CN217914162U

CN217914162U - Air clamp type positioning tool

Info

Publication number: CN217914162U
Application number: CN202222409999.8U
Authority: CN
Inventors: 乜建民
Original assignee: Hebei Hengxing Machinery Co ltd
Current assignee: Hebei Hengxing Machinery Co ltd
Priority date: 2022-09-09
Filing date: 2022-09-09
Publication date: 2022-11-29
Anticipated expiration: 2032-09-09

Abstract

The utility model relates to a machinery processing technology field, the utility model provides an air jig formula location frock, including base and fixed establishment, fixed establishment includes the shaft section of thick bamboo, the drive shaft, first clamp plate and second clamp plate, the shaft section of thick bamboo slides and sets up on the base, the drive shaft cover is established in the shaft section of thick bamboo, the shaft section of thick bamboo lateral wall has first logical groove and the logical groove of second, be equipped with the logical groove of third in the drive shaft, first clamp plate and second clamp plate slide respectively and set up at first logical groove and the logical inslot of second, and the butt or break away from the butt in the logical inslot of third, first clamp plate and second clamp plate all have direction inclined plane and bearing face, bearing face and third through-hole groove lateral wall butt or break away from the butt, the direction inclined plane of first clamp plate of butt and second clamp plate is distinguished to two arriss of third through-hole, be equipped with the limiting plate in the drive shaft section of thick bamboo bottom butt or break away from the butt. Through above-mentioned technical scheme, the problem that manual installation clamp plate is wasted time and energy among the prior art has been solved.

Description

Air clamp type positioning tool

Technical Field

The utility model relates to a machining technology field, it is specific, relate to gas clamp formula location frock.

Background

The machine is also called a fixture, which is used to fix the object to be processed to make it occupy the correct position for receiving construction or detection. In a broad sense, any device used to quickly, conveniently and safely mount a workpiece at any stage in a process may be referred to as a jig. Such as welding jigs, inspection jigs, assembly jigs, machine tool jigs, and the like. Among them, the machine tool clamp is the most common, and is often referred to as a clamp for short. When a workpiece is machined on a machine tool, the workpiece needs to be well assembled (positioned) and firmly clamped and clamped before machining in order to enable the surface of the workpiece to meet the technical requirements of size, geometric shape, mutual position precision with other surfaces and the like specified in a drawing.

In the prior art, when a workpiece with a through hole is processed and positioned, a positioning screw rod is vertically arranged on a base and penetrates through a through hole of the workpiece to position the workpiece, then a pressing plate is manually added at the end part of the screw rod, then the pressing plate is tightly pressed on the workpiece by a nut to fix the workpiece, and the pressing plate is detached after the workpiece is processed; the pressing plate is required to be detached and installed at each time when the workpiece is machined, time and labor are wasted, and the grinding tool and the turning tool for machining the workpiece are always in working states, so that certain potential safety hazards are also provided.

SUMMERY OF THE UTILITY MODEL

The utility model provides a clamp type location frock has solved the problem that manual installation clamp plate is wasted time and energy among the correlation technique.

The technical scheme of the utility model as follows: air clamp formula location frock, including base and fixed establishment, fixed establishment includes a shaft section of thick bamboo, drive shaft, first clamp plate and second clamp plate, the shaft section of thick bamboo slides and sets up on the base, and with the base terminal surface is perpendicular, the drive shaft cover is established in the shaft section of thick bamboo, the shaft section of thick bamboo lateral wall has first logical groove and second and leads to the groove, be equipped with the third in the drive shaft and lead to the groove, first logical groove the second lead to the groove with the third leads to the groove and communicates with each other the back, runs through the shaft section of thick bamboo with the drive shaft, first clamp plate with the second clamp plate slides respectively and sets up first logical groove with the second leads to the inslot, and the third leads to the inslot butt or breaks away from the butt, first clamp plate with the second clamp plate leads to the inslot butt, be equipped with the drive shaft, the limiting plate with shaft section of thick bamboo bottom butt or break away from the butt, be connected with the shaft section of thick bamboo with the butt or break away from the butt are connected with between the second through the groove, the spring arris provides the vertical power to the shaft section of thick bamboo.

