Before starting any mirror processing phase, it is essential to make sure that the edges of both mirror that tool are blunted.
This precaution is essential to minimize, during processing, the risk that by the sharp edge of one of the two discs coming off a flake that can slip between the two surfaces during a past and produce undesirable effects on the surfaces. This will obviously be more serious the finer the grain that we are using, since in order to remedy any scratches will obviously work the surface with grit sufficient to eliminate, forcing us to go back to bigger trouble if the grain “in progress” It was noted insufficient for this purpose.
A particular operation importance of chamfering of the edges is obtained if the mirror and the tool have the same diameter, since the edges of the two discs will be constantly in contact during the whole processing.
It may be that, the purchase of the two discs, we see that the craftsman who has cut them has provided also to carry out a good chamfering of the edges. Surely, identified the glassmaker that will produce there the two discs, it is useful to request that this operation is carried out. In this case the two edges of the mirror and the tool of the two machining surfaces will be ready to work.
Only after several hours of processing we will see initially consumed the tool edge, why, as you might guess, being the surface thereof destined to become convex, the part that most of it will be consumed immediately it is precisely the edge.
The mirror, instead, early roughing will almost consumed mainly in the center and probably the bevel “factory” It lasts a long time and only in the final stages of grinding will be affected (below the picture of the edge of a mirror in the grinding step with grit 400; the initial bevel was 2,5 mm approximately and a good part of this is still present on the edge).
Of course, during machining we should not hesitate in correcting the mirror chamfering also, as well as tool,, at the moment when we should note that the original is dangerously reducing stà.
BUT HOW CAN WE MAKE THE ROUNDING OF OPERATION ?
First of all there is to say that the operation is the same, both for smooth two glass discs at the beginning of new work, that during the processing in the case of excessive reduction of the bevel.
All that said, , you must obtain an abrasive dough, readily available at any hardware store, which will be enough to ask a whetstone for sharpening knives.
Before proceeding, it is necessary to humidify with plain water is the whetstone that the glass disc, to maintain the low temperature of the surface subjected to abrasion.
We are ready: at this point it is necessary to firmly grasp the glass disk with one hand and with the other the dough abrasive, which will be rubbed vigorously on the edge, longitudinally at the same and holding the abrasive surface at 45 ° with respect to the glass disc flat surface: it is important to avoid the temptation to operate orthogonally, in order to avoid sticking with an angle too “decided” the glass and to facilitate the detachment of flakes.
CHAMFERING AS ?
Is’ certainly you should always be avoided to stay with less than 1 mm bevelled edge, better anyway keep 1,5mm as minimum limit: it is therefore appropriate, especially during the roughing phase with large grits, often control the size but also the state of the edge, preferably with the help of a laptop or a microscope eyepiece, in order to identify the possible scales that could become detached and subsequently terminate prior remedy.