Wednesday, March 7, 2012

Draw Bored?

The cabin front porch beam is up and in place. Interesting project and some new learning in the process of cutting and housing the braces then draw boring the mortice and tenon joint.

Through the years I have found that there are always at least two ways of doing things. In the classroom, as the "teacher" I (but not many of my students) considered this a strength of sorts. However, it never failed during a demonstration of some process that an "experienced student" would challenge the method I had selected saying, "That's not the way we do it at home." My response would be, "Well, try this way, and then you will have two ways of doing the same thing. See how it goes, then you can choose the way you want to do it." Need the patience of Job at times!

On Bridge #3

 I wanted to use mortise and tenon joinery with wooden pegs. "I was lost and did not know it." I even pegged the ends of the braces! Oh my. Then, on my own, for braces, I decided to center the tenon and achieve one of the goals of housing by cutting the tenon back 3/4" from the front surface of the brace. I had read a bit about housed joints but dismissed the idea as to complex. My "solution" to my problem did the job! I had seen posts with braces in place but had never seen one disassembled like in the picture below. I just didn't get it. Imagine that! Now I do.

It's all about the details. Something about actually doing one or two of these that gets the housing idea to literally and figuratively "sink in"! On a 45 degree brace like this the diagonal length can be calculated by simply multiplying one of the triangle legs by 1.4142 or you can go through the whole Pythagorean Theorem thing if you want to make one of your old math teachers happy. Just make sure to add the two depths that you plan to house your brace to the legs of the triangle! If you do this right you will get a joint the looks very clean with no way to see into the joint at the edges because they are housed by the surrounding wood of the post and beam.
See, neat and clean. Also no pegs required because when the post and beam are pinned the brace is mechanically locked in place.

I wanted the tightest fit possible between the post and the beam. To do this I would draw bore the hole for the pin. First the hole was drilled through the beam. I then inserted the post tenon into the mortise and used the drill bit screw point to mark the center location on the tenon. Then I moved that center point 1/16" closed to the shoulder on the post. Note: here you have a 50/50 chance of going the wrong way with this so it is a good idea the think about it a bit before you drill the tenon. The idea is to make the holes not line up and when the pin is driven in it pulls the post up (in) and tight to the beam.

Looking at the assembly picture above and the draw bore hole. Beam is on top. Post is on the bottom. See how a pin, when driven in would "draw up" the post to the beam? Neat idea.

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