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Complete the Bending of Rear Spars

Here are some pictures of finishing the rear spar bends.  As usual the first time you try something new, like these really long bends, it takes a while and you learn the little subtleties.  For example we noticed that the ends of the bend would form much more than the center, slightly bowed, perhaps the center of the brake is bending a little.  Since we have to go past 90 degrees we have to bend it a second time since the brake can only rotate 90 degrees before it binds.  We have to bolt another flange (or a peice of wood) onto the brake.  Well if we don’t push at the ends for this second bend it all seems to average out.

Here we can see that we got the first flange angle but it looks pretty wavy along the length

When you bend the flange on the other side it all straightens out:

That looks awesome!!

Here are the two completed rear spars.  These are the long lengths (108 7/8″) so we don’t need the splice plate (snx w12-04).

During this process you can see we were using lots of C-Clamps.  Here’s what happens when Dan wants something tight:

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Rear Spars First Bend

Since we finished “Big Bend” (the David Clay bending brake design) we were eager to try out the beast.  This is the method we have developed for accurate bends.

Here is the rear spar cut to shape and edges deburred and smooth.  One can calculate the width from the standard bending formula tables.  We mark the centerline of the spar blank

We clamp the flange side in the bending brake so we can push up against the larger center portion.  From the bend formulas you can calculate the tangent points of the bend.  Since the part will be formed around the radiused nose of the brake, we need to locate the part’s tangent line right on the tangent line of the nose of the brake.   How can you do this if the part’s tangent line is covered up?  What we need is called the “Sight Line”.  Looking straight down on the un-bent part this theoritical line should be located right at the nose of the profiled brake angle.  It happens to be the radius of the bend from the tangent line.  I will post a summary of this with lots of pictures.  It is tricky to get this line in the right position visually, so we use a caliper and measure from the center line out to the nose of the brake.  (In the picture below we are using the top fingers of the caliper.  The paint on brake nose was sanded off so it is a bit shiny.)

Tighten up the clamp bolts on the brake

** Important **  When we clamp on the narrow flange section we have less than .5″ of the sheetmetal clamped so the top angle will tilt back since it is 3″ long.  This reduces the clamping force and the little flange can slip during the bend.  We insert shims of the same thickness of the bend piece in the backside of the clamp to keep it level.

Here is the first bend, we can only get about a 90 degrees (with the spring back) since we can only rotate the brake up a little more than 90 degrees.

We put in a piece of wood to continue the bend.

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Fabricating Big Bend Part 4

During the week Dan aligned the second hinge to the other angle and match drilled them.  While this sounds easy is involves having all five hinge sections joined with their hinge pins in supporting the angle in the right position wile match drilling.

This Brake design uses one of the angle pieces at the bending nose for the sheet metal.  That is why we bought 1/4″ thick angle, so we could get a 1/8″ radius bends.  Now standard angle does not have a full radius at the end of the legs.  We broke out the vixen files and filed until we got a nice bull nose.  Here is a little 1/8″ radius template from a piece of scrap.

Once we liked the bend radius we located this angle and drilled holes for the clamping bolts

Here is the completed Big Bend brake:

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Fabricating Big Bend Part 3

We had a six foot P3 stainless steel hinge to use on the 9′ brake.  From the small brake on can see the middle will bow during a bend for a thicker material.  We decided to place break the hinge up into sections.  We put 2′ in the middle and on each side we have a 9″ space then a 1′ hinge section, another 9″ space and another 1′ section of hinge.  This leave a 1″ gap from the outside edge to a hinge.

Here is Dan cutting the stainless hinge with a Dremel wheel (Always wear safety glasses when using a Dremel!! ask my Dad)

We used some stainless rivets to attach the hinges.  We used the “yardstick hinge hole template” to drill the pilot holes.  Stainless is a lot tougher to drill through than alumunim.  Dan would spot face the hinges with teh template and I used the drill press to finish the holes.  Here is four of the five hinge pieces:

Aligning the first hinge halfs with the fisrt angle wasn’t too hard.  Match drilling through the 1/4″ steel angle was a pain.  Dan used a older electric drill for this task.

Aligning the other angle with the hinge was more work.

Fabricating Big Bend Part 4

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