step 6Lens Scaffold
Now that we have a set of focusing lenses, we need to devise a scaffold to hold them in place out in front of the Fresnel lens. After a good deal of thought we conclude the easiest way is to use thin (1x1) wooden stakes held together by plywood gussets.
Materials Required:
Odds are you're going to do this your own way if you try it, so I won't go into too much detail about the construction. I assembled the sides first (minus the 2x4s) by cutting the 1x1 stakes with a miter saw to get the necessary angles, then cut plywood gussets to hold these together. We used 2 right-angle brackets (inside corners) to attach these gussets to the plywood crosspiece that will eventually hold the lenses.
Note: A very important thing here is the orientation of the Fresnel lens. I found out the hard way that when the flat side of the lens is facing the sun, it doesn't work right (but well enough that you might not notice). So make sure the ridges are facing out, away from the scaffold - that means they'll be facing down if you build this with the lens on the ground, as I did.
After the sides are completed, two long plywood gussets secure them onto the side of the frame. Since we want the whole device to rotate about its center of gravity (somewhere between the Fresnel and the small lenses), we need a strong beam that passes through that point (hence the 2x4 s in the diagram), so we screwed the 2x4s onto the necessary gussets, providing a substantial increase in strength.
Finding the Center of Gravity
To find the center of gravity of this whole scaffold (it will be along the centerline of the 2x4), you and a friend each grab one of the 2x4s and see where the thing balances. You'll want to choose a point closer to the Fresnel (so the Fresnel wants to hang down) because the lens assembly hasn't been installed yet. Finally, drill 1/4" or 5/8" holes (depending on the carriage bolt in the next step) through the points you choose.
Note: when using wood screws in the small wooden stakes, you definitely want to pre-drill/countersink holes, because wood this thin is very easy to crack.
Materials Required:
- 4 1x1 stakes
- Scrap plywood
- Woodscrews
- Drill, countersink if available
- 2x4 plank
- 2" hole saw (or larger)
- Several right-angle brackets
Odds are you're going to do this your own way if you try it, so I won't go into too much detail about the construction. I assembled the sides first (minus the 2x4s) by cutting the 1x1 stakes with a miter saw to get the necessary angles, then cut plywood gussets to hold these together. We used 2 right-angle brackets (inside corners) to attach these gussets to the plywood crosspiece that will eventually hold the lenses.
Note: A very important thing here is the orientation of the Fresnel lens. I found out the hard way that when the flat side of the lens is facing the sun, it doesn't work right (but well enough that you might not notice). So make sure the ridges are facing out, away from the scaffold - that means they'll be facing down if you build this with the lens on the ground, as I did.
After the sides are completed, two long plywood gussets secure them onto the side of the frame. Since we want the whole device to rotate about its center of gravity (somewhere between the Fresnel and the small lenses), we need a strong beam that passes through that point (hence the 2x4 s in the diagram), so we screwed the 2x4s onto the necessary gussets, providing a substantial increase in strength.
Finding the Center of Gravity
To find the center of gravity of this whole scaffold (it will be along the centerline of the 2x4), you and a friend each grab one of the 2x4s and see where the thing balances. You'll want to choose a point closer to the Fresnel (so the Fresnel wants to hang down) because the lens assembly hasn't been installed yet. Finally, drill 1/4" or 5/8" holes (depending on the carriage bolt in the next step) through the points you choose.
Note: when using wood screws in the small wooden stakes, you definitely want to pre-drill/countersink holes, because wood this thin is very easy to crack.
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