Plying using a ball winder and a center pull ball. I gleaned it off of a friend from the Desert Weavers and Spinners Guild (www.adwsg.org). However I used the technique and liked it; so I had to post.
The Jest of it is: Say you only have a few bobbins (especially over sized bobbins as I only have two) and it doesn't work so well to fill them both up and then try and ply on something else or a smaller bobbin.
The Answer is: Fill up the bobbin, use a center pull ball winder (Like the one from Royal) and then take the center pull ball and put the ends together and start making a 2-ply yarn. You could make a Navajo 3-ply yarn also and if you redo the steps from the 2-ply yarn stage, you can make a 4-ply yarn. The great thing nothing gets tangled and the plying makes a very balanced yarn.
I will outline details here just in-case you want to see what it looks like. I even signed up for You-Tube just to video this (my first video! can you believe it) So I have the Pictures here in Sequence...Then the video at the bottom, so I guess feel free to skip to the bottom.
1. I used a over-sized flier and bobbin on my Lendrum wheel. I have seen this done on many brands of wheels since I was at a group meeting when Sue Shared it with me she was using a louet.
Fill the bobbin with a spun single.
2. Attach the center pull ball winder to the wheel or flier like so... As I said already this is how I found it easiest on my wheel. The winder should attach to any wheel somewhere.
3. Wind right off the bobbin.
4. Once wound remove the winder and then take the inner end and the outer end and combine as to ply the two together. Attach to the leader thread on the bobbin and start treadling the opposite direction of you single twist just as to ply two bobbins together.
5. Ply until the entire ball is used up!
The great thing is...
-the skein is completely even. You end exactly what you started with
-since we took what was on the bobbin, then used the same exact amount of material it all fits back on the bobbin!
-Do more - make a 4 ply yarn by repeating the process the ply the opposite way again. Suggestion: to over twist the 2-ply a bit so the 4-ply is balanced.
Hope this helps!
Or Navajo ply right out of the center of the ball.
Video: