Entries by Onat Ekinci


Datum Reference Frame (DRF) in Geometric Dimensioning and Tolerancing (GD&T): An explanation with figures

A datum reference frame is a coordinate system against which the geometric dimensions and tolerances of a part are defined. The main function of the datum reference frame is to specify a foundation for the inspection of the part. It is the common coordinate system of all tolerance zones. Without this common coordinate system, product definition is unclear, rendering the inspection results unreliable. Read More Read More


Comparison of tolerances used for coaxiality control: Position, Concentricity, Circular Runout and Total Runout

Coaxiality conditions can be vital for shafts supporting heavy and varying loads, such as car and truck axles, electric motors, generators and pumps. There are four different types of tolerances for defining coaxiality controls: Position, concentricity, circular runout and total runout. This post proposes brief and practical definitions regarding which type of tolerance to choose for certain applications as well as the advantages and disadvantages to each. For more information, refer to the ASME standard [1] and other related reference articles [2]. Read More Read More

Building Photogrammetry: Comparing Camera Results of iPad VS DSLR

If 800 people are working on the iPhone camera, would this mean that smartphone / tablet cameras will soon match the performance of DSLRs?

The short answer is “No”, as long as the camera sensor size is not increased.  A larger camera sensor allows the capture of more light and reduces noise levels. Their applicability to smartphones / tablets will always be limited, however, since a larger sensor size would also require a larger lens, which would not be very practical for a smart device. Read More Read More

Photogrammetry in Cultural Heritage: Experiments with a Cloud Based Service and an iPad


Can we document cultural heritage monuments with affordable tablets / smartphones and cloud-based photogrammetry services such as Autodesk Recap 360?  And how can the performance of these systems reach the accuracy and resolution levels of established devices?  What is the procedure for obtaining a 3D model of a monument by photos?  This blog post will try to present some of  the potential answers to these questions. Read More Read More



Photogrammetry, despite sounding rather complex, is basically  the stitching together of a series of photos to obtain a 3D model. In this post, we will analyze the results of a 3d model provided by Autodesk Recap 360. This post will just be a simple example; we will delve deeper in future posts for more detailed analyses. Read More Read More


5 Laser Tracker Warm-up Tips for Ideal Measurement Conditions

An Important Factor in Precise Measurements: Laser Tracker Warm-up Time

In aerospace, one of the most extensively used measurement instruments is the laser tracker. Laser trackers are very precise devices composed of extremely complex subcomponents such as interferometers and angular encoders. They are basically robots capable of following reflective targets. And, as with all robots, they are subject to specific sensitivities. One of the most crucial of these is their sensitivity to thermal effects. Read More Read More

, ,


In my last blog post, I talked about measurement assisted assembly (MAA). Measurement Assisted Assembly is a key operation for the reduction of time in aerospace assembly, which can account for as much as 40% of aircraft manufacturing costs. In this post I will present an interesting example of MAA: Assembly of aircraft through the guidance of measurement devices. Read More Read More

, ,


Aerospace assembly is the finest jewel among assembly applications. It presents a daunting and unique challenge: The assembly of very large structures to very close tolerances along with huge fastening and drilling operations.

Assembly can take up to as much as 40% of the total cost of manufacturing an airframe due to the labour and quality issues because of drilling thousands of holes per aircraft. Around 5% of the total manufacturing cost of an aircraft or 10% of the airframe cost is caused by the use of fixed tooling. Read More Read More