Wizcrafts

The knots should always be buried inside the layers, or at least the bottom layer. If you cannot hide the knots, the thread is too thick for the material thickness. Unlike some fancy home machines, industrial sewing machines are mostly manually adjusted 100% of the time. The amount of thread tension used in heavy leather stitchers, like your CB3500, is enormous, compared to an everyday domestic sewing machine. Those fancy plastic machines use cotton or poly-core thread in sizes 50 and under. The faster machines prefer #27 thread. You would be pushing one of those machines to its limit by running #69 bonded nylon through it. Even if the machine can tension #69 thread, it is usually limited by the mechanism to only sewing 1/4" of soft material. In contrast, real leather stitchers use thread sizes starting at #92 and going up from there. Most 441 clones, like the CB3500, are setup by the dealers to sew into 3/4 inches of veg-tan leather with #277 or #346 bonded nylon thread. I usually set the bobbin tension for a smooth, steady pull. Then I balance the knots by adjusting the top tension as needed. When adding layers, give the knob a turn or two inward. When leaving a layer, back it off, if you see the knots appearing near the top.

The hook point must intersect the scarf area above the eye of the needle on the upstroke, after about 1/8" of lift. If you can't lower or raise the needle bar to meet the hook, try re-timing the hook. This calls for loosening the screw/bolt/clamp that secures the hook to the shaft that drives it. Using the hand wheel, lower the needle to BDC, then raise it about 1/8 inch and stop. If the point of the hook is rotationally before the needle, advance it. If it has passed the needle, retard it. If your needle is still too high or low, adjust the needle bar to place the hook above the eye on the upstroke. If you have trouble balancing these two items, the hook point may be damaged. Replace the entire unit. Dinking around with old worn out parts is a losing proposition more often than not. There were a couple of system 135 designations. The more common one is 135x16 and 135x17, which is the standard walking foot machine needle. There is/used to be a 135x7, which is not the same needle. Singer no longer makes patcher needles. Patch owners now have to use system 135x16. The difference is that these needles have a cut-out scarf and the old 29x4 are straight all the way down the shaft.

Adjust the position of your needle bar to place the hook inside the scarf area, above the eye of the needle.

After you do the things that Constabulary recommended, check the top thread where it goes around the upper tension disks and make sure it is firmly seated inside the disks when you start sewing. Birdnests in the bobbin case are often caused by total loss of upper tension. Also, make sure the top thread is going through the check spring and take-up lever.

Aw shucks Maam, it twern't nuthin'!

If your 31-15 has an industrial motor, it doesn't matter what type of belt you use. The motor has an adjustable nut and bolt to raise or lower it. You can lower it for more belt tension until your leather belt stretches too much. Then, remove the belt and take out the C clamp from one of the ends. Cut that end about an inch shorter, punch a #0 hole about 5/16" in from the end and bend the C clamp into it. The leather should just touch when the clamp is in position. If you get a v-belt, make sure you get on that will fit tightly with the motor adjuster in the center of its travel. A stretched out 43 inch leather belt, already adjusted to the bottom of the motor adjusting bolt, would probably be replaced with a new 42" v-belt (type 3L only).

Is your machine motor powered, or treadle powered? If motor, is it a big industrial motor under the table, or is it a tiny home style motor on the back of the machine? The reason I ask is because most treadle powered machines use looooooong leather belts, cut to size as they stretch out with age. Industrial motor powered sewing machines are normally equipped with rubber or composition v shaped type 3L belts. These belts don't slip as easily as leather does. They are tightened by lowering the motor via its adjusting nut and bolt.

Just measure your leather belt around the pulleys and replace it with a standard type 3L v-belt of the same length.

Nope and nope. It is a post machine with a roller feed. These are typical machines for the shoe and hat trades.

Servo motors can be bought for about $110.00 + shipping for a Family Sew FS-550s

It looks like a standard walking foot machine from a picture I found. It says that they take system 135x17 needles. This hints that it also takes standard walking foot, type 111 presser feet, including zipper feet.

10 months of side-shock from a badly melded belt may have warped the bearing on the speed reducer, or even caused some slop to develop in the flywheel pulley on the machine. De-belt the reducer and spin it by hand, checking for side wobble. If there is an appreciable wobble, remove the wheel and try tightening up the flange on the inside of the reducer wheel, if this is possible. The reducer should revolve smoothly, but not wobble sideways. Lineups I go to great lengths to line up my motors > reducers and machine pulleys. The straighter the pull, the less stress there is on the three sets of bearings. Motors can be shifted laterally by loosening the three nuts under the motor mounts, while clamping the cap bots with a vise grip or suitable pliers. Reducers are usually attached to a movable mounting block that can be moved sideways to line the large pulley up with the motor pulley. It may or may not not be as easy to move the machine pulley to line it up with the reducer. I would say to seek out "Gates" brand belts and see if they are properly welded inline. The first thing I do when a new belt arrives it to unfold it and lay it on a flat table. If it lays flat, or almost flat, after a few minutes, it goes into the "for use" hook. If it sits high in one area, I check it out to see if I can flatten it out. I also press it down at the weld joint and check to misalignment. One can shave off a small amount of material sticking out one side or the other, or just throw it away. I always throw away new belts that don't lay flat AND have misaligned weld joints.

Maybe there is a piece of broken thread, or foreign material stuck in the teeth of the worm gears driving the shuttle, or between the shuttle and bobbin basket?

