A thread depth gauge

Abstract

Disclosed is a thread depth gauge 100 having a tubular outer member 102 and an inner member 104, received in a bore 114 of the outer member. The outer member 102 comprises a threaded end portion 116 for insertion into a threaded opening 10 of a workpiece 1. The threaded end portion 116 comprises an external thread formation 103 that extends along a longitudinal axis 110 of the outer member 102, from a proximal first end 119 to a distal second end 112. The inner 10 member 104 is movably coupled to the outer member 102 and axially movable to engage a distal end 108 of the inner member 104 with a distal locating surface 44 of the threaded opening 10 when the outer member 102 is inserted into the threaded opening 10 of the workpiece 1. The length of the inner member 104 that extends between the second end 112 of the thread formation 103 and the locating surface 44 is indicative of the thread depth relative to a reference position. The thread depth gauge 100 further comprises indicator means for indicating the thread depth to an operator.

Description

TECHNICAL FIELD The present disclosure relates to a thread depth gauge. Aspects of the invention relate to a thread depth gauge, to a set of tools, and to a method of gauging or measuring a depth of a thread formation in a threaded hole or opening. BACKGROUND It is known to provide a measurement device, known as a thread depth gauge, for measuring the depth of an internal thread formation defined in a threaded opening relative to a reference surface in which the opening is formed. The gauge is therefore typically used as an inspection tool for checking a workpiece against specified tolerances. The gauge typically includes two major components, namely: a housing or sleeve component with an end face for location against the reference surface; and a threaded rod or probe member, movably coupled to the housing, for insertion into the threaded opening. The gauge is calibrated to measure or gauge the relative displacement of the probe member during insertion into the threaded opening, thereby indicating the relative depth to a distal end of the internal thread formation (i.e. to a final engageable thread). However, the accuracy of a conventional thread depth gauge is impaired in certain applications, for example where the reference surface is not flat or perpendicular to a depth of the opening, and / or where the reference surface has a relatively rough finish (as may be produced by a casting manufacturing method, for example). It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a thread depth gauge, a set of tools, and a method of gauging or measuring a depth of a thread formation in a threaded hole, as claimed in the appended claims. According to an aspect of the present invention there is provided a thread depth gauge comprising: a tubular outer member; and an inner member, received in a bore of the outer member. The outer member comprises a threaded end portion for insertion into a threaded opening of a workpiece. The threaded end portion comprises an external thread formation that extends along a longitudinal axis of the outer member, from a proximal first end to a distal second end. The inner member is movably coupled to the outer member and axially movable to engage a distal end of the inner member with a distal locating surface of the threaded opening when the outer member is inserted into the threaded opening of the workpiece. The length of the inner member that extends between the second end of the thread formation and the locating surface is indicative of the thread depth relative to a reference position. The thread depth gauge further comprises indicator means for indicating the thread depth to an operator. In this manner, an operator can insert the outer member of the thread depth gauge into a threaded opening and engage the distal end of the inner member with the locating surface. With knowledge of the distance or depth from a datum or reference position to the same locating surface, the operator can readily compare the thread depth, indicated by the gauge, to a threshold depth. The operator is therefore able to use the gauge to inspect various workpiece shapes, including examples where a conventional gauge is unable to accurately measure the thread depth from the top of the hole or opening. This serves to reduce the complexity for the operator, leading to improved inspection efficiency and lower costs. The indicator means or indicator may take the form of any suitable analogue or digital mechanism for indicating the thread depth. In an example, a relative position of a proximal end of the inner member to the outer member is indicative of the thread depth when the distal end of the inner member engages the locating surface, the relative position acting as the indicator means. The operator can therefore simply check the proximal end of the inner member, once engaged, and consider the relative position to the outer member to rapidly compare the thread depth to a threshold depth. This provides a simple and low-cost thread depth evaluation. Optionally, the proximal end of the inner member may project outside of a proximal end of the outer member when the distal end of the inner member engages the locating surface to indicate that the thread depth is less than a reference depth. Optionally, the proximal end of the inner member may be withdrawn inside the outer member when the distal end of the inner member engages the locating surface to indicate that the thread depth is greater than or equal to the reference depth. In an example, the outer member may include an axial slot and the inner member may include a projection, extending through the slot. The projection may act as the indicator means for indicating the thread depth when the distal end of the inner member engages the locating surface. The operator can therefore easily check the position of the projection and thereby determine the thread depth of the opening. The outer member may, for example, further includes a measurement scale, arranged along the axial slot, for indicating the thread depth when the distal end of the inner member engages the locating surface. The measurement scale serves to provide an accurate indication of the thread depth, for example providing a numerical value corresponding to the thread depth. Optionally, the indicator means comprises: a sensor for measuring displacement of the inner member relative to the outer member; and a display for indicating the thread depth based on the measured displacement. The indicator means may therefore provide an accurate and precise reading of the thread depth, that can be efficiently recorded