Manufacturing Excellence Control Using CMM or Scanner

A cylinder has a total of three surfaces: a top, bottom, and middle. The top and bottom, which are circles, are easy to visualize. The third is actually the curved wall of the cylinder. It is a surface that has measurable volume.

What is it?

Circles are simply closed curves. Where points along the curve converge to close the curve and the results are a circle.

With all instruments used for scanning, i.e. roundness machines and surface roughness gages, when scanning with a CMM the raw data must be filtered. When using a CMM to scan features on a part there are data filtering options that can affect the scanning results.

The software default selections may not always be the best option. As CMM programmers, when software messes with our data we better have a good understanding of what is going on with that data. Understanding filtering is key when faced with the multiple filtering options available.

Surface Normals

There are several issues that arise when bringing a CAD model into your CAD based programming software. One of these issues has to do with surface normals (surface vectors). You can bring in a model and the entire model or a portion of that model is visible, but dark (Figure1), or certain sections are not visible at all. This problem arises from the surface vectors pointing in the opposite direction than your CAD system views them. You are looking at the back side of the surface. You must reverse the surface normal (Figure 2). If your software has this capability, you are looking for something similar to ‘reverse surface normals’. This will flip the surface so the front faces in the correct orientation for your software to view the surface.

 In our on going series of covering the CMM basics we need to cover the all too familiar DFR, or the Datum Reference Frame. We see this DFR associated with a feature on the part but what does it mean? and how does it change my approach to programming this part?  We will attempt to answer these questions. This won’t be an attempt to address the overall make up of the DFR but we will look at the datum order and how that affects our programming

You’ve probably heard it said that “A CMM can’t check diameters correctly” or “Your CMM isn’t accurate because when I check the diameter with a pin it’s right”. This is never an enjoyable place to be in when you are not harmed with a good answer. So, I want to cover what happens when you are faced with situation.

What’s Happening?