First off welcome to the forum Bruce. Depending on the circumstances stress may not be helping much either. Dovetails, even using a very good jig can be grueling to setup properly depending on the jig. I say grueling in the sense if you haven't used it before and are unfamiliar with it. I have a Porter Cable jig that works great when you get things dialed in. The 1st step was setting the proper depth on the bit. Micro adjustments and scrap wood of the same thickness of the wood for the project you want to do is important. Once the depth is set then the offset of the pins and tails. Again scrap wood of the identical thickness is important. I've gotten to the point that when I'm doing such a project I would have more wood then necessary and mill it as needed. Cut the boards needed to size and then have at least an extra side and front piece just in case.
The other left over wood, and you want this, is cut into workable sizes to set the jig up. The left over wood you would want 2 pieces to work with cut off the remaining and long enough to have multiple tries cutting off the failed attempts. By this I mean you don't need identical lengths but you would want the same width. By being the same width you can set your spacing so the joint has at least 1/2 joint top and bottom. The trial an error of setting up the depth of cut can be more than a few tries and when the attempt doesn't give you the result you need simply cut that end off and try again. The PC jig has a bit depth gauge built in that you can adjust the depth and lock in. This helps if all you wood is the same thickness for each project but will likely always need a bit of tweaking as you will likely have some minor differences between millings.
Aside from the videos and manual I really don't know what to suggest. The PC jig I mentioned also has a adjustable stop for setting the alignment of the pins/tails. Not sure if the Rockler does. You may also want to look at this class that George did on WWGOA found
here
And if you're doing this just after your Father has passed you may want to wait until the stress and grief has subsided. If this is the case my sincerest condolences. It will just add a great deal more pressure to your project. And another thought, if the urn is to be buried check with your local and state requirements for certain materials, even cemetery requirements may be different.
Hope this helps.
