THREAD INSPECTION TOOL FOR MEASUREMENT OF PITCH DIAMETER, VISUAL CHECK OF PITCH AND THREAD PROFILE

Abstract: A thread inspection tool of the type, in which a sliding caliper is provided with holders, in which thread profile blades may be mounted, the holders being fastened to the jaws of the sliding caliper, and in which the thread profile blades, one of which having of at least two thread profiles, may be brought into mutual contact. With a view to providing a tool which may be calibrated without the use of additional equipment, and the measuring reliability of which may be immediately controlled, the thread inspection tool is characteristic in that the sliding caliper is of the zero positionable type, that the thread profile blades are adapted to measure pitch diameter and to visually check and evaluate the thread profile, that the holders comprise two grooves extending perpendicularly to each other, and in which one groove is adapted to receive and to be held by one of the jaws of the sliding caliper, and in which the second groove, which comprises a threaded hole for holding a fastening screw for the thread profile blades, is machined to such a depth and width that it may hold the guide lug of a thread profile blade, the grooves for the guide lugs extending mutually in such a way that when two thread profile blades are placed in each their groove, they are positioned in the same plane parallel with the beam of the sliding caliper, and in such a way that a centre line common for the thread profiles intersects a tread crest on one thread profile blade and a root on the other.

Description: THREAD INSPECTION TOOL FOR MEASUREMENT OF PITCH DIAMETER, VISUAL CHECK OF PITCH AND THREAD PROFILE The present invention relates to a thread inspection tool of the type, in which a sliding caliper is provided with holders, in which thread profile blades may be mounted, the holders being fastened to the jaws of the sliding caliper, and in which the thread profile blades, one of which having at least two thread profiles, may be brought into mutual contact. Prior art, i.e. thread plug gauges, thread ring gages and thread calipers only check if the thread is right or wrong, and with these instruments there is some uncertainty as to the scope of wear on the inspection tool after use. Moreover, it is only possible to use these instruments for one specific diameter and tolerance. Thread wires and thread inserts (both primarily for external micrometer screws) check first and foremost only pitch diameter and assume correct pitch and profile. Adjustable inspection and measuring tools require a calibration "master", and common for all these methods is a very difficult and/or expensive calibration. US-A-4,611,404 discloses a thread inspection tool which is based on a conventional caliper, onto the jaws of which a pair of arms is attached. These arms are provided with holders for thread profile blades which have in advance been calibrated such that the readout of the caliper corresponds to the external diameter of the thread. A drawback of this instrument is that the calibration cannot be performed without the use of additional equipment in form of calibration masters. Correspondingly, there is no possibility of discovering errors due to incorrect mounting, damage and/or wear, without controlling the instrument by means of calibration masters. The instrument is adjustable from measurement of external threads to measurement of internal threads, but the adjustment requires change of both arms and profile blades. Due to the shape of the arms only large, internal threads can be measured. The object of the invention is to eliminate the drawbacks described above. The thread inspection tool according to the invention is characteristic by the subject matter of the characterizing clause of claim 1. In connection with the thread measuring tool according to the invention a combination of holders, which allow the profile blades to be pushed together for check of the correct insertion for calibration of the tool, and a caliper of the zero positionable type is used. When measuring external threads the two profile blades are pushed together, whereby it becomes possible firstly to visually ascertain the condition of the profile blades, and secondly a reference is obtained which at the zero positioning of the caliper makes it possible directly at the subsequent measurements to read the pitch diameter of the thread in question. In a preferred embodiment according to the invention the plane of the profile blades extends perpendicularly to a plane through the jaws of the caliper. This embodiment makes it possible to measure threads which are longer than the jaws of the caliper and to measure external threads, while the workpiece is held by a tailstock centre in a machine. For measurement of internal threads the thread inspection tool according to the invention is provided with profile blades which comprise rear edges extending parallel with the thread profile, said rear edges being positioned in such a way relative to the guide lugs that the thread profile blades after mounting may be brought into mutual contact along the rear edges. The mutual contact between the rear edges of profile blades is used for control of the mounting of the blades and their condition as well as for calibration of the tool. When measuring