by the operator. The external thread formation may, for example, correspond to an industry standard thread size, optionally being an ISO metric thread size. The external thread formation may, for example, be configured as a go gauge for that thread size. In this manner, the thread depth gauge serves the further purpose of checking a minimum tolerance of a specified thread size. Optionally, the thread depth gauge further comprises a biasing element arranged to urge the inner member to engage the locating surface when the outer member is inserted into the threaded opening of the workpiece. The biasing element therefore automatically engages the inner member with the locating surface improving the ease of inspection for an operator, particularly where the operator has a physical impairment. In an example, the outer member may comprise a sleeve member and an end cap. The end cap may be releasably coupled to a proximal end of the sleeve member with a shoulder formation, or flange portion, of the inner member being retained in a cavity defined between the end cap and the proximal end of the sleeve member to guide the axial movement of the inner member relative to the outer member. In this manner, the inner member is conveniently constrained in its relative movement to the outer member. Optionally, the biasing element is arranged in the cavity, between the end cap and the shoulder formation, or flange portion, of the inner member. The end cap is releasably coupled and the biasing element can therefore be readily accessed, for example allowing replacement of the biasing element if it becomes defective. The inner member may, for example, comprise a rod-shaped probe and the shoulder formation, or flange portion, may be provided by a circlip member attached to the probe. The shoulder formation / flange portion is therefore easily incorporated into the inner member, reducing manufacturing costs. In an example, the distal end of the inner member may include a stepped or tapered end face for engaging the locating surface of the opening. The stepped or tapered face end face may provide more accurate readings when engaging a corresponding surface of the threaded opening. According to another aspect of the invention, there is provided a set of tools for inspecting threaded openings. The set of tools comprises a plurality of thread depth gauges, as described in a previous aspect of the invention. The external thread formation of each thread depth gauge corresponds to a respective screw thread size. In this manner, an operator on an inspection line may be equipped with the set of tools, and thereby execute quality control inspections on a range of threaded openings and / or workpieces. Optionally, the set of tools further comprises a depth gauge for determining the depth of the distal locating surface from the reference position. In an example, the set of tools may further comprise one or more no-go gauges. Each no-go gauge may correspond to a respective screw thread size. The no-go gauge may be used to easily check the maximum tolerance of a major diameter of the threaded opening. According to yet another aspect of the invention, there is provided a method of inspecting the thread depth of a threaded opening using a thread depth gauge as described in a previous aspect of the invention or a set of tools, as described previously in another aspect of the invention. The method comprises: obtaining a depth of the distal locating surface of the threaded opening from a reference position; inserting the outer member of the thread depth gauge into the threaded opening; engaging the distal end of the inner member with the locating surface; and comparing the thread depth, indicated by the gauge, to a threshold depth. In an example, the depth of the locating surface from the reference position may be determined using a coordinate measuring machine. Optionally, the method further comprises using a ‘no-go’ gauge to compare the maximum tolerance of the thread size of the threaded opening to a threshold. Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a cross-sectional view of a threaded opening of an exemplary workpiece for inspection; Figure 2 shows a perspective view of an exemplary thread depth gauge in accordance with an embodiment of the invention; Figure 3 shows a side view of the thread depth gauge shown in Figure 2; Figure 4 shows a cross-sectional view of the thread depth gauge shown in Figure 3; Figure 5 schematically shows an exemplary method, in accordance with an embodiment of the invention, of inspecting the depth of an internal thread formation in a workpiece opening using the thread depth gauge shown in Figure 2; Figure 6 shows a cross-sectional view of a portion of the thread depth gauge, shown in Figure 2, inserted into a threaded opening; and Figure 7 shows a perspective view of another exemplary thread depth gauge in accordance with an embodiment of the invention, DETAILED DESCRIPTION Embodiments of the invention relate to tools and methods for inspecting threaded openings that have been formed or machined in a workpiece, such as a component for a vehicle. In particular, embodiments of the invention relate to tools and methods for inspecting the length or depth of an internal thread formation formed in such openings. Embodiments of the invention may therefore be used to check a workpiece against specified tolerances, for example during a quality control stage of a manufacturing process. For this purpose, the thread depth gauge includes an outer member and an inner member, movably coupled to the outer member. The outer member has an end portion that features an external thread formation for insertion into a complementary formation of the threaded opening. The inner member is movable relative to the outer member such that, when the outer member is fully inserted into the threaded opening, the inner member can be displaced further into the opening to engage a distal locating surface formed by a restriction, such as an end face, of the opening. The length of the inner member that extends beyond the thread formation corresponds to the relative distance to the locating surface and is therefore indicative of the thread depth of the internal thread formation. In embodiments of the present invention, this relative distance can be indicated by various means, mechanisms and / or devices, and the gauge is therefore capable of determining and indicating a distance from the distal locating surface to the end of the thread formation (i.e. the distance to the last fully engageable thread of the opening). With knowledge of the distance or depth from a datum or reference position to the same locating surface, the