Hi All! (new user, Chaotic Lens Grinder Idea)

[nw_lton]

This site was recommended to me on the weekend, and I'm loving it so far!

I've been looking into building a lightweight Dobsonian scope for a few years now, but the thought of spending weeks grinding a primary doesn't quite appeal.

I know the issues of mechanical grinding jigs, and the repetition errors and symmetrical wear, but what if it's movements were slightly unpredictable.

(This idea has most likely been thought of already, but here goes...)

Consider a setup where:
The work top was solidly mounted, but could rotate to any degree.
The tool was mounted in an XY plotter style setup, with spring-loaded mounts to apply gentle pressure to the workpiece.

The workpiecewould do the regular W shaped movements over the edge of the tool as normal to produce the convex bottom piece, and the concave top piece, but here's the sneaky bit.

Have an AD converter take a sample from a radio station. This sample is then divided back to influence the final position of each of the four positions of the 'W' movement.

Say, for 0 input volume, and the top stroke in the middle of the 'W', it's position is X:300, Y:50, but, for 100% volume, it's X:320; Y:80.

These co-ordinates may only be a few millimeters apart, but that way, it could possibly simulate the slight randomness a human grinder gives to the piece.

Similarly, the bottom worktop would rotate 5% +- 1%/v of input signal every 20 seconds...

Any feedback on this idea?

Nige.

[rmcpb (Rob)]

It would certainly be random but till its tried we will never know if its feasible.

BTW, welcome to IIS

Cheers

[Blue Skies (Jacquie)]

Hi there,

I've got two suggestions:

1) Buy your mirror, don't grind it! Unless you are determined to have a hand in every inch of the scope and money is no object and you don't care how long it's going to take, my advice is to buy. (and yes I've tried making a mirror before...)

2) Join the ATM list here: http://www.atmlist.net/mailman/listinfo.cgi/atm Where some very knowledgeable people hang out and would know the answer to your question better than most. The BIG names of the ATM world are there and you'll get the very best advice.

Don't forget there is the atm and DIY forum on this site too and questions like this might be better asked down there - you don't seem quite the beginner to me and some of the people on here that might be able to help would see you question down in that section sooner than they would see it up here.

[nw_lton]

Alas, funds are tight at the moment, but I have a good supply of large servo motors and control electronics, so building a jig is certainly cheaper than splashing out and buying a primary...

I may even test the jig with 12"x2" rounds of aluminium, just to see how it grinds...a whole lot cheaper than ruining Pyrex blanks...

Hey, if you aluminium-coat a mirror anyway, why not make the whole thing out of alloy?
Ah, softer, easier to distort with bad mounting, lighter, easier to scratch, easier to polish scratches out, great conductor of heat, so it'd get to ambient temp insanely quickly...

Hmm. Might give it a bash anyway...

[nw_lton]

Found this reference to using solid aluminium to make mirrors...who knows!?!

http://frank.bol.ucla.edu/almirrors.htm

N

[Orion]

I have a mate that is making a 48" alloy mirror!
The telescope occupies most of his back yard.

[cristian abarca]

Making the mirror is more fun than simply purchasing one. Have a look at this site. http://www.oblivion.net/~astro/ .

Cristian

[Blue Skies (Jacquie)]

There is usually a good reason why thing are and aren't done in making optics, and there are good reasons for not making aluminium mirrors for amateur telescopes. I've seen this suggestion again and again but the aluminium is too soft and responsive to heat/temperature changes, plus I don't think you can get it smooth enough (I may be wrong, I'm working from memory, but aluminium was such a good product you would have to ask why aren't there more around - but you don't see them there must be some really good reaosns why there aren't!).

Again, I would highly recommend you join the ATM list at the link I gave above and the people there will be able to answer your questions.

[rmcpb (Rob)]

Cristian,

That is a great site on making the grinding machine. Love the manual in cartoons

Cheers

[cristian abarca]

Yeah it's great isn't it. The simplicity of it and the great instructions on that site have made this machine very popular and they do work.

Cristian