GB2040765A - Tap guide - Google Patents

Abstract

A tap guide is in the form of a tap holder in which a sleeve 1 defines a socket 9 for receiving the tap 11 and a coaxial socket 2 for receiving a guide pin 4 with an axially slidable and rotatable fit. A spring clip 7 in the sleeve exerts friction on the pin 4 to prevent the sleeve from dropping off the pin when the latter is clamped vertically in a chuck 13 before the tap has been offered to a workpiece 15. The socket 9 may be stepped for different tap diameters, or adaptor bushes may be used. <IMAGE>

Description

SPECIFICATION Tap guide The invention relates to a tap guide to facilitate the manual cutting of an internal screwthread.

When a hole has to be tapped, it is most difficult and often impossibleto ensure that the tap is offered and fed with its longitudinal axis precisely in registry with the longitudinal axis of the hole. This problem arises not so much with mass-produced workpieces tapped in an appropriately equipped tapping machine but rather with single articles or small runs of workpieces where it is not worthwhile to move each workpiece and spend considerable time in setting it up in the tapping fixture of a machine, if indeed a suitable machine and tapping fixture with work clamps are available.

The invention aims to provide a tap guide which enables a screwthread to be manually cut coaxially into a hole in a workpiece without the need for shifting the workpiece from the bed, table or other support of the machine tool by which the whole was produced.

According to the invention, the tap guide comprises a sleeve defining a first socket extending from one end for receiving the shank of a tap, a second socket coaxial with the first and extending from the other end of the sleeve, means for locking the tap shank in the first socket, a guide pin axially slidable and rotatable in the second socket and having a portion projecting from the second socket, a handle on the sleeve for turning the sleeve with respect to the guide pin, and means exerting sufficient friction to prevent the sleeve with habndle and tap from sliding with respect to the guide pin under gravity if the pin is held vertically.

By means of the invention, a conventional tap holder or wrench is replaced by a tap guide cum holder. After an appropriate tap has been secured in the first socket, the projecting portion of the guide pin can, if so desired, be clamped in the chuck of the same machine that was previously used to drill the hole to be tapped and before the workpiece has been removed from the machine. However, the guide pin can just as well be clamped in the chuck of any other stationary machine.

The chuck and the work-holding table or other support of the machine are than brought closer together, or the sleeve is axially displaced relatively to the guide pin, until the tip of the tap has been offered to the entrance of the hole in the workpiece.

With the chuck stationary and the pin held tight in the chuck, the sleeve is now turned with the aid of the handle and simultaneously biassed in the axial direction to feed the tap into the hole. Since the two sockets in the sleeve are coaxial, the tap will be fed accurately and, after the initial few covolutions of the screwthread have been cut, will feed itself in the usual manner, the axial slide fit of the guide pin in the second socket permitting the sleeve and tap to move axially away from the chuck.

The tap guide according to the invention is suitable for use with conventional hand taps or machine taps, the diameter of the first socket depending on the size of the tap shank. The means for locking the shank in the socket may be a grub screw engaged in a radial tapped hole provided in the sleeve. preferably there are two such grub screws for engaging the opposite sides of the usual square end of the tap shank.

Since the guide is cheap to produce, a set of such guides may be marketed, each with a different diameter for the first socket. However, it is also conceivable to provide a stepped first socket to receive alternate tap shank sizes or to provide a set of adaptor bushings of various thicknesses to fit in the first socket and each to take a different tap shank size, the bushings being apertured to enable the grub screw(s) to pass through them radially.

The preferred friction exerting means are a clip in the form of a length of round spring wire bent into a part-circular shape of an internal diameter slightly less than the diameter of the guide pin. The clip is received in a recess at the end of the second socket.

The guide pin is engaged in the clip and embraced by it.

It should be noted that the tap guide is useful not only for vertical tapping in conjunction with the drill stands of home workshops or the drilling machines of machineshops but also for horizontal tapping in conjunction with the smallest of do-it-yourself lathes or the largest turret lathes and machining centres.

An example of the invention will now be described with reference to the accompanying drawing, wherein Figure 1 is a side elevation of a tap guide, a chuck and workpiece being shown in ghost lines; Figure 2 is an enlarged fragmentary sectional elevation of the Figure 1 tap guide; and Figure 3 is a side elevation of a spring clip used in the tap guide.

The illustrated tap guide is also a tap holder and comprises a sleeve 1 of which the bore defines a socket 2 which extends from one end of the sleeve and has a preferably chamferred entrance 3 for a guide pin 4. Near the end with the entrance 3, the sleeve has an internal recess or groove 6 receiving a part-circular spring clip 7. At the same end, the sleeve is provided with a handle 8 in the form of two diametrally opposited heavy arms fixed or removably secured to the sleeve.

At the other end of the sleeve, its bore defines a socket 9, coaxial with the socket 2, for receiving the shank of a tap 11, two grub screws being provided at 12 in radial tapped holes of the sleeve, or in a collar thereof as shown in Figure 1, for the purpose of locking the tap shank in place.

The guide pin 4 is rotatable and axially slidable in the socket 2 and has a portion projecting from the socket. This projection can be clamped in the chuck 13 of any suitable machine, it being immaterial whether the pin 4 extends vertically or horizontally, i.e. the tap guide can be used for example in conjunction with a vertically operative drill stand or a horizontally operative lathe. When held vertically, it is of course undesirable for the sleeve to drop off the guide pin. For this purpose the spring clip 7, which is made from spring wire of round cross-section, embraces the pin 4 and exerts sufficient friction on it to counteract the weight of the sleeve 1 and its attachments 8, 11 and 12, without preventing rotation of the sleeve about the pin or intentional axial displacement of the sleeve.It is preferred that the clip 7 should serve as a bearing by turning with sleeve but the function would be in no way impaired if there is relative rotation between the clip and sleeve.

In use, the projecting portion of the guide pin 4 is held tight in the chuck. The tip of the tap 11 is offered to the entrance of the hole 14 to bS tapped in the workpiece 15 (which is clamped or loosely supported on a work support) by displacing, in the illustrated case lowering, the chuck 13 or displacing (raising) the work support, or by manually displacing the sleeve 1 relatively to the pin 4. With the chuck and thus the guide pin 4 stationary, the sleeve 1 is now turned about the pin by means of the handle 8 and also urged axially to feed the tap into the hole.

Eventually, the tap will feed itself.

It will be appreciated that, to exert some friction on the pin 4, the internal diameter of the clip 7 is very slightly less than the diameter of the pin. However, intentional axial displacement of the sleeve as the whole 14 is being tapped should be readily possible.

Withdrawl of the tap 11 from the tapped workpiece is effected by turning the sleeve 1 in the opposite direction, this being assisted by the momentum achieved as the heavy arms of the handle 8 are spun.

It will be evident that the tap guide as illustrated is of such simple construction that it will not be more expensive to acquire one guide for each tap size or group of sizes than it is to acquire a corresponding number of conventional tap wrenches. However, if the sleeve 1 were to be made somewhat longer than shown, the socket 9 could be stepped in diameter to permit two or more tap shank sizes to be accommodated, with the grub screws disposed radially opposite the larger or largest diameter of the socket 9, i.e.

near that sleeve end which is remote from the socket 2. Alternatively, it is possible to make the socket 9 suitable for receiving the largest tap shank size and provide adaptor bushings for insertion when smaller tape are used, the bushings being apertured to permit the grub screws to pass through them.

Claims (4)

1. A tap guide to facilitate the manual cutting of an internal screw-thread, comprising a sleeve defining a first socket extending from one end for receiving the shank of a tap, a second socket coaxial with the first and extending from the other end of the sleeve, means for locking the tap shank in the first socket, a guide pin axially slidable and rotatable in the second socket and having a portion projecting from the second socket, a handle on the sleeve for turning the sleeve with respect to the guide pin, and means exerting sufficient friction to prevent the sleeve with handle and tap from sliding with respect to the guide pin under gravity if the pin is held vertically.

2. A tap guide according to claim 1, wherein the locking means comprise a grub screw in a radial tapped hole of the sleeve.

3. Atap guide according to either preceding claim, wherein the friction exerting means comprise a spring clip of part circular shape embracing the pin and seated in an internal recess of the sleeve.

4. Atap guide substantially as hereinbefore described with reference to the accompanying drawing.