Picking up where I left off last night. Cutting the blank material for the blank. 1st operation. Cutting the material. When cutting sheet material, it is best to have, if possible, at least one edge a mill edge to provide a straight reference edge for layout. I didn't have a mill edge as the material was repurposed from the scrap bin. The plans only provide the finished dimensions which have to be flattened to 2 dimensions. In this case it is a triangle, so the two long dimensions get a 1/2 inch inch added for the flanges (for a total of 1 inch) and the short side gets 1/2 inch added for its flange, add a 1/8th inch to the resultant dimensions. Cut to rough size on the band saw. Then mill to square, final dimensions. The blank must be clamped vertically in order to be milled. In the photo below, on the right hand side,one can see that the end of the blank is supported by an angle block. I purchased the angle blocks on Amazon I believe they were about $65.00 for a set. They come in various angles and can be stacked to get accuracy to 1 degree.
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Remove from the machine and check. We are looking for 110 degrees. Note, the location of the corner holes has been marked for the next operation.
The next step is spotting and drilling the holes in the corners. I have a set of spotting/countersink bits. Start by marking the location of the hole. In this case I use the intersection of two lines. Other times it may be a spot, or circle. The photo below shows a good sight picture. The shadow/reflection of the bit on the part should point directly to the center of the hole from two views 90 degrees apart. My mill allows me to bring the bit right down close to the part and holds it there while I make any fine adjustments. With this method, I can locate a hole within a few thousands of an inch. When the drill is turned on, the tip of the bit presents a point which aides precision. Then drill to final size.
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The next operation is notching the ends so the flanges can be bent. Here, I am using a machinist square to mark the cuts. The blue marker is a fine line marker with a long tip, designed as a through-hole marker. Cheap and readily available through Amazon. I have an assortment of blue, black and red through hole markers.
Finally, I used tin snips to cut out the corner notches, and de-burr.
Then bend, starting with the short side and trial fit..