Wizcrafts

A type 3L v-belt is 3/8 inches across the outside edge. If you must use a leather belt, use either a 5/16 or 3/8 inch diameter belt. But, expect slippage unless the belt is very tight at all times. The leather belts expand with use and the motor mount will need to be tightened now and then. If at all possible, buy a suitable v-belt.

@Bugg, the only reason that this machine would not be great for leather flat presser foot. A flat foot machine like this one only has bottom feed. That's the same feed as virtually every domestic sewing machine. While a flat foot works fine with cloth, it drags leather and vinyl, or any bulky material. To overcome this limitation, Singer invented a so-called compound feed walking foot system. Their walking foot has triple feed, with the needle, inside foot and feed dog moving in sync as the presser foot lifts and lowers, pivoting off of the inside (alternating/vibrating) foot. Some versions of the Singer 153 have compound feed, like the 153w103 and 153k104. Unfortunately, yours isn't one of them. So, what can you do to make this a leather sewing machine? About the only thing that may be doable is to search for a roller foot and presser bar set that will fit into your machine. I don't know the specifics of that conversion. The bar would have to be the same exact diameter as the original. But, it would have to be shorter to accomodate the longer roller foot. This was just mentioned in a toopic in the leather sewing machines forum. If you are even able to obtain a roller foot and preser bar, you'll probably need to also find a single row feed dog and matching throat plate. This can get real tricky since Singer's industrial sewing machines has been out of business for many decades.

Needle "system" 135x16 (leather point) or 135x17 (round/sharp point for cloth or synthetics) I use #69 (T70) bonded nylon thread to sew patches onto vests. If the leather is very thick, like a leather jacket, I'll move up to #92 (T90) thread. I almost never run #138 thread in a Singer patcher. It will wear out the feed mechanism, causing ever shorter stitches, and the little spring inside the needle bar, and possibly also the hole in the take up lever. Furthermore, the tiny bobbins can't hold much #138 thread.

@tedbow, I see Facebook "groups" that specialize in sewing machine repairs, modifications, and usage. If you're a Facebooker, you might want to search some of them out and join them on a trial basis. As for guilds, the only one I personally know about is the Crispin Colloquy. I suggest you start there. It has been a source of inside information about sewing for decades.

@lukeoliver1776 I spent a few minutes looking for leather point needles in size 120/19 and found some on Thread Exchange and on Amazon. I haven't looked on eBay yet and have to go to work soon. You're going to have to use a leather point needle for your project. A round point wont get it done without great difficulty. One thing I didn't mention if foot pressure. Did you know that broken needles and kipped stitches can be caused by insufficient presser foot pressure? This is because the leather or other material can lift up with the ascending needle. This is always bad and could be part of your problem. Crank down the foot pressure screw a couple of turns and try again. But, either get #19 needle or use #69 thread with the #18 you have on hand.

Tex 90 thread requires a #19 or #20 needle. Your #18 needles hold the thread too tight and poke a hole that is too small to pull the knots up inside the layers. Thread Exchange sells Schmetz needles for your machine in #19, here. Try them and see if they work for you. Put some grease on the gears inside the head where the motor output gear drives the guts. Don't put oil in the motor. If it has cups with lids, they are probably for special grease that is available in syringes. Otherwise, use sewing machine oil in every oil hole and connecting rod inside the front cover. Hopefully, this will loosen up the drive. If your foot controller is old, it may have lost resistance at the startup position. You can replace it with a modern solid state controller. I am telling you all of this because I used to service and resell old Singer iron body machines. The 15-91 was a solid seller and I was able to sew 8-9 ounce bridle leather belting with #92 thread, using a #19 or 20 leather point needle. But, if the controller was worn, the motor lacked punching power. I have a page on one of my websites that is about the Singer 15-91. Maybe you'll find something there that helps you. It has manuals too.

No. You can use a thinner needle than the spacer width. It's job is to protect the hook when using a large needle.that could actually damage the tip. However, if you regularly sew with smaller needles, like #18 to 22, you might get better results by using a shim for a #22 needle. This puts the hook closer to the thin needle and the thread loop. Thinner needles actually get deflected slightly to the left as you sew on most lockstitch machines. The thread tension pulls the needle away from the hook unless I back off both tensions and have a looser stitch line. The longer and thinner the needle, the greater the deflection from thread tension alone. My Cowboy cb4500 and all of its related class 441 machines do not use hook spacer shims. I set my hook to work with the largest needle I regularly use and leave it there. I compensate for needle deflection by tweaking my check spring settings to give more top thread slack, creating a larger loop for the hook on the upstroke, and by backing off the tensions when using thin needles and thread. I rarely get skipped stitches. But, when I do, I tweak the spring again, or loosen the tensions more, or slow way down (a hot needle burns and holds leather fibers and creates more friction). Sometimes, if the inside foot rises up a little early, the leather lifts with the ascending needle and that causes skipped stitches. It happens mostly when I use a left or right toe foot instead of the standard double toe foot. I did install a narrow feed dog and throat plate set purchased from one of our members, and am limited to a #25 needle as the largest size. If I need to use a #26 or 27 needle, I have to change back to the standard feed dog and throat plate. I also have an even smaller profile set from @Patrick1that maxes out with a #22 needle. I use it to hem jeans or sew on soft cloth or very thin leather. It only takes a couple minutes to swap the feeder sets.

