WO2008122003A2

WO2008122003A2 - Piston arrangement and method for producing same

Info

Publication number: WO2008122003A2
Application number: PCT/US2008/058996
Authority: WO
Inventors: Frank H. Walker
Original assignee: Walker Frank H
Priority date: 2007-04-02
Filing date: 2008-04-01
Publication date: 2008-10-09
Also published as: WO2008122003A3

Abstract

A piston arrangement and a method for producing a piston arrangement include manufacturing a pair of pistons, each having a head and a foot. The foot of each piston is configured to mesh with the foot of the other piston such that both of the pistons are producible from a single piston blank. The pistons define a piston bore having a generally circular cross section when the piston feet are meshed together, and when the pistons are separated, they define a respective partial piston bore. Each of the partial piston bores is configured to receive a load-bearing element having a generally circular cross section, and each is further configured to surround the load- bearing element for more than 180° of the load-bearing element cross section.

Description

PISTON ARRANGEMENT AND METHOD FOR PRODUCING SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is claims the benefit of U.S. provisional application Serial No. 60/921,279 filed 2 April 2007, which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piston arrangement, and a method for producing a piston arrangement.

2. Background Art

Torque producing devices such as engines and motors often rely on pistons as part of the torque producing system. Similarly, pistons can be used in reciprocating pumps that receive torque as an input, and provide an increase in fluid pressure as an output. In such applications, the pistons are usually part of a mechanical linkage such as a slider-crank mechanism found in many internal combustion engines. In other applications, the piston may more closely cooperate with a cam, whereby bar linkages are eliminated, and only a roller or cam follower is positioned between the piston and the cam. Whether it is a wrist pin in the case of a slider-crank, or a cam follower as described above, pistons are often configured to receive a load-bearing element that helps to transfer linear motion of the piston into rotational motion, and vice versa.

Depending on the application, a piston may be configured with a through-hole for receiving a wrist pin or other load-bearing element having a generally circular cross section. In some cases, it may be necessary to maintain a complete 360° to receive the pin; whereas, in other cases only a partial piston bore — i.e., a bore that surrounds only a portion of the pin — is required. Some of the factors that can be useful in determining how much of the piston bore is required to be in contact with a load-bearing element such as a pin include the amount of load being transferred between the piston and the pin, and whether the piston is apt to disengage from the pin during operation.

The use of pistons in various hydraulic machines is described in the following patent applications filed by the inventor of the present application: U.S. Patent Application Publication No. 2006/0055238, published on 16 March 2006; International Patent Application No. WO2006/066156, published on 22 June 2006; International Application Publication No. WO2006/122241, published on 16 November 2006; and International Application Serial No. PCT/US08/53747, filed on 12 February 2008, each of which is hereby incorporated hsrein by reference. In some of the hydraulic machines described in the above-referenced patent applications, a load-bearing element such as a rotating roller cooperates with a reciprocating piston as described above. In at least some cases, a bearing surface of less than 90° will be sufficient to transfer the load between the roller and the piston. Because the loading may be non-uniform, however, there may be cases where the roller could separate from the piston during operation. Indeed, in some higher speed disengagement situations, the roller will be intentionally lifted from the cam. In such applications, it is necessary that the piston bore surround the roller by more than 180" to ensure that the roller remains with the piston in all cases of engagement and disengagement.

Manufacturing a precision bore in a piston can be difficult, expressive, and wasteful. If the requirement for roller retention is more than 180°, for example, a 210° bearing segment, it may be necessary for machining purposes to add enough material to the end of a piston to allow a complete 360° precision bore to be finished, and then remove the remaining 150" segment and sell it for scrap. A need therefore exists for a piston arrangement and a method for manufacturing a piston arrangement that allows two pistons to be produced from a single blank of material, each being configured to retain a load-bearing element with more than 180° of engagement, without boring two separate holes in the piston blank, thereby eliminating the scrap problem described above.

