A question for mirror makers

[cassiewoofer]

OK mirror makers, I have acquired a near full thickness (1.5 inch) 12 inch mirror with a 30ft focal length! I plan to hog this out with a lump of stainless I have, but what's the best way to make a tool when I get near the right sagittal?..... I have only used glass tools before and the 10 inch glass tool I used for the previous 12 inch mirror is now too thin.... (I think!)

 

Keith

[Glasspusher]

Here is link to my tile tool notes...

 

http://www.nicholoptical.co.uk/pdf/Making%20a%20Cement%20and%20Tile%20Tool.pdf

The notes cover a cement and tile tool but dental stone tools are a good alternative, in fact I tend to use them all the time. Google " plaster grinding tools" for more info.

Good luck with your project.

John

[Astrobits]

Cast it onto the mirror with plaster or cement. Seal with paint/varnish and stick glass squares on with epoxy or hard pitch.

Nigel

[Astrobits]

And make some extra ones of different sizes for the figuring while you're at it.

Nigel

[Ajohn]

Try this. It's very similar to what some one called Gordon Waits shows on youtube.  I might have the name slightly wrong. He uses a former to make sub diameter tools. Best look at the video.

Forgot to add. I have another some where that suggests that the best source of tiles is Homebase. Pass when I last did it I used tiles that were left over from some I had laid. Floor tiles so had to be cut into small squares. I feel it would be better to use ones of the correct sort of size.

 

tiletool.pdf

[mapstar]

23 hours ago, Glasspusher said:

Here is link to my tile tool notes...

 

http://www.nicholoptical.co.uk/pdf/Making%20a%20Cement%20and%20Tile%20Tool.pdf

The notes cover a cement and tile tool but dental stone tools are a good alternative, in fact I tend to use them all the time. Google " plaster grinding tools" for more info.

Good luck with your project.

John

I'll second the comments John made above and dental stone tools are probably the best way to go nowadays, although I've never used one when I retrace my steps and take up the challenge again I shall be using that method with glass mosaic tiles cast into It. 

[Ajohn]

That video I mentioned is this one. Slightly different to the methods used in the pdf I posted but similar and shows what may be needed to create grooves in it if the pdf method doesn't work out. Also how to make one suitable for rough grinding. In the UK it's dental stone rather than dental plaster. Some people have used rather large steel nuts rather than tiles for hogging out - pass but seems to work.

 

He's good source of information, might help avoiding using too much polishing compound and problems like that. Also plenty of examples of how to use a fixed post machine. I prefer to press onion sacking into a lap rather than use the wire brush. Each to their own etc.

I've also come across uk people using Hydrastone but believe this is a bit nearer ordinary plaster than the dental stone.

John

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[cassiewoofer]

That's great thanks all for the replies.... Just waiting for the Garage to get warm enough to get started.... OH and get through the silica layer on the old mirror with some sort of acid!... the conc Sulphuric I tried at the weekend didn't touch it! However the duck tape got the aluminium off but only near the centre. I think that was because the Al layer was thicker there.

 Roll on spring!

 

 

[hughgilhespie]

Hi,

Use a strong ALKALI (caustic soda) solution to strip off the old aluminium coating. Aluminium can be very resistant to acids due to it's surface oxide film but dissolves easily in strong alkalies. Caustic soda is readily available from hardware shops - follow the instructions regarding safe handling as it really does burn - ask me how I know........

A small aside, DON'T DO THIS AT HOME but many years ago when the world was a simpler place, I learnt that if you half filled a glass milk bottle with caustic solution, popped in a few milk bottle tops and then stretched a balloon over the mouth you could make your own hydrogen balloons that floated away nicely. Then, if you were feeling particularly wicked you could also attach a length of jetex fuse, light it, release balloon and - well, it was my first hydrogen bomb.... Small safety note - this is a very efficient way of making a powerful caustic soda spray that will get your eyes as well as everywhere else.

[cassiewoofer]

thanks, I eventually used some 4M sodium Hydroxide...(caustic soda!)... was pretty quick... think I'll use 2M next time. Will now do a Foulcault to see if the surface figure has changed but I somewhat doubt it.