Ok. Two flat bars should clamp ok I’d imagine
I have heard of using 2x4s just longer than the feather and a hand sanding block.Clamp the wood carefully so you don't crush the feathers.
A door hinge long enough to hold the entire feather works well for holding the feather for grinding. Then take it to a belt sander if you have one or a piece of sand paper glued down to a flat surface. I prefer to peel and thread wrap my feathers. Kyle