SUMMARY OF THE INVENTION

The present invention provides a piston arrangement, and a method for producing a piston arrangement, that includes a pair of pistons that are both producible from the same piston blank. In embodiments of the invention, each of the pistons includes a head and a foot, and the foot of each piston is configured to mesh with the foot of the other piston to facilitate production of both of the pistons from the single piston blank. When the piston feet are meshed together, the pistons define a piston bore having a generally circular cross section. Separately, each of the pistons define a respective partial piston bore that is configured to receive a load-bearing element having a generally circular cross section. Each of the partial piston bores is configured to surround the load-bearing element for more than 180° of the load-bearing element cross section.

In embodiments of the invention, each of the partial piston bores includes a respective pair of sides that are disposed generally opposite each other along a length of the respective partial piston bore. A portion of one side of each of the pistons is configured to cooperate with a portion of the other side of the same piston to surround the load-bearing element for more than 180°, in some cases, for approximately 210°. Embodiments of the invention include an elongate member and a recessed member alternately disposed along each of the sides of the piston bores, wherein each of the elongate members on one of the pistons is configured to mesh with a respective one of the recessed members on the other piston. In some embodiments of the invention, the elongate members are configured as tabs and the recessed members are configured as receiving surfaces.

In some embodiments, one of the sides of each of the partial piston bores includes a single tab and two of the receiving surfaces, and the other side of each of the partial piston bores includes a single receiving surface and two of the tabs. The tabs and receiving surfaces may be alternately spaced along the length of the piston bores, such that each of the tabs is disposed generally across from a respective one of the receiving surfaces on the other side of a corresponding one of the partial piston bores. In such embodiments, the greater than 180° circumscription of the load-bearing element may not occur at any one cross section of the load-bearing element, rather, the tabs may be staggered along a length of the partial piston bore such that no two tabs are across from each other.

Embodiments of the invention also include a method for manufacturing a piston arrangement that includes two pistons manufactured from a single piston blank. A bore having a length and a generally circular cross section can be formed through the piston blank. The piston blank can then be cut from an outside edge of the blank into the bore on two sides of the bore such that the blank is separable into the two pistons. The step of cutting through the piston blank can be performed such that each of the pistons includes a partial piston bore that is configured to receive a load-bearing element having a generally circular cross section. Each of the partial piston bores can be further configured to circumscribe the load-bearing element for more than 180° of the load-bearing element cross section. In some embodiments, water jet cutting, laser cutting or electrical discharge machining can be used to perform the step of cutting through the piston blank. When the pistons are manufactured such that they each include tabs and receiving surfaces such as described above, the step of forming the tabs on one oϊ the pistons can effect the forming of the receiving surface on the other piston.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a front plan view of a piston arrangement including two pistons made from a single piston blank;

FIGURE 2 is a perspective view of one of the pistons shown in

Figure 1;

FIGURE 3 is a perspective view of the oiher of the pistons shown in Figure 1; FIGURE 4A is a front plan view of one of the pistons shown in Figure 1;

FIGURE 4B is a bottom plan view of the piston shown in Figure 4A;

FIGURE 4C is a side sectional view of the piston shown in Figure 4A;

FIGURE 4D is sectional view of another side of the piston shown in

Figure 4A;

FIGURE 5 is a side plan view of the piston shown in Figure 4A cooperating with a cam follower and a cam;

FIGURE 6 is a top plan view of the piston shown in Figure 2 as it would appear unwrapped around an axis along the bore;

FIGURES 7-8 are top plan views of pistons from a piston arrangement in accordance with other embodiments of the present invention, each shown as it would appear unwrapped around an axis along the bore; and

FIGURE 9 is a top plan view of a piston from a piston arrangement in accordance with another embodiment of the present invention, shown as it would appear unwrapped around an axis along the bore.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Figure 1 shows a piston arrangement 10 in accordance with an embodiment of the present invention. The piston arrangement 10 includes a pair of pistons 12, 14 that are configured such that they can be made from a single blank of material, such as the piston blank 16 shown in phantom and defining a central axis 17. The piston 12 includes a piston head 18 and a foot 2CL Similarly, the piston 14 includes a head 22 and a foot 24. The piston feet 20, 24 are configured to mesh with each other to facilitate manufacturing of the two pistons 12, 14 from the single piston blank 16.

