GB2338067A

GB2338067A - Comparative measuring instrument

Info

Publication number: GB2338067A
Application number: GB9909331A
Authority: GB
Inventors: John Ian Mcturk
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-04-23
Filing date: 1999-04-23
Publication date: 1999-12-08
Also published as: GB9808525D0; GB9909331D0

Abstract

A comparative measurement instrument or calipers has a slide assembly (10) and a central slide support (11). Two abutments (13, 22) are slidably mounted on the slide assembly (10) and are fixable in selected positions along the slide assembly (10) via anchoring means (16, 17, 20, 21). The abutments (13, 22) can be fixed at positions which are symetrical about the central slide support (11) allowing the measuring instrument to be balanced.

Description

2338067 1 2 3 4 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25

Improvements in or relating to Comparative Measuring Instruments This invention relates to comparative measuring instruments, and relates more particularly but not exclusively to instruments for measuring the difference (if any) between the mutual separation of two locations and a predetermined datum distance.

For the purpose of measuring the external diameter of a pipe, it is known to employ callipers, ie a slide having a fixed abutment at one end of the slide and another abutment selectively movable along the slide to a predetermined position at which it is secured during measurements. The callipers include a DTI P'dial test indicator", which is a known device for accurately converting linear movement of a plunger into angular movement of a pointer around a calibrated dial) mounted on the fixed abutment such that a feeler-pin of the DTI engages the pipe at a location which is diametrally opposite the location engaged during measurement by the selectively movable abutment. The callipers are pre-set by sliding the selectively movable abutment along the slide to a position at which the selectively movable abutment has a separation from a movable tip of the 2 1 2 3 4 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 feeler-pin of the DTI on the fixed abutment marginally lesser than the diameter to be measured. At this position, the selectively movable abutment is rigidly anchored to the slide. A length gauge or other suitable member having a length exactly equal to the idealised diameter (ie exactly what the diameter should be) is placed between the abutments with one end of the length gauge in contact with the selectively movable but rigidly anchored abutment, and with the other end of the length gauge in a suitable position to be contacted by the feeler-pin of the DTI mounted on the fixed abutment. The feeler-pin is released to be biassed by the internal spring of the DTI against the adjacent end of the length gauge. If using a mechanical operation DTI, the calibrated dial of the DTI is then set to zero and the DTI revolution counter reading is then noted, this reading being the reading that the DTI will show during measurement of the diameter of an actual pipe, if the pipe has exactly the intended diameter. If the DTI reading during actual measurement indicates a greater extension of the feeler-pin, then the actual diameter of the pipe is less than the intended diameter. Correspondingly, if the DTI reading during actual measurement indicates a lesser displacement of the feeler-pin, then the actual diameter of the pipe is greater than the intended diameter. If an electronic indicator gauge is used (i place of a mechanical DTI), then the electronic gauge will indicate zero when set to the length gauge, and will subsequently indicate as plus or minus in the circumstances described above.

The above procedure enables the callipers to measure the diameter of a succession of pipes of the same nominal diameter, eg in the serial production of machined pipes where the actual diameters of successive 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 21 22 23 24 25 26 27 28 29 30 31 32 33 34 36 pipes may vary slightly from an intended diameter, the DTI reading in each case indicating the variance from intended diameter.

Other arrangements are known which allow measurement of internal diameters of pipes. Fitting the feeler-pin and the contact portion of the selectively movable abutment with suitably dimensioned ball-ended probes (or Illocator balls") will enable the measurement of pitch diameters of external screw-threads.

When it is intended to measure a substantially different dimension, the selectively movable abutment is unanchored and moved along to slide to a suitable new position where it is rigidly anchored, whereafter the callipers are set with a suitable length-calibrated gauge.

With such callipers, comparative diameter measurements are possible on a repetitive basis, but the callipers can be awkward to handle, especially in the larger sizes, e.g. much above 20 inches (50 centimetres). Such awkwardness arises at least in part from the inherently unbalanced weight distribution of large fixed-end callipers, which is exacerbated by the disproportionately increased weight of larger calliper sizes due to the need to maintain adequate rigidity over their greater abutment separations.

