Gymnast

I just noticed this other guy having a problem with the tensioner of the Consew 225, so perhaps you like to look at that: https://youtu.be/yjMxxdi_WaE?t=555 When you pull the thread through the tensioner, you should be able to feel a nice increasing tension while when you turn the nut on the tensioner clockwise. If you are able to put on a thread of tex 70 up to tex 135 and you can measure the thread tension, you should be able to make a tension from zero and up to about 10 N or 1 kg. This is a bit about some beehive tension springs and some of their measurements: https://youtu.be/5CCURZCvSI4

I made a small extra study of this presser foot with a notch to the back and the big roller foot, that got some of the same way of enhancing feed of a drop feed machine. The main reasons to use these presser foots is to significantly improve feed traction on drop feed machines. If you operate a drop feed machine with the normal foot, I like you to pay attention to how the stitch is formed. The upper thread is pulled up by the take-up lever, thread tension is applied and the lock of the stitch pulled up and ideally placed in center of the fabric stitched. It is however not only the take-up lever that pulls the thread, because the feed moves the fabric forward, and it is pulling the threads too. For most drop feed machines set to 4 mm stich length, you will get about 1.5 mm pull of thread with about twice the thread tension by the feed. I think I need to explain a bit more in detail what is going on for these normal drop feed machines. This is a simple test set up to measure the thread tension at the foot: With one setting of the tensioner, the take up lever can pull up to a thread tension of 3.8 N in thread measured by the spring dynamometer when the thread pass at the tensioner. If you pull in the dynamometer you will get a tension of 7.0 N when the thread pass at the tensioner. The higher tension is due to the thread friction to presser foot and a few fixed thread guides. This is why the feed can pull harder in the thread than the take-up lever motion. When you sew thin fabrics of about 1 mm, then it becomes very hard to set the correct thread tension to get a balanced stitch. It easily may be placed sometimes at lower surface and sometimes at top surface. But this last hard short pull by the feed helps a lot to make a balanced stitch in this situation. If you like to see more about the timing of the feed in relation to the take-up lever and how this is, you can look at this video - the link will start the video when the thread is around the shuttle: https://youtu.be/WqFjQyrKnO8?t=455 When you use the presser foot with the notch to the back or the similar large wheel presser foot, you interfere with the stitch forming and help from the feed, and therefore it makes it almost impossible to make a balanced stitch in 1 mm thin fabrics. The same will happen if you for some other reason advance the timing of the feed. Therefore I cannot recommend to use this kind of foot on such thin fabrics. I have tried to experiment with fabric thickness. If I had 2 mm or more thick fabric, you can get good control of the stitch balance again with the foot with the notch or large roller foot. Thicker fabrics makes it easier to make a balanced stitch, and then this help from feed is less needed. I guess, that walking foot machines have no means of increasing the thread tension in the same say, so they will have similar problems with thin fabrics to make a balanced stitch.

I live in Denmark, and quite often I see industrial sewing machines for sale at resonable price level. Depending on how good you can service machines, you may spend some money to get a used machine serviced. I know of two companies selling heavy sewing machines in Denmark.

I also find these old, special and simple mechanical designs intriguing. This Rotoscillo makes use of larger oiled internal surfaces to transfer the load, and I think it should be better than a round cam against a plane surface. The German Köhler engineers may have been inspired by the Free sewing machine, because both machines use the Rotoscillo, but they do also use rods and bearings to produce the needle bar motion and motion of take-up lever. Other long shuttle machines typically use special machined cams for that. The needle bar makes two dips each stitch. Later on in the video about the Free machine you can see this mechanic. This video show the similar mechanics in the Köhler machine:

@Silky I guess it should be exciting to make it from scratch like you do. Now that you know the name to be Reuleaux Triangle then you may know this other funny cam or mechanism. I have called it Rotoscillo from the US Free Sewing Machine Company, that used in about 110 years ago. I saw it used in a Köhler sewing machine from 1950ies. It may origin from some older work. I link to a couple of videos showing it: Look at 6:05 in video.