The pistons 12, 14 are manufactured foot-to-foot, rather than head-to- head to eliminate the problem of scrap material described above. For example, as shown in Figure 1 , a single piston bore 26 is used for both of the pistons 12, 14. The piston bore 26 defines a bore axis 27, which is normal to the central axis 17 of the blank 16, and is therefore shown as a point in Figure 1. If the pistons 12, 14 were manufactured head-to-head, two separate piston bores would be required. As shown in Figure 1, with the feet 20, 24 of the pistons 12, 14 meshed together, the piston bore 26 has a generally circular cross section. With the pistons. 12, 14 separated, however, two partial piston bores 28, 30 are defined — see Figures 2 and 3, respectively.

Figures 2 and 3 show the pistons 12, 14 in perspective views with each of the pistons 12, 14 resting on its respective piston head 18, 22. In these views, it is possible to see how the feet 20, 24 mesh together as shown in Figure 1. Each of the partial piston bores 28, 30 have a respective length Ll, L2, and each are configured to receive a load-bearing element such as the piston pin 31 shown in Figure 4A. As described above, other types of load-bearing elements such as cam followers and the like can be used with a piston arrangement, such as the piston arrangement 10 of the present invention.

Returning to Figures 2 and 3, it is shown that the partial piston bore 28 includes a pair of sides 32, 34 disposed generally opposite; each other along its length Ll. Similarly, the partial piston bore 30 includes generally opposing sides 36, 38 disposed along its length L2. It is clear from the drawing figures that the respective sides 32, 34 and 36, 38 of the partial piston bores 28, 30 do not run the entire length of Ll or L2, owing to the generally circular cross section of the pistons 12, 14. Partial piston bores 28, 30 constitute a retaining portion of the piston feet 20, 24. As described above, the partial piston bores 28, 30 are configured to receive a load- bearing element, such as the pin 31 shown in Figure 4A. Moreover, each of the partial piston bores 28, 30 are configured to surround such a load-bearing element by more than 180°. As shown in Figure 2, the partial piston bore 28 includes an elongate member in the form of a retaining tab 40, while the side; 34 includes two elongate members, each in the form of retaining tabs 42, 44. Adjacent the tab 40 is a recessed portion 46 having a receiving surface 48 configured to receive a tab from the piston 14 as described below. Also adjacent the tab 40 is a recessed portion 50 having a receiving surface 52 also configured to receive a tab from the piston 14. On the other side 34 of the partial piston bore 28, the two tabs 42, 44 have disposed between them a single recessed portion 54, having a receiving surface 56.

The receiving surface 56 is configured to receive a tab 58 of the partial piston bore 30 shown in Figure 3. On the opposite side 38 of the tab 58 are two other tabs 60, 62, which are respectively configured to mesh with the recessed portions 46,

50 on the piston 12 shown in Figure 2. Similar to the configuration of the piston 12, the tab 58 has adjacent to it a recessed portion 64 having a receiving surface 66, and a recessed portion 68 having a receiving surface 70. Likewise, between the tabs 60, 62 is a recessed portion 72 having a receiving surface 74.

The alternating tab and recessed portion configuration of the piston arrangement 10 not only allows the two pistons 12, 14 to mesh together such that they can be made from the single piston blank 16 having a single bore 26, but they also allow each of the pistons 12, 14 to retain a load-bearing element, such as the pin 31 shown in Figure 4A, while circumscribing more than 180° of the load-bearing element. As shown in Figure 1 by the angle (α), the cooperation of the tabs 40 and AA — and also the tab 42, which is behind the tab AA — provides 200°-240°, and preferably, approximately 210° of engagement for a load-bearing element having a generally circular cross section, such as the pin 31 shown in Figure 4A. The same is true for the piston 14 and the cooperating tabs 58, 60, 62.

