And the 15-90, as you can see, is belt driven. You can also use it as a treadle or handcrank machine.
This machine is pretty similar to the Singer 99 (another ubiquitous eBay machine), but the 99 has a horizontal rotary hook and different bobbin. And the 99's tension knob is on the front, not the side.
It's also kinda like the 221 featherweight (the machine I learned on), but the 221 has a rotary hook and smaller bobbin...and is portable.
If you're in the market for one of these you can usually get one for under a hundred bucks, unless it's a rare one or something. But they made like a trillion of these so they should be pretty cheap. This one was from a batch of 250,000. I think they pop up on eBay in waves...probably depending on garage sale season.
People do sell these on eBay for $200+ as industrial strength leather machines, which is sorta a scam. They will sew soft apparel leather and they are really tough little machines, but in no way are they true leather machines. If you're in the market for a leather machine, take a peek at Leatherworkers.net and see what's out there...or just buy a Juki 441 clone and call it a day.
Other old Singers that I haven't mentioned that would make good beginner/general-use machines: the 201 and the 66 (the full-size 99), and probably a handful of others that I don't know about.
Woo!
I just remembered that Sailrite used to offer a basic canvas machine years ago...
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