TECHNOLOGICAL ENGINEERING, Volume XIV, number 2/2017, ISSN 1336 - 5967 9 STUDY OF MEASUREMENT STRATEGIES OF GEOMETRIC DEVIATION OF THE POSITION OF THE THREADED HOLES Article history: Received 22.12.2017 Accepted 29.12.2017 Available online 31.12.2017 Mário Drbul 1 , Pavol Martikan 1 , Michal Sajgalik 1 , Andrej Czan 1 , Jozef Broncek 2 , Ondrej Babik 1 1 Department of Machining and Manufacturing Technology, University of Zilina, Univerzitna 1, 010 26 Zilina 2 Department of Machine Parts and Mechanisms, University of Zilina, Univerzitna 1, 010 26 Zilina Abstract Verification of product and quality control is an integral part of current production process. In terms of functional requirements and product interoperability, it is necessary to analyze their dimensional and also geometric specifica- tions. Threaded holes are verified elements too, which are a substantial part of detachable screw connections and have a broad presence in engineering products. This paper deals with on the analysing of measurement strategies of verification geometric deviation of the position of the threaded holes, which are the indirect method of measuring threaded pins when applying different measurement strategies which can affect the result of the verification of the product.. Keywords measurement strategy geometric deviations, threaded holes, geometric specifications 1 INTRODUCTION Threaded holes belong to the group of verified elements, which form a substantial part of detachable screw connections and have a broad presence in engineering products. In general, their construction is difficult to measure. Their positioning and orientation is very important to ensure that the screw connection is properly secured and that the connecting element does not fail. However, measuring the position of the threaded holes is something that is taken for granted. Incorrect techniques are often used, or measurements are made to save time and money at the cost of inaccuracies and measurement errors [1,2]. Among such improper methods, we can include a methodology whereby the position of the threaded hole or the position of the axis of the threaded hole is determined by inserting threadless calibers into the small diameter of the hole. This will then be scanned to locate only the surface of the component. This method gives us two-dimensional information about the three-dimensional element, namely that where one point is located on the axis of the small diameter of the thread instead of obtaining the position of the center diameter axis of the threaded hole [3]. In the industry, coordinate measuring machines (hereinafter referred to as 3D CMMs) are often used for this control to ensure high precision and repeatability of measurements. These measurement systems are complemented by software that can evaluate a large amount of data and interpret it correctly to ensure the credibility of the results. Flexibility and reliability in terms of measurement and control allows this machine to use several methods and techniques to determine the actual position of the threaded holes [4]. No matter how the thread was made, the best way to locate the axis of the thread hole is to locate axes of the center diameter of the thread. This is done using pins to detect the position of the thread hole. The pin is screwed into the thread hole and the axle position is then detected using a 3D measuring machine or other measuring system. The end of the pin that protrudes from the thread hole has a "known cylinder", that is the reference rate. It may also have crevices to facilitate insertion and removal. However, great care must be taken with these calibration pins. All pins should be used with caution when checking the position of the threaded holes. Not one such pin is subject to norms, so design, dimensions, tolerances, and efficiency may vary from one manufacturer to another. Among the most used threaded pins we can include: flexible, fixed, tapered [5]. Flexible Threaded Pins (Fig. 1a) - This type of caliber is made of spring tool steel. The threaded portion of the caliber has four grooves of 90° to provide a fixed position in the threaded hole, regardless of its diameter. When screwed into the threaded hole, it fits comfortably into the hole and adapts to the middle diameter of the thread. This feature provides firm hold of the pin in the hole and reduces the perpendicular error that can be brought into measurement. The disadvantage is that the coaxiality between the scanned cylinder and the threaded part can be changed when screwing and are difficult to calibrate. The advantage is that it acts by pressure on the middle diameter of the holes and thus holds it in place. It is questionable whether the coaxiality of the scanned cylinder and the threaded portion is maintained when the gauge thread is squeezed [6]. Fixed threaded pins (Fig. 1b) - Fixed calibers resemble flexible calibers, but do not have a grooved threaded portion. The caliber is firmly screwed into the hole of the component. The screwing pressure forces the caliber to automatically center in the threaded hole. They are used to determine holes on flat surfaces. The problem occurs if the planes on which it is screwed are not perpendicular to the axis of the thread. Then, the caliber can be skewed and so provide erroneous, badly repeatable data. The advantage is that they can be calibrated, but pay attention to the wear of the front that is attached to the TECHNOLOGICAL ENGINEERING volume XIV, number 2/2017 ISSN 1336 - 5967 DOI: 10.1515/teen-2017-0012