Revving up the blog again
This blog has been quiet for over two years, but it’s time to get it re-animated. While we’ve been experimenting with wikis for communicating progress at VMOA, we’ve also made significant progress on the 40-inch telescope and there is new public interest in the project (http://www.pressdemocrat.com/article/20090209/ARTICLES/902090270). Since the public doesn’t have easy access to the wiki, here we are back at the blog!
So what’s new?
- In December 2008, the mirror grinding team of Steve Follett, Mark Hillestad and Larry McCune (and other volunteers) completed the grinding phase of the mirror-making process. Grinding is the slowest part of the process but is the stage when you can see the most progress. Progress is marked by a succession from coarse grit to very fine grits and even more by the sound of glass on grit changing with the size of those grinding particles. Polishing begins when the pits from the smallest grit are all about the same size, estimated by eye and is a process that takes a slightly hazy surface to a surface that easily reflects light. Its end is marked by the absence of pits in the surface of the mirror.
- We expected that the polishing phase could take the next twelve months, but in March 2009 Steve, Mark and Larry announced that polishing was complete! The next step, riguring takes the spherical (or, perhaps, near spherical) surface and by using the same materials during polishing, and adjusts the surface to the desired final figure of revolution. The primary mirror is a paraboloid. The difference between a sphere and a paraboloid is not visible to the naked eye, but it brings the light to a focus for the rest of the telescope.
- A testing rig has been created that involves moving the mirror down the driveway to get enough distance from the knife edge tester.
- The rocker box design has been tweaked for the switch from aluminum members to steel, to give better access to the mirror for maintenance, and to remove unneeded strengthening members. Here’s a picture of the rocker box fabrication in progress.