Overmolded vial for use with a level

Levels are used by carpenters, masons, drywallers and the like for helping to assure that surfaces are horizontal, vertical, or at a specified angular relationship to the horizon. A typical level includes at least two vials, one each for ascertaining whether a surface is "level," i.e., horizontal, or "plumb," i.e., vertical. A level vial comprises a tube made of clear glass or, preferably, clear plastic (acrylic, for example), the barrel-shaped cavity of which is partially filled with a liquid such as mineral spirits. The vial is not completely filled and a bubble is thereby formed when the vial is closed. Typically, two marker rings are applied to the outside of the vial in positions to visually divide the cavity into three portions of about equal length. Level and plumb conditions are ascertained by noting the position of the bubble with respect to the marker rings. A problem with molding substantially-finished vials is that acrylic, the material predominantly used for making molded vials, does not stretch well. If one attempts manufacture of an acrylic vial which has thick walls (for breakage resistance), the stretch-resisting characteristic of acrylic causes breakage of core pins used in the injection molding process. On the other hand, a thin-wall vial is much more subject to breakage--builder's levels often receiving rough treatment in use. One known method of avoiding core pin breakage while providing a vial of satisfactory thickness with marker rings is to machine a barrel-shaped inner cavity in a preform. Inner grooves are machined in the inner surface to receive C-shaped rings like common snap rings. Such rings necessarily have a discontinuity or opening about the perimeter so that the ring can be compressed radially for insertion into the cavity. A ring is seated in each of two respective grooves. A problem with such construction is that the surface transition between the Cshaped ring and the inner wall of the tube will not be smooth, at least because of the existence of a small annular space (at the chamfer) between the ring and the wall. In other words, a slight edge will be presented to a bubble moving along the vial and such edge may cause the bubble to "hang up" in its travel and yield an inaccurate reading. Furthermore, positioning of the marker rings in the grooves is often not exact and often results in imprecise readings. Another problem with known level vials involves exteriorly-applied marker rings. Since such rings are at least somewhat exposed to contact by foreign objects, portions of such rings can be worn or chipped away over time. An improved level vial which has a sturdy, breakage-resistant wall, which permits the vial bubble to move smoothly and freely along the vial cavity would be an important advance in the art. Furthermore, such a vial which provides a singlematerial cavity surface would significantly improve upon the prior art. Finally, an improved vial comprising a machined cylinder with a sleeve molded thereon would solve these noted problems in the prior art. OBJECT OF THE INVENTION It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. SUMMARY OF THE INVENTION In a first aspect, the present invention provides a method of forming a vial comprising: providing a cylinder formed from a first material, the cylinder having a sidewall with an inner surface defining a cavity and an outer surface; positioning indicia on the outer surface; and molding a second material around and onto the outer surface of the cylinder to form an overmolded body wherein the second material is molded around the indicia and the indicia is enclosed between the cylinder and the second material. In such an embodiment, the cylinder is preferably molded and has an outer surface and the method further comprises embedding a marker ring into the outer surface of the cylinder such that the second material is molded around the marker ring and the marker ring is enclosed by the first material and second material. The second material may be molded around the cylinder and marker ring by positioning the cylinder and marker ring on a core pin; inserting the core pin into a mold; flowing the second material into the mold; and ejecting the cylinder, marker ring, and second material from the mold. It is preferred that the second material be heated to liquid form and flowed or injected into the mold around the cylinder and then allowed to harden to solid form. A bubble is preferably positioned in the cavity by partially filling the cavity with a liquid and enclosing the cavity with an end closure. The liquid is preferably has a freezing point below temperatures expected to be encountered during use and may be mineral spirits. The bubble is preferably air. In some embodiments it may be preferred that the first material have a melting point higher than the second material to facilitate molding of the second material in liquid form around the first material. In certain preferred embodiments, the first material is polycarbonate and the second material is acrylic. However, it has been found that the same material, acrylic, can be used for both the first and second material if the first material is cooled during molding of the second material. In these embodiments, the first and material and the second material have the same composition and the cylinder is cooled during overmolding such that the cylinder remains solid while the second material is molded about it. The marker ring is preferably made of a foil-type material which may be metallic, a thermoset material, a thermoplastic material having melting temperatures substantially higher than the melting temperature of the second material, ink, pigment, or other material. The method may further include putting indicia on the cylinder before the second material is molded around the cylinder. Such indicia may relate to degrees of pitch, logarithmic information, or other relevant information and may be of the same material as the marker rings. The placement of the marker ring and/or indicia between the cylinder and the second material allows the inner surface of the cylinder to be solely comprised of the first material. The inner surface is preferably machined such that the cavity is barrelshaped. Such machining is facilitating by the uniformity of the inner surface composition. The indicia may be hot stamped, laser printed or otherwise embedded into or positioned on the outer surface of the cylinder but, like the marking rings, does not extend through the inner surface. In a second aspect, the present invention provides a vial comprising: a cylinder formed from a first material, the cylinder having a sidewall with an inner surface defining a cavity and an outer surface; a sleeve formed from a