Tooling apparatus and methodology for machining a blank having multiple spin centers

A tooling apparatus and method for machining a blank having a first surface portion with a first spin center and a second surface portion with a second spin center offset from the first spin center. The improved tooling apparatus includes a turning fixture connectable to a rotatable spindle in one of a first position and a second position. The first spin center of the blank aligns with the axis of rotation of the spindle when the turning fixture is in its first position and the second spin center of the blank aligns with the axis of rotation when the turning fixture is in its second position. In the preferred embodiment, the rotatable spindle includes a dowel cooperative with first and second bores formed in the turning fixture to position the turning fixture relative to the spindle. The first and second bores are separated a distance equal to the distance between the first spin center and the second spin center of the blank. The method for machining the blank includes the steps of connecting the blank to the turning fixture, coupling the turning fixture in its first position for rotation with the spindle, machining the first surface portion, relocating and connecting the turning fixture in its second position for rotation with the spindle, and machining the second surface portion of the blank.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates generally to a tooling apparatus for 
machining a blank and, more particularly, to a tooling apparatus for 
machining a blank having first and second machined surfaces with first and 
second spin centers, respectively, offset from one another a predetermined 
distance. 
2. Discussion 
Traditionally, a tooling apparatus used to machine blanks includes a 
rotatable spindle to which the blank is removably coupled for machining. A 
cutting tool is used to remove excess material from the blank in order to 
provide a finished product within the required tolerances. Often times, 
the blank is comprised of either a single surface or multiple surfaces 
having a single spin axis. In these instances, the blank may be machined 
in a single tooling set-up, that is, without moving the blank relative to 
the spindle. With increasing regularity, however, tooled or machined 
blanks include multiple components or surfaces having more than one spin 
axis. In these situations, the blank must be repositioned on the spindle 
or placed upon a different tooling apparatus between the machining of the 
separate components. 
One environment where machining is commonly used as a finishing step is in 
the manufacture of optics used to reflect or refract light. Optics are 
currently manufactured by, among other techniques, machining an optic 
material such as glass or machining a substrate that is then coated with a 
reflective material to create a mirror. Optics generally are manufactured 
for mounting to another body and therefore require a mounting apparatus or 
mounting surface integral with the body of the optic. As with other tooled 
blanks, an optic having multiple surfaces can be machined in a single 
tooling set-up when the optical axis, i.e., the axis about which the optic 
material is rotated to form the convex or concave optical surface, is at 
the same location as the spin center of the mounting apparatus. 
However, in many applications, the optical axis is offset from the spin 
center of the mounting apparatus thereby requiring separate tooling 
set-ups to machine the respective surfaces. Just as with other multiple 
surfaced blanks, these optics are commonly machined by connecting the 
optic material to a first turning fixture and spindle whereupon one of 
either the optic surface or the mounting apparatus is machined. The optic 
is then connected to a second tooling fixture and spindle for machining 
the remaining optic surface or mounting apparatus. While this method of 
machining the separate surfaces of a blank has been generally effective at 
producing optics within the required tolerances, moving the optic between 
machining steps increases the potential for error. 
The position and orientation of the optical axis relative to the mounting 
surface of an optic is important to the effective operation of the optic. 
In many applications it is required that the mounting surface be 
perpendicular to the optical axis. However, the required tolerances 
related to this perpendicularity is often not achieved when the blank is 
moved between machining steps. Accordingly, a continuing need exists to 
provide a tooling apparatus and method for making machined products with 
multiple spin axes within required tolerances and, particularly, for 
machining optics wherein the potential for losing the perpendicularity of 
the optical axis relative to the mounting interface is minimized. 
SUMMARY OF THE INVENTION 
The present invention provides a tooling apparatus for machining a blank 
having first and second surface portions with first and second spin 
centers, respectively, offset from one another a predetermined distance. 
The apparatus includes a turning fixture to which the blank is connected 
for rotation and a spindle having a rotational axis. The tooling apparatus 
further includes locating means for selectively positioning the turning 
fixture in one of a first position and second position relative to the 
spindle and connecting means for securing the turning fixture for rotation 
with the spindle. The tooling apparatus provides that when the turning 
fixture is in its first position the first spin center of the blank aligns 
with the rotational axis of the spindle whereas when the turning fixture 
is in its second position the second spin center of the blank aligns with 
the rotational axis of the spindle. 