As shown in Figures 2 and 3, the single tabs 40, 58 have a greater width — i.e., they occupy a greater portion of the length of their respective partial piston bores 28, 30 — than any of the tabs 42, 44 and 60, 62 across from which they are disposed. This helps to ensure that there is enough piston material to adequately retain a load-bearing element, such as the pin 31 shown in Fig are 4A. In the embodiment shown in Figures 2 and 3, the approximately 210° of engagement for a load-bearing element will not occur in any given plane cut transversely across either of the partial piston bores 28, 30. This is because each of the tabs 40, 42, 44 and 58, 60, 62 is disposed directly across from a corresponding recessed portion 54, 46, 50 and 72, 64, 68, respectively. In fact, a cross section taken through any one of the tabs and its corresponding recessed portion, may provide, in the embodiment shown in Figures 2 and 3, approximately 180° of engagement for a load-bearing element. Of course, other configurations of retaining portions, such as the partial piston bores 28, 30 are contemplated by the present invention. For example, one of the pistons of a two- piston arrangement may have one center tab on each side, while the mating piston has four smaller surrounding tabs, two on each side. In fact, depending on the size of the piston and the particular application, different quantities and locations of elongate members and recessed portions could be used. For example, the piston arrangement 10, and the configuration of the partial piston bores 28, 30 may be effective for pistons having a diameter of less than one inch and load-bearing elements having a diameter of approximately one-half inch.

Figures 4A-4D show a number of plan and sectional views of the piston 12, thereby providing additional insight into its configuration. As described above, Figure 4A includes in phantom a load-bearing element, in form of the pin 31. The tabs 40, 44 are angled upward and outward from the partial piston bore 28 to an outer edge 76 of the piston 12. The receiving surfaces 74, 70 — and in the case of the tab 42 the receiving surface 66 — are configured with the mating angle such that the pistons 12, 14 mesh together as shown in Figure 1. Figure 4B shows a bottom plan view of the piston 12, while Figures 4C and 4D respectively show left and right sectional views of the piston 12 having some of the hidden lines removed for clarity.

The present invention also contemplates a method for manufacturing a piston arrangement, such as the piston arrangement 10 shown in Figure 1. The piston blank 16 from which the piston arrangement 10 is manufactured, can be any material effective for the given application, although cast iron has been shown to be effective in at least some of the hydraulic machine applications described in the references incorporated above. For a cast material, the piston blank 16 can be poured to a near net shape, or cut from a larger cast piece of bar stock. With the piston blank 16 ready to be worked on, one embodiment of the present invention contemplates forming a bore, such as the piston bore 26 through the piston blank 16. Each of the heads 18, 22 are machined, and can include one or more recess or grooves as desired for the application. Grooves, such as the grooves 78, 80 shown in Figure 1 may also be machined into the piston blank 16.

It is worth noting that the piston blank 16 is shown as much larger than the piston arrangement 10, although in practice, the dimensions may nearly coincide. Thus, in this description, as an operation is described as being performed on the piston blank 16, it may be performed on a partially completed piston arrangement rather than a completely unfinished blank of material such as the piston blank 16. For example, to form the tabs and recessed portions as described above, a number of cuts are made from outside the piston blank into the piston bore 26. In practice, the piston blank 16 will probably be machined to a final diameter before these cuts are made, such that the cuts will be made from an outside surface 82 of the piston arrangement 10, rather than being made from the actual outer surface 84 of the raw blank of material 16.

Any one of, or combination of, a number of different machining processes may be used in manufacturing a piston arrangement, such as the piston arrangement 10. For example, water jet cutting, laser cutting, or electrical discharge machining may be used to form the cuts from the outside surface 82 into the piston bore 26. Of course, more conventional manufacturing methods, such as turning, milling and boring may be used to create the outside dimensions of the piston arrangement 10 and the piston bore 26. Depending on the tolerances required, the piston bore 26 may be further reamed or ground to create a precision surface to interface with a load-bearing element. As shown in Figure 1, the tips of the various tabs and edges of the various recessed portions are labeled with letters A-D. In manufacturing the piston arrangement 10, cuts can be made from the outside edge 82 at points E and F into the bore 26 at points A-D. Cuts B-F and C-F are mirror images of cuts D-E and A-E, and intersect the bore 26 to define the angle α when viewed along the bore axis 27. It is understood that points A-F are shown as points for convenience, and really represent straight lines, and in the case of points E and F, arcuate perimeter lines around the surface 82 of the piston arrangement 10. The cuts are made such that retaining portions, such as the partial piston bores 28, 30, are formed in each of the pistons 12, 14. As described above, one or more tabs can be machined into each side of the piston arrangement 10, which correspond to opposite sides of the partial piston bores 28, 30. In addition, the cuts that form the tabs, such as the tab 62 will simultaneously form a receiving surface, such as the receiving surface 52. Thus, the elongate members and recessed portions of the mating pistons are formed simultaneously, thereby reducing the number of machining operations required. In addition, because two pistons 12, 14 are made using a single piston bore 26, the amount of scrap is significantly reduced over conventional manufacturing methods that would require two separate bores, one for each of the pistons.

