Past 1 / 3D c.o.c, alias the forward-backward centered race (or, all’americana: “center over center”), processing for abrasion, amplitude equal to one third of the mirror diameter, in which scratching of the glass is used to make a mirror (for example parabolic) is, with patience, UNIVERSAL WINNING WEAPON.
Like the:
- The new life acquired in videogame, that allows you to survive a "game over";
- The amnesty & pardon of the glass scratcher.
- The cure of a serious illness as well, but brief and not very painful.
- A good cold beer when thirsty
- The satisfaction of other requirements at the most scurrilous but entirely human.:yahoo:
…and more.
WHY 'TO USE:
By doing something, you are wrong, and who is wrong (at least in the glass scratching) It can recover and start over, after applying a "tot" of past 1 / 3D c.o.c. to go back to regain the rank previous the mistake.
WHEN AND 'USED:
In ANY time of processing; in so far as it and will, or returns towards BALL SURFACE THAT close to perfection, which is the only Ante-Chamber to the success of subsequent parabolization of a mirror.
This means that this type of strokes are applicable regardless of the abrasive grain currently in use:
1) In the course of aging of the surface or the following polishing: The is used to obtain a optimal spherical surface , while controlling, and maintaining the depth of the ARROW desired to obtain for the focal, knowing that:
- By placing a mirror on the bench and maneuvering the tool, it abrades more the edge;
- While conversely, positioning the tool on the bench and maneuvering the mirror, they abrade / deepens the longer the center.
- And so for logical, alternating the two position, the arrow remains unchanged for the entire polishing processing
2) During the parabolization: When one tries to correct the error constituted by the overcoming of the desired parabolic curve (This is because the glass it can only be removed by abrasion ... and when it is removed too much ... must go back recreating the new ball start).
LATERALLY HOW YOU CAN INADVERTENTLY MOVE?
An important caveat to keep in mind in the processing, is to contain the LATERAL overflow as much as possible at a value near 1/6, or 1/8 D ; which means do not protrude more than 1/12 or vice versa 1/16 each side, Since a higher value would result in a too early flaring the sphere ball in a more opened figure, which is first the ellipse or the parabola ...(and come to the dish before you finish to polish the mirror is a terrible setback !).
But the figure could also intrude (... Is in that case it would become for us a "game over") in hyperbole, that is not correctable. Or better, cannot be amenable to the parabola, If not returning towards the previous sphere, applyng 1/3D c.o. c strokes.
NUMBER OF MOVEMENTS NEXT BACK:
Also the number of the few forward movements back which the operator carries out before moving to the side and simultaneously rotate in the opposite direction mirror or tool which is located in the hand, It is arbitrary and not ironclad.
In the sense that in my case I rotate continuously at every single stroke, both one step left, and turning a little bit to right the object I'm holding in hand. Just because I found it easier and mechanic that doesn't count the go and FRO, with the advantages (in my opinion) of a more uniform machined surface ......(Basically because I probably now possess only one active neuron… always very busy ... and then I lose track easily!) 
What AFFECTS the LENGTH of 1/3D STROKES:
The length of the passes by 1/3D is suitable for the production of SHORT-focal ratio mirrors., or F3 to F5.
Instead, for the realization of mirrors with longer focal ratio (ie ARROW less deep), It MAY be elongated to a value of about 2 / 3D.
But this extension is not essential, and only serves to make it clear about what AFFECTS the length of the strokes c.o. c. as for those long focal lenses, having made 1/3D c.o. c strokes, naturally it obviates being parabolization, with a little longer job, and nothing more.
RIGIDITY 'IN THE APPLICATION:
In every part of the manual processing of the mirrors, There aren't strict rules, but it must be known that the LONGITUDINAL length of strokes, starting with those 1 / 3D c.o.c, It is directly proportional to the reduction in the depth of the arrow F of the sphere, that is mirrored center, which means that with over 1/3D c.o. c strokes . the mirror in the realization will have a longer focal length of the desired.
While one accentuated lateral movement changes the shape of the spherical surface in the most deformed.
MA…They CREATE IN MECHANICAL LIMIT FOR KEEPING CONSTANT THE MOVEMENTS OF THE MACHINES…Why not implement them also in the glass scratching?:
Because this is an error to be avoided absolutely in manual processing.
Because the mirrors are made of thousands of strokes back and forth each removing very little, We must leave the task to the law STATISTICS, or "large numbers", by itself erase the small mistakes made in one way or another, in many thousands of races.
Then: For once, in defiance of the "mechanical common thought" but in favor of the statistical, We must work freely, respecting the few rules, and leaving a DISORDER ORDERED from our having learned these rules the way you work, and their mutual interaction, the task of elimination to remove the small errors that instead, establishing rigid mechanical control mechanisms, It would add up becoming catastrophic mistakes zonal.