As a further technical solution, the method comprises the following steps,

two upper edges of the third through groove are respectively provided with a driving inclined plane, and the two driving inclined planes are respectively attached to the two guide inclined planes.

As a further technical solution, the method comprises the following steps,

the first pressing plate is provided with a containing groove, the second pressing plate is provided with a convex block, and the convex block is clamped or separated from the containing groove.

As a further technical solution, it is proposed that,

the first pressing plate and the second pressing plate are respectively provided with a first baffle and a second baffle, the side wall of the first through groove and the side wall of the second through groove are respectively provided with a first reset groove and a second reset groove, the first baffle and the second baffle are respectively positioned in the first reset groove and the second reset groove, the first reset groove and the second reset groove are internally provided with a plurality of first springs, and the first springs extrude the first baffle and the second baffle to provide the force which enables the first pressing plate and the second pressing plate to be close to each other.

As a further technical solution, the method comprises the following steps,

still include fastening device, fastening device includes bracing piece, air pressure bar and third clamp plate, the vertical setting of bracing piece is in on the base, the vertical slip of air pressure bar sets up on the base, be equipped with first backup pad on the bracing piece, be equipped with the second backup pad on the air pressure bar, first backup pad with the second backup pad is used for supporting the third clamp plate, just the third clamp plate is in first backup pad with slide in the second backup pad, the fourth logical groove has on the third clamp plate, the bracing piece with the air pressure bar tip all is located the fourth inslot, the air pressure bar tip is equipped with the stopper, after the air pressure bar lapse, the stopper provides the third clamp plate compresses tightly the power of part.

As a further technical solution, it is proposed that,

the limiting block is a nut and is in threaded connection with the air pressure rod.

As a further technical solution, it is proposed that,

the base is provided with a plurality of positioning holes, the supporting rods are arranged in the positioning holes, and the air pressure rods are arranged in the positioning holes in a sliding mode.

The utility model discloses a theory of operation and beneficial effect do:

the utility model discloses in, the axle sleeve slides and sets up on the base, it is equipped with the drive shaft to slide in the inside of axle sleeve, drive shaft and cylinder are connected, be equipped with the limiting plate in the drive shaft, when the drive shaft moves up, the limiting plate withstands the axle sleeve bottom and moves up, lateral wall at the axle sleeve has first logical groove and second logical groove, third logical groove has in the drive shaft, when first logical groove, second logical groove and third logical groove are in same horizontal plane, form the logical groove that runs through drive shaft and axle sleeve, it is equipped with first clamp plate and second clamp plate to slide respectively in first logical groove and second logical groove, first clamp plate and second clamp plate all have direction inclined plane and bearing surface, the direction inclined plane and the bearing surface of first clamp plate and second clamp plate all are located the third logical groove; when the fixing mechanism is not used for positioning and clamping a workpiece, the first pressing plate and the second pressing plate do not extend out of the outer sides of the first through groove and the second through groove and are mutually abutted in the third through groove, at the moment, the limiting plate is contacted with the bottom of the shaft barrel, and two upper edges of the third through groove are tightly attached to the top ends of the two guide inclined planes; when a workpiece needs to be clamped, the through hole of the workpiece is placed down to be aligned with the shaft barrel, the shaft barrel penetrates out of the through hole of the part, positioning is achieved, then the air cylinder drives the driving shaft to slide downwards in the shaft barrel, the driving shaft slides downwards and is divided into two stages, in the first stage, when the driving shaft slides downwards, the two upper edges of the third through groove extrude the first pressing plate and the second pressing plate to move towards the outer sides of the first through groove and the second through groove respectively, the spring can provide vertical and upward force for the shaft barrel, the first pressing plate and the second pressing plate extend out of the shaft barrel, in the process, the shaft barrel cannot be pulled downwards due to the action of the elastic force of the spring, and when the two upper edges of the third through groove slide to the surface along the guide inclined plane to support the surface, the limiting plate is separated from the bottom of the shaft barrel; in the second stage, after the bearing surface is attached to the upper wall of the third through groove, the driving rod moving downwards can prop against the bearing surface so as to drive the shaft barrel to move downwards, further drive the first pressing plate and the second pressing plate which are out of the shaft barrel to move downwards and tightly press the workpiece; in the positioning and pressing process of the part, a worker only needs to put the workpiece on the base, the shaft cylinder penetrates through the through hole in the workpiece, and then the pneumatic cylinder is used for completing positioning and clamping, so that the manual clamping after the workpiece is positioned is avoided, and therefore, the positioning and clamping tool not only solves the problem that manual installation of the pressing plate wastes time and labor, reduces potential safety hazards, but also greatly improves the working efficiency; the spring has been added to this equipment, makes first preforming and second preforming can realize automatic re-setting's effect, makes this equipment realize automatic clamp and unclamp the work piece.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic structural view of the air clamp type positioning tool of the present invention;

