by chh » Feb 20, 2011 10:19 am
There are also plenty of double braid kernmantle ropes around 11mm that can be easily spliced for nearly a full strength union. The splice will be slightly largher in diameter than the rest of the rope, instead of smaller, like the splice posted above, so you'll need to use appropriate pulleys and friction devices.
If I were installing a fixed treadmill, this would be the way I would go. No need for the backup rope.
Also, in regards to the splice junkman posted, if you have access to a beefy enough sewing machine, instead of whipping the splice you could run some bar tacks along the section where the sheaths overlap. I think this might retain some more of the strength of the sheath material and be less prone to wear and breakage than whipping twine. Though the flater profile might present a problem with your friction device if you are using a rack or something lke that. Also, with some fiddling, as suggested, you might find a filler cord that would make the union pretty close to the host rope's diameter and rounder.
Your words of caution are no match for my disaster style!