Hi Janet -
I have a Dewalt also. You only want to put the minimum pressure that will hold your blade. The wooden oval "wing" that Steve designed works great, but it is very easy to over tighten and strip the blade holder.
I stripped my top holder and had to order another. I went ahead and ordered two wing nuts and two of the holders. The unit is made of aluminum and it can bend, break or strip. I have some arthritis problems myself, and the wooden tightener is a lot easier to use.
Eventually most all parts break, so you may want to have one of these on hand.
Barry