CN220932241U - Force measuring calibration device for three-point inside micrometer - Google Patents

Abstract

The utility model relates to a force measuring calibration device for a three-point inside micrometer. The force measuring calibration device comprises: a support bracket on which a V-shaped groove having a first support slope and a second support slope opposite to each other is provided, and the first support slope and the second support slope are configured to support a first measuring jaw and a second measuring jaw of a three-point inside micrometer, respectively, such that a third measuring jaw of the three-point inside micrometer is positioned to extend along an angular bisector of the V-shaped groove and toward a direction away from the V-shaped groove; and the force measuring mechanism is provided with a force measuring head which can be abutted against the third measuring claw, so that the force measuring mechanism can detect the acting force exerted on the force measuring head by the third measuring claw when the force measuring screw of the three-point inside micrometer is rotated. The force measuring calibration device can conveniently detect the measuring force of each measuring claw of the three-point inside micrometer, thereby ensuring the measuring precision of the three-point inside micrometer.

Description

Force measuring calibration device for three-point inside micrometer

Technical Field

The utility model relates to the technical field of test equipment, in particular to a force measuring calibration device for a three-point inside micrometer.

Background

A three-point internal micrometer (Holtest), also called as three-jaw internal micrometer, is an internal micrometer which uses the principle of screw pair to make three measuring jaws uniformly spaced by 120 deg. make radial displacement by means of rotary column-shaped Archimedes screw body or moving cone body, and make them contact with the measured internal hole so as to measure the internal hole size. The three-jaw inside micrometer is an automatic centering measuring tool for measuring the inside diameter, has the characteristics of high measuring precision, stable indication value, simple operation and the like, and is widely used for measuring the aperture of through holes, blind holes, step holes and the like.

Because the measuring claw of the three-point inside micrometer directly influences the measuring accuracy on the acting force of the measured inner hole, the measuring force needs to be detected before the three-point inside micrometer is used for measuring the aperture. However, since the three-point inside micrometer has a special shape, it is difficult to detect the measuring force of the measuring claw, and it is difficult to ensure the measuring accuracy of the three-point inside micrometer.

Accordingly, there is a need in the art for a new solution to the above-mentioned problems.

Disclosure of utility model

The utility model provides a force measuring calibration device for a three-point inside micrometer, which aims to solve or improve the technical problem that the measuring force of a measuring claw of the three-point inside micrometer is difficult to detect in the prior art to a certain extent. The force measurement calibration device comprises: a support bracket on which a V-shaped groove having a first support slope and a second support slope opposite to each other is provided, and the first support slope and the second support slope are configured to support a first measuring jaw and a second measuring jaw of the three-point inside micrometer, respectively, such that a third measuring jaw of the three-point inside micrometer is positioned to extend along an angular bisector of the V-shaped groove and toward a direction away from the V-shaped groove; and a force measuring mechanism having a force measuring head abuttable against the third measuring jaw such that the force measuring mechanism can detect a force exerted by the third measuring jaw on the force measuring head when the force measuring screw of the three-point inside micrometer is rotated.

It will be appreciated by those skilled in the art that the force calibration device for a three-point inside micrometer of the present utility model includes a support bracket and a force measuring mechanism. Wherein, be equipped with the V-arrangement groove on the support frame, the V-arrangement groove has the first inclined plane and the second inclined plane that support of mutual opposition, and first inclined plane and second inclined plane support can support the first measurement claw and the second measurement claw of three-point inside micrometer respectively for the third measurement claw of three-point inside micrometer is located along the angular bisector of V-arrangement groove and extends towards the direction of keeping away from the V-arrangement groove. The force measuring mechanism is provided with a measuring head which can be abutted against the third measuring claw, so that the force measuring mechanism can conveniently detect the acting force exerted on the measuring head by the third measuring claw when the force measuring screw of the three-point inside micrometer is rotated. Through the arrangement, the force measuring calibration device can conveniently detect the measuring force of each measuring claw of the three-point inside micrometer, so that the measuring precision of the three-point inside micrometer is ensured.