FIG. 2 is a side view of the air clamp type positioning tool of the present invention;

FIG. 3 is a schematic structural view of the pressing plate resetting mechanism of the present invention;

FIG. 4 is a cross-sectional view of the shaft cylinder of the present invention;

FIG. 5 is a schematic view of a first baffle of the present invention;

fig. 6 is a schematic diagram of a second baffle structure of the present invention;

in the figure: 1. the base, 2, the shaft barrel, 3, the drive shaft, 4, first clamp plate, 5, the second clamp plate, 6, first logical groove, 7, the second leads to the groove, 8, the third leads to the groove, 9, the direction inclined plane, 10, the holding surface, 11, the limiting plate, 12, the drive inclined plane, 13, the holding tank, 14, the lug, 15, first baffle, 16, the second baffle, 17, first groove that resets, 18, the second resets, 19, first spring, 20, the bracing piece, 21, the pneumatic rod, 22, the third clamp plate, 23, first backup pad, 24, the second backup pad, 25, the fourth leads to the groove, 26, the limiting block, 27, the locating hole, 28, the second spring, 29, the work piece.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive work, are related to the scope of the present invention.

As shown in fig. 1-6, this embodiment provides an air clamp type positioning tool, including base 1 and fixed establishment, fixed establishment includes shaft barrel 2, drive shaft 3, first clamp plate 4 and second clamp plate 5, shaft barrel 2 slides and sets up on the base 1, and with base 1 terminal surface is perpendicular, the drive shaft 3 cover is established in shaft barrel 2, 2 lateral walls of shaft barrel have first logical groove 6 and second logical groove 7, be equipped with the logical groove 8 of third on the drive shaft 3, first logical groove 6 the second logical groove 7 with the communicating back of third logical groove 8 runs through shaft barrel 2 with drive shaft 3, first clamp plate 4 with second clamp plate 5 slides respectively and sets up in first logical groove 6 with in the second logical groove 7, and be in the logical groove 8 butt of third or break away from the butt, first clamp plate 4 with second clamp plate 5 all has direction inclined plane 9 and bearing face 10, bearing face 10 with 8 lateral wall butt or the butt of third logical groove 8 or break away from the butt of third logical groove 8 the butt of second clamp plate 4 with second clamp plate 5 through the straight arris of second straight limiting plate 2, spring 2 is connected with the vertical limiting plate 11 of second clamp plate 11 and spring seat 2, spring straight limiting plate 11 are connected with the shaft barrel 2.