The method disclosed and claimed herein for making the blank includes the 
steps of connecting the blank for rotation with the turning fixture and 
connecting the turning fixture in its first position relative to the 
spindle for rotation therewith. The first blank surface is then machined 
and the turning fixture is repositioned into its second position relative 
to the spindle. Finally, the turning fixture is coupled for rotation with 
the spindle, the spindle is rotated, and the second surface of the blank 
is machined.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The following description of the preferred embodiments of the present 
invention is merely exemplary in nature and is not intended to limit the 
scope of the claimed invention. Moreover, the following description, while 
depicting the invention in an environment specifically relating to the 
machining of a substrate for a mirror, is intended to adequately teach one 
skilled in the art to make and use the tooling apparatus and method 
described herein to produce a variety of machined products. Specifically, 
those skilled in the art will appreciate that the tooling apparatus 10 
described and claimed herein is applicable to many machining tasks wherein 
the workpiece requires multiple tooling setups. 
As illustrated in FIG. 1 of the drawings, a tooling apparatus 10 is 
generally shown to include a turning fixture 12 connectable for rotation 
with a rotatable spindle 14. A workpiece, shown as a blank 16, having 
multiple surfaces with offset spin centers is in turn connected for 
rotation with fixture 12 and spindle 14. Specifically, in the preferred 
embodiment, blank 16 is shown to include a first portion 18 having an 
optical surface 20 with an optical axis 22 and a second portion 24 
including a mounting structure such as a plurality of mounting pads 28 
each with a mounting surface 30. Mounting pads 28 are preferably 
circumferentially spaced about blank 16 and located a constant radial 
distance from a spin center 31. Spin center 31 is offset from optical axis 
22 by a predetermined distance. In the preferred embodiment, mounting pads 
28 are provided with mounting apertures 26 used to secure blank 16 to 
another body. Those skilled in the art will appreciate that while the 
present invention is described with respect to a blank having only two 
offset spin centers, the novel tooling apparatus can easily be modified to 
allow accurate machining of blanks having components with more than two 
offset spin centers. 
The present invention provides for the machining of the various surfaces of 
blank 16 without removing and relocating blank 16 relative to turning 
fixture 12. Specifically, spindle 14 includes an axis of rotation 34 
relative to which turning fixture 12 is positionable in either a first 
position (FIGS. 2 and 3) wherein optical axis 22 aligns with an axis of 
rotation 34 of spindle 14 or a second position (FIGS. 1, 4, and 5) wherein 
mounting structure spin center 31 aligns with axis of rotation 34. As is 
further discussed in greater detail hereinafter, the present invention 
provides for the repositioning of blank 16 relative to spindle 14 through 
the movement of turning fixture 12. Accordingly, blank 16 remains fixed 
relative to turning fixture 12 throughout the machining process. 
Tooling apparatus 10 includes blank locating means for properly positioning 
blank 16 relative to turning fixture 12. In the preferred embodiment, the 
blank locating means includes first and second guide pins 38 and 40, 
respectively, cooperative blind holes 42 and 44, respectively, formed in 
turning fixture 12, and apertures 46 and 48, respectively, defined in 
second portion 24 of blank 16. Blind holes 42 and 44 are positioned in 
turning fixture 12 so that optical axis 22 and mounting surface spin 
center 31 of blank 16 align with a first and a second dowel bore 50 and 
52, respectively, formed in turning fixture 12. 
Once properly positioned, blank 16 is secured to turning fixture 12 for 
rotation therewith by coupling means known in the art. In order to 
minimize the stresses created in blank 16 and/or turning fixture 12, it is 
preferred that an epoxy or equivalent adhesive be used to couple blank 16 
to turning fixture 12. 
As previously discussed, turning fixture 12 may be selectively positioned 
relative to, and coupled for rotation with, spindle 14. Accordingly, 
tooling apparatus 10 further includes fixture locating means for 
selectively positioning turning fixture 12 in its first or second position 
relative to spindle 14 and fixture connecting means for securing turning 
fixture 12 for rotation with spindle 14. In the preferred embodiment of 
the present invention, a chuck 54 operates as a component of both the 
fixture locating and connecting means. Specifically, chuck 54 is removably 
secured to spindle 14 via a plurality of cap screws 56 that cooperate with 
a plurality of countersunk bores 60 formed in chuck 54 and threadably 
engage a plurality of threaded bores 62 formed in spindle 14. 