According to the present invention, there is provided a comparative measuring instrument for measuring and comparing the difference (if any) between the mutual separation of two locations and a predetermined datum distance, the measuring instrument comprising slide means, first and second abutment means each slidable on said slide means for selective variation of the mutual 4 1 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 separation of said first and second abutment means, said first and second abutment means each being selectively anchorable at a selected location along said slide means, said first and second abutment means each being constructed or adapted to contact a respective one of said two locations in use of the measuring instrument.

The comparative measuring instrument is preferably substantially balanced by substantially symmetrical disposition of its abutments about the midlength of the slide means for substantially equal weight distribution to enable confident handling by the user, and to facilitate use of the instrument for gauging.

Said slide means may comprise a plurality of slide members mutually clamped together at or near opposite ends thereof, and preferably also substantially at the midlength thereof.

Said first and second abutment means may each comprise a slide portion slidable on said slide means, and an arm portion detachably secured to the respective said slide portion to project laterally of said slide means by a certain distance, said arm portion being substitutable by a further arm portion detachably securable to said slide portion to project laterally of said slide means by a respective distance different from said certain distance.

Said first abutment means may rigidly mount a testpiece-contacting member, and said second abutment means may mount a dial test indicator providing a display indicative of displacement of a displacementsensitive member of said indicator. The dial text indicator may be a mechanical operating indicator, or 1 2 3 4 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 an electronic indicator. Said second abutment means may pivotally mount a lever means carrying a respective testpiece-contacting member, said lever means transferring movement of said testpiece-contacting member to said displacement-sensitive member of said indicator. At least one of said testpiece-contacting member and said respective further testpiece- contacting member is preferably substantially spherical on parts thereof contacting the testpiece in use of the measuring instrument.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which:

Fig 1 is a top plan view of a first embodiment of comparative measuring instrument in accordance with the invention; Fig 2 is a side view of the first embodiment; Fig 3 is a front view of the first embodiment; Fig 4 is a fragmentary sectional view, to a muchenlarged scale, of a pair of anchoring means for one of the abutments in the first embodiment, showing one fixing means in a retracted position and the other fixing means in a locking position; Fig 5 is a plan view of an alternative form of movable abutment suitable for use in the first embodiment; Fig 6 schematically depicts the first embodiment in use for measuring an internal screw thread; Fig 7 schematically depicts the first embodiment in use 6 for measuring an external screw thread; 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Fig 8 is a plan view of a second embodiment of comparative measuring instrument, this second embodiment having detachable and exchangeable abutments; Fig. 8a is a fragmentary view, to an enlarged scale, of part of the second embodiment; Fig 9 is a plan view of a third embodiment of comparative measuring instrument; Fig 10 is a front view of the third embodiment in use for measuring a narrow groove on a flange face; Fig 11 is a cross-section of an end stop of the third embodiment; Fig 12 is a cross-section of the anchoring means of a movable abutment of the third embodiment; Fig 13 is an end view of one of the movable abutments of the third embodiment; Figs 14 and 15 are respectively plan and front views of the third embodiment in use for measuring a wide groove in a flange face; and Figs 16 and 17 are respectively plan and front views of a modification of the third embodiment.

Referring first to Figs 1, 2 and 3, these illustrate a first embodiment of comparative measuring instrument in accordance with the invention. The first embodiment comprises a slide assembly 10 of slide rails 10a, 10b, 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 & 10c, a central slide support 11, and end stops 12 and 23. The central slide support 11 comprises anchoring means 18 and 19 by which the slide support 11 can be clamped to the slide rails. The end stops 12 and 23 have similar anchoring means. Each of the central slide support 11 and the end stops 12 & 23 is clamped to the slide rails 10a, 10b, & 10c so as to provide a lightweight but rigid assembly of parallel slide rails.

