Well, hopefully not the Toil and Trouble when you use a doubling stand!
I'm trying to use up this extremely fine singles linen Lynn gave me last fall, and the only way it will work on the fine cotton warp is to double it. Yes, it's that fine! :O
However, as I mentioned in a previous post, trying to wind two strands of yarn together can produce less than desirable results. When I need to double a yarn for weft, I use this handy bucket arrangement as a doubling stand. One cone is inside the bucket, threaded through a hole in the lid, then through the centre of the cone on top of the lid. This yarn is so fine, you may not be able to actually see it in the photo.
You can use any number of things - there are purpose built gizmos, but the one I have is too small to handle these large cones (nearly 4 pounds each!) - and another simple solution is a plastic milk crate or wire file bin. Set the cone on the floor, then tip the crate over it and run the thread up through one of the holes in the crate. Then thread the yarn through the bottom of the second cone (I use a long threading hook to fish the yarn up through the cone) and set the second cone centered over the first cone. If the crate or bin has smooth sides, you can also set it on the side so that you don't have to lift it up to get at the bottom cone.
I've found that the longer a length the two yarns run together the better they wind onto the bobbin, so my bucket is approximately 6 feet away from the bobbin winder. The yarn goes straight up to a hook in the ceiling so the length the yarn travels before winding onto the bobbin is probably close to 15 feet.
When winding, the hand that guides the yarn onto the bobbin is held about 1 inch away from the bobbin. The closer you hold, the less likely the yarns will split apart as they wind on, and the more evenly they will load.
I've got 3 of these almost four pound cones. I don't know how much I can use up on this 40 yard warp, but I'm hoping that most of the two cones I'm using will go. There is still a little of the very fine cottons left, so those pale blues will get combined with bleached white for one more warp - which will hopefully use up the very fine cottons, and most of the very fine linens. :)