GB2374829A

GB2374829A - A countersink guide

Info

Publication number: GB2374829A
Application number: GB0109906A
Authority: GB
Inventors: Andrew William Hodgkinson
Original assignee: BAE Systems PLC
Current assignee: BAE Systems PLC
Priority date: 2001-04-23
Filing date: 2001-04-23
Publication date: 2002-10-30
Also published as: GB0109906D0

Abstract

The countersink guide comprises a body 10 having thereon a pilot 16 insertable into a hole formed in a surface to be countersunk and a marker 28 spaced from the pilot 16. With the pilot 16 inserted in the hole 46, the body 10 can be rotated with the marker 28 in contact with the surface to cause the marker 28 to mark the surface 47 with a circle 48. The circle 48 has a diameter corresponding substantially to the required diameter of the countersink at the surface.

Description

A Countersink Guide The invention relates to a countersink guide and is particularly, but not exclusively, concerned with a countersink guide for use on an aircraft skin panel.

The production of accurately formed countersunk holes in panels is important in many cases and particularly so in aircraft skin panels where heads of fasteners such as bolts or rivets need to lie flush with the outer skin surface. In the latter case, the forming of the countersink has traditionally been carried out using a countersink cutter having a pilot.

The pilot leads into a previously formed hole in the skin and guides the cutter whilst the cutter removes material to form the countersink. In order to ensure that countersunk holes are drilled to the correct depth, it is known to use a countersink tool which has an adjustable sleeve surrounding the cutter. The sleeve is adjusted to prevent the cutter cutting beyond the required depth in scrap material. Once correctly adjusted, the tool can then be used to form countersunk holes in the skin panel. Such a tool is, however, suitable only for flat skin surfaces.

Where the skin surface is curved, the depth of the countersink cutter has to be judged visually by an operative. Usually, it takes several attempts to remove material up to the correct depth to ensure that too much material is not removed. The process is time consuming and tedious and anything up to around 30 seconds can be involved in producing a single countersink. Bearing in mind that an aircraft skin can have thousands of boles to be countersunk, the total countersinking time can be substantial.

The present invention is intended to reduce the foregoing problem to enable an accurate countersink to be formed, particularly in a curved surface, in a less tedious and time consuming manner.

According to the invention there is provided a countersink guide comprising a body having thereon a pilot insertable into a hole formed in a surface to be countersunk and a

marker spaced from the pilot whereby with the pilot inserted in the hole, the body can be rotated with the marker in contact with the surface to cause the marker to mark the surface with a circle having a diameter corresponding substantially to the required diameter of the countersink at the surface.

Once such a circle has been marked, the countersink tool can be used as before. When the countersink diameter at the surface reaches the circle the operative knows that the countersink has reached or is nearing the required depth. In practice, the diameter of the circle formed by the marker will preferably be slightly smaller than the actual countersink diameter required at the surface and the operative will continue the countersinking operation up to the point where the mark is just visible. The countersink may then be finished and checked with a check tool.

The body is preferably elongate and may have the pilot extending from one end thereof.

The body may be of cylindrical form and the pilot preferably extends coaxially therewith with the marker radially spaced from pilot.

Preferably, the pilot projects from the body further than an end of the marker.

The marker may be housed at least partly within the body and may take the form of a ball point marker, such as a ball point pen refill. The marker or a portion thereof is preferably housed in a bore in the body which may be of complementary shape to said portion of the marker. The marker is preferably held in place by means of a fastener such as a grub screw.

The body may be roughened, for example by milling or knurling, for ease of grip by the operative when rotating the body.

A countersink guide in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which :-

Figure 1 is an elevation of a preferred form of countersink guide in accordance with the invention and shown partly in cross section, Figure 2 is an end view of the countersink guide looking in the direction of arrow II in Fig 1 but with a pilot removed, Figure 3 is an elevation of a pilot of the countersink guide shown in Fig 1, Figure 4 is a perspective view of the countersink guide of Fig 1 in use and Figure 5 is a cross-section through a skin panel showing a countersink tool and a countersink formed thereby in the skin panel.

Looking at Figs I to 3, a cylindrical body 10 made, for example, of aluminium has an axis 11 and is formed with a coaxial blind bore 12 which receives a mounting section 14 of a pilot 16. The pilot 16 is cylindrical and the mounting section 14 is of circular cross section and extends coaxially from one end of the pilot 16. The mounting section 14 may be push-fitted into the bore 10 or may be held in place by an adhesive. A groove 18 is formed between the pilot 16 and the mounting section 14 to ensure that the pilot 16 can be pushed right up against the adjacent end of the body 10.

The body 10 is also formed with an axially extending cylindrical bore 20 parallel with the axis 11. The bore 20 has a first section 22 leading from the end of the body 10 remote from the pilot 16, a second section 24 of reduced diameter leading from the pilot end of the body 10 and a tapered intermediate section 26. The shape of the bore 20 is complementary to the shape of a marker such as well known type of ball point pen refill 28. Such a refill 28 may be of a type used in Parker (Registered Trade Mark) retractable ball point pens. The refill 28 has an ink reservoir 30 which locates in the first section 22 of the bore 20, a reduced diameter feed tube 32 which locates in and extends from the second section 24 and a ball 34 at the free end of the feed tube 32. Angle x of the tapered section 26, is selected to match a corresponding tapering section 36 on the refill 24. The refill 28 is held in place by two grub screws 38 which screw into spaced apart

screw-threaded holes 40 in the body 10. The body 10 is formed with a milled or knurlcd area 42 adjacent the end of the body remote from the pilot 16.

Looking at Fig 4, a curved panel 44, for example a skin panel of an aircraft, is formed with a multiplicity of holes 46 (two only of which are shown). The holes 46 receive fasteners of known kind such as bolts or rivets (not shown) which have heads shaped to be received in a countersink. To provide a guide for a countersink tool, the body 10 is held by an operative and the pilot 16 is inserted in one of the holes 46 until the ball 34 of the refill 28 contacts a surface 47 of the panel 44. Once contact is made, the operative grips the milled area 42 between a finger and thumb of one hand or in some other suitable way and rotates the body 10 so that the ball 34 marks the surface 47 of the panel 44 with a circle 48 of ink concentric with the hole 46. The pilot 16 is then located in the next hole 46 and so on until circles 48 have been inscribed around all of the holes 46. As the body 10 is rotated, the ball 34 will follow the curvature of the panel 44, the pilot 16 rising and falling in the hole 46 as it does so.

The diameter of the pilot 16 is such that it can enter the hole 46 with slight working

clearance. For example where the hole 46 is to receive a commercially available 2 inch (12. 700mm) INT, ASNA2026VHK8 bolt, the pilot 16 may be between 12. 471 and 12.496 mm in diameter.

The diameter of each circle 48 corresponds substantially with the diameter of the required countersink at the surface of the panel 44. That diameter will correspond with the diameter of the bolt head, and the diameter of such a head is used to determine the radial distance of the bore 20 from the axis 11 to position the centre of ball 34 at the correct location. In practice, however, the diameter of each circle 48 may be made fractionally less than the required diameter of the countersink at the surface 47 for the reason set out below. For the above 2 inch bolt, the radial distance of the centre of ball 34 from the axis 11 may be between 10.426 and 10.86 mm.

As will be appreciated, the diameter of the pilot 16 and the radial position of the refill 28 is selected for a particular sizes of bolts or rivets and many combinations are

envisaged. The detail for any particular tool can be inscribed on a flat 56 formed on the body 10 so as to be readily visible.

With reference to Fig 5 and with the circles 48 completed, a pilot 50 of a countersink tool 52 of known kind is located in each hole 46 in turn and is driven to cut a countersink 53 in the surface 47 of the panel 44. The tool 52 is shown diagrammatically in Fig 5. The operative using the tool 52 watches the tool remove metal and sees the edge of the developing countersink 53 move outwards towards the circle 48 which acts as a material removal guide for the operative. Countersinking is continued until the circle 48 is just visible and the operative then stops rotation of the tool 52, knowing that the countersink 53 is nearing the correct depth. By making the diameter of the circle 48 fractionally less that the final required diameter, when the line is just visible the cutter takes the diameter of the countersink at the surface 47 very close to the diameter required. In Fig 5, the countersink tool 52 is shown in a position nearing the inscribed circle 48, the thickness of the circle being exaggerated in Fig 5.

The invention provides a simple yet precise guide for the machining of countersunk holes.

The countersink guide reduces the time involved in producing countersunk holes and ensures that the countersinks will be consistently and accurately formed. In practice it has been found that production time can be reduced from around 30 seconds per hole to around 13 seconds. It will be appreciated that time saving will be very significant where large numbers of countersunk holes need to be produced. Therefore, the present invention will reduce considerably the expense involved in producing countersunk holes and will, at the same time, improve quality.

Claims

Claims 1 A countersink guide comprising a body having thereon a pilot insertable into a hole formed in a surface to be countersunk and a marker spaced from the pilot whereby with the pilot inserted in the hole, the body can be rotated with the marker in contact with the surface to cause the marker to mark the surface with a circle having a diameter corresponding substantially to the required diameter of the countersink at the surface.
2 A countersink guide according to claim 1 in which the diameter of the circle formed by the marker is slightly smaller than the actual countersink diameter required at the surface.
3 A countersink guide according to claim 1 or 2 in which the body is elongate and has the pilot extending from one end thereof.
4 A countersink guide according to claim 1, 2 or 3 in which the body is of cylindrical form.
5 A countersink guide according to claim 4 in which the pilot extends coaxially of the body with the marker radially spaced from pilot.
6 A countersink guide according to any preceding claim in which the pilot projects from the body further than an end of the marker.
7 A countersink guide according to any preceding claim in which at least a portion of the marker is housed within the body.
8 A countersink guide according to claim 7 in which at least said portion of the marker is housed in a bore in the body.
9 A countersink guide according to claim 8 in which the bore is of complementary shape to at least said portion of the marker.

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10 A countersink guide according to claim 7,8 or 9 in which the marker is held in place by means of a fastener such as a grub screw.
11 A countersink guide according to any preceding claim in which the marker has a ball point for producing the mark on the surface.
12 A countersink guide according to claim 11 in which the marker is in the form of a ball point pen refill.
13 A countersink guide according to any preceding claim in which the body is roughened for ease of grip by the operative when rotating the body.
14 A counstersink guide according to any preceding claim for use in the production of countersunk holes in aircraft skin panels.
15 A countersink guide according to claim 14 where the aircraft skin panel is curved.
16 A countersink guide constructed and arranged substantially as described herein with reference to the accompanying drawings.