thread depth can therefore be checked and assessed against specified tolerances. The gauge can therefore be used to inspect various workpiece shapes, including examples where a conventional gauge is unable to accurately measure the thread depth from the top of the hole or opening. According to embodiments of the present invention, the thread depth gauge may therefore be part of a set of tools that includes a plurality of such gauges, each being dimensioned according to a particular thread size specification and used across various applications. It is envisaged that embodiments of the invention will therefore lead to reduced costs of the gauging system, and the inspection stages of a manufacturing process, reducing the complexity for the operator, and leading to improved inspection efficiency. To give an example, Figure 1 shows a cross-sectional view of an exemplary workpiece 1 that may be inspected using the thread depth gauge of the present invention. In this example, the workpiece 1 takes the form of an electric drive unit housing for use in a passenger car. However, the applications of the invention are not particularly limited in this respect and the inspected workpieces may take all manner of forms that include a threaded opening for inspection. By a ‘threaded opening’ it is intended to mean an opening that includes an internal thread formation extending at least partially along its length. The workpiece 1 is shown to include a threaded opening 10 that extends from a first end 12 to second end 14 along a longitudinal axis 16. The opening 10 includes a threaded portion 18 defined part way along the longitudinal axis 16, between the first and second ends 12,14. The first end 12 of the opening 10 is defined at an external surface 20 of the workpiece 1 and defines a proximal end of the opening 10. The opposing second end 14 of the opening 10 is defined at a distal end of the opening 10, where a terminal connection to an oil inlet of the housing is provided. The threaded portion 18 may be formed by various machining operations, and provides a thread formation for the attachment of a corresponding male part. The threaded portion 18 is therefore formed according to a thread specification, which includes a thread size, and start and end points of the thread formation, which define a depth or length of the threaded portion 18 extending therebetween. In this example, the thread size is specified as an ISO metric screw thread size. For example, the threaded portion 18 may be formed as an M8 screw thread, featuring an 8 millimetre nominal outer diameter or major diameter of the thread formation. However, it is necessary to check the dimensions of the threaded portion 18 in order to ensure adequate mechanical engagement with the connected male part. At this point, the opening 10 shall be discussed in more detail, considering the respective portions of the opening 10 formed in longitudinal succession from the first end 12 to the second end 14. As shown in Figure 1, the opening 10 includes a first conical portion 22 that converges radially inwardly from the first end 12 to a first cylindrical portion 24. The first cylindrical portion 24 extends distally from the first conical portion 22 to a second cylindrical portion 26 having a smaller diameter, such that a first shoulder formation 28 is defined between the first and second cylindrical portions 24, 26. The second cylindrical portion 26 extends distally to a third cylindrical portion 30, which has an even smaller diameter, with a second shoulder formation 32 being defined between the second and third cylindrical portions 26, 30. A separate feed channel 34 connects to the third cylindrical portion 30 partway along its length. A second conical portion 36 is defined at a distal end of the third cylindrical portion 30 tapering radially inwardly towards the second end 14. The threaded portion 18 extends from a distal end of the second conical portion 36 and defines a thread formation 38, extending from a proximal first end 41 to a distal second end 43, where the thread formation 38 terminates at a final thread 39 adjacent to a fourth cylindrical portion 40. The fourth cylindrical portion 40 extends to a distal restriction 42 of the opening 10. The restriction 42 is defined by a conical surface 44 in this example and extends distally to a fifth cylindrical portion 46 that further extends to the second end 14 of the opening 10, where the terminal connection is formed. In this manner, the threaded portion 18 is defined part-way along the length of the opening 10 and extends a prescribed length from the first end 41 to the distal second end 43, defined by the final thread 39, which is adjacent to the fourth cylindrical portion 40. Due to this arrangement, it shall be appreciated that a conventional thread depth gauge is unsuitable for inspecting the depth of the threaded portion 18. Instead, the threaded portion 18 must be inspected against the specifications by alternative means. An exemplary thread depth gauge, in accordance with an embodiment of the present invention, is therefore described herein with reference to the accompanying Figures 2 to 4. With reference to Figure 2, there is illustrated a thread depth gauge 100 for inspecting threaded openings, such as the opening 10 depicted in Figure 1. It shall be appreciated that the gauge is not 100 limited to the inspection of such a workpiece 1 and that the gauge 100 may be used in various other applications to inspect threaded openings defined in all manner of components, including various vehicular components or other workpieces featuring a female internal thread formation for the attachment of a male counterpart. The thread depth gauge 100 is shown to include an outer member 102, with an external thread formation 103, and an inner member 104 movably coupled to the outer member 102. The outer member 102 is configured for insertion into a corresponding threaded portion of an opening defined in a test subject, such as the opening 10 of the workpiece 1. The inner member 104 is movably coupled to the outer member 102 and received in a bore thereof (not shown in Figure 2) such that the inner member 104 can act as a probe, being axially movable relative to the outer member 102 to indicate a distance from a final thread of the inspected opening to a distal locating surface formed further inside the opening (typically by a restriction such as an end face that limits the relative displacement). The gauge 100 may include various means for indicating the relative distance, in a binary or continuous manner, as shall be described in more detail. In turn, the thread depth can be obtained, or otherwise compared to a