kgg

Yes it could be but I would suspect that since you are having this problem with the bobbin popping out more often that it has more to do with the mechanism that keeps the bobbin case in place is worn or misaligned. I would check out the video on "How to fix a Juki DNU-1541S that is jammed or stuck" ( youtube.com/watch?v=6PGPtkjsqus&t=68s ) even through it is for a Juki it may help you see how the bobbin assembly is kept in place for your machine. Also it could be as simple as when replacing the needle in a hurry it wasn't installed all the in or backwards. Done that a couple times. kgg

I am going to assume you mean the little off colored white felt pad in the thread guide located after the thread take-up arm and just before the needle. A lot of machines have what you call an "oil pad". My opinion is that this felt pad is to maintain correct top thread tension and correct top thread routing while the take-up arm cycles up / down. The top thread is sandwiched behind not through the felt pad and the machines body. It is probably a good place to very lightly lubricate the top thread with a little silicon spray for certain incidents of sewing tough, thick or sticky stuff to help the thread slide through the material easier and reduce heating as well this pad helps remove and small particles of loose thread that maybe on the thread from the manufacturing process. This felt pad is not meant to be a sewing machine oiling station for the top thread under normal sewing conditions. I have never needed to lube this felt pad for my type of sewing on my machines. kgg

The most important thing I find is how close you can get to the needle without having the pressor foot touch and the proper back tension being applied to the binding tape. Personally, I prefer the inline binders over the 90 degree binders which I think has more to do with personal preference rather then performance and of course cost is always a factor. kgg

To you visualize the 1/2" long exit fold that is at 90 degrees to the binder tip and another alternative using a 90 binder mounted to a feed dog cover-plate. The one mounted to the plate hasn't got a 90 exit piece as it can be set really close to the needle. This may give you some idea's. kgg

This is the problem with the style of binder you are using on the flatbed. The 90 degree binder is more suited to the cylinder arm machines. I find using the cheap inline binders much better as you can get the exit part of the binder to just about touching the pressor foot to stop binder tape run away. I even built an adapter for my cylinder bed to accept the inline binders. I'm cheap and why have to styles of binders. An option if you really want to use an 90 degree binder is to find one that has a 1/2" long exit fold that is at 90 degrees to the binder tip. That will allow you to get it closer to the pressor foot. kgg

Depends on a couple of things. If your drive motor is a clutch motor or a servo motor also whether the sewing machine is a upholstery class machine or a 441 class machine. Clutch Motors: i) Are always running at their top speed which is typically either 1725 rpm or 3450 rpm and use a clutch to transfer the power to the drive belt. ii) Have a steep learning curve to get use to feathering the clutch to get the proper sewing speed. iii) Noisy since there is always a humming noise when the motor is powered. iv) Energy inefficient. Servo Motors: i) Only consumes about 75 percent what would be required to power a clutch motor when running. Since the motor isn't consuming energy when not running it probably works out to be closer to 90 percent less energy consumed for the same amount of sewing. ii) More available low end torque. iii) Quiet more like a domestic sewing machine. The noise difference would be like that of standing alongside of gasoline car verse a diesel truck. kgg

I forgot to mention that you need to be care that you do not let you pressor foot ride onto the zippers teeth otherwise use a zipper foot. It will mostly depend on the size of the zipper tape and the size of your pressor foot as well as where you need the seam. kgg

The side pocket zippers seem to be ripple free but the longer top zipper definitely has a pronounced ripple. Is the side material of the zipper cotton or nylon. Are you sewing the sides of the zipper first then installing the slider, please explain your method of installation. My six step method: I usually install buy i) installing the slider on the roll of tape ii) cut more then enough a zipper off the roll so I am then left with a zipper length complete with the slider longer then I need and the zipper teeth are meshed together iii) I then slide the slider to open the zipper up and then back to re-close the zipper iv) I iron the top side of the closed zipper tape to flatten out any inconsistency in the zippers side tapes v) I then use double sided basting tape on one side of the closed zipper tape to hold the zipper in place for sewing vi) I then install double sided basting tape on the other side to line up the closed zipper with the other side of the material. There is probably a better / faster way but it stops me from installing one of the zippers side tapes upside down or miss aligned and it works for me. kgg