The preferred fixture locating means shown in the drawings include a dowel 
64 formed on an upper surface 66 of chuck 54. Dowel 64 extends along axis 
of rotation 34 when chuck 54 is secured to spindle 14. As will be 
discussed in greater detail hereinafter, dowel 64 is disposable within the 
first and second dowel bores 50 and 52, respectively, formed in turning 
fixture 12. As best seen in FIGS. 3 and 5, respectively, first bore 50 has 
a longitudinal axis 68 aligned with optical axis 22 of blank 16 and second 
bore 52 has a longitudinal axis 70 aligned with mounting surface spin 
center 31. As a result, the fixture locating means, including dowel 64 and 
bores 50 and 52, allows turning fixture 12 and, accordingly, blank 16 to 
be selectively positioned relative spindle 14 in either a first position 
(FIGS. 2 and 3), wherein optical axis 22 of blank 16 aligns with 
rotational axis 34 of spindle 14, or a second position (FIGS. 1, 4, and 
5), wherein mounting surface spin center 31 aligns with rotational axis 34 
of spindle 14. By this arrangement, optical surface 20 and mounting 
surfaces 30 of blank 16 may each be machined by sequentially positioning 
turning fixture 12 in its first and second positions relative to spindle 
14 rather than removing and repositioning blank 16 relative to turning 
fixture 12. 
Again referring to FIG. 1 of the drawings, turning fixture 12 also includes 
a plurality of countersunk bores sized to cooperate with cap screws 74 and 
threaded bores 76 in chuck 54 to form the fixture connecting means. 
Specifically, in the preferred embodiment, turning fixture 12 includes 
five countersunk bores including a first bore 78 that cooperates with a 
pair of second bores 80 to form a first set of countersunk bores usable to 
secure turning fixture 12 in its first position relative to spindle 14 
(FIG. 2). Similarly, first bore 78 cooperates with a pair of third bores 
81 to form a second set of countersunk bores for securing turning fixture 
12 in its second position relative to spindle 14 (FIG. 4). 
As best seen in FIGS. 1, 2, and 4, the plurality of threaded bores 76 
formed on chuck 54 are arranged to form three sets of linear threaded bore 
segments 82, 84, and 86, respectively, each separated by a constant 
angular space. The individual threaded bores 76 are radially spaced along 
their respective radial segment to provide an array of threaded bores 
through which turning fixture 12 may be secured to chuck 54 and spindle 
14. Cap screws 74 cooperate with countersunk bores 78, 80, and 81 and 
selected threaded bores 76 to secure turning fixture 12 to chuck 54 for 
rotation with spindle 14. 
While the cap screw and bore arrangements illustrated and discussed herein 
provide the preferred structure for securing the turning fixture for 
rotation with the spindle, those skilled in the art will appreciate that 
other equivalent connecting means may be used without departing from the 
scope of the claimed invention. 
It should also be appreciated by those skilled in the art that once blank 
16 has been connected to turning fixture 12, the multiple surfaces of 
blank 16, i.e., optical surface 20 and mounting surface 30, can each be 
sequentially machined by moving turning fixture 12 relative to spindle 14 
rather than blank 16 relative to turning fixture 12. Further, while it is 
contemplated that the spindle 14 and chuck 54 described herein may be used 
to machine blanks of various geometries, turning fixture 12 is preferably 
specifically manufactured for each type of blank 16. 
FIGS. 2 and 3 illustrate the tooling apparatus 10 wherein the turning 
fixture 12 is in its first position relative to spindle 14 for machining 
optical surface 20 of blank 16. As best seen in FIG. 3, and as previously 
described, dowel 64 and first bore 50 cooperate to locate turning fixture 
12 in its first position relative to spindle 14. In this position, optical 
axis 22 of optical surface 20 aligns with rotational axis 34 of spindle 
14. Threaded cap screws 74 cooperate with threaded bores 76 and the first 
set of countersunk bores 78 and 80 formed on turning fixture 12 to secure 
turning fixture 12 for rotation with spindle 14. 
As shown in FIG. 3, a cutting tool 90 is positioned relative to tooling 
apparatus 10 in order to remove the desired material from blank 16. It 
will be appreciated that when tooling apparatus 10 is used to machine 
substrates for mirrors, blank 16 typically has been finish machined to 
require the removal of only a thin layer of material. For example, in one 
operation contemplated by the Applicants, the substrate layer removed 
through the use of the tooling apparatus disclosed and claimed herein is 
approximately 0.004 inches in depth. 