In the embodiment, a shaft barrel 2 is arranged on a base 1 in a sliding manner, a driving shaft 3 is arranged in the shaft barrel 2 in a sliding manner, the driving shaft 3 is connected with an air cylinder, a limiting plate 11 is arranged on the driving shaft 3, when the driving shaft 3 moves upwards, the limiting plate 11 is abutted against the bottom of the shaft barrel 2 to move upwards, a first through groove 6 and a second through groove 7 are arranged on the side wall of the shaft barrel 2, a third through groove 8 is arranged on the driving shaft 3, when the first through groove 6, the second through groove 7 and the third through groove 8 are positioned on the same horizontal plane, through grooves penetrating through the driving shaft 3 and the shaft barrel 2 are formed, a first pressing plate 4 and a second pressing plate 5 are respectively arranged in the first through groove 6 and the second through groove 7 in a sliding manner, the first pressing plate 4 and the second pressing plate 5 are both provided with a guide inclined surface 9 and a bearing surface 10, and the guide inclined surfaces 9 and the bearing surfaces 10 of the first pressing plate 4 and the second pressing plate 5 are both positioned in the third through groove 8; when the fixing mechanism is not used for positioning and clamping the workpiece 29, the first pressing plate 4 and the second pressing plate 5 do not extend out of the first through groove 6 and the second through groove 7 and are mutually abutted in the third through groove 8, at the moment, the limiting plate 11 is contacted with the bottom of the shaft barrel 2, and two upper edges of the third through groove 8 are tightly attached to the top ends of the two guide inclined planes 9; when a workpiece 29 needs to be clamped, the through hole of the workpiece 29 is placed down to be aligned with the shaft barrel 2, the shaft barrel 2 penetrates through the through hole of the part, and positioning is achieved, then the driving shaft 3 is driven by the air cylinder to slide downwards in the shaft barrel 2, the driving shaft 3 slides downwards and is divided into two stages, in the first stage, when the driving shaft 3 slides downwards, the first pressing plate 4 and the second pressing plate 5 stretch out of the shaft barrel 2 due to the fact that the spring 28 provides vertical upward force for the shaft barrel 2, the shaft barrel cannot be pulled downwards in the process due to the effect of the elastic force of the spring 28, the two upper edges of the third through groove 8 extrude the first pressing plate 4 and the second pressing plate 5 to move towards the outer sides of the first through groove 6 and the second through groove 7 respectively, and when the two upper edges of the third through groove 8 slide to the bearing surface 10 along the guide inclined surface 9, the bottom of the limiting plate 11 and the shaft barrel 2 are in a separated state; in the second stage, after the bearing surface 10 is attached to the upper wall of the third through groove 8, the driving rod moving downwards can prop against the bearing surface 10, so as to drive the shaft cylinder 2 to move downwards, further drive the first pressing plate 4 and the second pressing plate 5 extending out of the shaft cylinder 2 to move downwards, and press the workpiece 29; this part location and compress tightly the in-process, only need the staff to put into base 1 to work piece 29 on, make a barrel 2 pass the through-hole on the work piece 29, pneumatic cylinder has just accomplished the location and has pressed from both sides tight work afterwards, has avoided realizing work piece 29 location back, carries out manual clamping work again, therefore this location presss from both sides tight frock, has not only solved the problem that manual installation clamp plate is wasted time and energy, reduces the potential safety hazard, has also improved work efficiency greatly.

Further, the method also comprises the following steps of,

two upper edges of the third through groove 8 are provided with driving inclined planes 12, and the two driving inclined planes 12 are respectively attached to the two guide inclined planes 9.

In this embodiment, all be equipped with drive inclined plane 12 in two upper arriss departments of third traffic trough 8, two drive inclined planes 12 of third traffic trough 8 are hugged closely first clamp plate 4 and two direction inclined planes 9 of second clamp plate 5 respectively, during the bead butt direction inclined plane 9, sharp-pointed edges and corners scrape direction inclined plane 9 badly very easily, reduce the life who uses the clamp plate, during drive inclined plane 12 and direction inclined plane 9 butt, because be the face with towards the butt, consequently, the condition of scraping can not exist, and the resistance that receives when drive inclined plane 12 drive direction inclined plane 9 is also less relatively, the life of work efficiency and equipment has been improved.

Further, the method also comprises the following steps of,

first clamp plate 4 has holding tank 13, second clamp plate 5 is last to have lug 14, lug 14 joint or break away from the joint holding tank 13.

In this embodiment, the first pressing plate 4 has a through accommodating groove, the second clamping plate is provided with a bump 14, the bump 14 can be clamped in the through accommodating groove, the guiding inclined planes 9 are respectively arranged on two side plates of the through accommodating groove and the bump 14, and the bearing planes 10 are also respectively located on the two side plates of the through accommodating groove and the bump 14; compared with the clamping mode of containing the through groove and the protruding block 14, the mode that the first pressing plate 4 and the second pressing plate 5 are directly abutted is capable of lengthening the horizontal length of the first pressing plate 4 and the second pressing plate 5, so that when the first pressing plate 4 and the second pressing plate 5 extend out of the shaft barrel 2, the longer length can be extended out, and the clamped workpiece 29 is more stable.