These are true tinkers paradise machines. Basic, rough as a gad, cheap, one arm bandit but can get the job done. There is a FB group dedicated to their use and modification which you may find helpful. The needle can be changed to a standard industrial needle system of 135 X 16 for leather or 135 X 17 for fabric really easily. Changing the needle system to either 135 X 16 or 17 will give you better quality options for both the needle and thread size selection. kgg

I think you selected two good brand name choices. I would recommend the Juki over the Alder but get the Juki DNU-1541" S " which has a safety clutch. If I am not mistaken the Alder (made in China) can handle a size 140 (#22) needle good for V138 thread on top and in the bobbin while the Juki (made in Japan) can handle a size 180 (#24) needle which technically is good for V207 but the machine is rated for V138 top and bobbin. My opinion of the Alder's size 140 (#22) needle capacity is it really is the bottom end of using V138 thread and limits the thread size to V92 in thick/tough leather or multi layers of heavy canvas. I prefer the reverse paddle lever of the Juki versus the stitch lever style of the Alder. On this side of the pond Alders parts and accessories tend to be much more expensive and not as abundant as those for the Juki machines. kgg

Another method that may also work, since V69 (TEX 70) has a breaking strength of 10.6 lb and V92 (TEX90) has a breaking strength 14.2 lbs you could try tying a length of thread to 14 lb of weight and see if you can lift it without it breaking. If it breaks it is V69 or smaller and if not it is V92. Just be careful that the thread when it snaps doesn't cause an injury to your eyes, etc. A lot of the sewing thread listed on such places are from a lot of "unknown manufacturers" (probably Chinese) made thread with consistency all over the place. The best thing is buy a brand name thread like say American & Efird (www.amefird.com) which is made in both Canada and the USA. Brand name companies put the engineering and effort in providing quality thread for a wide variety of applications. Brand name thread is labelled just inside the bottom of the spool with information detailing date of manufacture, thread size, type, brand, etc. Yes, they are more expensive but you get what you pay for without the frustration of contenting with lesser quality thread. I do have some of the cheaper stuff but rarely use it, just not worth the effort. kgg

I have not used them myself but they are supposed to better then your regular needles. I do recommend you check out Wawak (www.wawak.com/Sewing/Needles/Industrial-Machine/) for your needles as they usually have really good prices. kgg

No, for leather get DP X 16 (135 x 16) in what ever size you need for your size of thread and get a few one size up for tough thick leather. kgg

If you check your manual the needles you should be using are DP x 17 (135 x 17) for fabric. What you have are DP x 35S (134-35 S) which are not the correct needles for your machine. kgg

I don't know how the shutdowns have affected the tanneries but if it is like a lot of businesses they maybe running low on quality inventory and hoping for customers just to accept anything. I would take some photo's of the problem leathers and email them to the suppliers. I would give them a reasonable amount of time to call / email you to help resolve the problem but I wouldn't accept grade 4- when you expect / pay for grade 1. kgg

A couple of photo's of how you have your machine is threaded from the thread spool to the needle may help in identifying your problem. I think the needle size you are using (#19) is probably the cause of your fraying where the needle isn't creating a hole big enough so the thread is getting ever so slightly caught and not making the correct size loop for the hook to properly catch. I would recommend moving up to a size 22. I am assuming you are using a 135 X 16 needle meant for leather not a 135 X 17 Multi-Purpose Needle. kgg

Sewing through the plastic is also what caused me the most concern. kgg

I would go for a cylinder bed machine as I think it would overall be more versatile then a post bed. I think most post beds would limit your thread size to V92. I would recommend you drop by to a machine vendor with a sample and test drive it on a post bed and a cylinder bed. kgg

To help you visualize the differences of how the Juki 1181N and Juki 1541S handle Light, Medium and Heavy material I here are two links which might help. Also a link that details the difference between the compound feed Juki 1541S and the Juki 1508. i. Juki DU-1181N (walking foot) sewing Light, Medium and Heavy fabric www.youtube.com/watch?v=IKJuKTrjsbw ii. Juki DNU-1541S (compound feed) sewing Light, Medium and Heavy fabric www.youtube.com/watch?v=4JES-2I7h3o iii. Juki DNU-1541S versus Juki LU1508 (both machines are compound feed) www.youtube.com/watch?v=SWvi1wYfc9A kgg