It is preferred that while spindle 14, chuck 54, turning fixture 12, and 
blank 16 rotate about rotational axis 34, cutting tool 90 is moveable only 
in the x and/or y and z direction. The preferred geometry and composition 
of the cutting tool depends upon the specific application of the novel 
tooling apparatus and, particularly, to the material and finish quality of 
the workpiece or blank 16 being machined. In the preferred embodiment, and 
as shown in FIGS. 3 and 5, cutting tooling 90 includes a body portion 92 
and a diamond cutting tip 94. 
After the desired layer has been removed from optical surface 20, turning 
fixture 12 is repositioned into its second position relative to spindle 14 
to allow machining of the mounting surfaces 30. Accordingly, each of the 
three cap screws 74 are removed from engagement with threaded bores 76 and 
the first set of countersunk bores 78 and 80, and turning fixture 12 is 
repositioned relative to chuck 54 and spindle 14 such that dowel 64 is 
disposed within second turning fixture bore 52. In this position, as 
illustrated in FIGS. 4 and 5, mounting surface spin center 31 aligns with 
rotational axis 34 of spindle 14. The second set of countersunk bores 78 
and 81 formed in turning fixture 12 cooperate with cap screws 74 to 
removably connect turning fixture 12 to chuck 54. 
As further illustrated in FIGS. 1, 4, and 5, a counterbalance 96 is shown 
connected for rotation with chuck 54 when turning fixture 12 is in its 
second position. As will be appreciated by those skilled in art, 
counterbalance 96 is included in tooling apparatus 10 when, absent 
counterbalance 96, the rotational mass of tooling apparatus 10 would be 
undesirably offset from rotational axis 34. Counterbalance 96 includes a 
plurality of countersunk bores 98 cooperative with cap screws 100 to 
connect counterbalance 96 to threaded bores 76 of chuck 54 for rotation 
therewith. It should be appreciated that a counterbalance can be included 
in tooling apparatus 10 for all or none of the specific tooling set-ups 
without departing from the scope of the claimed invention. 
Again, the machining of blank 16 is performed by rotating spindle 14 about 
rotational axis 34 and reciprocating cutting tool 90 in the x and/or y and 
z directions as needed to remove the desired material from mounting 
surfaces 30. 
In addition to the novel tooling apparatus disclosed and claimed herein, a 
corresponding method for machining a blank having a first surface with a 
first spin center and a second surface with a second spin center offset 
from the first spin center is disclosed and claimed. Specifically, 
performance of the novel method includes connecting blank 16 for rotation 
with turning fixture 12. As previously described, the preferred means for 
locating blank 16 on turning fixture 12 includes guide pins 38 and 40, 
cooperatively sized apertures 46 and 48, and blind holes 42 and 44. Once 
properly positioned, blank 16 is connected for rotation with turning 
fixture 12 preferably by an adhesive such as an epoxy. 
Turning fixture 12 is then connected for rotation with spindle 14 so that 
the first spin center of blank 16, i.e., optical axis 22, aligns with 
rotational axis 34. In the preferred embodiment, chuck 54 is coupled to 
spindle 14 in order to locate turning fixture 12 relative to spindle 14 
and secure turning fixture 12 thereto. Specifically, cap screws 56 
cooperate with countersunk bores 60 formed in chuck 54 and threaded bores 
62 in spindle 14 to connect chuck 54 for rotation with spindle 14. Turning 
fixture 12 is then placed in its first position relative to spindle 14 by 
disposing dowel 64 on chuck 54 within first bore 50 of turning fixture 12. 
A plurality of cap screws 74 cooperate with countersunk bores 78 and 80 
and threaded bores 76 to secure turning fixture 12 to chuck 54 and spindle 
14 for rotation therewith thereby ensuring that the first spin center of 
first surface 20 remains in alignment with axis of rotation 34. Spindle 14 
is then rotated about axis 34 and cutting tool 90 is used to remove the 
desired material from first surface 20. 
In order to machine mounting surfaces 30 of blank 16, turning fixture 12 is 
repositioned relative to spindle 14 and chuck 54 such that second spin 
center 31 aligns with rotational axis 34. The proper position is ensured 
by placing dowel 64 within second bore 52 of turning fixture 12. Cap 
screws 74 again secure turning fixture 12 to chuck 54 for rotation 
therewith. The spindle is rotated about rotational axis 34 and cutting 
tool 90 is reciprocated so as to remove the desired material from mounting 
surfaces 30. It should be appreciated that the additional step of securing 
a counterbalance 96 to chuck 54, as previously described, for rotation 
therewith may be performed as needed. 
Various other advantages of the present invention will become apparent to 
those skilled in the art after having the benefit of studying the 
foregoing text and drawings, taken in conjunction with the following 
claims.