Well after looking and doing alot of reading. We did a little brain storming and used up a few pieces of scrap wood but think we have us a jig made that works pretty good. Here what we did.
We put on 3/4" worth of Dado blades and ran them as high as my table saw would go. We then started stacking wood up besie blade and fence. We did this till we found the right depth cut we wanted in our box. As we was checking this we would angle the table saw blade all the was to 45 degree angle. Once we had the right cut for us we measured the wood we had stacked up. We ended up framing a jig with 2x4 and planning a board down to when placed on frame it would reach the hieght we needed.
We cut our first 2x4 at 19 7/8" this would be the size of the long side of box and make for easy centering.
We figured out how far down we wanted the handle to be. The start of our handhold is 2 1/8" from the top of the box. (All our boxes will be cut like this no matter the size) So we ripped a 2x4 down to that size.
We took what was left on the ripped off side and cut 2 9" pieces from it.
Then we cut a full width 2x4 to the size of the short side of the box.
We measured center of both size boards and marked them.
We attched the 9" boards to the side of the long bard and to the top and bottom of the short board which made the short board the size of the small side of the box.
We then took a piece of 1x ripped it to fit on top of jig leaving the ends of the longer board sticking out from it.
We planned the 1x down to make the thickness we needed to get our measurement we found we needed during the test at the begining. Then attached it to frame of jig. Here is a picture of frame before 1x placed on it.
After jig finished we placed fence against jig and then clamped the jig down to table and to fence. We ran the Dado blade up slow till it reached the bottom of the 1x and we cut it straight and as blade was running we began to angle the blade to a 45 degree. Once we cut thru the 1x on jig we lowered blade back down below jig and place box on top. Centered the box and began. Repeated the same step as cutting jig 1x and it did a pretty nice job here is a picture of finished jig and first box done on it.
Close up of box handhold