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Leon gluing a stiffener between the rips

Copyright 2006

Student Solar Forge

It is important that today's students learn knowledge and develop skills in alternative energy. This is a pictorial summary how a high school student, Leon White, built a section of a Solar Forge of about three feet by four feet and tested its ability to hold shape.

Leon used the Solar Forge section to study the quality of the finished optics and to work out safety procedures for the use of a full size solar forge by a student team. He completed a science fair project on these tests.

For more details of the Solar Forge construction technique see" The Solar Forge and General Purpose, All Around, Light Bucket

  1. Lofting

    To do the lofting, Leon taped together sections of red resin paper to cover the floor work area. He set the height of the target just over his head at seven feet and the distance to the base of the mirror section at 40 inches.

    Tools for lofting 1

    The lofting tools are simple wooden straight edges, some very long, and a few fixed wooden compasses. It is easier to have several simple nail and pencil compasses of fixed length than to have one adjustable compass that you have to adjust all the time.

    For the largest circles, a set of trammel points are needed to make a great compass. These clamp to the long wooden straight edge. One of them acts as the compass point and the other holds a pencil.

    Leon bisecting an angle on the lofting

    Leon then drew in the sun lines, the refection line the bisector line, and the mirror line. His tools were a ten foot wooden straight edge, a four foot "T" square normally used on sheet rock, a 18 inch fixed wooden compass, a 12 inch fixed wooden compass, and a small woodworker's compass.

    Leon drawing purpendicular on the lofting

    He then drew in the mirror segments and a frame rib under it. He then transferred the rib measurements to a paper pattern and cut out five ribs from foam board with an Exacto knife. (Do you know what function having to do with ones toes this knife was designed for?)

    He used measurements from the lofting to design four stiffeners to hold the ribs in a circle. He was able to draw these carves directly on the foam board with the great compass.

  2. Frame Construction

    Leon made his forge from foam board, assembled with a hot glue gun, and covered with heavy duty aluminum foil. The ribs were notched to take the four stiffeners.

    Leon glueing a stiffener between the rips

    The finished frame was very light, but strong.

    Completed frame without the reflecting surface

    Leon drew the surface arcs out directly on the foam board using the grate compass. All measurements were transferred from the lofting by simply setting the compass to marks developed in the lofting. A tape measure is never needed.

    Surface circle arcs layed out on lofting

    The reflective surface strips are four inches wide. They are sections of a simple circle and are curled slightly over the frame to form conic sections.

    Leon glueing aluminum foil to reflective surface

    Leon attached the heavy duty aluminum foil to the reflective surface with spray adhesive. The aluminum foil is reflective enough for testing the Solar Forge's concentrating ability without being so good that the concentrated light become a serious fire hazard. More powerful forges will need better reflective surfaces.

  3. Carriage

    The carriage for this small forge was made of scarp wood and is about the size of a child's wagon. The wheels are six inches in diameter and on 1/4" steel rods for axles. The hinges for the sun line have loose pins so the frame can quickly be removed. The upper hinged section is bolted to the central rib.

    Small carriage made of plywood with removable pin hinges
  4. Sun Pointer

    Leon made the sun pointer full size. It is made from a 10" section of 4" diameter PVC pipe. The top has a cap with a 1/2" hole in it and the lens from a cheap pair of reading glasses glued inside it. The lower end has a union with a piece of clear plastic cut to fit inside it. The plastic is ground with emery paper and cross-hair lines cut into it. The inside of the sun pointer is painted flat black.

    Pointer target with cross-hair marks

    The sun pointer is mounted on the back of the forge frame and held in place with Velcro strips.

    Pointer being installed
  5. Testing

    Leon's testing program for his science project was limited to checking the ability of a mast and four stays to improve the focusing power of the Solar Forge. This shows both how a much energy concentration device like the forage can sensitive to its shape, and how closely its surface approximates a parabola. The quality tested is called the Figure of an optical device.

    Testing on roof 1

    The testing was carried out on the roof of a building on five different days. Some days were clear and some were partly cloudy. Three different stay tensions were tested: loose, medium, and tight.

    Testing on roof 2

    The sun was focused onto a target. The target was photographed with a digital camera. Later the pictures were analyzed to compare the overall light on the target with the light concentrated on the central region.

    Testing target

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