internal threads a measured value has, however, to be added to the readout measurement, which measured value is characteristic for the profile blades in question. This measured value may, however, be found by means of the zero positionable caliper before the profile blades are mounted. The thread measurements which are performed with the tool according to the invention get a higher degree of accuracy the thinner the profile blades. It is, therefore, preferable according to the invention that the second groove is adapted to hold strengthening blades too which substantially follow the contour of the profile blade, and in such a way that the strengthening blade is shortened such that the thread profile of the profile blade itself is free of the strengthening blade, when the strengthening blade is abutting the profile blade. By means of the strengthening blades it is possible to reduce the thickness of the profile blades to a few tenths mm, which reduces the influence of the thread pitch on the measurement to such a degree that it may be disregarded in practice. By means of the strengthening blade the profile blade obtains a rigidity which is sufficient, without any risk of damaging the profile blade, for the tool to be used under normal conditions in a workshop. According to a preferred embodiment at least one strengthening blade is permanently fastened to the thread profile blade. When the strengthening blades are permanently fastened to the profile blade, for instance by soldering or glueing, a lamination effect is obtained which impart to the profile blade an even bigger resistance than is the case with detachable blades towards pushing and pulling, when the profile blades are used for measuring and checking. In a particularly advantageous embodiment according to the invention the guide lug is staggered by one quarter of the pitch from the centre line. By such an embodiment of the profile blades it is possible to use two similar profile blades in the inspection tool, which substantially simplifies the manufacture of the profile blades. The invention will be described in detail in the following with reference to the drawing, in which Fig. 1 shows an electronic sliding caliper with modified jaws as well as the modified jaws enlarged and equipped with the profile blades or the blades ready for being mounted, Fig. 2 shows different views of a profile blade holder mounted on the fixed jaw of a caliper, Fig. 3 shows a set of profile blades which have been brought in contact during zero positioning of the caliper, Fig. 4 shows thread profile blades during measurement and control of an external thread, Fig. 5 shows thread profile blades for internal threads during measuring of the characteristic measured value, Fig. 6 shows a set internal profile blades which have been brought in position for zero positioning of the caliper, Fig. 7 shows thread profile blades for internal threads during measuring of the thread, Fig. 8 shows a thread profile blade provided with strengthening blades, and Fig. 9 shows a thread profile blade for measuring external threads, and in which two identical blades may form a pair. Fig. 1 shows an electronic digital caliper 1 with a profile blade holder 2 fastened to the fixed jaw 7 and a profile blade holder 3 fastened to the movable jaw 8. The enlarged figure shows the two jaws 7,8 with holders 2,3, in which a pair of profile blades 4 for measurement of external threads has been mounted. Moreover, a pair of thread profile blades 5 for measuring internal threads is shown as well as a pair of fastening screws for fastening the thread profile blades in the grooves in the bottom of the profile blade holders 2,3. Fig. 2 shows the fixed jaw 1 of a caliper with a profile blade holder 2 mounted for instance by soldering or glueing to the jaw. The profile blade holder on the movable jaw is designed in the same way, but is laterally reversed. The holder comprises a block 2 which partly serves as strengthener, partly prevents foreign particles from penetrating into the fastening groove, in which the jaw is held. In the bottom of the holder 2 a groove is provided for receiving the guide lug of the profile blades. The grooves in the two holders have to be machined in such a way that the profile blades which are inserted in the two blocks align, i.e. are parallel with and equidistant from the beam of the caliper. The fastening means 9 is for fastening the block to the jaw and the fastening means 6 is for fastening the thread profile blade in the groove. Fig. 3 shows how a set of external thread profile blades 4,4' should touch for check of correct mounting and the positioning for calibration, by means of which the caliper is zero positioned. The figure shows the guide lugs of the profile blades, said guide lugs being the part of the profile blade which is fastened in and guided by the groove in the bottom of the profile blade holder 3. The measuring of an external thread is shown in Fig. 4. The two external thread profile blades 4,4' are brought in contact with the thread at opposide sides. When the caliper is zero positioned, as mentioned in connection with Fig. 3, the measurement result will be equal to the pitch diameter of the thread. Fig. 5 shows the position of a pair of unattached thread profile blades 5,5' for measurement of the characteristic dimension K. The