threshold, for example with knowledge of the depth of the locating surface from a reference position, such as a proximal end of the opening. In this respect it shall be appreciated that the thread depth is the depth from such a reference position to a distal end of the internal thread formation defined in the opening. Figure 3 shows a front view of the thread depth gauge 100 and Figure 4 shows a cross-sectional view of the thread depth gauge 100 taken along the line B-B. As shown in Figures 3 and 4, the gauge 100 is substantially cylindrical in this example and extends from a first end 106 to a distal second end 108 along a longitudinal axis 110. Herein, the term ‘proximal’ is used to refer to a portion of the gauge 100 (or a component thereof) that is near to the first end 106 of the gauge 100, which is typically close to a user of the gauge 100 during inspection. Conversely, the term ‘distal’ is used to refer to a portion of the gauge 100 (or a component thereof) that is closer to the second end 108 and distant or furthest away from the user during inspection (inserted into the threaded opening). The overall length of the gauge 100, between the first and second ends 106, 108, is not particularly limited, but may be between approximately 10 cm and 100 cm for example. However, such dimensions are provided for reference only and are not intended to be limiting on the scope of the invention. The outer member 102 of the gauge 100 may be formed of one or more parts or sub-assemblies that collectively define a tubular member for insertion into a threaded opening of a workpiece, such as the workpiece 1. The outer member 102 therefore extends along the longitudinal axis 110 from a proximal first end 106 (defining the first end 106 of the gauge 100) to a distal second end 112. The outer member 102 also features a bore 114, extending along the longitudinal axis 110, for receiving the inner member 104. The inner member 104 is therefore capable of relative translational movement along the longitudinal axis 110, as shall be described in more detail. The outer member 102 features a threaded end portion 116 disposed towards or at the distal second end 112, which may extend away from the second end 112 and partially along an outer surface of the outer member 102 in a proximal direction. The threaded end portion 116 includes the external thread formation 103, which is configured for insertion into a threaded opening of a workpiece, such as the workpiece 1. In particular, the thread formation 103 may have a length and thread arrangement corresponding to a particular thread specification. For example, the threaded formation 103 may have a thread size corresponding to a particular ISO metric screw thread and extend along a length of the outer member 102 corresponding to a respective standard. For example, the threaded end portion 116 may have a thread pitch configuration, major diameter size, and length, as specified by a particular industry standard. In this manner, the thread formation 103 complies with minimum requirements for achieving predictable mechanical engagement strength between coupled complementary components, such as the M8 thread size of the opening 10 depicted in the workpiece 1 shown in Figure 1. The external thread formation 103 therefore extends along the longitudinal axis 110 from a proximal first end 119 to a distal second end 121. In examples, the threaded end portion 116 may, for example, be configured as a so called ‘go-gauge’, having a major diameter corresponding to a minimum tolerance of a specified thread size. In this manner, if the threaded end portion 116 is insertable into the threaded opening, the possibility of such insertion indicates that the threaded opening satisfies the minimum tolerance. A separate gauge may be used to check the maximum tolerance of the major diameter, known as a ‘no-go gauge’, which should not be insertable into the threaded opening to satisfy the test. In this example, the outer member 102 is shown to include a sleeve member 118, featuring the threaded end portion 116, and an end cap 120 releasably fastened to a proximal end 122 of the sleeve member 118, as shown in Figure 4. The end cap 120 features a through-bore 124 aligned with the longitudinal axis 110 of the gauge 100, which forms a portion of the bore 114 and receives a proximal end 126 of the inner member 104. In this manner, the through-bore 124 allows the proximal end 126 of the inner member 102 to protrude from a proximal end 128 of the end cap 120 and thereby provide a visual indication of the inspected thread depth when the gauge 100 is inserted into a threaded opening, as shall be described in more detail. As shown in Figure 4, the through-bore 124 features a first bore portion 130 and a second bore portion 132 in this example. The first bore portion 130 extends from a distal end 134 of the end cap 120 that engages, and interfaces with, the proximal end 122 of the sleeve member 118. The first bore portion 130 extends proximally to the second bore portion 132, which extends to the proximal end 128 of the end cap 120. The second bore portion 132 has an inner surface substantially corresponding to an interfacing (outer) surface of the inner member 104. For example, a clearance fit may be provided between the second bore portion 132 and the inner member 104, allowing the inner member 102 to move along the axis 110 through the second bore portion 132. The first bore portion 130 is wider than the second bore portion 132 and defines a cavity around the inner member 104. The cavity provides a void of space around the inner member 104 within which a biasing element 136, such as a spring, may be arranged in examples to passively urge the inner member 104 to project from the distal end 112 of the outer member 102, as shall be described in more detail. An outer surface 138 of the end cap 120 may gripped by an operator and used to turn the outer member 102 into a threaded opening during inspection. In examples, the outer surface 138 ofthe end cap 120 may therefore feature one or more ridge formations, for example defining a knurled surface, for enhancing operator grip. Moreover, in order to withstand such torque from an operator, the end cap 120 may be releasably fastened to the sleeve member 118 with one or more fastening elements 140 arranged therebetween. For example, as shown in Figures 3 and 4, the end cap 120 may be attached to the sleeve member 118 by way of a plurality of fastening elements 140 such as bolts, arranged circumferentially around the end cap 120 and extending axially through the end cap 120 to engage a flange formation 142 ofthe sleeve member 118, disposed towards the proximal