In the above preferred technical solution of the force measurement calibration device for a three-point inside micrometer, the force measurement calibration device further includes: the base, the support frame detachably is fixed on the base, the force measuring mechanism is fixed on the base in a lifting mode and is positioned on the upper portion of the support frame. Through setting up the base, can be with support bracket and dynamometry mechanism stably fixed on the base to improve the calibration accuracy. Further, the support bracket is detachably fixed on the base, and can be conveniently disassembled, maintained and replaced according to actual needs. Further, the force measuring mechanism is configured to be liftably fixed to the base and positioned at an upper portion of the support bracket, so that the force measuring head of the force measuring mechanism can be conveniently abutted against the third measuring claw.

In the above preferred technical solution of the force measurement calibration device for a three-point inside micrometer, the force measurement calibration device further includes: the auxiliary support bracket is movably arranged on the base and can be positioned on one side of the support bracket far away from the force measuring mechanism, and the auxiliary support bracket is provided with a limit groove capable of supporting the blade of the three-point inside micrometer. The auxiliary support bracket can conveniently support the body of the three-point inside micrometer, and avoid the influence of larger shaking and displacement of the three-point inside micrometer on the calibration accuracy.

In the above preferred technical solution of the force measuring calibration device for a three-point inside micrometer, the auxiliary support bracket is provided with a height adjusting member for adjusting the height of the limit groove relative to the base. The height adjusting piece is arranged, so that the height of the limiting groove relative to the base can be conveniently adjusted, and the ruler body of the three-point inside micrometer always keeps a position approximately parallel to the base.

In the above preferred technical solution of the force measuring calibration device for a three-point inside micrometer, the auxiliary support bracket is further provided with a pressing plate capable of restraining the blade in the limit groove. The setting of clamp plate can further retrain the blade, prevents that it from rocking or displacement from appearing.

In the preferable technical solution of the force measurement calibration device for a three-point inside micrometer, the first support inclined surface and the second support inclined surface form a predetermined included angle, and the predetermined included angle is 60 °. Through the arrangement, the measuring claws are enabled to be propped against the first supporting inclined plane or the second supporting inclined plane approximately vertically at the uniform intervals of 120 degrees, so that the stress of each measuring claw is more uniform, and the calibration precision is further improved.

In the above preferred technical solution of the force measurement calibration device for a three-point inside micrometer, the flatness of the first support inclined surface and the second support inclined surface is less than or equal to 2 μm. Through the arrangement, the first supporting inclined plane and the second supporting inclined plane can be provided with smooth surfaces, friction force between the measuring claw and the first supporting inclined plane and friction force between the measuring claw and the second supporting inclined plane when the measuring claw and the second supporting inclined plane are abutted against each other are reduced, and therefore calibration accuracy is improved.

In a preferred embodiment of the force measuring calibration device for a three-point inside micrometer, the first support ramp and the second support ramp are symmetrically arranged with respect to a vertical section of the support bracket. Through the arrangement, the V-shaped groove can have a simple and regular structure, and is convenient to process and manufacture.

In the preferable technical scheme of the force measurement calibration device for the three-point inside micrometer, a first interval is formed between the bottom of the first supporting inclined plane and the bottom of the second supporting inclined plane, and a second interval is formed between the top of the first supporting inclined plane and the top of the second supporting inclined plane, wherein the first interval is 0mm, and the second interval is 100mm; or the first interval is 80mm, and the second interval is 190mm; or the first spacing is 160mm and the second spacing is 270mm. Through the arrangement, the support bracket can have various dimension specifications so as to meet the force measurement and calibration requirements of three-point inside micrometer with different measuring ranges.

In the above preferred technical solution for the force measuring calibration device of a three-point inside micrometer, the support bracket is made of stainless steel, cast iron or granite. Through the arrangement, the material of the support bracket can be enriched, and the support bracket has good mechanical strength.

Drawings

Preferred embodiments of the present utility model are described below with reference to the accompanying drawings, in which:

FIG. 1 is a schematic structural view of an embodiment of a force calibration device for a three-point inside micrometer of the present utility model;

FIG. 2 is a schematic structural view of an embodiment of a support bracket of the force calibration device for a three-point inside micrometer of the present utility model;

Fig. 3 is a schematic structural view of an embodiment of a support bracket of the force measuring calibration device for a three-point inside micrometer of the present utility model supporting the three-point inside micrometer.

