Using Rapidform to Reverse Engineer from Manual Scanning (Zeiss Scanmax)

Try not to laugh too hard at the Scanmax. Scanning can be tedious but it is often better (much quicker) than our other option. Our Scanmax has been in use for almost 10 years. Parts are not available and Zeiss will not even service it. Thanks. So if it breaks – it’s done. Anyways, I have 100′s of hours of reverse engineering with it. For trim sections, it is the quickest thing going. For form sections – not so fast.

To get a good surfacing result, you need to scan in a cross-hatch pattern to cover the area. This is done by hand, covering small areas one at a time. The machine can be finicky, especially when scanning vertical surfaces. The software bundled with the Scanmax is called Dimension. It is a bit limited in creating surfaces. Actually, it works very well in some ways, but it is tedious. The User Interface needs work.

Below, I describe in very little detail how I recently used the Zeiss to scan, and Rapidform to reverse engineer a forming tool. The customer modified an existing design by grinding away problem areas. They returned the tool and asked us to update our information and make replacement parts. In the first picture I show the scanlines. What is not shown in the picture is the scanline of the plate I fastened the tool to. It defines the Z-plane.

Here is what the scanlines look like brought into AutoCAD – you can’t fit surfaces in this program.

Here is the same thing in Rapidform

…and meshed

…then regionalized

… fit a surface onto selected regions

check the deviation of the surface to the point cloud. This is showing +/-.002″ [+/-.05mm]

skip a few steps and you end up with this

Somebody pointed out that I missed describing more than a few steps. Yup. It’s not that bad, though:

• Create a sketch on the Z-plane. Use a silhouette to capture the base shape. Extrude this shape to the height of the scan.
• Cut off the fitted surfaces I describe above.
• Add fillets. Adjust the fillets until the allowable deviation is met.

If you are eagle-eyed, you would have noticed that the finished part is thinner than what the meshed data shows. The reason for this is that the point cloud is uncompensated. All the points are to the center of the ball. After modeling the part, I had to offset everything inward by 2.5mm per side.

Using just a few scanlines, you can usually capture enough detail to recreate a machined part. Below is an example of some very basic scanlines that capture the shape but cannot be meshed. The part was aligned in the Zeiss CMM to the chosen geometry. The shape of the part is evident when looking from directly above. Trace around it (remembering to offset inward half the ball diameter) to get the shape. Extrude and add the remaining features.

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