The sides are going to be tapered; thinner at the top than the bottom. My dad is doing this with hand planes. (How's that, Bruce?)
<a href="http://www.flickr.com/photos/happymonkey/68170862/" title="Photo Sharing"><img src="http://static.flickr.com/20/68170862_931d7e8e8a.jpg" width="500" height="375" alt="Glued" /></a>
The pencil mark shows how far down we have to get at this end. Click on the photo (or, indeed, any of them) for the flickr page, then click "All Sizes" to see the line clearer.
<a href="http://www.flickr.com/photos/happymonkey/68171614/" title="Photo Sharing"><img src="http://static.flickr.com/30/68171614_5a3d880754.jpg" width="500" height="375" alt="The Goal" /></a>
And these are the planes he's using to do the tapering.
<a href="http://www.flickr.com/photos/happymonkey/68172811/" title="Photo Sharing"><img src="http://static.flickr.com/9/68172811_f96fb1886d.jpg" width="500" height="375" alt="Planes" /></a>