My latest cardboard sprang frame has holes punched on the side so I can adjust the size by moving the sheets of cardstock. A piece of string holds the position and rubber bands help prevent it from flopping. This is adjusted about 13 inch long.
Here is the frame with a warp on it. The red yarn on the bottom helps hold the yarns in position.
As the sprang gets closer and tighter it is difficult to get my fingers in the sprang so I used a chopstick to work the yarns. I put a little groove in it and tapered the point.
The bag is big enough to hold a water bottle. The yarn ends will be tied off and cut. I was testing an idea for a little bag that had it's own handles that could be made on a the cardboard frame. And no cutting!
Have a good day!