The Atlas AT335 ($1495) is a class 335 cylinder bed Chinese clone machine which is going to limited you to V92 as a maximum thread size while the Cobra Class 26 ($2255) which I think is a Class 341 machine with a maximum thread size of V207. Most any cylinder bed machine can accept binder/ folder attachments if you need / want them. Based on your photo's of your trouble projects I would firstly recommend a flatbed triple feed (needle, feed dog, pressor foot) over a cylinder machine in the upholstery class of machines like a Juki DNU-1541S ($1500 US). The price of binders and folders for the flatbeds are considerably cheaper ($15 versus $100) and easier to install. If you don't need a triple feed I would recommend a Juki DU-1181N ($1400 US) which is just a walking foot (feed dog and pressor foot). My main machines are: i) Juki DU-1181N (Walking Foot) which is used mainly for thinner fabrics and binding. Mostly using V92 but have used V138 on top and in the bobbin. I just completed a nice little kneeling pad (42"x 3.5" x 16") with this machine using 21 oz cotton canvas with military lapped seams and double reinforced corners using 21 oz natural canvas. ii) Juki DNU-1541S (Triple Feed) which is used mainly for thicker items like double 3/4" hard back Sherpa. Mostly using V92 and V138 on top and in the bobbin. It hates thin stuff and has to be dumbed down to do them properly. The 1181N excels at the thinner stuff that the 1541S hates. iii) Kobe LS-1341 (Triple Feed clone of the Juki LS -341) which is used mainly for thicker items with curved or round surfaces and binding. Mostly using V138 on top and in the bobbin. Keep in mind there is no ONE machine that will do everything. I would recommend you buy a brand name machine and that you take a sample of your materials or projects to a dealer and test drive a few different machines. Buy Once, Cry Once kgg

The needle specification for the Juki's needle size is the guaranteed rated needle size that will work for both top and bobbin thread size. Some people like one manufacturer of needles over another. My choice is the SCHMETZ brand. The nm 125 (#20) is for V92 thread in both the top and bobbin while the NM180 (#24) is for V138 thread in both the top and bobbin. Even through the NM180 (#24) can accept V207 thread. It appears Juki has allowed for going up one needle size to accommodate using V138 in thick, tough leather so to give the V138 thread enough head clearance at the hook. Some clone machines will say they can accept V207 but may not accept V207 in the bobbin which is something to check. On the lower end the Juki probably will accept a needle slightly smaller but the head clearance at the hook will probably be to great and may not consistently pickup the top thread to form a stitch and end up with no or skipped stitches. Since the Juki 1508 is made for thick heavy sewing to get it dumbed down for material that would normally require V46 or V69 thread maybe a bit off a challenge. If you are only needing to use V46 or V69 thread I would recommend you look at a Juki 1541S that has a rated thread usage of V46 to V138. With my 1541S it really doesn't like thin material and has to be dumbed down so I would imagine the 1508 would be the same or worse. If all you need is a walking foot the Juki 1181N rated at V46 to V92 maybe a option.I have used V138 top and bobbin with no problems in my Juki 1181N. kgg

For leather you will need use 135x16 needles for the size of thread you are using. Depending on the thickness and toughness of the leather as well as the type/size of thread you may have to go up a needle size. I am not sure about the sizes available for the Groz-Beckert needles but would assume you can get them up size 24 as I use Schmetz needles. I would recommend Schmetz Diamond Point Straight Stitch Industrial Machine Needles - 135x16 (www.wawak.com/Sewing/Needles/Industrial-Machine/schmetz-diamond-point-straight-stitch-industrial-machine-needles-135x16-10pack/?sku=SMND135118 ). You maybe able to use your 135X 17 needles with the leather but 135 X 16 would be recommended. Example: i) V92 thread use a number 20 needle may have to go to a 21 ii) V138 thread use a number 22 needle may have to go to a 23

On a range (indoors or outdoors) you don't want to see someone carrying a handgun in their hand that maybe readied ((loaded and safety off) or someone stuffing a readied down their pants pocket (might discard and wind up with a DSO). kgg

I agree that the days of open carry have long passed but holsters are still a saleable item in Canada as you need to have one to properly contain your gun on any firing range. kgg

Glad you got the noise problem under control. Neighbors come in a types, some good, some bad. I pity people living in such close quarters.Glad I don't have that problem as my closest neighbor in any direction is about a mile away. Real social distancing. kgg