I guess the basics regarding timing of needle, take-up-lever and hook are almost the same for most sewing machines. But perhaps some variation between machines with oscillating hooks and rotating hooks. I made a study of my Singer 201k with rotating hook regarding how much the check spring was engaged when the thread go around the far side of the shuttle. I tried 4 different situations: 1) 1 mm thick fabric and 4.5 mm stitch length. 2) 7 mm thick webbing fabric and low tension, so the stitch lock of the threads is near bottom surface. 3) 7 mm thick webbing fabric and average tension, so the stitch lock of the threads is expected to be in center of fabric. 4) 7 mm thick webbing fabric and high tension, so the stitch lock of the thread is near the upper surface of fabric. Here is a photo of the check spring positions: I do not think that the differences are that significant, but I did not know that before I tried it. I looked at some details of movement of the parts as shown in this diagram: You got max check spring deflection at this far shuttle point, when the take up lever is on its way up. I did a calculation on a change of hook timing, so it catches the thread when the needle had moved 0.5 mm less up than before. It is a 3 degree change that makes about 3.6 mm more thread to be used when the thread comes around the shuttle. So if you have got a problem with wrong check spring deflection at this point, it can be right to look at hook timing, because it is sensitive to that.

Thank you for this reference. I actually did look for information on internet and found some mechanical engineering books that showed this cam. Unfortunately they did not made a reference to some of the original descriptions like Euler or Reuleaux. But it is obvious, that some of the early mathematicians should have looked at this. When I look the in this wikipedia article, it is not that clear, that the rounded corner triangles can be considered Reuleaux triangles too. It is a funny shape, and I guess it could make some fun for children to learn about,

@UweI looked at your video and noticed your comment, that the check spring should only engage a bit at this position in sewing cycle. After thinking a bit about that, I would guess, that it should depend on the thickness of the fabric. With higher thickness of fabric, you got more thread use and then more pull of the check spring should be expected at that point. Can you agree to that? Edit: I am not so sure about this. I guess some trial or analysis in more detail is needed.

Good to know, that other sewing machine users have found this needle eye thread friction important too. I know that many people sewing garment prefer top stitch needles, that have got a longer needle eye. I have not got such needles, but I guess they might very well reduce this eye friction this way. Interesting discovery, if such coating can reduce friction. Less friction cause less heating. I have also discovered, that the thread U-turn near the hook is another important place to have a nice round pass for the thread. I got a Singer 237 with sharper edges at this place, that frayed the thread. I then grinded this place. The Pfaff 30 is produced with much nicer machining finish at this place. But I guess most industrial sewing machines should be made smooth there. When I got the needles in 2020 for household machines, I could not get stretch needles above size Nm90, Universal needles above Nm130, and Ball point needles above size Nm90. So I needed to look for alternative brands and suppliers. In this way i also got some stretch needles from AMF, that got no issues. So I guess most brands are OK except for some few.

Sometimes I do studies, that may or may not got any interest. You decide. This time it is about the thread friction of the needle eye of sewing machines needles. I got some needles from some not that reputable brands, and have tried to test them without actual sewing with them. A whole lot of new needles I got was actually bad. I could clearly see, that the needles I got with high needle eye friction did also create problems whey I used them in a sewing machine. If you only got good quality needles, you may never encounter a problem with this. If you like to check or compare some needles you got, then measuring the needle eye friction can be one more way to evaluate needles. I made this video about it:

I would have guessed, that final result would have been 5 stitched to the inch forward and backwards. But it seems, that your adjustment increased max stitch length as well.

Yes I agree. The Rotary hook got much less vibration issues, so it can stitch faster. But I guess that for leatherwork, you will normally not need the high speeds, and then it may be other issues that can be of interest. And yes, I guess that there is probably more involved.

I hope that is in order to start this thread again, because I did not find other general threads about this issue of check spring stroke adjustment. I agree with Dave4 regarding how books and most people will tell you to adjust the stroke. But I do find Erics comment interesting. I like to make two questions about it: 1) What can the problems be, that is caused by too little a check spring stroke? And I have seen these answers: - Needle can hit own thread - You can get thread tangled 2) What can the problems be, that is caused by too large a check spring stroke? And I have seen these answers: - If the check spring pulls the thread when loop below fabric is formed to be catched, you risk that you got too little a loop - A bit higher thread tension for the hook at parts of the way it pulls the thread down. I guess this means, that you want the check spring to be at resting position, when the needle start to rise from lowest position. I think the setting may be changed, so you have a larger stroke when you use thin fabric and short stitched (little use of upper thread each stitch). And when you use more upper thread each stitch, you man need shorter stroke. I tried to experiment with a Household Pfaff 30 machine, and it do not think to care about this stroke setting. It will work anyway:

I wish your luck in regarding your communication with the seller of the machine. I have got several vintage sewing machines, but not from dealers. One of the first things I do is to remove the driving belt to the machine or some motor driving it. In this way you can feel how easy the machine turn. I is quite normal, that a machine can be completely stuck or got high frictions. But after lubricating all the right places and operating the machine by hand (there is youtube videos about this) the machine will normally free up and run smoothly. Then I start to use the motor. With your case bearing I would think I had noticed that something was wrong in this process.

I am sorry to see these marks on one of the inner surfaces of your bearing. It looks like the machine have been used a long time with no lubrication there. If you got this machine from a qualified dealer, I would contact him about this. I think it can be hard to repair. I hope someone in forum might help you evaluating this further. Regarding the slow speed control of sewing machines, you can find this issue debated in several threads in this forum. This is the latest two I can remember:

What is the advantages and disadvantages regarding the use of a machine with oscillating hook compared to a machine with rotary hook? Of cause a lot of other parameters matters too, but I like to focus on this alone. I got some experiences regarding heavy use of household machines, but I am not sure it can be extended to leather sewing machines. I noticed this previous comments regarding jam: I cannot say, that I noticed this. I did not made any direct measurements or comparisons. But this is my impression and I know my experience is limited. 1) The rotating hook can sew with lower bobbin thread tension and therefore less overall thread tensions. This is in order to get the same quality appearance of the stitch on the lower side of the fabric. It seems like you need to crank up the tensions for the oscillating hook machines to make the bobbin thread lay down nicely on fabric. 2) The oscillating hook machines runs easier. It is like the rotating hook machine needs more power to produce each stitch. Therefore it might be, that the wear on thread sewn is somewhat less on the oscillating hook machine. I should like to know your impression of the differences.

I hope some older specialists in sewing machines might see this and give me some guidance. Or perhaps somebody else got a clue. Lately I noticed a blogger writing about sewing knit stretch delicate fabrics with low tension. She got the impression, that the older type long shuttle machines is able to sew with lower bobbin thread tension than newer machines, as we know them. This is the blog: https://vintagesewingmachinesblog.wordpress.com/2018/04/20/that-elusive-flexible-stitch/ So I have tried to do some experiments with a household vibrating shuttle machine, and this is a photo of it: It is a quite heavy machine with some interesting mechanical details. I did however put on a motor and something to gear is somewhat down to make some experiments. In one trial I sewed Tex 210 thread in vinyl. However I got some issues regarding stitch balance, and I am not quite sure how you should expect to set timing of the shuttle movement in relation to the take up lever. The timing you know from normal sewing machines between needle and hook is not that much an issue with long shuttle machines, because you got a special movement of the needle bar with two dips for each cycle. This kind of needle bar movement is also used with patchers like the Singer 29. Therefore the needle do not move much when the point of the long shuttle catch the thread loop. Furthermore this kind of machines do not have any hard point in sewing cycle as normal modern machines, because the needle remains down while the needle thread is pulled down. So in this special way this kind of sewing machines got an advantage with heavy fabrics compared to normal leather sewing machines. I think this kind of machine cause less wear on thread too. When I got the machine, the timing was like this: 1) when the long shuttle is in most forward position, the full bobbin thread tension is applied to fabric. At this position, the take-up lever is 6 mm (1/4 inch) lower than max height. 2) When the take-up lever is at max height and the upper thread tensions is applied, then the shuttle have moved 5 mm (1/5 inch) back from max forward position, so it somewhat have loosen the lower thread tension. I have tried to move the the timing a bit so the shuttle only moved 2 mm back at max take-up position, but I am not sure I can identify any sewing quality change. I have tried to look in a German book for sewing machine mechanics from about 1955, but it do not provide clues on this. So I hope that somebody in this forum may have got some knowledge about this timing.

