The rough grinding usually digs a depression in the center of the upper disc which gradually deepens and spreads toward the edge of the disc. It is a fairly simple matter, by regulating the extent of overhand, to arrange to have the curve on the mirror face reach its proper depth just as the edge of the ground out area reaches the edge of the ... read more
Rough Grinding. Rough grinding (hogging out) is the first stage of grinding performed on a new flat blank and tool. The purpose of rough grinding is to generate a ‘dish’ in the center of the mirror. This dish is deepened until the correct radius of curvature (R.O.C.) is produced. read more
When delivered, the mirror blank should be square on both sides. In the process of Rough Grinding one side gets the the desired sperical curvature using an abrading medium (silicon carbide) and a very simple grinding tool. In this phase the demanded accuracy is comparatively low, the grindig tool is made from a simple granite plate. read more
Rough Grinding. Unless the mirror comes pre-generated, the initial curve will have to be ground into the mirror. A ring tool of half the diameter of the mirror used on top of the mirror's flat face with the coarsest grit will rapidly grind a spherical curve into the mirror. Grinding a 6 inch [15cm] mirror to F/2.8 using a ring tool. Mirror ... read more
A good starter size is the 150 mm (6 ) mirror. A 200mm (8 ) will also work. Most ATM books and websites recommend a Pyrex mirror blank, but in my opinion, annealed plate glass is better for this first, learn and practice mirror.It is cheaper, it is softer and grinds faster, needing less abrasives and with these small sizes, the low expansion glass like Pyrex has no practical (visible at ... read more
Photo #2 shows the mirror at the end of rough grinding. I was aiming for an f/4.5 mirror, so the required depth of the curve is 0.175 inch. Once the required depth is reached, the rough grinding is complete. Amazingly, the rough grinding has removed over a pound of glass. The mirror now weighs in at only only 8 pounds 15 ounces. read more
Sep 21, 2014 Page 1 of 3 - Mirrors - using undersize tool - posted in ATM, Optics and DIY Forum: I am working on a 13in mirror, at rough grinding stage #100 grit now.TOOL Is 10in diam.To keep within my design f ratio can I work with MOT ?? If so working towards a sphere, what Overhang and stroke is Acceptable ?? Macleod. read more
Jul 27, 2021 A mirror blank is ready for grinding in this image. A layer of grit and water will be added to the top of the blank before the machine is turned on. ... high-speed rough polishing machine ... read more
The rotating table set up for a 6 mirror. The central pin is a 1/4x20 bolt. Two of the furniture glides are shown. For a 12 mirror, I just used smaller blocks. I use a rotating table for fine grinding and polishing. Rubber feet on the bottom of the base are all it needs to keep it in place on the kitchen counter. read more
FINE GRINDING THE MIRROR. After generating the mirror curve by rough grinding it remains for us to smooth it by fine grinding and polishing before finally correcting it to a parabola of revolution. Fine grinding is done in about the same way as the last wets of rough grinding, but with a series of finer and finer grits such as 100, 220, 320 ... read more
Once the rough grinding has been completed the mirror, tool, work plate etc. should be thoroughly scrubbed and cleaned using soap solution and an old tooth brush for example. If possible, the cleats should be replaced with new ones; the work post should be cleared, the newspapers and used cloth pieces thrown away. read more
Fine grinding and smoothing Once the rough grinding has been completed the mirror, tool, work plate etc. should be thoroughly scrubbed and cleaned using soap solution and an old tooth brush for example. If possible, the cleats should be replaced with new ones; the work post should be cleared, the newspapers and used cloth pieces thrown away. read more
31 rows Rough Grinding The first milestone is putting a curve into the mirror face. The curve's depth dictates the mirror's focal length. The curve should be spherical. Creating the curve can be done by several methods: The curve is ground into the mirror face using a grinding tool. The curve is pre-generated for you. read more
Rough grinding is often called Hogging Out , as your goal is to remove the majority of the glass needed to form the curve of your mirror. It is not particularly elegant work, being the noisiest and messiest part of the whole mirror making process. read more
Rough Grinding The purpose of rough grinding is to start to cut a spherical concave surface into the mirror blank. For a 6 mirror with a 48 focal length, the depth of the curve is 0.047 . A full sized tool is rubbed against the mirror blank, with a wet grit mixture, to abrade the glass (and also the tool, which becomes convex). read more
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