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Aluminium flashing


dark star

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On the Cloudy Nights website people have mentioned using aluminium flashing for the circular form to pour the cement or dental plaster in to, to make a tool for grinding a mirror. Or a base for a pitch lap.

Does anyone know what aluminium flashing is called in the UK? It is thin enough to bend easily but thick enough to stand up without flopping around. I have found something called Alcan alumiumn flashing on- line from a roofing merchant. But I am not at all sure that it will be the right thickness, and it is sold in 8 meter rolls. It looks like it might be too floppy.

I pour the dental plaster on to the  mirror, which is borosilicate (like pyrex). I have done this a few times and not had any problems. I protect the mirror with aluminium foil. The dental plaster eventually gets rather hot, but I take it off the mirror before it gets too hot, as it gets hard quickly.

I have used cardboard and also plastic sheet for this, but although they worked they were not ideal.

I need to make a 15 inch tool for fine grinding my 20 inch mirror. I picked up some scratches when using the pitch lap to figure the mirror.  So I am going back to fine grinding.

I poured the pitch lap on to the tool I used for grinding so I have to make a new one. In future I will make a new pitch lap base instead.

I spin grind and spin polish on a fixed post mirror making machine. I have had good success with this. But figuring the mirror is proving a challenge. I have made a 14 inch f/4.8 mirror without too many problems. But a 20 inch f/4.1 mirror is an order of magnitude more difficult! However, I am learning a lot about mirror making and different figuring strokes,

David

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I was wondering if Alcan would be a little bit too thin. There is also zinc flashing but that can be very thin as well. I work with sheet metal, so if you are stuck I could post a  piece over to you. I have 1.2mm thick aluminium (or thicker) which is quite robust but pliable or there is galvanised steel sheet starting at 0.7mm and thicker which is also rigid but pliable. 

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Aluminium flashing is very thin scraps of aluminium usually filed, machined, cast off a product. I would not use it for high temp application as it's usually very thin. Are you trying to make a temporary mould?

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Just a suggestion, see link.

Cut the handles off turn upside down make large hole in the bottom place on protected mirror & pour in plaster. 

Guess that's how you'd do it...

https://www.amazon.co.uk/YouGarden-Pack-Heavy-Duty-Handles/dp/B009W4XBW4/ref=mp_s_a_1_61?keywords=Large%2BPlastic%2BTubs&qid=1675373727&sr=8-61&th=1&psc=1

 

Peter

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I guess it is like a mold. It is just something to make the dental plaster or cement make a circular shape, and to stop it spreading all over the surface of the mirror.

The garden buckets are a good idea. But I need the grinding tool to be 15 inches in diameter. As a 2/3 sized tool works well for spin polishing. So they are a bit too big.

I guess some kind of plastic sheet would work fine. I have some but it is not quite thick enough to work really well. The circumfrence of the tool is around 50 inches, 1300 mm, so I need quite a big sheet or strip.

 

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  • 2 weeks later...

Flashing here is thin aluminum sheet that's used as a water barrier around chimneys, etc.  It usually comes in rolls since roofers can use a fair amount when doing a roof.

Maybe you could use a short piece of round furnace ductwork?  

Edited by jjohnson3803
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On 02/02/2023 at 17:36, dark star said:

On the Cloudy Nights website people have mentioned using aluminium flashing for the circular form to pour the cement or dental plaster in to, to make a tool for grinding a mirror. Or a base for a pitch lap.

Does anyone know what aluminium flashing is called in the UK? It is thin enough to bend easily but thick enough to stand up without flopping around. I have found something called Alcan alumiumn flashing on- line from a roofing merchant. But I am not at all sure that it will be the right thickness, and it is sold in 8 meter rolls. It looks like it might be too floppy.

David

David,

Alcan is a trade name for a particular brand of roofing flashing, sold as an alternative to the standard lead flashing. It would work for what you are trying to do - pour mirror tool - but you would be buying a fair bit to use a little. All you need is a flexible material that will wrap around your mirror - as you say carboard is often used, but you could also try an off-cut of floor vinyl if you have that to hand. It doesn't really need to have any significant material strength.  Another alternative, cheaper than aluminium flashing, would be a roll of damp proof course - stiff plastic sheet on a roll.  Wrap the damp proof round the mirror circumference a few times and secure in place with suitable tape or garden wire; a lot cheaper than Al flashing. 

Jim 

Alcan

Damp Proof Course Roll

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The work I've done using aluminum flashing makes me think it would work depending on its thickness.

.024 or .032 would be flexible enough to easily form to the shape of the mirror. It would not be much wider than double the mirror thickness.

I think once you had it around the mirror, several wraps with what we call duct tape would keep its circular shape.

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My understanding from the OP is that a free-standing wall is required so that a 15" tool can be made on a 20" mirror. Flexible material will take on a circular shape when filled with the plaster mixture so I would go with Jim's (saac) suggestion of damp proof course. Any non flexible material will have to be circular to start with.

When making my full size plaster tools for mirrors I have used material as thin and flexible as thick plastic bags ( e.g big dog food bags ). Once taped round the perimeter of the mirror they are remarkably strong. Fortunately, I was making a number of different sized mirrors so had small blanks available for making sub-diameter tools.

You don't need to use special or fast setting plaster, any stuff will do, even concrete can be pressed into service. Just cover the back and sides of the tool with PVC tape ( prevents any of those little holes trapping gritty bits ).

Nigel

 

 

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I suggest something a little more rigid, dams like that don't just fall into a circular shape they will take on all sorts of variances. 

Cutting the rim off a garden plant drip tray did the job for a small grinding tool. Held its shape well.

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