/525i/0791_523901.pdf

Thank you for the preliminary review. I am able to download the video-file with your link, and then start the video with a video-player. I guess some readers here expect a window to play right away as a YouTube link, but this do not happen for me. I Guess you have seen the Jason of all trades video as I have, and it do also show how the RI compensation or load compensation works - this link go directly to the sewing with the load compensation in action: https://youtu.be/Sg5XHjqHMw4?t=745 However, I am not that impressed with the speed range that Jason show. I think the lowest speed I see in video is about 20 SPM and the highest speed is about 250 SPM. My guess would be, that the motor should be able to provide a higher speed, but the power supply do not provide the power for the higher speed. But the low speed control shown is much better than the normal household motors, and I would estimate the price level to be lower than normal servo motors. The normal leather machine set up with a speed reducer and a brushless servo motor is able to provide a wider speed range in both ends. But I like how WorkerB motor makes a slow start, and you can hear it hum, before it start to move. Most brushless servo motors is more like an unpredictable jump start. And just to set the standard - this DIY motor with controller got a speed range of 8 to 540 SPM: https://youtu.be/uTB8DnyYAlA I think it should be relatively easy for the manufacturers of the servomotors with brushes to include a similar load compensation as the WorkerB got, so they will get less sensitivity to load changes at low speed. Perhaps some of them actually have got that.

Many of the vintage domestic straight stitch machines got a central bobbin shuttle hook. Some call them Class 15 shuttle hook, because the Singer 15 used them in some versions. But the shuttle hook of these machines are not made with the same quality. When you sew heavier thread or heavier fabrics, then this detail gets more important. The detail is regarding how smooth the thread U-turn at the hook is. This is a video about that: I have seen a Singer 237 and some pictures of other spare parts with a poor quality and sharp edges at the thread U-turn. My Pfaff 30 and other German made machines got good quality here, so I guess this detail of the Pfaff 60 should be well made too.

Yes, I agree - this is most likely one of the cheap Chinese copies. In picture I can see a black plastic knob to lower the feed dogs, and it gives away identity.

I think more of the Vintage domestic straight stitch machines can do thinner leather, and perhaps the Pfaff 60 can be a bit more expensive to get. Alternatives are Singer 201, Singer 15, Pfaff 30 and many brands of Japanese made machines. If you sew a combined thickness of leather below 1.5 mm, I think the drop feed machines are likely to produce a better balanced stitch than a combined feed walking foot machine. However a combined feed walking foot machine will cause less marks on the leather on lower side from the feed dogs, and you got much more controllable and consistent feed. But drop feed machines are simple to maintain and use, and if you add a speed reducer you will find them easy to control as well.

I do not agree, that this machine or the table is highly collectable. A lot of these machines and tables were produced. In general I have found the price level of vintage domestic sewing machines to be higher in US than in mainland Europe. You may have machines and tables restored to a pristine condition, that may have some fashion value or decoration value. But this can be hard to evaluate by pictures in internet trade. You will find very high and likely unrealistic prices of such machines everywhere. The shipping costs from Europe to US is high, so most likely only the Singer Featherweights may be able to cover shipping costs. In Europe you can find machines like this sold for $50. In my opinion, the vintage SInger sewing machines got less quality than average sewing machines, but they got a huge advantage of being produced in high numbers. Therefore spare parts are easy and cheap to get and many of these parts are still produced.

It is nice to know, that this shaft most likely is the only problem, and you can get spare parts to fix it. Furthermore, It is good, that you could reach an agreement with the seller. Thank you for the update.