measurement result K is noted for later use in connection with measuring of internal threads. After measurement of the dimension K the profile blades are mounted in the holders which are brought together to the position shown in Fig. 6, in which the caliper is zero positioned when it has been checked that the two profile blades abut one another and consequently are correctly mounted. The thread profile, the guide lug and the groove in the bottom of the holder have to be designed in such a way that a centre line (shown as a dotted line) intersects one profile blade through a thread crest and the other through a thread root. This is the requirement for a theoretically correct touching when measuring a thread. Fig. 7 shows how the thread profile blades 5,5' mounted on the holders should touch when measuring an internal thread. When the thread profile blades are zero positioned after having been fastened in the profile blade holders, the measurement result will equal the pitch diameter, when the noted distance K, measured as described in connection with Fig. 5, is added to the measurement result. The profile blades are inserted in the thread in a plane parallel with the axis of the thread. The pitch of the thread thereby extends obliquely relative to the edges of the profile blades. It is therefore desirable in respect of the accuracy of the measurement that the profile blades are as thin as possible. As shown in Fig. 9 the profile blades may therefore be equipped with strengthening blades, the contour of which substantially corresponds to that of the profile blade apart from the fact that the strengthening blade is somewhat shorter than the profile blade, the contour of the profile blade protruding over the contour of the strengthening blade. The profile blade shown in Fig. 9 for measurement of an external thread is characteristic in that the symmetry axis of the guide lug is staggered by one quarter relative to a centre line for the thread profile. The centre lines for the thread profile run through the tooth tips of the profile. In this embodiment of the profile blade two identical profile blades may be used as a set, one of the blades being merely turned a half round about the axis of the guide lug.

Claims: C L A I M S 1. A thread inspection tool of the type, in which a sliding caliper is provided with holders, in which thread profile blades may be mounted, the holders being fastened to the jaws of the sliding caliper, and in which the thread profile blades, one of which having of at least two thread profiles, may be brought into mutual contact, c h a r a c t e r i z e d in that the sliding caliper is of the zero positionable type, that the thread profile blades are adapted to measure pitch diameter and to visually check and evaluate the thread profile, that the holders comprise two grooves extending perpendicularly to each other, and in which one groove is adapted to receive and to be held by one of the jaws of the sliding caliper, and in which the second groove, which comprises a threaded hole for holding a fastening screw for the thread profile blades, is machined to such a depth and width that it may hold the guide lug of a thread profile blade, the grooves for the guide lugs extending mutually in such a way that when two thread profile blades are placed in each their groove, they are positioned in the same plane parallel with the beam of the sliding caliper, and in such a way that a centre line common for the thread profiles intersects a thread crest on one thread profile blade and a root on the other. 2. A thread inspection tool according to claim 1, c h a r a c t e r i z e d in that the plane of the thread profile blades extends perpendicularly to a plane through the jaws of the sliding caliper. 3. A thread inspection tool according to claim 1, c h a r a c t e r i z e d in that profile blades for measurement of internal threads comprise rear edges extending parallel with the thread profile, said rear edges being positioned in such a way relative to the guide lugs that the thread profile blades after mounting may be brought into mutual contact along the rear edges. 4. A thread inspection tool according to any of the claims 1-3, c h a r a c t e r i z e d in that the second groove is adapted to hold also strengthening blades which substantially follow the contour of the profile blade, and such that the strengthening blade is shortened such that the thread profile of the profile blade itself is free of the strengthening blade, when the strengthening blade is abutting the profile blade. 5. A thread inspection tool according to claim 4, c h a r a c t e r i z e d in that at least one strengthening blade is permanently fastened to the thread profile blade. 6. A thread inspection tool according to claim l for measuring external threads, c a r a c t e r i z e d in that the guide lug is staggered by one quarter of the pitch from the centre line. 7. A thread inspection tool according to claim 6, c h a r a c t e r i z e d in that two thread profile blades of a thread measurement set are identical.

Inventors: CLARKE GORDON, NIELSEN FRANK JUHL, CLARKE, GORDON, NIELSEN, FRANK, JUHL
Applicants: CLARKE GORDON, NIELSEN FRANK JUHL, PRO TECH INTERNATIONAL A S, CLARKE, GORDON, NIELSEN, FRANK, JUHL, PRO-TECH INTERNATIONAL A/S
Application year: 1995
Main classification: G01B3
IPC codes: G01B3