Further, the method also comprises the following steps of,

first clamp plate 4 with be equipped with first baffle 15 and second baffle 16 on the second clamp plate 5 respectively, first logical groove 6 with the second leads to the groove 7 lateral wall and has first reset groove 17 and second reset groove 18 respectively, first baffle 15 with second baffle 16 is located respectively first reset groove 17 with the second resets in the groove 18, first reset groove 17 with the second resets and is equipped with a plurality of first springs 19 in the groove 18, and is a plurality of first springs 19 extrusion provides behind first baffle 15 and the second baffle 16 first clamp plate 4 with the power that second clamp plate 5 is close to each other.

In this embodiment, the first pressing plate 4 and the second pressing plate 5 are respectively provided with a first baffle 15 and a second baffle 16, the first baffle 15 and the second baffle 16 are respectively located in a first reset groove 17 and a second reset groove 18 of the side walls of the first through groove 6 and the second through groove 7, the side walls of the first baffle 15 and the first reset groove 17 are connected with a plurality of springs 19, the side walls of the second baffle 16 and the second reset groove 18 are connected with a plurality of springs 19, and the springs 19 provide a force for the first pressing plate 4 and the second pressing plate 5 to approach each other; after the workpiece 29 is machined, the workpiece 29 needs to be disassembled, the shaft barrel 2 and the driving shaft 3 need to be reset before the disassembly, when the shaft barrel is reset, the driving shaft 3 is driven by the air cylinder to move upwards, the first baffle 15 and the second baffle 16 can be gradually reset under the action of the spring 19 along with the upward movement of the driving shaft 3, when the driving inclined plane 12 on the third through hole slides to the uppermost end of the guide inclined plane 9, the limiting plate 11 is abutted to the bottom of the shaft barrel 2, the shaft barrel 2 is driven to move upwards for a certain distance and then stops moving, the fixing mechanism restores to the original shape, and at the moment, the workpiece 29 is directly taken out; the automation of positioning the tool and fixing the part is realized, and the working efficiency is greatly improved.

Further, the method also comprises the following steps of,

fastening device, fastening device includes bracing piece 20, pneumatic rod 21 and third clamp plate 22, the vertical setting of bracing piece 20 is in on the base 1, the vertical slip setting of pneumatic rod 21 is in on the base 1, be equipped with first backup pad 23 on the bracing piece 20, be equipped with second backup pad 24 on the pneumatic rod 21, first backup pad 23 with second backup pad 24 is used for supporting third clamp plate 22, just third clamp plate 22 is in first backup pad 23 with slide on the second backup pad 24, fourth logical groove 25 has on the third clamp plate 22, bracing piece 20 with pneumatic rod 21 tip all is located in fourth logical groove 25, pneumatic rod 21 tip is equipped with stopper 26, after pneumatic rod 21 slided downwards, stopper 26 provides the power that third clamp plate 22 compressed tightly the part.

In this embodiment, the support rod 20 is vertically arranged on the base 1, the air cylinder is further arranged on the base 1 in a sliding manner, the air cylinder 21 is connected with the air cylinder, the air cylinder drives the air cylinder 21 to vertically slide on the base 1, the support rod 20 and the air cylinder 21 are respectively provided with a first support plate 23 and a second support plate 24, the third press plate 22 is provided with a fourth through groove 25, the end parts of the support rod 20 and the air cylinder 21 are positioned in the fourth through groove 25, the third press plate 22 is arranged on the first support plate 23 and the second support plate 24 and can slide on the first support plate 23 and the second support plate 24, and the end part of the air cylinder 21 is provided with a limit block 26; during operation, the third pressing plate 22 slides to the upper side of the pressed part of the workpiece 29, the air pressure rod 21 moves downwards, the limiting block 26 drives the third pressing plate 22 to extrude the workpiece 29, so that the fixing effect is achieved, the supporting rod 20 is used for balancing the force of the third pressing plate 22, the third pressing plate 22 is prevented from inclining when the stress is unbalanced, the fastening mechanism is simple to operate, further fastening is performed on the workpiece 29, the workpiece 29 is prevented from sliding along the horizontal direction, and the stability of the workpiece 29 is enhanced.