end thereof. The sleeve member 118 defines the main functional features ofthe outer member 102 and is designed for insertion into the threaded opening of a workpiece, such as the workpiece 1. For this purpose, the outer I external surfaces ofthe sleeve member 118 may include one or more lead-in formations and / or geometry 144 in addition to the threaded end portion 116. For example, the sleeve member 118 may be a rigid element that includes lead-in features / geometry on its outer I external surfaces to facilitate the insertion of the gauge 100 into the threaded opening of a workpiece with relative ease. For example, the sleeve member 118 may include changes in shape, particularly on the outer surface, that define a gradual, stepped, or general narrowing ofthe sleeve member 118 from the proximal end 122 to the distal end 112. Indeed, as depicted in Figures 3 and 4, the sleeve member 118 may include first, second, and third cylindrical portions 144a, 144b, 144c arranged in longitudinal succession extending toward the distal end 112. Each successive portion 144a-c has a smaller outer diameter than the preceding portion 144a-c, thereby defining a narrowing profile with intermediate transition portions or shoulder formations 144d, 144e arranged therebetween. Such lead-in formations / geometry 144 serve to improve the alignment ofthe gauge 100 during insertion into the threaded opening. Notably though, in this example, the bore 114 extending through the sleeve member 118 has a substantially constant diameter, which allows for ease of relative movement ofthe inner member 104. The inner member 104 may similarly be formed of one or more parts, elements or sub-assemblies that collectively define a rod-shaped probe that projects beyond the outer member 102 to engage a distal surface ofthe threaded opening. The distal surface may be an end surface or a similar restriction ofthe opening, as shown in Figure 1, which is engaged by the inner member 104 during inspection to provide a reference for inspecting the thread depth. The distal surface may therefore take various forms within the scope of use of the gauge 100 and the distal end 108 of the inner member 104 may therefore be configured for engagement with a variety of such surfaces. The inner member 104 therefore extends along the longitudinal axis 110 from a proximal first end 126 to a distal second end 108 (defining the second end 108 of the gauge 100). The second end 108 of the inner member 104 projects outside of the bore 114 and, in this example, the inner member 104 includes a first flanged portion 148 that inhibits the second end 108 of the inner member 104 from entering the bore 114. The flanged portion 148 combines with the second end 108 to define a shoulder of a stepped I flanged tip or end face 148 in this example, which is well-suited for engagement with a variety of receiving surfaces, as may be defined by a blind bore, a restrictor bore and / or an E-bore, for example. In other examples, it shall be appreciated that the distal second end 108 of the inner member 104 may instead be defined by an alternative tip-shape or end-face, such as a conical or tapered tip, and / or different tips may be attachable to the distal end of the inner member 104 for engaging the particular locating surface of a threaded opening. The inner member 104 is otherwise shown to be substantially cylindrical, in this example, and extends through the bore 114 of the outer member 114. In this example, the inner member 104 is movably coupled to the outer member 102 by way of a second flange portion 150 defined towards the proximal first end 126 of the inner member 104. The second flange portion 150 is retained inside a guide portion of the outer member 102, defined by the cavity extending between the end cap 120 and the sleeve member 118. The second flange portion 150 is provided by a separate element in this example, such as a circlip, attached to a rod-shaped body of the inner member 104. For example, the circlip may be releasably attachable to a respective groove of the rod-shaped body to present an obstruction that abuts against respective opposing ends of the cavity as the inner member 104 is displaced relative to the outer member 102. The biasing element 136 may therefore be arranged inside the cavity, between the end cap 120 and the second flange portion 150 to urge the inner member 104 to project from the distal second end 112 of the outer member 102. The length of the inner member 104 is greater than that of the outer member 102 such that, in use, one end of the inner member 104 projects from the outer member 102. For example, the length of the inner member 104, or a respective portion thereof, may be calibrated to indicate, in a binary manner, whether the distance between the distal end of the internal thread formation of the opening and the locating surface, presented by the restriction, is less than, equal to, or greater than, a predetermined distance. For example, the length of the inner member 104 may be configured such that proximal first end 126 of the inner member 104 projects from the proximal end 106 of the outer member 104, or projects therefrom by a predetermined distance, when the distance between the distal end of the internal thread formation of the opening and the locating surface presented by the restriction is equal to the predetermined reference distance. In this manner, the projection of the first end 126 of the inner member 104 from the outer member 102, orthe projection by a particular distance, may be indicative that the thread depth is greater than or equal to a minimum specification, and therefore satisfies the tolerance. Conversely, if the first end 126 of the inner member 104 does not project proximally outside the outer member 102, or does so by less than a threshold distance, the gauge 100 may indicate that the thread depth is too short and out of tolerance. In this manner, the projection of the inner member 104 may serve as a means for visually indicating the thread depth of the threaded opening to an operator. In other examples, the gauge 100 may include other means for indicating the thread depth though and this example is not intended to be limiting on the scope of the invention. An exemplary method of assembling the gauge 100 shall now be described. Initially, the first end 126 of the inner member 104 may be inserted into the bore 114 of the outer member 102 (from the distal second end 112 of the outer member 102) and urged therethrough such that the inner member 104 projects from the proximal end 122 of the sleeve member 118. Thereafter the second flange portion 150 of the inner member 104 may be formed by attaching a