If there is enough room (at least 1.2mm), I use micro paracord to replace drawbands. It has no flex or stretch, can have its knot sealed with a little heat, is tested to 100lbs, and is pretty cheap for more than you’ll probably ever need. I have used Atwood micro cord purchased from Amazon for my projects.
via https://old.reddit.com/r/typewriters/comments/1hc2olg/royalite_64_replacement_draw_band/
Royal Typewriter KMG Mainspring Drawband Tightened Adjusted Tension by [[Phoenix Typewriter]]
On the left rear corner underneath the carriage when moved to the right, one can easily see the mainspring and drawband assembly. Just behind it is a worm drive operated by a screw. Turning this screw counterclockwise will advance the worm drive to the left and increase the tension on the mainspring.
Smith Corona Manual Vintage Typewriter Main Spring Removal Flush and Re-Lube Draw Band Attached by [[Phoenix Typewriter]]
Duane puts a few drops of red oil on the mainspring of typewriters as a lubricant before blowing it out to thin it down.
Here he demonstrates how to re-tension the mainspring of a Smith-Corona typewriter.
I twist together two lengths of kevlar fishing line that's 0.4mm diameter and rated for 29kg, so combined roughly 0.8mm diameter and ~58kg pull. This is about the sweet spot imo in terms of thickness, slim enough to fit in small routing holes on mainspring housings and thick enough to get a good sized knot when you tie it. It's also pretty close to the thickness of old sinew drawbands I've replaced. The rated strength is definitely overkill but better over than under. In practise a drawband shouldn't experience more than 750g-1,5kg of pull under normal use.
u/Koponewt aka Pelicram's advice for using fishing line to replace drawbands.
Re-inserting the carriage of an Olympia SM3 timestamp 17:32
Not shown in the video is the reinstallation of the square screw and nut at the end of the carriage to hold the carriage into the machine.
Smith Corona Vintage Typewriter 5 Series Draw Band Install Mainspring Connection Wind Tighten by [[Phoenix Typewriter]]
Smith-Corona 5 series drawband and mainstring attachment and tightening.