Buy mirror tool or make one?

[earth titan]

Just about to order my 8" mirror blanks from Galvoptics. Decided to make an 8" f7 scope.

Any advice on using a tile tool v buying the tool with the kit? By the time I've purchased the dental plaster, tiles etc. to make the tool, I can't see there is much cost difference.

Any difference in performance? Bearing in mind I am a mirror virgin, which would pepople suggest? I'm veering toward buying the kit with the tool, but will be guided by those with more experience.

[ponytale]

have you read Glasspusher's( Making a 12" mirror) on this forum in DIY section excellent tutorial, and John will always help should you need it

[BinocularSky]

I've only used tile tools twice: once was when I was teaching my lad to grind a mirror with a 4" disc of glass I had; it was the simplest way to go, but the tile thickness would have been inadequate for (say) a 6" f/5. The other time was after I had already hogged out a 12" with a sub-diameter tool (actually a dumbell weight). Casting a tile tool was the only way to go.

I don't think a tile tool is worth it for hogging out (unless it's your only easily-available option), but it certainly makes a difference for fine grinding. For your first miror, your 8" f/7. I'd advise keeping everything as simple as possible, and that means a glass tool.

Oh, and if you do decide to cast a tool, the dental plaster you need is a grade called "Kaffir-D".

[FraserClarke]

Make a tile tool. By all accounts they cut faster than glass tools (because the grit gets extra working edges in the channels).

I think you could probably make one for £10.

You can use dental plaster (dental *stone* preferably) which can be a bit pricey, or just normal plaster of paris which is cheaper (then you will need to seal it with varnish/epoxy). I believe John (Glasspusher) likes to use cement for his tools, which probably has the best of both worlds.

Get good porcelain or similar tiles from a tile stockists -- you want the type that are the same all the way through, not the kind with the glaze on top and fluffy crud below (I'm sure there is a technical name for the difference, but I can never remember it!!). If you go and find a broken floor tile or something, they'll usually just give you it for free.

I recently made a tool with two-pence pieces as the surface (mirror already hogged out, so tool already had a good curvature). That worked very well and was super cheap (36p for the whole surface I think! ), though the epoxy I used failed after a few months, so I couldn't reuse the tool to fix a problem in polishing (just spent more time polishing and got rid of it).

[earth titan]

I like the idea of keeping it as simple as possible. So much else to worry about, think about etc.

I presume of I made a tile tool, for initial grinding, then I would use the face of the mirror blank as the underside of the mould? Or is flatish, flat enough....

Taking the plunge next month and ordering the kit. Waiting for the books to go through the accountant before I can spend too much money - sigh...... Self employed woes....

[FraserClarke]

I presume of I made a tile tool, for initial grinding, then I would use the face of the mirror blank as the underside of the mould? Or is flatish, flat enough....

Yep, that's right. There are lots of guides on the internet on how to do this (there is a thread on here "making a 12-inch mirror" or such which shows a good technique).