I finished up one set of turned Ms and Os scarves (neutrals) and decided to do another set (in greens/browns), so, there it is - tied onto the previous warp. I just hold the yarns together so the ends line up and tie an overhand knot with both threads acting as one, if that makes sense. The knots didn't slip at all.
A slight hitch in the process - my first warp didn't have a whole heck of a lot left over, so I tied my warp bar (temporarily, lol) to the fourth shaft on my little Harrisville loom, just to take the tension off the yarn and hold it in place while I tied on in front of the reed.I timed the whole warping process for both sets - and, surprise, surprise, it actually took about 15 minutes *longer* to tie on than to just start over entirely! Interesting.
A couple caveats - I can do this threading more or less in my sleep. I'm also a relatively quick threader, from what I've seen (hard to tell, of course). But, I did come to the conclusion that for smaller projects and projects that I can whiz through the threading, tying on doesn't make sense for me.
For larger projects with more complex threading (like the 16s advancing twill on my Weavebird), I would probably tie on if I were repeating a design, even if it takes a long time, just because it eliminates all possibility of threading errors.
Anybody else try this little experiment? I'd love to hear if it's faster for you. Maybe I'm just incredibly slow at tying all those knots!
