The true test of the amateur astronomer is building their own telescope. Grinding and polishing your own mirrors is a long, arduous process. Instead of lapping the blank by hand, Laurie Hall built this mirror grinding machine from scratch. His site has notes covering his mirror creation machines and other projects.
Saw something like this when I was a little guy in 1959.
An old record player/changer was used to turn the mirror blank and the arm that stabilized the next records to drop had a cam in it to give a secondry side/ side movement.
Posted at 8:58 pm on Sep 27th, 2006 by Frank Powell
Solid concept, but there is a reason telescope mirrors are made by hand — machines are too regular, whereas humans are random and flawed. the problem with a machine is that it develops patterns which can induce surface irregularities. the random error and deviation of a hand-polished surface averages out to a near-perfect surface. this is, of course on a near-undetectable scale, but when it comes to fine optics, even nanometers of surface deviation can mean the difference in a focused star and a blob of light. Mirror surfaces are often graded in f/# numbers, corresponding to fractions of a wavelength of light. An average commercial mirror might be f/4 or 1/4 wavelength surface deviation, whereas a very high-end morrir might be between f/10 and f/20. Hubble used to be f/2 back when it was broken, but it is now f/50-ish. Most modern mirrors (from Celestron or Meade, for example) are machine surfaced and ground, but finished and tunes by hand. This machine is prettymuch ideal for roughing aout a surface, but a hand-polish at the end would be crucial to obtain that last bit of perfection. Still, it beats the hell out of hand-grinding an entire surface from the glass blank.
Posted at 10:52 pm on Sep 28th, 2006 by Byron
Utter cock about f/4 etc. What you mean is lambda/4 where lambda is the wavelength of light used for measuring the surface departure from a parabola. lambda/20 is considered very good. lambda/4 is passable. F/4 means the focal length of the mirror is four times the diameter – just like on any camera.
PS I have a mirror-o-matic grinding machine, they can be just as random as a human and don’t need to give a patterened surface. Its all in the tools and who uses them.
Posted at 2:59 pm on Jun 22nd, 2007 by hazardmike
Looks like it has potential for those doing a lot of heatsink lapping.
Posted at 7:31 am on May 28th, 2009 by Squirepuck
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when i used to manufacture optics we did the same sort of thing but upside down. The mirror was attached to the plate the spindle rotated in, and swept across a large, thick, rotating steel plate that the liquid abrasive was dripped onto. No stabilizer arm was needed but to do a good polish the big turntable/plate absolutely had to be thick and flat so it didnt flex.
That and the whole thing sat in a tub so the abrasive slinging off didnt make a mess all over.
Posted at 5:49 pm on Sep 27th, 2006 by Phugedaboudet