A Giant Magellan Telescope Needs Giant Mirrors

The Giant Magellan Telescope doesn’t seem so giant in the renderings, until you see how the mirrors are made.

The telescope will require seven total mirrors each 27 feet (8.4 meters) in diameter for a total combined diameter of 24.5 meters. Half of an Olympic size pool’s length. A little over four times the diameter of the James Webb Space Telescope.

According to the website, the mirrors are cast at the University of Arizona mirror lab and take four years each to make. They’re made from blocks of Japanese glass laid out in a giant oven. The whole process of casting the glass takes a year, from laying it out to the months of cooling, it’s a painstaking process.

Once the cooling is done there’s another three years of polishing to get the mirror just right. If you’ve ever had to set up a metal block for precision machining on a mill, you might have an idea of why this takes so long. Especially if you make that block a few tons of glass and the surface has to be ground to micron tolerances. A lot of clever engineering went into this, including, no joke, a custom grinding tool full of silly putty. Though, at its core it’s not much different from smaller lens making processes.

The telescope is expected to be finished in 2024, for more information on the mirror process there’s a nice article here.

[James] Multiplies His Floor Sander by Four

Hackaday contributor and new homeowner [James Hobson] had a dilemma on his hands. He had rented a commercial drum sander to begin a floor refinishing project. Like many before him, James was a bit too aggressive with the drum sander in places. The uneven stripes didn’t show up until the sander was returned and the floor was stained. Renting the sander again would be an expensive prospect. There had to be a better answer…

That’s when [James] put on his [Hacksmith] cape and got to work. He built himself a DIY floor sander (YouTube Link) using four Ryobi orbital sanders, some scrap wood, and a bit of ingenuity. [James] screwed the four sanders to a plywood sub plate, then added a top plate with a handle. He even gave the sander its own outlet strip so he wouldn’t be dragging four power cords behind him.

[James] found that synthetic steel wool pads weren’t cutting through the floor very well, so he upgraded to 220 grit sandpaper. That did the trick, and the sander worked great. Now he won’t have to rent a drum sander when it comes time to refinish the first floor of his new house!

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