circlip to a groove defined in the rod-shaped body, such that the first and second flange portions 148,150 are arranged either side of the tubular member 118, restricting the range of axial movement of the inner member 104 relative to the outer member 102. The biasing element 136 may then be arranged over the first end 126 ofthe inner member 104 and located against the second flange portion 150. Thereafter the end cap 120 may be fastened to the sleeve member 118 to complete the assembly and compress the biasing element 136 such that the inner member 104 is urged away from the second end 112 ofthe outer member 102. A method of using the gauge 100 to inspect the thread depth of a threaded opening shall now be described with additional reference to Figures 5 and 6. Figure 5 illustrates an exemplary method 500 according to an embodiment ofthe invention. To continue the previous example, the method 500 shown in Figure 5 may be carried out to inspect the workpiece 1 shown in Figure 1 and, particularly, to inspect the thread depth ofthe internal thread formation 38 defined in the opening 10. In this respect, it shall be appreciated that the threaded opening 10 includes an M8 thread formation and the gauge 100 used for the inspection may therefore have a complementary M8 thread formation for the purposes of this example. For example, the gauge 100 may be selected from a set of tools including a plurality of such gauges 100, each having an external thread formation 103 corresponding to a respective thread size specification. In step 502, the gauge 100 is inserted into the threaded opening 10 of the workpiece 1. Specifically, the outer member 102 is inserted into the opening and rotated such that the external thread formation 103 ofthe threaded end portion 116 engages the respective internal thread formation 38 ofthe threaded opening 10. The outer member 102 is therefore urged into the opening 10 and rotated until the respective thread formations 103, 38 are fully engaged, i.e. with a distal end 121 ofthe thread formation 103 on the outer member 102 engaging a final thread 39 ofthe internal thread formation 38. Such engagement may be indicated by a sudden increase in the torque required to continue turning the outer member 102, or by a threshold resistance torque being encountered. For example, an operator may handle the knurled surface ofthe end cap 120 and turn the outer member 102 into the opening 10 until they encounter a resistance that prevents or substantially inhibits further rotation without significant additional effort. In step 504, the inner member 104 is engaged with the distal locating surface 44 of the threaded opening 10, which is defined in this example by the restriction 42. In this condition, the outer member 102 is fully engaged with the internal thread formation 38 of the opening 10 and the inner member 104 may be axially displaced, as necessary, further into the opening 10 to engage the second end 126 of the inner member 104 with the distal locating surface 44. The relative displacement of the inner member 104 may be achieved passively, for example by way of the force from the biasing member 136 acting on the second flange portion 150, or actively by an operator providing an additional force to urge the inner member 104 into such engagement. For example, an operator may press on the proximal first end 126, to the extent that it protrudes from the outer member 102, to urge the opposing second end 108 into engagement with the restriction 42 of the threaded opening 10 and engage the locating surface 44. Figure 6 schematically illustrates the exemplary condition achieved in step 504. As shown, the distal end 121 of the thread formation 103 on the outer member 102 engages a final thread 39 of the internal thread formation 38 and the inner member 104 projects beyond the final thread 39 to engage the locating surface 44 defined by the restriction 42. The relative distance, D, between the distal end 121 of the thread formation 103 and the second end 108 of the inner member 104 is indicative of the thread depth, i.e. the depth of the final thread 39 into the opening 10, or relative to a reference position. It shall be appreciated that, in this condition, the opposing proximal end 126 of the inner member 104 may therefore be indicative as to whether the thread depth complies with the tolerance specification. For example, if the proximal end 126 is retracted into the bore 114 of the outer member 102, this may be indicative that the thread depth is greaterthan or equal to the specified requirement. Alternatively, if the proximal end 126 remains outside of the outer member 102, this may be indicative that the thread depth is less than the specified requirement and therefore inadequate. In each case, the condition is observable to the operator by inspection of the proximal end 106 of the gauge 100. In step 506, the relative position of the inner member 104 to the outer member 102 is therefore used to compare the thread depth of the internal thread formation 38 to a threshold depth. In this example, the relative position or displacement of the inner member 104 is determined relative to a reference feature of the outer member 102 and used to assess such thread depth. To give an example, the operator may determine whether or not the first end 126 of the inner member 104 protrudes from the proximal end 106 of the outer member 102, or the extent to which the first end 126 protrudes therefrom, and associate that determination with a respective thread depth. For example, the inner member 104 and the outer member 102 may be configured such that the distance between the distal end 43 of the threaded portion 18 and the locating surface 44 of the opening 10 is: (i) equal to a predetermined distance - if the first end 126 of the inner member 104 is flush with the first end 106 of the outer member 102; (ii) less than the predetermined distance - if the first end 126 of the inner member 104 protrudes externally from the first end 106 of the outer member 102; or (iii) greater than the predetermined distance - if the first end 126 of the inner member 104 is retracted inside of the outer member 102. The predetermined distance may be suitably calibrated to reflect a threshold thread depth relative to a further reference position. For example, the predetermined distance may correspond to a minimum thread depth tolerance, as defined relative to a proximal end of the opening 10. In which case, determining that the distance between the distal end 43 of the threaded portion 18 and the locating surface 44 of the opening 10 is less than or equal to the predetermined distance would indicate that the thread depth is