He should have demonstrated that it’s necessary to readjust the miter angle of the blade for chopping the complimentary bevel on the mating piece…..by rotating the left hand template on its longitudinal axis, butting it up back up against the fence, and then swinging the arm to the left until the blade is flush against the mitered end of the template. And those cuts of his still need to go to the shooting board.
The fact that he cut both blocks is what is confusing. He did this to show the final angle cut would fit the pieces together. The wood is the same thickness. He marked the a line on each side of of the angle on one piece of wood. These are extension lines of the angle. He then connected the ends of these lines to show the cutting angle. You could do the same thing on the 90 degree side of a carpenters square and you would get 45 degrees.
Jim
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sheworkswood.com 
He should have demonstrated that it’s necessary to readjust the miter angle of the blade for chopping the complimentary bevel on the mating piece…..by rotating the left hand template on its longitudinal axis, butting it up back up against the fence, and then swinging the arm to the left until the blade is flush against the mitered end of the template. And those cuts of his still need to go to the shooting board.
The fact that he cut both blocks is what is confusing. He did this to show the final angle cut would fit the pieces together. The wood is the same thickness. He marked the a line on each side of of the angle on one piece of wood. These are extension lines of the angle. He then connected the ends of these lines to show the cutting angle. You could do the same thing on the 90 degree side of a carpenters square and you would get 45 degrees.
Jim
Hello friends, I just found an amazing woodwork plains collection formula which will help you to maintain your business. I am using this for last 2 months. Make 16,000 projects with step by step plans.
https://tinyurl.com/y9okomdr