GregO29

Typically if you have the entire dish assembly with the feed horn (LNB or whatever), that will be the focal point. But in this case I did not. I googled a formula like this one to calculate the focal point, then I added a few platters on the outer edges and some on the center to measure it more accurately.

Sometimes I like to binge watch tv while disassembling drives: Netflix and unscrew.

Thanks for the question. Multiple reasons:1) Reflectivity. This is a mesh dish, not solid, so there is not a smooth surface to apply it to. Wrinkles equals diffraction. Flapping tape equals diffraction. Hard drive platters are hard, and retain their mirror like surface, even in wind.2) Cost. The drives were free. The HD tape is $7.68 and could cover 5sq ft. This dish is 8ft or just over 50sq ft. Using 3/4s of it, I would need 7-8 rolls of tape making an out of pocket cost of $50-60.3) A solid 8ft dish can become a sail. The 'wasted' space by the holes in the center of disks and the gap in between their outer edges provides a bit of wind relief so it does not become too unmanageable in slight winds. Think of advertising banners that you may have seen with the holes punched in ...

Thanks for the question. Multiple reasons:1) Reflectivity. This is a mesh dish, not solid, so there is not a smooth surface to apply it to. Wrinkles equals diffraction. Flapping tape equals diffraction. Hard drive platters are hard, and retain their mirror like surface, even in wind.2) Cost. The drives were free. The HD tape is $7.68 and could cover 5sq ft. This dish is 8ft or just over 50sq ft. Using 3/4s of it, I would need 7-8 rolls of tape making an out of pocket cost of $50-60.3) A solid 8ft dish can become a sail. The 'wasted' space by the holes in the center of disks and the gap in between their outer edges provides a bit of wind relief so it does not become too unmanageable in slight winds. Think of advertising banners that you may have seen with the holes punched in them so there is less wind stress.

Thanks, but your first link is my 4ft solid dish with Hard Drive Platters, NOT cd's. CD's will diffract light as well, and do not have as high of reflectance as plated aluminum. Think of the rainbow you see on a CD/DVD, compared to the mirror image you get looking at a Hard Drive Platter.

Standard household mirrors are good, but glass quality is poor. Astronomical glass with Aluminizing is above 90% reflectivity. CDs are written by a laser burning the interior to DEFLECT light, thus when you look at them you see the rainbow, or spectrum of visible light. I would guess the reflectivity is below 20%. The Hard Drive platters are usually Aluminum with a finish coat so that a Hard Drive head can float within microns above the surface, meaning they have really smooth surfaces and high reflectivity. If you search on Instructables, there is a large 8ft satellite dish with CDs on it, but I don't know what kind of results they achieved.

Materials:2 sheets of 3/8 plywood = $25 each2 metal springs for Worm Gear = $1.25 each12ft of brass metal piano hinges = 2 at $15 eachOld finishes and stain already on hand.Misc hardware $25, original optics $125Total cost about $250

Thanks for the comments. If the base is about waist high on the average person, the hand cranks are easily reachable, unless you have T-Rex arms.