Tool for roughing, full diameter or less?

[Stefanosky]

Nothing, unfortunately I can't make it work… Create only single lines in two or three points, For the rest it slips on how nothing had happened. I tried with more strength but nothing changes. At the moment I went back to the full diameter with the tiles.

[Giulio TiberinI]

There will be a particular trick that escapes us, (I know…Maybe as for example that it is not a ring but a disc, and therefore does not present the internal step determined by the forum (Although the image at the beginning of the article of Mel shows a flange of aqueduct that a disc has, having in practice as a hole the only diameter of the tube lengthening that uses like mnopola).

Mel Bartel in that article thus writes on ring iutenseils:
The joy of making a mirror (Mel Bartel)

Dwelling (Then you can do it wet which is even better for your health)
The "coarse abrasion" devastation is the first universally used approach for the creation of a telescope mirror, digging a spherical cap in the glass.
Mel Bartel recommends the method that provides for the use of "ring" tools as it takes time compared to the work that uses a tiled chalk tool.
Systems other than the use of a classic glass or chalk -tiled gesso tool for the excavation, have their specific inconveniences. The use of a diamond wheel in particular can be very dangerous due to the inhalation of silicon/glass powders transported by the air, which are known to create the disease “Silicosis”.
Moreover (With any different method from the classic one of mutual abrasion of two glass records, applied with historians, guaranteed and precise methods) There is the difficulty of creating a spherical curve in the surface of the glass disc which will be the mirror.
A corner grinder hanging on an oscillating pole like a pendulum, It is an approach made difficult by the great difficulty of anchoring the mirror and the fulcrum of the oscillating arm so that they do not move mutually compared to each other.
in the use of a glass tool, This can be glued for extreme clutch and cause large scratches, but it is an equally important fact that it can be preserved and used later, as a raw mirror for another project.

Ring tools:

A metal ring of half the diameter of the mirror abrads the surface when it is rubbed with its center above the center of the mirror, and with a slight overflow at each end.
The mirror diameter size tools are complex the best compromise between efficiency and abrasion speed of a curve.
(In the use technique)..Usually a dozen racing and forth are accomplished, So you move to one step in one direction. Repeat, repeating and repeating again.
This behavior excavates rapidly in the glass creating a curve.
With this principle Mel Bartel claims to have dug a 400f6 mirror in about 4 hour, with grain silicon carbide 80.
When the noise decreases, It recharges with another splash of parmesan 80 and not many drops of water, And then we start again.
The most common mistake is to use too much abrasive grit, and/or too little water (Of this about thirty drops , or even someone less, they are enough and avoid the transport of the abrasive outside the ca mpo of its use).
The abraded glass and the worn abrasive accumulate on the mirror as a mud to be removed. Better if you remove it with diving and washing the mirror inside a basin. (Be careful not to pour the mud in the house drain because it would clog the hydraulic system).

Extreme pressure must be applied on the ring tool.
A plaster tool with tiles, wear both tiles and glass, and starting from both the flat surfaces, The tiles are used by becoming convex, while the glass is wear out becoming concave.
The ring utensils reach the desired depth with a speed that is about double the tiled ceramic tools.
Ring tools for small mirrors must not exceed half the size of the mirror diameter; Otherwise the abrasion time increases. Don't be afraid, or forget to apply strong pressure on smaller ring tools, Because they grip to very hardly.
You have to stop just before having reached the desired arrow depth: Is’ Good thing, for example, stop by reaching about 5/6 of that deep since the center will then be further deepened in the first part of the subsequent end abrasion operation, When the good contact of the mirror will be reached within it against all that of the tool (…and the two concave curves and Consassa will be perfectly unified).
On larger mirrors, The ring tool can leave a circular crown not abraded around the mirror margin.

For these mirrors, When approaching the desired depth, You can change the races by lengthening them with a slightly greater debt. This will prevent the areas of the mirror other than the edge are not deep enough. (NDT: But this is unnecessarily dangerous, And it is better to get to the edge by means of the races 1/3 D center on center).

Mal Bartel says: I use an discarded pulley. Ring tools can be pipe flange, or any round metal object that it will touch with a ring on its perimeter.

Geometrically, Two surfaces when they rub each other create a concave sphere on one surface and a convex sphere on the other. This also applies to flat surfaces, which are to be understood as particular surfaces having infinite curvature radius. With abrasion any high point drops, and all the low points are not touched.
Another reason why a ring tool generates a concave sphere, It is because a circle that touches a two -dimensional curve acts in both already said ways, lowering the high points and avoiding the low points.

[Stefanosky]

The step has Giulio…it's as if it were a flange, The abrasive part is in relief so it should only touch that but it doesn't seem to do anything. Maybe I made a mistake but being for granite etc. it seemed to me the most suitable one. I will try to experiment with waste window later, Now I have left and I don't want to stop

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