List of reference numerals:

100. A force measuring calibration device; 110. a base; 120. a support bracket; 121. a support bracket body; 122. a V-shaped groove; 1221. a first support ramp; 1222. a second support ramp; 1223. a horizontal connection surface; 130. an auxiliary support bracket; 131. an auxiliary support bracket body; 132. a height adjusting member; 133. a pressing plate; 140. a force measuring mechanism; 141. a force measuring mechanism body; 1411. a force measuring head; 142. a liftable support; 200. three-point inside micrometer; 210. a force measuring screw; 220. a micro-cylinder; 230. a fixed sleeve; 240. a lengthening rod; 250. a main body, 261, a first measuring jaw; 262. a second measuring jaw; 263. and a third measuring claw.

Detailed Description

Preferred embodiments of the present utility model are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are merely for explaining the technical principles of the present utility model, and are not intended to limit the scope of the present utility model.

It should be noted that, in the description of the present utility model, terms such as "upper," "lower," "left," "right," "inner," "outer," and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, which are merely for convenience of description, and do not indicate or imply that the apparatus or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present utility model. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

Furthermore, it should be noted that, in the description of the present utility model, unless explicitly specified and limited otherwise, the terms "mounted," "configured," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be directly connected, can be indirectly connected through an intermediate medium, and can also be communicated with the inside of two elements. The specific meaning of the above terms in the present utility model can be understood by those skilled in the art according to the specific circumstances.

In order to solve or improve the technical problem that the measuring force of the measuring claw of the three-point inside micrometer is difficult to detect in the prior art to a certain extent, the utility model provides a force measuring calibration device 100 for the three-point inside micrometer 200. The force calibration device 100 comprises: a support bracket 120, on which a V-shaped groove 122 is provided, the V-shaped groove 122 having a first support slope 1221 and a second support slope 1222 opposite to each other, and the first support slope 1221 and the second support slope 1222 being configured to support the first measuring jaw 261 and the second measuring jaw 262, respectively, of the three-point inside micrometer 200 such that the third measuring jaw 263 of the three-point inside micrometer 200 is positioned to extend along an angular bisector of the V-shaped groove 122 and toward a direction away from the V-shaped groove 122; and a force measuring mechanism 140, the force measuring mechanism 140 having a force measuring head 1411 that can be abutted against the third measuring jaw 263, such that the force measuring mechanism 140 can detect the force exerted by the third measuring jaw 263 on the force measuring head 1411 when the force measuring screw 210 of the three-point inside micrometer 200 is rotated.

FIG. 1 is a schematic structural view of an embodiment of a force calibration device for a three-point inside micrometer of the present utility model; FIG. 2 is a schematic structural view of an embodiment of a support bracket of the force calibration device for a three-point inside micrometer of the present utility model; fig. 3 is a schematic structural view of an embodiment of a support bracket of the force measuring calibration device for a three-point inside micrometer of the present utility model supporting the three-point inside micrometer. As shown in fig. 1-3, in one or more embodiments, the force calibration device 100 of the present utility model for a three-point inside micrometer 200 includes a base 110, a support bracket 120, an auxiliary support bracket 130, and a force measuring mechanism 140. Alternatively, the force calibration device 100 may be configured in other suitable structures according to practical needs, for example, including only the support bracket 120 and the force measuring mechanism 140, or including only the support bracket 120, the auxiliary support bracket 130, the force measuring mechanism 140, and so on.

In one or more embodiments, as shown in FIG. 1, the base 110 is a generally rectangular plate. Alternatively, the base 110 may be provided in a square or other suitable shape. The base 110 may be made of stainless steel, cast iron, or other suitable materials, so as to have good mechanical strength. The horizontally disposed base 110 may provide a suitable fixing area for the support bracket 120, the auxiliary support bracket 130, the force measuring mechanism 140, and the like, so as to ensure structural stability of the entire force measuring calibration device 100.

As shown in fig. 1-3, in one or more embodiments, the support bracket 120 has a generally rectangular parallelepiped support bracket body 120, which is simple in structure and easy to machine. Alternatively, the support bracket body 120 may be provided in a square or other suitable shape. The support bracket body 120 may be made of stainless steel, cast iron, granite, etc., and has good mechanical strength. The support bracket body 120 is detachably fixed to the base 110 to facilitate the disassembly, maintenance and replacement thereof. The fastening means include, but are not limited to, threaded connections, snap-fit connections, and the like.

