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Forgive me if I’m breaking some kind of unwritten code, but my vision for a line shaft wouldn’t be complete without some semblance of flat belts.  Soooo, I bought a roll of 6mm timing belt, as a reasonable approximation. YouTube university offers a few ideas on splicing these toothed belts. 

Here’s what I’ve gathered so far. I’d like to run it by those who may have been there and back before I get too deep into it.

Using what I have, especially since I’m pretty well welded to the house for the duration, I’m thinking of using a straight rack style metal coupler that came with the belt material as a jig to align the belts for cutting so the tooth spacing is preserved, perhaps bandaging the flat side of the splice with good old fashioned cloth adhesive tape to keep it aligned while I sew the ends in the manner of the staples used on leather belts. I’ve got some 14 lb test braided berkley fireline that is absolutely zero stretch, and I’d sew it with individual suture style stitches, the knots on the flat side. After sewing, the cloth tape could be removed, or inked black with a sharpie To camouflage it a bit and left in place. (Hint. If ever you try to thread a needle with fireline or similar, it’s easy if you stiffen the last quarter inch of the line with thin CA, run it between your fingers with the glue wet to flatten the line, then trim the stiff bit at an angle. Now ya got something that will go through the eye of the needle easily.)

Does this method sound feasible, or am I missing an easier way?

Strictly speaking it’s not a flat belt like the old time leather belts.
It’s meant to be a reasonable approximation in a readily available, very good material.

Meant as a non stretch timing belt for such things as copying machines, the belt is fabric reinforced rubber, much like a car tire. It’s flat on top, with teeth like a gear on the bottom.  The one I’m using is 6mm wide, and 1.5mm total thickness.
Though designed as a timing belt, to run on sprocket pulleys reminiscent of miniature dragster supercharger drive, it runs very nicely on wooden pulleys crowned as if for a flat leather. 

Since writing this post, I’ve built a little splicing jig that is in essence a miter box for a single edge razor blade, with a section of toothed timing rack in the bottom of the miter box, so accurate splicing can be achieved.  After bandaging the top with Mylar glued with CA, im sewing them with a 2-0 silk suture in the manner of the staples used on leather belts. The key turned out to be the miter box and the Mylar, a no stretch positioning medium to insure the suture line ends up straight and even.

Looks like you can order welded endless, custom length flat belts from this site

https://www.ebelting.com/index.php?main_page=index&cPath=10&zenid=smjso0l7o5r9aa4rlbu318pom1

I have made many belt in my old hobby of Edison cylinder record players.
Here is how I did it and have done with my S 50 and generator setup.

First I cut the leather belt at an angle and mark about 3/8" on the front
and back. On the front I removed the black part of the belt. on the I filed
or sanded the back. I worked both sides until the belt on each side was
half as thick before I started. See the picture below.

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After gluing with superglue if the back side I would file it down.

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This is the the front sid of belt.

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Here is the belt running a PM generator and a S50

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I hope this is helps with making a leather belt. If it does not make
any sense I could answer any questions you have in making a belt.

PM Research belting is a rubber coated cloth and works very well. It is available in 1/4" and 1/2".

I’ve been fine tuning my belt splicing method. The most recent was a redo of a belt failure when using my mini wood lathe, powered by a sewing machine engine. I had it hauling along at about 2500 guesstimated rpms, and the belt parted, slithered out of the machine and whacked me in the face, lol.

Did I mention I’m legally blind? Sewing 1:4 inch wide belts end to end is a bit of a challenge with my very limited vision and complex eyeglass prescription allowing a very critical focal length.

So I have cobbled together a bit of technology to do things like the belts, scroll saw, critical operations with a milling machine, lathe, etc.

I’m able to do a running lock stitch, five or six stitches across an end to end seam, with 40-0 (about .006”” nylon surgical sutures, now that I can accurately see what I’m doing. Then the seam gets coated with thick CA.

The secret weapon is a 6mp borescope With a 3-16 inch focus range,  set up with an iPad monitor so I can see what I’m doing.

Really clever way of working in miniature with the camera/iPad

I’ll have to show this setup to Dad, he always says when working on small parts “Wait till you’re my age! F#&%^@! glasses, can’t see with them and can’t see without them!”