PeGASus Newsletter Issue #25 – Nov. 23, 1991

Hello, everyone!! Well, not a lot has been happening (astronomically speaking); the weather has been poor (this is the ‘blah’ season!). Work is proceeding on the design of the new observatory and plans are afoot to start a mirror-grinding group. Indoor activities seem best for now.


LAST MEETING:

Your new executive was elected. The members are:

  • President: Bob Nelson
  • Vice Pres: Al Pretty
  • Secretary: Brian Potts
  • Treasurer: Jim Livingstone
  • Mem. at Large: Rod Marynovich

Many, many thanks to David Sundberg for serving as treasurer for a number of years. While the duties were not extensive, David was there when he was needed in spite of a busy workload. Thanks, Dave.


SPECIAL FEATURE – MIRROR MAKING:

Three people at the last meeting expressed an interest in mirror making. This is not an arduous task (it’s really quite a lot of fun) and provides a means of obtaining a decent-sized telescope (8″ or 10″) for a very modest cost ($100 – $200 or so). I’ve sent for information and we hope to get our orders off soon. Since one or two other people might be interested in participating, let’s have a look at the basics. (Ref: Jean Texereau, How To Make A Telescope.)

The basic requirements are a mirror blank (usually made of pyrex, but other materials can be used), a tool (made of pyrex, ceramic material or whatever) of the same diameter, various abrasives (grinding powders) ranging from 60 grit (coarse) to 500 (fine), rouge (powder) for polishing, polishing pitch, a squeeze bottle (for water) plus a working stand (oil drums work well). Various testing equipment is also needed.

One starts by mounting the tool so that is is firmly supported on the work surface. Holes may be (previously) punched in the oil drum so that grinding powders may be flushed safely into the drum, out of harm’s way. (Cleanliness must be followed scrupulously to prevent contamination of the finer powders by the coarser ones.) With a little of the coarse powder plus some water to make a ‘slurry’ of just the right consistency, one is ready to start.

The basic motion is one of sliding the blank back and forth over the tool. Long strokes, where the blank overhangs almost 50% at the end of each stroke, should be used. Every once in a while, one rotates the blank 10 or 15ΓΈ or so and rotates oneself the other way. It will be necessary to add a few drops of water when the slurry dries out; also, (less frequently) one should replace the slurry altogether. Because of the overlap at the ends of each stroke, the motion is such that material is gouged from the edges of the tool and