From your photo, the hook timing is really close to spot on. But, it may be a tish too early for your material. Try backing off the hook a couple of degrees so it is just 1/8" above the eye as the needle ascends. As for regularly skipped stitches, they can be caused if the leather lifts as the needle comes up. On a standard foot machine, there are toes on either side of the needle to hold down the material. On a roller foot machine there is only the edge of the roller holding down the work. If the edge of the roller is too far away from the needle the material can lift. This causes the loop to dissolve before the hook picks it off the eye of the needle. So, see if there is an adjustment screw on the top of the roller foot to move it closer to the needle. If moving the roller doesn't solve the skipped stitches, try changing the settings and positions of the check spring assembly. Perhaps you need to have a little more slack in the top thread so the loop is bigger and last longer at pick-off time. Most check springs have a stopper on the shaft that sets when the spring stops moving down. It only needs to hold the top thread taut until the tip of the needle touches the top of the material being sewn. If there is a curved slot with a set screw on the check spring's disks, try moving it to the right or left. If the check spring action is too strong, it can pull the loop out as the take-up lever starts up. There's an adjustment on the shaft where it mounts to the body. If you loosen a screw that connects the assembly to the body, you can use a screwdriver in the split threaded stud to turn the unit to loosen or tighten the spring action. Tighten the screw after you are happy with the new setting. The spring must have enough force to rise and lower all the way down to its bottom stop bracket (which is also movable).

The are only three ways to get a replacement top shaft and balance wheel for Singer walking foot machines with stitch length adjusters on the end of the balance wheel: Buy a donor machine and salvage the good parts. Have a new top shaft and balance wheel milled at a machine shop. Find a long-time industrial sewing machine dealer, like Toledo Industrial Sewing Machines, or Hoffman Brothers, or Ralph's Industrial Sewing Machine Co, and pray that they have a salvage machine, or parts in a dusty bin from the early to mid 20th Century.

Yes. A dealer can do it for you. Here are the operating instructions at D.A. Or, somebody who owns one and has done the mods may chime in and tell you what must be done to sew fabrics. The main problem is that the 669 is a triple/compound feed walking foot machine. Due to the way the feet alternate and the inside foot actually presses directly on the moving feed dog, light fabrics may be forced into the feed dog hole, ruining the job. I speculate that unless the hole in the feed dog is very small, only clearing a #22 needle, this is likely to happen. However, if you are going to sew cloth that has some body, like denim, it could resist being pushed into the hole, or the large rectangular slot it rides in. To add some experience to this point, I was sewing garment leather belts and straps at a friend's shop, about a decade ago. The machine was a Cobra Class 4, which is an extremely heavy duty leather stitcher. I was using #138 bonded nylon thread and a #23 leather point needle. It was very difficult to keep the sides from getting pushed into the rectangular slot during edge stitching, especially when it came to the tips. They were constantly getting pushed into the gap, or the wide oblong hole in the feed dog, ruining the stitch line and wasting a lot of time. To solve this problem my friend had a machinist cut down a spare feed dog to 1/4" wide, then he made a new throat plate with a narrower slot. Nowadays, owners of the big Cowboy, Cobra and Techsew 441 clones can buy ready made narrow feed dog and.throat plate sets that allow them to sew thin and floppy work. Some of these aftermarket feed dogs have much smaller needle holes that the material wouldn't get shoved into as easily. I have to ask, do you really want a compound feed walking foot machine if your primary use is sewing fabrics? Wouldn't a flat foot bottom feed machine be better suited? Most garments are made and repaired on bottom feeders. Every tailor shop uses bottom feed straight stitch machines for alterations. My Dad had a Singer 31-15 in his tailor shop. I learned to sew on it.

@Safiremedic, you can go to the Techsew website and contact their support department for a manual. Here is the page for your motor: https://www.techsew.com/us/techsew-smartservo-motor.html

This is an important, often overlooked issue for most sewing machines, but especially the 441 clones. I have a long-time buddy who bought a Cobra Class 4. After a few years the presser and alternating foot bars started getting stuck in the up position. He added more foot pressure to get them to drop, marking the leather even worse. He had me come over to troubleshoot it and I unthreaded the machine and removed the front cover plate. IIt was dry inside and there were scoring marks visible. I removed the presser bar and pulled it through Emory cloth to get the marks off. After putting it back together, I oiled every moving part. The machine worked perfectly afterward. So, remove the front cover and oil every crank and rod that moves against or through something.

You do have to be careful to not sew too short stitches when using an S point needle. It slices inline and can weaken the stitch line if the holes are too close. OTOH, diamond/tri points punch a shorter hole and the thread stays on top of the leather, as opposed to being almost buried by the S points. So, I try to stay above 7 to the inch with S points.

@Patrick1 I'd like to have a slide-on/bolt-under flat table attachment for my Adler 30-7 patcher. I sometimes have to sew patches on the back of vests that have a zip open lining that must be preserved. An small flat table would support the patch areas better than the narrow arm does, keeping everything aligned.

I'm following this conversation. Definitely interested.