Geometrical instruments – Gauge – Screw thread
Patent
1983-12-12
1985-05-28
Haroian, Harry N.
Geometrical instruments
Gauge
Screw thread
33178B, 33169B, G01B 348
Patent
active
045191441
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a thread measuring tool with a plug gauge at each end, said gauges being formed as thread gauges of the "go" and "no go" type.
When it is required to check whether the thread inside a bore is correct and within certain given tolerances, a thread gauge is used. A thread gauge for checking the thread inside a bore is normally in the form of a plug gauge with a thread at each end, namely a so-called "go" side and a "no go" side. The "go" side is a profile-ground threaded portion which is machined as closely as possible to the correct profile and the correct dimensions. The "go" side must be able to be screwed in without the use of force. The "no go" side is normally provided with a flank diameter which is just in excess of that permitted by the stated tolerance. The top and bottom of the thread is ground free, thus ensuring that these do not restrict the screwing in, but the "no go" side must not be capable of being screwed into the threaded hole. With such a plug gauge, one can reveal most of the errors which can arise when producing threads in bores.
In connection with work demanding a very accuarate thread, and where one therefore uses a limit gauge to check the quality and the tolerance of the thread, it is also often prescribed that the threaded bore must be of a certain depth, and possibly how great the tolerance must be with regard to the depth. Therefore, after having checked the thread tolerance, one must measure the depth of the hole, for example with a micrometer depth gauge. This, however, provides a check only of the depth of the hole, and not of how far the thread extends down into the hole.
The object of the present invention is to provide a thread measuring tool capable of checking the quality of a thread inside a bore, while at the same time measuring the depth of said bore in that it measures how deep the thread extends down into the hole.
With the measuring tool according to the invention one can carry out a simultaneous measurement of the depth of the threaded hole and the quality of the thread. It is thus possible to ensure that the threaded hole is as specified while at the same time avoiding all the disadvantages and possibilities of error involved in carrying out two measurements, namely a measurement of the depth of the bore and a measurement of the quality of the thread.
By forming the measuring tool according to the present invention, a correct and uniform measurement is achieved every time, the reason being that spring pressure is used to press the plug gauge holder down against that surface in which the threaded hole to be checked has been bored. What is thus provided is a very simple tool which is always ready for use, and wherein the spring pressure always returns the tool to the zero position when it is not in use, and wherein the plug gauge is protected by the holder.
By forming the measuring tool according to the present invention, a very plain and simple mechanical construction is achieved.
The invention will now be explained with reference to the accompanying drawing, which shows an example of a measuring tool according to the invention, in that
FIG. 1 shows a cross section of the measuring tool, and
FIG. 2 shows the tool during the measurement of a threaded hole.
In FIG. 1 is seen a measuring tool with a plug gauge 4 which comprises the "go" side, and a plug gauge 3 which comprises the "no go" side. The plug gauge 3 can be of the normal "no go" type having a flank diameter corrresponding to the greatest permissible tolerance or corresponding to the smallest permissible tolerance, all depending on the measuring principle one uses.
In a housing 1 is disposed a plug gauge holder 5, which under spring pressure from the spring 8 is biased towards an internal shoulder 12 in the housing 1. Through the whole of the tool there extends a through-going spindle 2, the one end of which forms the "no go" gauge 3 and the other end the "go" gauge 4.
The plug gauge holder 5 is freely rotatable around the through-going spindle 2, this rotation being restricted only
REFERENCES:
patent: 1459896 (1923-06-01), John
patent: 2330453 (1943-09-01), Smith
patent: 2861347 (1958-11-01), Von Tarnik
patent: 3064355 (1962-11-01), Herman
patent: 3075892 (1962-01-01), Stuart
Western Electric Tech. Dig. #24, 10/71, Gauge for Measuring the Threaded Depth of Holes, J. O. Landis.
IBM Technical Disclosure Bulletin, vol. 13, No. 5, issued Oct. 1970, J. F. Straitwell, "Thread Depth Measurement", p. 1335.
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