kgg

This maybe caused by the needle not reversing into the same holes it made going forward. A quick check is to put some heavy weight paper under the presser foot as if you were going to sew something except with NO thread in the needle. Handle wheel the machine for about a half dozen stitches and then hand-wheel in reverse. The if the machine is setup properly the needle should fall into the same hole as when you were going forward. Also be for-warned from my experience the Consew 206RB-5 (made in I think China) is not the equivalent of a Juki DNU-1541S (made in Japan). That said there isn't much difference between the two machines with the Consew being about $300 less then the Juki DNU-1541S. kgg

I often go to a industrial sewing machine shop and buy an old sewing machine frame with the pedal setup. The old sewing machine table frames are so much better as they were constructed with heavier real metal. Then go to your local hardware depot and pickup two pieces of 3/4" plywood then glue / clamp them together. From there you could get fancy and put a pretty laminated top on. The standard kitchen counter typically is only is about 3/4" thick and constructed more often with press board. For the weight I would recommend going with the standard 1 1/2" thickness. kgg

I do agree. To name a few variables the results will depend on: i) leather type and thickness, chrome vs veg tan ii) thread size iii) thread type, nylon, polyester, etc iv) needle size and tip shape v) stitches per inch vi) stitch patterns About a month or so ago I got a new metal lathe, We had to move the wooden crate from the driveway to the rear of the house about a 60 foot or so move. We used my little 25 hp tractor using chains wrapped around the crate and hooked to the bucket hooks. No problem and in the basement we used a 1 ton shop hoist, 600 lb capacity hydraulic table and a combination of 2" and 3" nylon lifting straps. I always use backup straps as a just in case. One of the lifting strap on the last lift failed at the seam stitching of one of the end loops. It took the weight initially then went off like a gun glad we had the backup straps on or it could have been a bad day. kgg

This formula can very misleading as it was develop mostly for fabric and indicates that by increasing the number of stitches per inch increases the seam strength it leaves out the practical factor before you damage / weaken the material, fabric or leather. As a note the strength factor would be 1.7 if you were using a Chainstitch machine. Using the formula in that article for Lockstitch machines: i) 6 stitches per inch x V92 having a breaking strength of 14.5 lbs x the strength factor= 130 lbs / inch ii) 20 stitches per inch x V92 having a breaking strength of 14.5 lbs x the strength factor= 435 lbs / inch The stitches per inch is stitch density and for leather it is recommend the stitch density should not be more then 3 to 4 per cm which converts to 6.35 - 8.46 stitches per inch. The reference article for this is Schmetz, Sewing Focus Technical Sewing Information -- Section 3.3 ( https://www.schmetz.com/mm/media/zh/web/7_tochtergesellschaften/bilder_18/schmetz/pdfs_4/sewing_focus/SewingFocus_20_3075-22_Lederbekleidung_D.pdf ) kgg

In Canada a major consideration is that with customer 3 phase service drops is the billing. A lot of companies charge the customer on their 3 phase peak so they pay that demand for the whole year even if their peak is never again reached throughout the year. So for the small or individual customer 3 phase is not a viable option from a cost point of view let along trying to contend with typical 3 phase voltages, 4.16 kv, 12.47 kv and 25 kv. In Canada distribution is similar except that a 3 phase trunk feeder with small 4.16 kv, 12.47 kv and 25 kv will have a ground wire travelling along with the phase conductors from the electrical substation. Single phase taps necessary to feed single phase customers like small business and housing subdivisions a phase and ground are tapped along the 3 phase trunk feeder route. The single phase voltage is then further to reduced to 120v / 240 volts at 60 hz by either pole mounted or pad mounted transformers. Large customers are usually feed at line voltage ( 4.16 kv, 12.47 kv and 25 kv). kgg

I guess it depends on how large the bag is and how much stuff it will be loaded with as well as your stitch length. It comes to a point where if your stitches per inch are to small the seam will act like a perforated paper tear off strip like you see with a cheque book. As a comparison the V69 you used to attach the handle has a breaking strength of 11 lbs and is about 0.012 thick versus the 6mm thread you are use to having a diameter of 6mm and a breaking strength of about 50+ lbs. If you want to use thinner thread as V69 is really in my opinion a domestic size thread. Typically the domestic sewers refer to that size, V69, as heavy duty as it is the largest size most domestic sewing machines can take. I would move up to V92 with a breaking strength of 14.5 lbs and probably a stitch length of 6 stitches per inch. As a note: i) B69 is basically the same as V69, Tex 70, M40, Tkt 40, D236/3 just a different designation standards. In North America the two typical standard ways of referring to a thread size is either by the US designation, " V " and in Canada the metric " M " and the US " V " designation. ii) The Consew 206RB-3 uses system 135 x 17 x (needle size) needles for fabric and 135 x 16 x (needle size) needles for leather. When sewing leather use the 135 x 16 x (needle size) appropriate for the size of thread. Here is a good cross reference chart for thread size and the corresponding needle size that should be used. ( https://www.tolindsewmach.com/thread-chart.html ) kgg