Try running the machine with the top belt off the machine's pulley. See if the variation in speed and thumping exists with just the motor (and speed reducer, if any). In the unlikely event that the thumping continues with the machine out of the equation, make sure that the motor mounts and pulley are fully tightened. If you have a speed reducer between the motor and machine, unbelt it and run just the motor. A mis-adjusted reducer could cause this type of problem. You might have to dink with the bolt securing the reducer, or replace it if it wobbles. If you don't have a reducer between the motor and machine, try running the motor with the belt off. I have thrown away v-belts that were poorly melded out of alignment where they are joined. In fact, it happens more and more all the time. I now only buy top of the line v-belts. It is possible that your belt or belts are not up to snuff and could cause this problem. If everything on the motor is tight and it thumps on its own, with no belt at all, replace the motor. Hand wheel the machine and listen or feel for occasional binding. If you encounter binding, or any unusual resistance, mark/note the position and direction of the needlebar and presser feet and we can investigate further.

Boa; Your first YouTube video is marked Private and cannot be seen by anybody but you.

Greg is right, in that the standard build of the LU-1508 has the same foot lift and sewing capacity as most other walking foot machines. I mistakenly forgot to append the "NH" designation when I mentioned this particular Juki machine. The LU-1508NH has higher lift and sewing clearances and uses system 190 needles. I modified my National 300N to sew just under 1/2 inch, using system 190 needles. Because these needles are 3/16" longer than standard system 135x16 and 17 needles, the bottom of the needle bar, at BDC, is also that much higher. This allows the presser feet to be raised 3/16" higher using the knee lever. The hand lift lever only raises them the standard height.

Something might be wrong with the bobbin case or basket, or the bobbins themselves. Make sure that the shuttle mechanism is fully tightened and not able to slip as you sew. Also, after winding your bobbins, cut off the beginning thread stud flush with the bobbin. An exposed stub can catch and cause intermittent tension problems. Try to watch the bobbin as you sew. See if the thread is twisting as it feeds out of the slot and under the bobbin tension spring. This action would cause sudden changes in bottom tension and cause the knots to appear near the top. If this is happening, troubleshoot the bobbin area and your bobbin thread winding technique. I usually recommend inserting your wound bobbins so that they feed against the direction of the loading slot, making a sharp turn backwards to the spring. Going the other way sometimes results in changes in tension as you sew. You might try altering both the top and bottom tensions to see if there is a happier place for both of them to get along and give a consistent knot placement.

The 1508 is a beefed model, with higher presser foot lift. It was designed to sew leather goods and even some shoes. It can take more pounding than the 1541 before wearing out. Also, it has extra clearance inside the head to allow for longer needles and higher sewing thickness: about 12 mm. Without this extra clearance one cannot sew a compressed thickness beyond 10 mm. Even with these improvements and higher lift (plus longer needles), the 1508 is not a substitute for a harness stitcher, like the Juki 441 or Adler 205 and their clones, that many leather crafters here are using. Highlead is a well respected brand name, Worldwide. If you will have dealer support in your own locality for a Highlead machine, you probably won't be sorry. Also, if you decide you need something stronger, your dealer may allow some value on a trade in.

Juki makes top of the line sewing machinery. The 1541 is a very good machine for light to medium weight material. It will easily make clothing. If you should decide to venture into also producing leather clothing and accessories, a Juki LU-1508 is one of the best in the business, for walking foot, flat bed machines. These are just recommendations. You should bring your tailor along when you go to look at machines. The actual sewer will know which machine is best for the tasks at hand.

VanDutch; Try placing the stitch lever in the zero position; not moving the feed dog forward or backward. Then rotate the flywheel as before and see if the binding stops happening. If so, a clamping screw or bolt may be loose on the stitch length/direction crank arm. This can be checked from the large round cover plate on the right front and back of the head. I have heard of cases where the one accessed from the back shook loose and made it difficult to balance forward and reverse stitches. It could also halt the machine if one of these bolts backs out too far.

You should look for a walking foot machine, with triple feed, and thread handling capacity of at least #138 bonded thread (double what the two machines you asked about can handle). The machine I refer to is used by upholstery shops, not tailors.

I have had a 96k40, which is about the same machine as the 96-10. I do have a 31-15. I would say they are equal in characteristics and capabilities. That means either can sew with #69 bonded thread, using a #18 needle, into about 3/16 inch of material, or slightly more. Feed is bottom only and not much good for vinyl and leather, unless you convert into a roller foot machine.

I used Emory cloth on my throat plates that had grooves on top and then buffed them to a high polish. I can't imagine why those grooves are there, other than the Chinese copied a standard Juki TSC 441 and simply know nothing about sewing veg-tan leather. Someone needs to tell them to produce smooth throat plates for leather sewing machines.

Not specifically. Not specifically, Bob. It depends on whether or not the stitches are decorative or required for securing pieces together, and on how large the thread is and how thick the leather is. Also, if the object is bendable, shorter stitches are better. While there is no rule of thumb, I prefer between 5 and 6 stitches per inch on most leather belts, straps and holsters, using thread sizes 207 or 277. I enlarge the spacing to 4/inch on thick weight belts, using #346 thread. Going the other direction, I'll use 6 or 7 per inch on thin wallets and 8 or 9 on shoes and watch bands, using #69 thread.

FYI: The difference in strength between #69 (T70) and #415 bonded threads is #69 has a breaking strength of just 11 pounds, whereas #415 breaks at 72 pounds. Most of us use #277 bonded thread on holsters and double leather straps and belts. #277 has a breaking strength of 45 pounds. I routinely sew the edges of single leather belts with #207 thread, which has 32 pounds strength per stitch. These heavy threads reinforce belts and straps and prevent holsters and sheathes from coming apart under stress or duress. Domestic sewing machines, whether made of iron, aluminum or plastic, are not built with heavy thread and hard leather in mind. Most honest dealers will tell you that their machines on eBay that they call industrial strength are not able to sew with anything much thicker than #69 thread. This is upholstery thread, for light weight seat covers. It is not even strong enough for motorcycle seats unless you go around twice.