With continued reference to fig. 2 and 3, in one or more embodiments, a V-groove 122 is provided on the support bracket 120 to stably support the measuring jaw of the three-point inside micrometer 200. Specifically, an upwardly opening V-shaped groove 122 is provided at the top of the support bracket 120 (based on the orientation shown in fig. 2 and 3). The V-shaped groove 122 has a first support slope 1221 and a second support slope 1222 opposite each other. The first support bevel 1221 is located to the left of the V-groove 122 and the second support bevel 1222 is located to the right of the V-groove 122. The first support slope 1221 and the second support slope 1222 are clamped to form a predetermined angle α. Referring to fig. 3, in one or more embodiments, the predetermined angle α is 60 ° such that measurement jaws (e.g., first measurement jaw 261 and second measurement jaw 262) evenly spaced at 120 ° can abut substantially perpendicularly against first support ramp 1221 and second support ramp 1222, thereby improving the uniformity of force applied by each measurement jaw. In one or more embodiments, the first support bevel 1221 and the second support bevel 1222 are symmetrically arranged with respect to a vertical cross section C of the support bracket 120. This not only allows the support bracket 120 to have a regular structure for ease of processing, but also allows the third measuring jaw 263 of the three-point inside micrometer 200 that abuts against the V-shaped groove 122 to extend in a generally vertical direction for ease of abutment against the force measuring head 1411 of the force measuring mechanism 140. In one or more embodiments, the flatness of the first and second support ramps 1221, 1222 is 2 μm or less, providing a smooth surface to reduce friction of the measurement jaw against the first and second support ramps 1221, 1222, thereby improving calibration accuracy.

With continued reference to fig. 2, in one or more embodiments, the support bracket 120 has V-shaped grooves 122 of different sizes to meet the calibration requirements of the three-point inside micrometer 200 of different gauges. Specifically, a first distance L1 is spaced between the bottom of the first support slope 1221 and the bottom of the second support slope 1222, and a second distance L2 is spaced between the top of the first support slope 1221 and the top of the second support slope 1222. Referring to fig. 2 (a), in one or more embodiments, the first spacing L1 is 0mm (i.e., the bottom of the first support slope 1221 and the bottom of the second support slope 1222 are connected), and the second spacing L2 is 100mm. Referring to fig. 2 (b), in one or more embodiments, the first spacing L1 is 80mm and the second spacing L2 is 190mm. In other words, a horizontal connecting surface 1223 extending in a substantially horizontal direction is provided between the first support slope 1221 and the second support slope 1222. Further, referring to fig. 2 (c), the first pitch L1 is 160mm and the second pitch L2 is 270mm. Alternatively, the V-shaped groove 122 of the support bracket 120 may be provided in other suitable dimensions as long as the calibration requirements of the three-point inside micrometer 200 of different gauges can be met.

As shown in fig. 1, in one or more embodiments, the load cell 140 includes a load cell 140 body and a liftable support 142. Based on the orientation shown in fig. 1, the liftable bracket 142 is fixed to the base 110 and is located on the right side of the support bracket 120. Alternatively, the liftable bracket 142 may be disposed at the left side of the support bracket 120 or at other suitable positions. The body of the force measuring mechanism 140 is liftably fixed to the liftable stand 142 and positioned above the support stand 120 so as to be abutted against a measuring jaw (e.g., the third measuring jaw 263) of the three-point inside micrometer 200 placed on the support stand 120 by adjusting the height of the body of the force measuring mechanism 140. Adjustment means include, but are not limited to, screw, gear-rack, etc. The body of the load cell 140 may employ a level 2.0 accuracy load cell (e.g., SH100 load cell, etc.). The load cell 140 has a load head 1411. In particular, the force-measuring head 1411 is arranged at the bottom of the force-measuring mechanism 140 so as to abut against a measuring jaw facing away from the V-groove 122.