second material and being molded around and onto the outer surface of the cylinder; and indicia positioned on the outer surface, the inner surface not being penetrated by the indicia and the indicia being bounded by the cylinder and the sleeve. In certain embodiments, the vial further comprises a first end closure at the first end and a second end closure at the second end, the vial enclosing a liquid and a bubble. The vial also may comprise at least one marker ring or indicia bounded by the cylinder and the sleeve with the marker ring or indicia hot stamped, printed onto or otherwise positioned on the outer surface of the cylinder before the sleeve is molded thereto. It is preferred that the cylinder be molded and have an outer surface with at least one marker ring positioned on or embedded into the outer surface such that the second material is molded around the at least one marker ring and the marker ring is enclosed by the first material and second material. Most preferably two marker rings are provided equidistant to the intended position of the maximum diameter of the cavity. The sleeve is preferably molded around the cylinder and marker ring(s) by positioning the cylinder and marker ring on a core pin; inserting the core pin into a mold; flowing the second material into the mold; and ejecting the cylinder, marker ring, and second material from the mold. The bubble is preferably positioned in the cavity by partially filling the cavity with a liquid and enclosing the cavity with an end closure. The inner surface of the cylinder is preferably machined such that the cavity is barrel-shaped, i.e., the inner surface is machined to be curvilinear and include a cross section having a maximum diameter. To prevent melting of the cylinder during molding of the second material, it is preferred that the core pin be cooled to keep the cylinder below its melting temperature. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of a level having three vials. FIGURE 2 is a front elevation of a cylinder and marker rings in accordance with the principles of an embodiment of the present invention. FIGURE 3 is an enlarged cross section view of a top portion of the cylinder of FIGURE 2. FIGURE 4 is a cross section view of a cylinder with marker rings, the cylinder being positioned on a core pin and inserted into a mold with a second material molded over the cylinder in accordance with the principles of an embodiment of the present invention. FIGURE 5 is a cross section view of a vial in accordance with the principles of an embodiment of the present invention. AI N.DED SHEET DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIGURE 1 is a perspective view of a level 11 having three vials 10. As shown, vials 10 are arranged in predetermined angular relationships to the measuring surface of the level. FIGURE 2 is a front elevation of a cylinder 20 and marker rings 40 used to form a vial 10. Cylinder 20 extends from first end 24 to second end 25 and includes an inner surface 21 (see FIGURE 3) defining a cavity 22. Cylinder 20 is preferably a transparent plastic, most preferably polyearbonate. As shown in FIGURE 3, marker rings 40 are embedded into the outer surface 23 of cylinder 20. Rings 40 maybe comprised of foil hot stamped into cylinder 20, ink or pigment printed onto cylinder or other materials positioned on outer surface 23 through other methods. Rings do not penetrate inner surface 21. Rings 40 may be a foil comprising metal, a thermoset material or a thermoplastic with a high melting temperature or ink, pigment or other material. FIGURE 4 is a cross section view of a cylinder 20 with marker rings positioned on a representative core pin 60 and inserted into a represmatative mold where a material 30 is flowed around cylinder 20 to form a sleeve 31 molded over the cylinder 20. As is understood, material 30 is injected or otherwise forced through port 71 into the space between mold 70 and cylinder 20 and rings 40. Material 30 is preferably heated and flows into such space before cooling and hardening to form sleeve 31. Sleeve 31 and cylinder 20 are both preferably transparent acrylic and are bound together such that the interface therebetween is indistinguishable. In the preferred method, the cylinder 20 is formed first, preferably with a core pin and a first mold. Then marker tings 40 or indicia 41 may be hot stamped, printed, or otherwise embedded in or positioned on the outer surface 23 of cylinder 20. After such applieation of rings or indicia, cylinder 20 is positioned on core pin 60 and is positioned in mold 70 which is larger than the first mold. A flowable material 30, such as heated acrylic, is then injected into the space between mold 70 and the cylinder 20 and rings 40 or indicia 41, if present on outer surfaee 23. Cylinder 20 is preferably cooled by core pin 60 to prevent it from reaching its melting point from contact with material 30. It is preferred that cylinder 20 and material 30 have the A ENDED SHEET same composition of acrylic. After injection, second material 30 then cools, hardens, and forms sleeve 31 around cylinder 20. At this point, the overmolded dual component vial 10 has sufficient thickness to be machined without risking breakage; therefore, vial 10 is removed from core pin 60 and the inner surface 21 of cylinder is machined such that the cavity 22 is of a desired shape, specifically eurvilinear or barrel-shaped. As is clearly evident in the dual component vial 10, marker rings 40 are not exposed to cavity 22 nor to the external environment. Due to this design, creation of the desired shape of cavity 22 in cylinder 20 does not require specialized machining in which both the first material and the marker tings are machined. Furthermore, tings cannot be damaged during normal use of the level 11. This method also avoids human error in the placement of marker rings at the proper position in the vial since the stamping procedure consistently positions the rings on vials. FIGURE 5 is a cross section view of the f'mished overmolded vial 10 after it is removed from the mold 70 and core pin 60, partially filled with liquid 51, and capped. Inner surface 21 has been machined to form the desired barrel-shape in which the cavity 22 has a maximum diameter 27. First end closure 12 has been formed during the molding process. The cavity has then been partially filled with liquid 51 and its end 25 has been capped with second end closure 13 to seal cavity 22. Bubble 50 is shown at the maximum diameter 27 between the marker rings Thus, it should be apparent that there has been provided, in accordance with the present invention, a vial for use with levels that fully satisfies the objectives and advantages set forth above. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.