Finally, Created the Piece I Needed

A cube of acetal 2.83" on a side with a right angle 30 degrees offset from the top.  I had tried to do this with a ball end mill, but the programming turned out to be harder than I thought.  This beautiful sine vise:

turned out to be a bit big to fit on the Sherline's mill table, so I returned it.  After much upset, I noticed that the Sherline tilting table had enough space between the sides and enough holes in the bottom to attach the workpiece with two 5/16"-18 bolts.  They held it very solidly.  While the piece does not need .001" accuracy, I did make sure the workpiece was within .005" of square on the tilting table.

I had to turn the tilting table 90 degrees from how the holddown screws fit into the T-slots, because there is barely three inches of travel in the Y axis, and for making a cut from -.25" to 2.98" (the end mill is 1/2" diameter), I needed to cut along the X axis.  One of the things that I like about Sherline in spite of the limited power and Y axis travel, is how much thought went into the accessory designs.  The Sherline vise is held in place by holddowns that grab at the sides of the vise.  The tilting table has holes at each end that take screws to go into T-nuts.  (You can see both of these features in the video below.) But I was going 90 degrees from the intended direction so those holddowns would not work. The base plate of the tilting table is the right thickness for the mill vise holddowns to securely hold it. 

In the video, the mill is going ,1 inches/minute.  Why so slow?  I wanted to leave it unattended during my afternoon nap and at .1 ipm, nilling .1" off per slice, even 1" high, I could be sure it would not jam.