As the blade gets narrower towards the tip it also gets thinner. The picture above shows how to taper the thickness of the board. The top of the image is the front of the blade and you don't taper that part. All the material is removed from the bottom of the blade. The edge view is looking at the board from the leading edge, the 'end' view shows the cross section of the blade (white) and the scrap (darkened) at the tip, R= 30 inches and R= 12 inches. It's better to be too thick than too thin at this point - be sure not to get things too thin or the blade will be weakened. The dimensions we give for thickness in the drawing are the absolute minimum.
Getting the board thickness right with a band saw
A band saw is probably the best tool for cutting the board thickness. Give yourself room for slop - don't crowd the line. When cutting this with a band saw its possible the board will not be perfectly square with the table and it's easy to get different thickness on one side than the other so give yourself room! The band saw is useful for removing most of the scrap. After that it's best to finish the job with a hand plane or a power planer.
Calipers work well for making sure you've got the thickness right throughout the length and width of the blade. If you don't have a band saw the whole job can be done with a plane or planer (or even a draw knife) - it just takes longer and makes more mess. When finished the back of the blade should be smooth, and square with the sides.
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