Fixed post mirror grinder advice

[Velikovsky]

Hi John

I used a glass tool - the one you can see which forms the base of the lap. The mirror is is a 10 inch and is almost exactly f4.5.

OK, so if I make a tile tool do you have some tool data that works? What size tile squares, what gap between them, what kind of tile, what surface, , glaze up or down, what adhesive?

I kinda started a tile tool early in grinding when a big chip came off the side of the tool, but chickened out. I was using 3/4 inch squares of some stoneware tiles I had (the terracotta colored stuff). They have a surface texture which is quite coarse. I made the base out of some leveling compound but there seemed too many possible errors & unknowns so I went back to the glass tool.

Advise plz?

Steve

[Glasspusher]

Hi Steve,

Tiles can be 25mm to 45mm square...not critical.

Gap between then 6-10mm...not critical.

Tile type...standard ceramic wall or floor tiles.

Glazed surface uppermost...this will soon grind off...no problem.

Adhesive....fibreglass resin as used in car body repairs, do not forget to add the hardener.

You will find my description of making a tiles tool here...http://stargazerslounge.com/diy-astronomer/113596-making-12-inch-mirror.html

Here is a pdf on tile tool making....http://www.nicholoptical.co.uk/pdf/Making%20a%20Cement%20and%20Tile%20Tool.pdf

Hope this helps.

John

[achour]

I am looking for plans in  order to build my own fixed post for grinding machine

[fwm891]

I used an oil drum for quite a few mirrors with a varnished plywood top with cleats to hold the mirror/tool that I could rotate manually. I didn't have the space to 'walk round' a stand so rotated the top instead. Drill a few holes in the top to take slurry.

Francis

[Chriske]

Me and my pal Marc have a M-o-M each. It can handle mirrors up to 20".

One is now loaded with a 20" mirror.  It'll be a f/4.5.
To feed the carbo we work with peristaltic pumps. Fully automated. When the container runs out of slurry the M-o-M stops. Containers completely filled with carbo the M-o-M will run for about 1.5 hours.
The peristaltic pump/ units(partly printed) are interchangeable, so no need to clean these units at all. For every grade of carbo it takes us under a minute to install the nexy peristaltic unit.
The only carbo we still do manually is while hogging out (#120). It takes me 2 hours or so to clean up a  20" mirror. That 'cleaning up' has all to do with this ugly looking machine...
For smaller mirrors I use this one.

[Gina]

Very impressive Chris   I had ideas a few years ago for building a M-o-M - even joined a group but never got round to it - decided it was just too much trouble and cost, and I didn't have the facilities.

[Chriske]

We did join that group too Gina, but decided to go our own way.
I completely redesigned the inner structure (drive system.)
The original MoM did run on bronze bushings. Well I replaced that all with large ball bearings + very sturdy holders for them. That's one of the changes I made. If I would have had my 3Dprinters back then, I would have printed these holders. Now they’re made of 15 mm thick aluminium. Way to thick, but that's what I had at hand at the time.

[Gina]

That sounds very sensible.  I wonder if plain bearings were used to avoid any problem from grit in ball bearings causing errors.  OTOH I think you can keep grit out of the bearings even with a lot around.

I might add that i'm in awe of those who grind their own mirrors and then go on to make the rest of the telescope.  Particularly a huge 20" one.