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More Testing Work on the Homemade Box and Pan Brake

Gap between the hinged board at 90 degrees and the base board with no metal.

Gap between the hinged board at 90 degrees and the base board with no metal.

Another step forward with the brake project. I cannot say the light at the end of the tunnel is very bright yet, but I am pretty sure it is not a train. I am a whole lot more hopeful of getting something accomplished than I was in the last post “Debugging the homemade Box and Pan Brake“.  Way back there in the post “Progress on the Sheet Metal  Box and Pan Brake” I had determined that there was a gap at each hinged end and this was because the hinged board was bowed.  I decided at that time full speed ahead, and I would go ahead and test it “as is”.  In the last post I decided that was part of my problem and I needed to fix it.   Basically the hinged board had a little curvature and was slightly shaped like a rocking chair rocker.

I removed the hinges at the back board, hand sanded the edge of the hinged board until I got a nice fit against a straight edge and the base board. I then reinstalled the hinges back on the base board while I had the hinge board clamped against the base board. Because the hinge is attached to the base board with wood screws, I needed a way to force the screws to move slightly and create a new hole.  I did this by gluing match sticks inside the existing holes on the hinged board side of the hole.   I installed the screws while the glue was still wet.  This is a trick I have learned when a wood screw strips out a hole, but I was not 100% sure it would work in this case where I wanted to slightly move the hole.  So far it seems to work.

The Gap Adjustment

The Gap Adjustment

One of the final goals will be to know how to accurately set the gap between the clamping board and the break between the hinge board.  For all these tests I set it exactly the thickness of the metal to be bent.

The Clamping Arrangement to be repeatable for these tests.

The Clamping Arrangement to be repeatable for these tests.

To ensure the gap would be the same for all tests I clamped a board behind the clamping board. This meant I only had to set the gap one time and it would be the same for all tests.

 

 

 

 

One inch wide metal set up for bending.

One inch wide metal set up for bending.

I then proceeded to bend a one inch piece of metal. The reason for bending this very small piece of metal was I wanted to see if I really had reasonable expectations of a nice tight bend. The one inch piece would put the minimum amount of stress on the hinged board and create the minimum extra gap. This should give me the tightest possible bending radius.

Three one inch wide pieces with a 90 degree bend.

Three one inch wide pieces with a 90 degree bend.

IT WORKED! I was able to get a nice tight bend radius. Using my homemade scale I created last time I was able to get a bend inside radius of no more than 0.035. Finally a positive sign.

 

 

 

Results with a piece of metal 5.5 inches wide.

Results with a piece of metal 5.5 inches wide.

Things did not go so good when I tried bending a piece of metal 5.5 inches wide. 5.5 is the width of the clamping piece I built. I did watch the gap as I bent the piece but unfortunately I did not have camera in hand to take a photograph of it.
The good news is this piece had an bend radius I.D. of about 0.080 inches which is an improvement over the measurement last time of greater than 0.100 inches.

Gap while bending a 1 inch piece of metal.

Gap while bending a 1 inch piece of metal.

For one final check I bent one more 1 inch piece and had my camera in hand to take a picture of the gap. There was a small gap, but very small.

So… where does this leave me? The problem is the hinge board is bending under the stress even with the 1″ X 1″ X 1/8″angle I installed on the back of the board. This actually makes sense because most of the manufactured, professionally designed brakes have lots of bracing and they use a steel plate for the hinged plate. I am currently designing an adjustable brace to stiffen this board.

I have noticed some dings in the wood on the hinged board. That will be the next bridge to cross after the stiffening assembly. However, although this whole thing will be less than ideal, it is definitely a learning exercise and so far it has not been that expensive.

Gary

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