acceptable (i.e. within the specified tolerance). However, if it is determined that the distance between the distal end 43 of the threaded portion 18 and the locating surface 44 of the opening 10 is greater than the predetermined distance, this would indicate that the thread depth is insufficient and unacceptable (i.e. outside of the specified tolerance). It shall be appreciated that, for this purpose, it may be further required to determine the depth from the reference position to the distal locating surface 44 of the threaded opening 10 in examples. Accordingly, the method 500 may further include a step 508 of determining the depth from the reference position to the distal locating surface 44 of the threaded opening 10. Such depth may be determined according to various methods, which are not intended to be particularly limiting on the scope of the invention. However, to give an example, the depth to the distal locating surface 44 may be determined using a conventional depth gauge, for example measured relative to the proximal end 12 of the opening 10, or the depth may be determined by a co-ordinate measuring machine (CMM), for example relative to a reference co-ordinate position. Once determined, the depth to the distal locating surface may be used as part of a calculation, or calibration of the gauge 100, to determine whether the whether the threaded opening 10 satisfies the threshold depth in step 506. If it is determined that the threaded opening 10 satisfies the inspection criteria, the workpiece 1 may pass the quality control process or one or more further checks may be performed on the threaded opening 10. For example, if the gauge 100 is configured as a go-gauge, confirming the tolerance of the minimum diameter of the thread formation 38, a further test may subsequently be carried out using a no-go-gauge, in step 510, to check the maximum tolerance of the diameter of the thread formation 38. As mentioned previously, the gauge 100 may therefore be removed from the opening 10 and an operator may attempt to insert an oversized no-go gauge, in step 510. Again the no-go gauge may be selected from the set of tools, which may further include a plurality of no-go gauges, each configured for a respective thread specification. If the thread formation 38 of the opening 10 inhibits or prevents insertion of the no-go gauge, then the tolerance of the thread formation 38 may be considered satisfactory. However, if the no-go gauge is insertable into the threaded portion 18 of the opening 10, the workpiece 1 may be rejected, as the diameter is too large for secure connection to the male counterpart. In this manner, the thread depth gauge 100 is usable to inspect a wider range of threaded openings, and particularly threaded openings that are relatively inaccessible by conventional means, leading to greater quality control of the formed workpiece 10. Moreover, an operator on an inspection line may be equipped with a set of tools including a plurality of the thread depth gauges 100, each configured fora respective screw thread size, and / or a plurality of corresponding no-go gauges, and thereby execute quality control inspections on a range of threaded openings and / or workpieces. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. Figure 7 shows another exemplary thread depth gauge 200 in accordance with an embodiment of the invention. The thread depth gauge 200 is substantially identical to the thread depth gauge 100, shown in Figure 1, except that the outer member 102 has a simpler cylindrical geometry, without any lead-in formations 144, and the biasing element 136 is arranged at the distal end 108 of the gauge 200, between the outer member 102 and first flanged portion 148, instead of the proximal end 106. Accordingly like references are used to describe like features of the thread depth gauge 200. In the example shown in Figure 7, the thread depth gauge 200 is shown, in situ, inserted inside a threaded opening 210 in the form of a blind hole. An end face 242 presents the restriction in this example and a tapered surface leading toward that end face forms a distal locating surface 244, engaged by the second end 108 of the inner member 104. In other examples, it shall be appreciated that the inner member 104 may be movably coupled to the outer member 102 by various means for achieving relative translational and / or rotational movement. For example, although a slidable coupling is depicted in Figures 2 to 4, it shall be appreciated that the movable coupling may take the form of a threaded coupling in other examples, for example in the manner of a leadscrew or a ratchet mechanism for adjusting the axial position of the inner member 104 relative to the outer member 102. Similarly, whilst the distance between the end of the thread formation 38 and the locating surface 44 is indicated by the projection of the inner member 104 from the proximal end 106 of the outer member 102 in the examples described above, it shall be appreciated that the indicator means could take many other forms within the scope of the present invention for indicating that distance based on the relative position of the inner member 104. For example, although the inner member 104 provides an end projection in the examples described above, in other examples the inner member 104 may include a radial projection, towards the proximal end thereof, extending through a respective slot in the outer member 102 for indicating the relative position. For example, the outer member 102 may include a measurement scale or similar indicator alongside the slot and against which the position of the projection may be compared to determine the relative position of the inner member 104. In other examples, the indicator means may include a sensor (not shown), interposed between the inner and outer members 102, 104, for measuring the position of the inner member 104 relative to the 5 outer member 102. A user interface device (not shown) with a display may be provided on the outer member 102, towards the proximal end 106 of the gauge 100, and connected to the sensor to indicate the relative position. In this manner, the relative position may be expressly measured and communicated to an operator by way of the display, for example as a continuous measurement or a binary tolerance judgement. It shall be appreciated that the user interface device may include one or more processor(s) in the manner of other depth 10 gauges and / or callipers for allowing an operator to set a reference depth for example and compare the determined thread depth to the tolerance. However, such examples shall not be described in detail here to avoid obscuring the invention. 15