In one or more embodiments, as shown in FIG. 1, an auxiliary support bracket 130 is secured to the base 110 and is located on a side of the support bracket 120 that is remote from the load cell 140. Preferably, the auxiliary support bracket 130 is detachably fixed to the base 110 to facilitate the disassembly, maintenance and replacement thereof. The fastening means include, but are not limited to, threaded connections, snap-fit connections, and the like. The auxiliary support bracket 130 has a substantially rectangular parallelepiped auxiliary support bracket body 130. Alternatively, the auxiliary support bracket body 130 may also take a square or other suitable shape. The auxiliary supporting bracket body 130 can also be made of stainless steel, cast iron or granite and other suitable materials, so that the auxiliary supporting bracket body has good mechanical strength. A limit groove (not shown) for restraining the blade of the three-point inside micrometer 200 is provided on the top of the auxiliary support bracket body 130. The limiting groove can be semicircular, V-shaped or other suitable shapes, so long as the limiting groove can be matched with the ruler body. In one or more embodiments, a pressure plate 133 is also provided on the auxiliary support bracket body 130 for restraining the blade within the restraint slot to further enhance the stability of the three-point inside micrometer 200 placed on the support bracket 120. In one or more embodiments, a height adjustment member 132 is also provided on the auxiliary support bracket 130 to adjust the height of the limit slot relative to the base 110 so that the entire blade of the three-point inside micrometer 200 can remain substantially parallel to the base 110 (i.e., the blade of the three-point inside micrometer 200 extends in a substantially horizontal direction) when the three-point inside micrometer 200 is placed on the support bracket 120 and the auxiliary support bracket 130. The specific manner in which the height adjusting member 132 adjusts the height of the limit groove is not limited, and for example, the height of the limit groove may be adjusted by adjusting the length of the screw between the auxiliary support bracket body 130 and the base 110, etc.

As shown in fig. 1, the three-point inside micrometer 200 includes a force measuring screw 210, a micro cylinder 220, a fixed sleeve 230, an extension rod 240, a main body 250, and a measuring jaw. Based on the orientation shown in fig. 1, the fixed sleeve 230 is located to the left of the extension rod 240 and the body 250 is located to the right of the extension rod 240. The measuring jaws include a first measuring jaw 261, a second measuring jaw 262, and a third measuring jaw 263 uniformly spaced apart at 120 ° along the circumferential direction of the main body 250. The micro-cylinder 220 is rotatable relative to the stationary sleeve 230 to control the first, second and third measuring jaws 261, 262, 263 to extend radially outwardly or inwardly of the body 250 to control the measuring jaws to abut the bore wall of the bore being measured. The load screw 210 is located on the side of the micro cartridge 220 remote from the stationary sleeve 230. When the measuring claw abuts against the hole wall of the measured inner hole, a certain measuring force can be applied to the measured inner hole by the measuring claw through rotating the force measuring screw 210, and the phenomenon that the measuring precision is affected due to the fact that a gap exists between the measuring claw and the hole wall is avoided.

When calibrating a three-point inside micrometer 200 using a force measuring calibration device 100 of the present utility model, as shown in fig. 1-3, a support bracket 120 of an appropriate gauge is first selected based on the range of the three-point inside micrometer 200 (e.g., 6mm-12mm, 12mm-100mm, 100mm-300mm, etc.), as shown in fig. 2 (a) -2 (c). Next, the support bracket 120 is fixed to the base 110, and the position of the auxiliary support bracket 130 is adjusted by the height adjuster 132 to ensure that the three-point inside micrometer 200 can be laid flat on the support bracket 120 and the auxiliary support bracket 130. Specifically, the first and second measuring jaws 261 and 262 of the three-point inside micrometer 200 abut the first and second support ramps 1221 and 1222, respectively, in the V-shaped groove 122 of the support bracket 120; the third measuring jaw 263 of the three-point inside micrometer 200 is positioned to extend along the angular bisector of the V-groove 122 and toward a direction away from the V-groove 122 (i.e., in a vertically upward direction based on the orientation shown in fig. 3); the blade (e.g., extension rod 240) of the three-point inside micrometer 200 is placed in the limit slot of the auxiliary support bracket 130 such that the entire blade extends in a generally horizontal direction. Then, the pressing plate 133 on the auxiliary support bracket 130 is rotated to a position to restrain the blade, to further improve the stability of the three-point inside micrometer 200. Next, the position of the load cell 140 is adjusted such that the load head 1411 of the load cell 140 abuts the third measuring jaw 263 of the three-point inside micrometer 200. Then, the force measuring screw 210 of the three-point inside micrometer 200 is rotated, and the force exerted on the force measuring head 1411 by the third measuring jaw 263 is obtained by the force measuring mechanism 140. If the measured acting force is within the set range, it is determined that the accuracy of the third measuring jaw 263 meets the requirement; if the measured force exceeds the set range, it is determined that the accuracy of the third measuring jaw 263 is not satisfactory, and further debugging and maintenance thereof are required. The setting range may be performed according to the following criteria: when the measuring range of the three-point inside micrometer 200 is 6mm-12mm, the setting range is 6N-15N; when the measuring range of the three-point inside micrometer 200 is 12mm-100mm, the setting range is 10N-30N; when the three-point inside micrometer 200 has a measuring range of 100mm to 300mm, the setting range is 15N to 45N. Alternatively, the setting range of the force measurement can be adjusted according to actual needs.

