Hi,
I've always be bothered by the shafts flopping around on my 1-m-wide Glimakra Ideal counterbalance loom when I had only a scarf or sample warp on. First I tried the suggestion from the Big Book of Weaving, theading some string through the last heddle on both sides of each shaft (i. e. 8 pieces of string altogether) and tyeing it to breast and back beam. But I wasn't all that happy - the shafts still flopped around (even if somewhat less) and the strings broke much too often.
Then Joanne Hall (of Glimakra USA) suggested to hang the ends of the shafts from the castle by means of some elastic - and that works a treat! The shafts stay beautifully aligned and I think they are even better to treadle - especially with a direct tie-up and when 1 shaft works against 3 (I'm experimenting with double cloth at the moment). THANK YOU Joanne! (Tip: Don't use too thick a piece of elastic - you have to treadle against its resistance. I bought the thinnest - and cheapest - fabric-covered cord they had in the DIY store).
Happy Weaving, Klara