Claims

1. A thread depth gauge comprising:a tubular outer member; andan inner member, received in a bore of the outer member;wherein the outer member comprises a threaded end portion for insertion into a threaded opening of a workpiece, the threaded end portion comprising an external thread formation that extends along a longitudinal axis of the outer member, from a proximal first end to a distal second end;wherein the inner member is movably coupled to the outer member and axially movable to engage a distal end of the inner member with a distal locating surface of the threaded opening when the outer member is inserted into the threaded opening of the workpiece,wherein the length of the inner memberthat extends between the second end of the thread formation and the locating surface is indicative of the thread depth relative to a reference position; andwherein the thread depth gauge further comprises an indicator means for indicating the thread depth to an operator.

2. The thread depth gauge according to claim 1, wherein a relative position of a proximal end of the inner member to the outer member is indicative of the thread depth when the distal end of the inner member engages the locating surface, the relative position acting as the indicator means.

3. The thread depth gauge according to claim 2, wherein the proximal end of the inner member projects outside of a proximal end of the outer member when the distal end of the inner member engages the locating surface to indicate that the thread depth is less than a reference depth; and / or wherein the proximal end of the inner member is withdrawn inside the outer member when the distal end of the inner member engages the locating surface to indicate that the thread depth is greater than or equal to the reference depth.

4. The thread depth gauge according to claim 1, wherein the outer member includes an axial slot and the inner member includes a projection, extending through the slot, and acting as the indicator means for indicating the thread depth when the distal end of the inner member engages the locating surface.

5. The thread depth gauge according to claim 4, wherein the outer member further includes a measurement scale, arranged along the axial slot, for indicating the thread depth when the distal end of the inner member engages the locating surface.

6. The thread depth gauge according to claim 1, wherein the indicator means comprises: a sensor for measuring displacement of the inner member relative to the outer member; and a display for indicating the thread depth based on the measured displacement.

7. The thread depth gauge according to any preceding claim, wherein the external thread formation corresponds to an industry standard thread size, optionally being an ISO metric thread size.

8. The thread depth gauge according to claim 7, wherein the external thread formation is configured as a go gauge forthat thread size.

9. The thread depth gauge according to any preceding claim, further comprising a biasing element arranged to urge the inner member to engage the locating surface when the outer member is inserted into the threaded opening of the workpiece.

10. The thread depth gauge according to any preceding claim, wherein the outer member comprises a sleeve member and an end cap, the end cap being releasably coupled to a proximal end of the sleeve member with a flange portion of the inner member being retained in a cavity defined between the end cap and the proximal end of the sleeve member to guide the axial movement of the inner member relative to the outer member.

11. The thread depth gauge according to claims 9 and 10, wherein the biasing element is arranged in the cavity, between the end cap and the flange portion of the inner member.

12. The thread depth gauge according to claim 10 or claim 11, where the inner member comprises a rod-shaped probe and the flange portion is provided by a circlip member attached to the probe.

13. A set of tools for inspecting threaded openings, the set of tools comprising a plurality of thread depthgauges according to any preceding claim, the external thread formation of each thread depth gauge corresponding to a respective screw thread size.

14. The set of tools according to claim 13, further comprising a depth gauge for determining the depth of the distal locating surface from the reference position.

15. A method of inspecting the thread depth of a threaded opening using a thread depth gauge according to any one of claims 1 to 12 or a set of tools according to any one of claims 13 to 14, the method comprising: obtaining a depth of the distal locating surface of the threaded opening from a reference position; inserting the outer member of the thread depth gauge into the threaded opening;engaging the distal end of the inner member with the locating surface; and comparing the thread depth, indicated by the gauge, to a threshold depth.Application No: GB2402996.9Claims searched: 1-15Examiner: Contract Unit ExaminerDate of search: 17 October 2024Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-15 CN113532240 A (HANGZHOU DAHE THERMO MAGNETICS CO LTD) paragraphs [0001] - [0007], [0025] - [0029]; figures 3-5, paragraphs [0020] - [0024]; figures 1, 2 X 1-15 CN218916179U (MAGNA POWERTRAIN JIANGXI CO LTD) paragraphs [0024] - [0030]; figure 1 X 1-15 CN210664283 U (TIANJIN TIANHA1PREC FORGING CO LTD) paragraphs [0001], [0026] - [0048]; figures 1-4 X 1-15 CN207163382U (QINGLING MOTORS GROUP CO LTD) paragraphs [0001] - [0003], [0053] - [0064]; figures 2-4 X 1-15 CN210718966 U (ZHANGZHOU HENGCHANG MACHINERY MFG CO LTD) paragraphs [0001] - [0004], [0012] - [0022]; figures 1-3 v A 1-15 CN204007465 U (WEICHAI POWER CO LTD) the whole documentCategories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO &US patent documents classified in the following areas of the UKC~X :Worldwide search of patent documents classified in the following areas of the IPC____________GO IB_________________________________________________________The following online and other databases have been used in the preparation of this search reportInternational Classification:Subclass Subgroup Valid From GO IB 0003 / 28 01 / 01 / 2006 GO IB 0003 / 48 01 / 01 / 2006

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