I make my belt with two layers of 6.5 oz glued back to back and stitched with V138 on the edge. I like a heavier belt and it holds it's shape better. Also looking at your photo's I noticed the wriggling starts at the holes you wear the belt at. The holes you punched are round rather then oblong but the holes will sorta go oblong which maybe contributing to the wriggles which are I think caused by the leather stretching. Also doing a stitch line about 3 or 4 mm in from the edge will help the leather from stretching. kgg

In North America the standard residential / small business electrical service is single phase 120 / 240 volts at 60 Hz on a 200 Amp service drop. There are smaller older service drops, old 60 Amp, 100Amp but typically 200 Amp is the norm. Over 200 Amp service drops do require a different metering installation but in rural areas a single phase 300 Amp service drop like mine is not that uncommon particularly if there are other out buildings like barns / garages on the property. Most commercial applications, at least in Canada, will have three phase service drops but usually peel off 120 Volts for small motor usage like what is used with sewing machines. kgg

On my cylinder arm I use a my flatbed attachment then use a edge guide. I prefer a standard bolt down type edge guide rather then the drop down style. The edge guide gives me a consistent stitching distance from the edge. kgg

Typically top tension issue. This also crops up when using dull, incorrect needle size, thickness of leather, worn hook, incorrect tension on bobbin tensioner spring. The correct needle for leather in the Sailrite is a 135 x 16, the max thread size is V92, the max needle size is #22 and the max thickness is about 1/4" in chrome tan leather. Are you doing a drop test on your bobbin / bobbin case to get the tension correct. Keep in mind these machines were designed for sewing sail cloth on the open water. What needle are you using??? What thread size you are using??? What type of leather and in what thickness??? kgg

Keep in mind that the strength of the stitch will be of the smaller thread size where V138 has a breaking strength of approximately 22 lbs and V92 has a breaking strength of approximately 14.5 lbs so the stitch strength would be limited to 14.5 lbs. Most times I think this is done for top stitch appearance. kgg

I agree with @dikman there are just to many possible machines available from brand name machines to clones in both flatbed and cylinder bed configurations then add to that the class of machine capabilities. To further muddy the waters it also depends on where you live with Europe being more accustomed with machines like PFAFF and Adler type machines while North America tend towards the Juki type machines. If you find a machine just post and I'm sure someone can give you an idea as to it's capabilities. kgg

Your clutch motor is probably a 1 hp (745 watts) and with a typical speed of 1750 rpm. That motor on startup could have a inrush current draw of 6 times that of normal current draw (~6amps) on initial startup. Anytime you reduce the input voltage on a motor the motor will run hotter and it will draw more current in order to keep it's wattage rating until it blows the motors inline fuse or circuit breaker in the main electrical panel. My opinion is that you have done almost all the normal mods except for reducing the size of the pulley on the motor. However until you master feathering the clutch you got what you got or until you install a servo motor which will set you back about $150 USD.

I missed or skipped over that point and I do agree with @fredk. If you want to almost eliminate aggravating your arthritis you are going to need a motorized machine. The Juki LS-1341 and older LS-341 as well as their clones will handle up to 7/16" of material with V138 thread and if you need / want to sew thicker or use heavier thread close to what is normally used when hand stitching then you are into a Class 441 machine. A couple of 441 clone machines that you might want to consider would be similar to the Cowboy CB 3200, CB 3500. It really comes down to what you normally sew, what thread thickness you want to use and how thick your pocket book is. kgg

The problem with buying used is like buying a used car, you have to be careful. My rules of thumb when buying a used machine for myself: i) is it has to be in impeccable condition or as close to new condition, ii) not have been used in an industrial setting iii) the price is 70 percent, max. of what a new one lists for. Example: The Boss you mentioned for $850. A new Boss is $999 x .70% = $699.30. The max price I would pay would be $700. Yes those machines use the 794 needles. A typical 135 x16 needle used in the Juki LS-341 has a shank diameter of 2.0 mm while the 794 has a diameter of 2.5 mm. As a note a 2 1/2 " finishing nail has a shank diameter of 0.099" or 2.51 mm. kgg