I agree with Nobby – a handle is a very useful accessory. It takes all the stress out of those occasions where it is vital that you release the clasp nut at the just right moment!
I think mine took a mornings work and I made it up as I went along. The large knurled knob avoids over tightening and a light blow with the heel of the hand releases the cone shaped nut from the taper. If you are going to make one however don't forget the little pin which fits in one of the slots and stops the nut rotating. I don't have the sprung loaded feature that Nobby does but I do remove the drive belt from the pulleys when using it.
A worthwhile exercise between projects – I dread to think what the price of the "pukka" item might be!
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Regards
Norman