I think you can make it sew quite much, if you are prepared to do some modifications to the machine, such as a speed reducer and other things. A serious issue with this machine will be marks from the feed dogs in the leather surface. So it do also depend on how nice you like results to be. As DoninReno points out, it can be a good machine to start learning on. A big roller foot will help, as Wizcraft points out. In my experience the main problem is, that thread tensions work against the move from the feed dog. With the roller foot the thread gets another direction to the fabric, so it do not pulls back the fabric that much. The same can be done by a modified food with a notch to the back, and it holds the fabric better than a roller foot, when the needle is down. This is a video about this kind of foot, and you will be able to find some tips for domestic machines on the same channel: https://youtu.be/rBIulDuhDDs

If you look at the linked video about thread twisting, you will find, that it is important how you make the pass of the thread through the steel plate with holes in it. You go clockwise in forward direction. I would chose to go anticlockwise to reverse the twisting from this steel plate.

Two years ago we had a debate on thread twisting and tension. If the pre tension for a tensioner becomes two low in relation to the "output" tension, small kinks can formed or the thread can get a different and unstable pass through the tensioner causing tension variations. Perhaps you may be interested in the findings and videos there:

In my experience, thread tension variations can be caused by a lot of different issues. And for some machines tensioners you cannot get rid of too much annoying tension variation. I disagree with Doninrino about getting such instruments, and I can get them for about $1.5 each. I have seen the same issue about tension variation due to direction of thread from bobbin case. You save time, if you have got an instrument to help you instead of doing test sewing to get results all the time, when you diagnose the machine. The issue of tension gauges have been discussed some times in this forum. This is one of them:

I think the Towa bobbin gauge is too expensive and over complicated. Its simpler and cheaper to use spring dynamometers, and they can measure the thread tension in more ways and be used to measure needle thread tension as well. Last time I looked for these dynamometers you could get them for about $1.5 each via Aliexpress from China. I would choose to get three types, 0-1 N, 0-5 N and 0-25 N. I prefer them over digital types, because you can get a better idea of the tension variation. This a short video that shows how these gauges look like:

I just read a few specifications for a Dürkopp Adler 525i-811. As far as I can see, it is a fast stitching zig zag industrial machine. A user wanted it second hand to be used for DIY sailmaking and some marine canvas work. It is not a walking foot machine. https://www.duerkopp-adler.com/en/main/products/shoes_FB_ZZ/525i-811.html The gearing will normally be 1:1 to the motor, but it is possible to change it. When I read the parameter settings for the controller here, you can set the minimum speed of the motor down to 10 RPM. It is page 15 here: https://www.duerkopp-adler.com/commons/download/public/525i/0791_523901.pdf So it is much lower speed for this kind of motor compared to what I have seen before.

Your garage table saw may be with an induction motor. I argue that most smaller table saws at about 1800 W for home use or craftsmen got universal motors. This is three examples of that: This is a link to a small Metabo 1700 W table saw. The small size of motor and gearing to motor clearly indicate, that it is a universal motor. The gear ratio is above 3 and no load saw speed is 4200 RPM, so the no load motor speed is about 12000 RPM. https://youtu.be/2kVjOW-VMrk This is a 2000 W Dewalt DWE7491-QS. I can hear on the noise, that this is a high RPM motor. https://youtu.be/I_uLAz7ferE?t=334 This is a Bosch GTS 10J table saw. In this video you can see the sparks for the brushes of the universal motor. An induction motor got no brushes. And you can hear the high speed of motor. https://youtu.be/RDMBiUF80Gc?t=142 Saws in this size becomes cheaper and lighter, when you use universal motors. I guess that bigger and more industrial table saws may use induction motors. Perhaps older table saws for craftsmen got induction motors and you may have an example of that.

I think most of the smaller table saws are made with a brushed universal motor. Universal motors are used for most of the vintage household sewing machines and in a power input range of 50-250 W. A lot of Universal motors are used in tools, vacuum cleaners and other household equipment. They are good small motors with a high power, but with a limited operating time due to wear on brushes. They typically can run at high speed, so they will make more noise. A vacuum cleaner typically runs 25,000 RPM and can have an input power of 2000 W. Induction motors are very silent in operation, because their speed will be below 3,600 RPM and they got no brushes. Both universal motors and induction motors got a higher inrush current, which can be reduced by a soft starter.