Figure 5 shows the piston 12 in use as part of a hydraulic machine, such as a transformer, pump or motor. The piston 12 reciprocates in a cylinder 86 within a housing 88 to pump or receive fluid through a port 90 as shown by arrow 92.

A cam follower 94 is engaged by the piston foot 20 for more than 180° of the of the cam follower cross section, yet the piston foot 20 is open enough to allow the cam follower to protrude beyond the foot 20 to contact a cam 96. In the application shown in Figure 5, the cam 96 is stationary, while the housing 88 will rotate in the direction shown by the arrow 98. The greater than 180° of engagement inhibits separation of the piston 12 and cam follower 94 when it disengages from the cam 96, as is contemplated in certain applications.

Figure 6 shows a top view of the piston 12 as it would appear if it were unwrapped around the piston bore axis 17. As discussed above, the width (tl) of the tab 40 is greater than the width (t2, t3) of either of the tabs 42, 44. In practice, the width (tl) of the tab 40 may be less than one half the length (Ll) of the partial piston bore 28, while the widths (t2, t3) may each be greater than one quarter of Ll. This may be desired, because the generally circular cross section of the piston 12 — see Figure 4B — will cause the tabs 42, 44 to be thinner near the outer surface 82 of the piston 12 — see Figure 2. It is also clear from the "unwrapped" view shown in Figure 5, that the tabs 40, 42, 44 will engage a load-bearing element, such as the cam follower 94 shown in Figure 5, for more than 180°.

Figure 7 shows a piston 100 that is part of a piston arrangement in accordance with another embodiment of the present invention. like the piston 12 as shown in Figure 6, the piston 100 is shown in Figure 7 in as it would appear unwrapped. As discussed above, different configurations of retaining portions, including different tab and recessed portion configurations are contemplated by the present invention. As shown in Figure 7, the piston 100 includes four tabs 102, 104,

106, 108, and only two recessed portions 110, 112. It is configured to mate with a piston 114 shown in Figure 8, which makes up the second piston of the piston arrangement.

The piston 114 includes tabes 124, 126 configured to mate with recessed portions 110, 112 on the piston 100. The piston 114 also includes recessed portions 116, 118, 120, 122, configured to mate with the tabs 102-108 on the piston 100. As shown in Figures 7 and 8, the pistons 100, 114 are not mirror images of one another, but rather, the two would mesh together such that they could be made from a single piston blank. In addition, the tabs 102-108 on the piston 100, and the tabs 124, 126 on the piston 114 are each configured to engage a load-bearing element for more than 180° of its cross section, as described and illustrated above.

Figure 9 shows a single piston 128 from a piston arrangement in accordance with another embodiment of the present invention. The piston 128 is part of a mirror-image set, such as the pistons 12, 14 shown in Figure 1. The piston 128 includes tabs 130, 132, 134 disposed opposite recessed portions 136, 138, 140. The piston 128 further includes larger tabs 142, 144 disposed opposite recessed portions 146, 148. It is readily understood that the tabs 130, 132, 134, 142, 144 will mate with corresponding recessed portions on another piston from the piston arrangement, and the recessed portions 136, 138, 140, 146, 148 on the piston 128 will mate with corresponding tabs on the other piston from the piston arrangement. While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A piston arrangement comprising: a pair of pistons, each having a head and a foot, the foot of each piston being configured to mesh with the foot of the other piston such that both of the pistons are producible from a single piston blank, the pistons defining a piston bore having a generally circular cross section when the piston feet are meshed together, each of the pistons separately defining a respective partial piston bore having a respective length, and each of the partial piston bores being configured to receive a load- bearing element having a generally circular cross section, and being further configured to surround the load-bearing element for more than one hundred eighty degrees of the load-bearing element cross section.

2. The piston arrangement of claim 1 , wherein each of the partial piston bores includes a respective pair of sides disposed generally opposite each other along the length of the respective partial piston bore, a portion of one side of each of the pistons being configured to cooperate with a portion of the other side of the respective piston to surround the load-bearing element for more than one hundred eighty degrees of the load-bearing element cross section.