The first embodiment also comprises adjustable abutments 13 and 22 which are selectively slidable along the slide assembly 10. When at a selected position, the abutments 13 and 22 are anchored by anchoring means 16, 17, 20 and 21, (separately detailed in Fig 4). The outboard end of the abutment 13 remote from the slide assembly 11 carries a mounting 14 for a ball locator (not shown in Figs 1-3). The outboard end of the movable abutment 22 remote from the slide assembly 10 incorporates a locator 14 for a measuring ball (not shown in Figs 1-3), and a locator 15 for a DTI (not shown in Figs 1-3) When measuring the external screw thread of a pipe (for example), the measuring instrument is adjusted accordingly so as to match the diameter of the pipe, by slackening the abutment anchoring means 16, 17, 20, and 21, adjusting the positions of the abutments 13 & 22 along the slide assembly 10, and then re-anchoring the abutments 13 & 22 at the selected positions. These positions are preferably selected to be not only at a suitable mutual separation, but also substantially equidistant on either side of the central slide support 11 so that the measuring instrument as a whole is substantially balanced about its middle.

Referring now to Fig 4, this illustrates a fragmentary 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 sectional view of the anchoring means on either one of the abutments 13 and 22, and of the similar anchoring means on the central slide support 11. Re-location of the abutments and/or of the slide support is carried out by loosening of the hand screws 30 and 31, thus allowing locking bushes 32 and 33 to become free. is aided by a conical compression spring 35 and a cylindrical compression spring 36 which push the locking bush 32 away from contact with the face of recess 39, after loosening of the screw 30. The abutment and/or slide clamp is now free to have its position adjusted. The abutment 13 (or 22) may also mount attachments (not shown) affixed by means of the internally threaded holes 37 and 38 also used for tightening of the clamping screws 30 & 31. Such attachments could (for example) be a ball-shaped thread-tracking device for pitch measurement of grooves and undercuts to flange faces as will subsequently be described in connection with the third embodiment.

Where it is desired to reduce the overall weight of a measuring instrument in accordance with the invention (which could be particularly advantageous in the larger sizes of instrument), a weight reducing scheme such as is depicted in Fig 5 could be adopted. The weight reducing modification of the abutments 13 & 22 comprises cutting or otherwise forming a series of holes 50 located and dimensioned so as to provide a useful reduction in overall weight but with minimal reduction of strength and rigidity. Additional or alternative forms of weight reduction comprise relieving selected parts of the abutments by routing or otherwise forming channels.

Referring again to Fig 1, the abutments 13 and 22 both have respective means for selective attachment of a DTI 9 1 2 3 4 5 6 7 8 9 11 12 13 14 is 16 17 18 19 20 21 22 23 24 26 27 28 29 31 32 33 34 36 (not shown) or a measuring ball locator (not shown) which may comprise various sizes of measurement balls or conical points (not shown). At the choice of the operator, the abutment 13 mounts either the measurement ball locator or the DTI, and conversely the abutment 22 mounts either the DTI or the measurement ball locator. With provision for interchanging the locations of the measuring ball locator and the DTI, both internal and external screw threads can be measured by the first embodiment as schematically depicted in Figs 6 and 7 respectively wherein the first embodiment can be seen in use for measuring an internal screw thread 40 and external screw thread 42, using a DTI 44 and a measuring ball locator 46 positioned to suit the respective type of measurement.

Referring now to Fig 8, a second embodiment 80 of measuring instrument in accordance with the invention is adapted to be provided with a pair of interchangeable abutments 81. This interchangeability enables the instrument 80 to measure greater or lesser diameters of screw threads if necessary or desirable.

The adaptation of the instrument 80 comprises forming the abutment slides 82 as separate components (i.e. not integral with the abutments 81 as in the first embodiment). Since the slides 82 will be of a light metal such as an aluminium alloy, the slides 82 are each provided with a respective adaptor plate 84 of a relatively hard metal permanently secured to the front face of the slide 82 by means of a pair of screws 86. The adaptor plate 84 is formed with a pair of threaded holes 88 for a purpose to be detailed below.