It should be noted that, after the calibration of one measuring jaw (e.g., the third measuring jaw 263) of the three-point inside micrometer 200 is completed, the other two measuring jaws (e.g., the first measuring jaw 261 and the second measuring jaw 262) of the three-point inside micrometer 200 may be calibrated according to actual needs, which is not described herein.

Thus far, the technical solution of the present utility model has been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of protection of the present utility model is not limited to these specific embodiments. Equivalent modifications and substitutions for related technical features may be made by those skilled in the art without departing from the principles of the present utility model, and such modifications and substitutions will fall within the scope of the present utility model.

Claims (10)

1. A force calibration device for a three-point inside micrometer, the force calibration device comprising:

A support bracket on which a V-shaped groove having a first support slope and a second support slope opposite to each other is provided, and the first support slope and the second support slope are configured to support a first measuring jaw and a second measuring jaw of the three-point inside micrometer, respectively, such that a third measuring jaw of the three-point inside micrometer is positioned to extend along an angular bisector of the V-shaped groove and toward a direction away from the V-shaped groove; and

The force measuring mechanism is provided with a force measuring head which can be abutted against the third measuring claw, so that the force measuring mechanism can detect acting force exerted on the force measuring head by the third measuring claw when the force measuring screw of the three-point inside micrometer is rotated.

2. The force calibration device for a three-point inside micrometer of claim 1, further comprising:

The base, the support frame detachably is fixed on the base, the force measuring mechanism is fixed on the base in a lifting mode and is positioned on the upper portion of the support frame.

3. The force calibration device for a three-point inside micrometer of claim 2, further comprising:

The auxiliary support bracket is movably arranged on the base and can be positioned on one side of the support bracket far away from the force measuring mechanism, and the auxiliary support bracket is provided with a limit groove capable of supporting the blade of the three-point inside micrometer.

4. A force calibration device for a three-point inside micrometer according to claim 3, wherein a height adjustment member is provided on the auxiliary support bracket to adjust the height of the limit slot relative to the base.

5. A force calibration device for a three-point inside micrometer according to claim 3, wherein a pressure plate is provided on the auxiliary support bracket to restrain the blade in the limit groove.

6. The force calibration device for a three point inside micrometer according to any one of claims 1 to 5, wherein the first support ramp and the second support ramp clamp at a predetermined angle, and the predetermined angle is 60 °.

7. The force calibration device for a three-point inside micrometer of claim 6, wherein the flatness of the first support slope and the second support slope is 2 μm or less.

8. The force calibration device for a three-point inside micrometer of claim 6, wherein the first support ramp and the second support ramp are symmetrically arranged with respect to a vertical cross-section of the support bracket.

9. The force calibration device for a three-point inside micrometer of claim 6, wherein a first spacing is provided between a bottom of the first support ramp and a bottom of the second support ramp, a second spacing is provided between a top of the first support ramp and a top of the second support ramp,

Wherein the first spacing is 0mm and the second spacing is 100mm; or alternatively

The first interval is 80mm, and the second interval is 190mm; or alternatively

The first spacing is 160mm and the second spacing is 270mm.

10. The force calibration device for a three-point inside micrometer of claim 1, wherein the support bracket is made of stainless steel, cast iron or granite.