Further, the method also comprises the following steps of,

the limiting block 26 is a nut and is in threaded connection with the air pressure rod 21.

In this embodiment, stopper 26 is the nut, and the nut is as stopper 26, conveniently carries out position control and dismantlement to stopper 26, changes convenient and fast more when making the preforming impaired.

Further, the method also comprises the following steps of,

the base 1 is provided with a plurality of positioning holes 27, the support rod 20 is arranged in the positioning holes 27, and the air pressure rod 21 is slidably arranged in the positioning holes 27.

In this embodiment, a plurality of positioning holes 27 are provided on the base 1, and position adjustment is performed for the support rod 20 and the drive rod, so that the present device can be applied to workpieces 29 having different diameters.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The air clamp type positioning tool comprises a base (1) and a fixing mechanism, and is characterized in that the fixing mechanism comprises a shaft barrel (2), a driving shaft (3), a first pressing plate (4) and a second pressing plate (5), the shaft barrel (2) is arranged on the base (1) in a sliding mode and is perpendicular to the end face of the base (1), the driving shaft (3) is sleeved in the shaft barrel (2), the side wall of the shaft barrel (2) is provided with a first through groove (6) and a second through groove (7), the driving shaft (3) is provided with a third through groove (8), the first through groove (6), the second through groove (7) and the third through groove (8) are communicated, the first pressing plate (4) and the second pressing plate (5) are respectively arranged in the first through groove (6) and the second through groove (7) in a sliding mode, the first pressing plate (4) and the second pressing plate (5) are respectively provided with a guide inclined plane (9) and a bearing surface (10), the edges (9) at two ends of the third through groove (8) are abutted against the limiting plate (11), and a spring (11) is connected between the shaft barrel (1) and the limiting plate (11), the second spring (28) provides a force vertically upward on the shaft barrel (2).

2. The air-clamp type positioning tool according to claim 1, wherein two upper edges of the third through groove (8) are provided with driving inclined planes (12), and the two driving inclined planes (12) are respectively attached to the two guide inclined planes (9).

3. The air-clamp type positioning tool according to claim 1, wherein the first pressing plate (4) is provided with a receiving groove (13), the second pressing plate (5) is provided with a convex block (14), and the convex block (14) is clamped or separated in the receiving groove (13).

4. The air-clamp type positioning tool according to claim 1, wherein a first baffle (15) and a second baffle (16) are respectively arranged on the first pressing plate (4) and the second pressing plate (5), a first reset groove (17) and a second reset groove (18) are respectively formed in side walls of the first through groove (6) and the second through groove (7), the first baffle (15) and the second baffle (16) are respectively located in the first reset groove (17) and the second reset groove (18), a plurality of first springs (19) are arranged in the first reset groove (17) and the second reset groove (18), and after the first baffle (15) and the second baffle (16) are squeezed by the plurality of first springs (19), a force for enabling the first pressing plate (4) and the second pressing plate (5) to be close to each other is provided.

5. The air-clamp type positioning tool according to claim 1, further comprising a fastening mechanism, wherein the fastening mechanism comprises a support rod (20), an air pressure rod (21) and a third pressing plate (22), the support rod (20) is vertically arranged on the base (1), the air pressure rod (21) is vertically slidably arranged on the base (1), a first support plate (23) is arranged on the support rod (20), a second support plate (24) is arranged on the air pressure rod (21), the first support plate (23) and the second support plate (24) are used for supporting the third pressing plate (22), the third pressing plate (22) is slidably arranged on the first support plate (23) and the second support plate (24), a fourth through groove (25) is arranged on the third pressing plate (22), the ends of the support rod (20) and the air pressure rod (21) are both located in the fourth through groove (25), a limit block (26) is arranged at the end of the air pressure rod (21), and after the air pressure rod (21) slides downwards, the limit block (26) provides a pressure part for pressing the third pressing plate (22).

6. The air-clamp type positioning tool according to claim 5, wherein the limiting block (26) is a nut and is in threaded connection with the air pressure rod (21).

7. The air-clamp type positioning tool according to claim 5, wherein the base (1) is provided with a plurality of positioning holes (27), the supporting rod (20) is arranged in the positioning holes (27), and the air pressure rod (21) is slidably arranged in the positioning holes (27).