3. The piston arrangement of claim 1 , wherein each of the partial piston bores includes a respective pair of sides disposed generally opposite each other along the length of the respective partial piston bore, each of the sides of the partial piston bores including an elongate member and a recessed portion alternately disposed thereon, each of the elongate members on one of the pistons being configured to mesh with a respective one of the recessed portions on the other piston.

4. The piston arrangement of claim 1 , wherein each of the partial piston bores includes a respective pair of sides disposed generally opposite each other, each of the sides of the partial piston bores including a respective retaining tab and a respective receiving surface, each of the retaining tabs on one of the pistons being configured to mesh with a respective one of the receiving surfaces on the other piston.

5. The piston arrangement of claim 4, wherein the tabs on each of the pistons are configured to circumscribe a respective one of the load-bearing elements for approximately two hundred degrees to two hundred forty degrees of the respective load-bearing element cross section.

6. The piston arrangement of claim 4, wherein one of the sides of each of the partial piston bores includes a single tab and two of the receiving surfaces, and the other side of each of the partial piston bores includes a single receiving surface and two of the tabs.

7. The piston arrangement of claim 4, wherein each of the tabs is disposed generally across from a respective one of the receiving surfaces on the other side of a corresponding one of the partial piston bores.

8. A piston arrangement comprising: a pair of pistons, each having a head and a foot, the foot of each piston being configured to cooperate with the foot of the other piston such that both of the pistons are producible from a single piston blank, each of the piston feet including a semi-cylindrical retaining portion for retaining a rotatable pin having a generally circular cross section, and each of the retaining portions being configured to circumscribe a respective one of the pins for sufficiently more than one hundred eighty degrees of the respective pin cross section such that axial separation of the respective pin and piston is inhibited, while allowing a portion of the respective pin to protrude beyond the foot of the respective piston.

9. The piston arrangement of claim 8, wherein each of the retaining portions includes a pair of sides generally disposed opposite each other, each of the sides including a tab and a receiving surface, each of the tabs on each of the pistons being configured to mate with a respective one of the receiving surfaces on the other piston, thereby facilitating production of both pistons from a single piston blank.

10. The piston arrangement of claim 9, wherein the retaining portions of each of the pistons are configured to circumscribe a respective one of the pins for approximately two hundred degrees to two hundred forty degrees of the respective pin cross section.

11. The piston arrangement of claim 9, wherein one of the sides of each of the retaining portions includes a single tab and two of the receiving surfaces, and the other side of each of the retaining portions includes a single receiving surface and two of the tabs.

12. The piston arrangement of claim 9, wherein each of the tabs is disposed generally across from a respective one of the receiving surfaces on the other side of a corresponding one of the retaining portions.

13. A method for manufacturing a piston arrangement including two pistons from a single piston blank, the blank being generally cylindrical and having an outer surface and defining a central axis, the method comprising: forming a bore having a length and generally circular cross section through the piston blank normal to the central axis, the bore defining a bore axis; and cutting through the piston blank from the outer surface of the blank into the bore on two sides of the bore such that the blank is separable into the two pistons, the step of cutting through the piston blank being performed such that each of the pistons includes a partial piston bore that is configured to receive a load- bearing element having a generally circular cross section, and further configured to circumscribe the load-bearing element for more than one hundred eighty degrees of the load-bearing element cross section.

14. The method of claim 13, wherein each of the partial piston bores includes a respective pair of sides disposed generally opposite each other along the length of the respective partial piston bore, the step of cutting though the piston blank including forming at least one tab and at least one receiving surface on each of the sides of the partial piston bores.

15. The method of claim 14, wherein the step of forming the tabs on one of the pistons effects the forming of the receiving surfaces on the other piston.

16. The method of claim 14, wherein the step of cutting though the piston blank includes forming one of the tabs and two of the receiving surfaces on one side of each of the of the partial piston bores, and two of the tabs and one of the receiving surfaces on the other side of each of the partial piston bores.

17. The method of claim 13 , wherein the step of cutting through the piston blank includes at least one of: water jet cutting, laser cutting, or electrical discharge machining.