The pair of detachable abutment arms 81 are each provided with shoulders 90 having holes 92 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 therethrough. Fastening screws 94 pass through the holes 92 and into the threaded holes 88 in the adaptor plate 84 so as to anchor the abutment arms 81 to the abutment slides 82. Alignment of the abutment arms 81 with respect to the abutment slides 80 is ensured by means of locating pins 96 in the arms 81 which register in holes in the adaptor plates 84. The adaptor plates 84 are similarly positionally stabilised on the slides 82 by locating pins 98 in the slides 82 which also register in holes in the adaptor plates 84.

The outboard ends of the abutment arms 81 (i. e. the ends remote from the slides 82) incorporate mounting holes for attachment of a ball locator. 14 and a DTI locator 15 (as shown in Fig. 8). With the arrangement shown in Fig. 8, and with a measuring ball (not shown) in the locator 14, external diameters can be measured by the measuring instrument 80. Simply by transposing the two abutment arms 81, or by reversing the arms 81 on their respective slides 82 (without transposition), the instrument 80 is converted for measurement of internal diameters.

When it is desired to transform or reverse the arms 81 as referred to above, or to substantiate the arms with other abutment arms of a different length, the fastening screws 94 are unscrewed, the now-detached arms 81 are repositioned or replaced, and the screws 94 are re-inserted and tightened. Substitute abutment arms will have locating pins matching the locating pins 96.

Referring now to Figs 9 and 10, a third embodiment 100 of measuring instrument in accordance with the invention is illustrated. The third embodiment 100 comprises three parallel slide rods 102, 104, and 106 4 6 7 8 9 10 11 12 13 14 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 rigidly held mutually parallel by means of a central clamp 108 and a pair of end clamps 110 & 112 to form a 3 slide assembly. The clamps 108, 110, & 112 are each anchored to the slide rods 102, 104, & 106 by respective anchoring means generally as previously described with reference to Fig 4 (except for the replacement of hand-screws with flush-headed set screws), and as shown in cross-section in Fig 11.

Between the central clamp 108 and the right-end clamp 110, the slide rods 102, 104, & 106 slidably mount a first movable abutment 114. Similarly, a second movabl abutment 116 is slidably mounted on the slide rods between the central clamp 108 and the leftend clamp 112. Each of the slidable abutments 114 and 116 can be independently selectively anchored at a selected location along the slide assembly by a respective anchoring means generally similar to that described with reference to Fig 4, and as shown in cross-section in Fig 12.

e Referring particularly to Fig 10, the first abutment 114 rigidly supports a locator ball 118 on the lower end of a mounting rod 120. The second abutment 116 supports a locator ball 122 on the lower end of a mounting arm 124 which is pivotally mounted about a horizontal pivot 126 carried by the second abutment 116 in an alignment which is orthogonal in plan to the lengths of the slide rods 102, 104, & 106. A DTI (dial test indicator) 128 is carried atop the second abutment 118 such that the DTI feeler-pin 130 is acted upon by the upper end of the arm 124. Thereby movement of the locator ball 122 about the pivot 126 is translated into inverse movement of the upper end of the arm 124 and corresponding displacement of the feeler-pin 130 which, in turn, registers upon the dial of the DTI 128. A 12 1 2 3 4 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 right-end view of the abutment 116 and of the components carried thereby is shown in Fig 13.

Use of the measuring instrument 100 for comparative checking of the dimensions of a narrow groove 990 is depicted in Fig 10, the movable abutments 114 and 116 being anchored at respective positions relatively close to the centre of the slide assembly (compare Fig 10 with Fig 15).

Use of the measuring instrument 100 for comparative checking of the dimensions of a wide groove 992 is depicted in Figs 14 and 15, the movable abutments 114 and 116 being anchored at respective positions relatively far from the centre of the slide assembly (compare Fig 15 with Fig 10).

