Full size 20" tile tool has been poured

[JRM]

After  aquiring a 20" pyrex 2" thick pre generated blank in June, It is now time to

get this show on the purposely slow grinding road so to speak.

 I have just poured a full size 1-1/2" thick hydro stone tile tool with 1" tiles, I have yet to get my

barrel setup for grinding but should have it all set by months end.

 My goal for now is to grind down to the 12 or 9 micron size before taking a brake for the

winter season, so by Oct 1st I should be rinding with the 120 grit size to set in the tile tool.

will keep you posted.

Rick

Oh btw... My wife said I should have been taking pics, will post a pic of tile tool when I get the chance.

[JRM]

Here is the tile tool on top of mirror after dam has been removed

and also the tile tool after removed from the top of the glass,

the black spots are pieces of the plastic used between the two. will clean up channels tomorrow. and yes they are 1" tiles but

they sure look small in the pic.

[faulksy]

nice one mate, keep us posted and good luck

[Rustysplit]

Fantastic!! I shall be following this with keen interest. As many pics as possible would be cool.

After grinding my 14" mirror, I am starting to get twitchy and eyeing up a larger project......

[crashtestdummy]

Nice job fella!

You going to risk a full size pitch lap?

[JRM]

Thanks Guys,

     Alan I will take photos during this project for sure and keep you all updated.

Crashtest (Rich) I believe, forgive me if I am wrong, yes full size for now, I want to get the tile

set in, and the glass to a sphere, it has been ground down to 120 grit already,before I purchased,

so I want to confirm sphere is in full contact before moving to 220, and sphere is much easier to

achieve with full size tile tool, the grinding is always better (imho) with full size tile tool just more

weight to handle. Will see how it goes once I start to grind, lots of hydro stone left if need to  

make a smaller one.

I will keep you posted.

Rick

[crashtestdummy]

Yes it's rich.have just done a mirror making course and I'm after doing a 22" 3.6 and was told a full size pitch was a real pain to make hence why I asked

[JRM]

Rich,

    The full size tile tool was rather easy to make, I used a full tile mat then strips of another one to fill in the

edges and glued them together in a few places with a glue gun.

A full size pitch lap would not be much more of a pain to make then say one three quarter size but the full size

pitch lap might be a real pain to polish with, I will try the full size pitch lap when I start to polish but will switch to a smaller size if it is to hard to push.

22" F 3.6  -  a very ambitious to say the least, I am nowhere in that league, I figure the 20" F4.5 to be a major challange.

I did a focus test of the glass both by sun and flashlight and came out with a focal length of F 5.4 which is good because I was wanting

the 20" to be no faster then a F-5, will have to setup for a foucault test to confirm my measuring.

Rick

[crashtestdummy]

Yeah I have a 12" part ground blank and an 8" to start with and I have technical help if I get stuck so I'm not too worried but I understand it will be a massive challenge

[Gina]

WOW!!  Now that is one enormous project - I salute you :icon_salut:   Good luck

[Glasspusher]

Making and using a 20 inch pitch lap is no easy task. I would recommend a 75% D pitch lap for the following reasons...

It is easier to make than a 20 inch

It needs less pitch than a 20 inch

It is easier to maintain good contact with the mirror

It is easier to move a 16 inch pitch lap across the mirror than a 20 inch lap

It is easier to make/find a suitable substrate for a 16 inch mirror

There are no real disadvantages in using a sub diameter lap, all you need to do is to work off centre  to compensate for the smaller diameter.

Hope this helps.

John

[JRM]

I totally agree John,

    more likely then not by the time I get around to polishing, it will be with a sub diameter lap or two,lots

of hydro stone left to make more when the time comes.

Thinking I will epoxy a piece of plywood to the bottom of the tile tool, make it thicker, should have used more

hydro stone, but oh well live and learn, 1-1/2 inches is probably thick enough but an extra half inch or more of ply would not hurt.

Rick M