It is to be particularly noted that in the configurations of Figs 9 & 10, and of Figs 14 & 15, the measuring instrument 100 had its movable abutments 114 and 116 disposed substantially symmetrically about the midlength of the slide assembly (i.e. in each of these two configurations, the movable abutments were on either side of and about equally displaced from the central slide clamp 108). This approximate symmetry results in an approximate static mechanical balance, and consequent ease of handling of the measuring instrument in comparison to prior art instruments wherein mass tended to be concentrated at or towards one end of the respective slide assembly.

Although (approximate) symmetry is desirable and technical provision for selecting (approximate) symmetry is an essential feature of the present invention, actual symmetrical disposition of the movable abutments is not essential in all circumstances 13 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 for correctness of comparative measurements. In certain circumstances, it may be necessary or desirable to adopt a nonsymmetrical disposition of the abutments, for example if the clearance adjacent the dimension being checked was insufficient to accomodate one end of the slide assembly. In an extreme circumstance, e.g. where clearance is minimal, it is possible for (say) the first abutment 114 to be dismantled and removed, and the mounting rod 120 with its locator ball 118 to be temporarily remounted on the end clamp 110, but with the second movable abutment 116 and its attachments remaining unaltered. This provides the modified measuring instrument depicted in Figs 16 and 17 wherein the clearance required around the right end of the slide assembly is minimal (compare Fig 17 with Fig 10) Any suitable known diameter for the part-spherical locator balls 118 and 122 may be employed, the locator balls being substantially spherical on all parts which could come into gauging contact. The rod 120 upon which the ball 118 is carried preferably has ground parallel shanks to allow the ball to have its rotational alignment varied from time to time, (the rod being locked for the time being at each selected rotational position), such as to distribute wear on the ball and thereby effectively to increase its useful life.

The present invention is not restricted to the several exemplary embodiments described above, and other modifications and variations can be adopted without departing from the scope of the invention as defined in the appended claims.

14 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Claims

CLAIMS:

1. A comparative measuring instrument for measuring and comparing the difference (if any) between the mutual separation of two locations and a predetermined datum distance, the measuring instrument comprising slide means, first and second abutment means each slidable on said slide means for selective variation of the mutual separation of said first and second abutment means, said first and second abutment means each being constructed or adapted to contact a respective one of said two locations in use of the measuring instrument.

2. A comparative measuring instrument as claimed in claim 1, wherein the instrument is substantially balanced by substantially symmetrical disposition of its abutments about the mid-length of the slide means.

3. A comparative measuring instrument as claimed in claim 1 or claim 2, wherein said slide means comprises a plurality of slide members mutually clamped together at or near opposite ends thereof.

4. A comparative measuring instrument as claimed in claim 3, wherein said plurality of slide members are mutually clamped together substantially at the midlength thereof.

5. A comparative measuring instrument as claimed in any preceding claim, wherein said first and second abutment means each comprise a slide portion slidable on said slide means, and an arm portion detachably secured to the respective said slide portion to project laterally of said slide means by a certain distance, said arm portion being substitutable by a further arm portion detachably securable to said slide portion to project 1 laterally of said slide means by a respective distance different from said certain distance.

3 4

6 7 8 9 11 12 13 14 is 16 17 18 19 20 21 24 25 26 27 28 29 30 31 32 33 34 6. A comparative measuring instrument as claimed in any preceding claim, wherein said first abutment means rigidly mounts a testpiece-contacting member, and said second abutment means mounts a dial test indicator providing a display indicative of displacement of a displacement- sensitive member of said indicator.

7. A comparative measuring instrument as claimed in claim 6, wherein said second abutment means pivotally mounts a lever means carrying a respective further testpiece-contacting member, and said lever means transfers movement of said respective further testpiece-contacting member to said displacementsensitive member of said indicator.

8. A comparative measuring instrument as claimed in claim 7, wherein at least one of said testpiececontacting member and said respective further testpiececontacting member is substantially spherical on parts thereof contacting the testpiece in use of the measuring instrument.

9. A comparative measuring instrument substantially as hereinbefore described with reference to the accompanying drawings.