How to Reverse Engineer Physical Objects

Updated Feb 10, 2023
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PublishedDec 23, 2020in CNC
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Reverse engineering physical objects is a process that basically involves reproducing a product – often either digitally or on paper – through a careful and detailed examination of its construction and assembly. This process of acquiring and analyzing detailed design information is useful for detecting design flaws, analyzing product specifications for commercial reviews, and even competitive analysis. Every man-made product – and even some organic ones – can be reverse-engineered given the right tools, with every reverse-engineering process being unique. But almost always, the start of the process will entail taking the object apart to understand its inner workings and mechanisms. This crucial first step is the first big obstacle to those just getting started with reverse engineering.

Video Tutorial: How to Reverse Engineer an Object

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Scan2CAD is commonly used by manufacturing companies to reverse-engineer physical objects. So what we want to achieve in this case is take an image of a physical object and convert that to a CAD or CNC file, which can be used for manufacturing. So first, we’ve opened up Scan2CAD. We’re gonna go to “open file” and select this image. The first thing to mention is it’s important to acquire a suitable image of your physical object. In this case, we’ve got a gasket which has been scanned using a flatbed paper scanner. That’s just the usual scanner that you’d see in an office for scanning paper. The reason that’s a good solution for physical objects is because the camera, as it were, is always perfectly parallel to the object, it has good lighting, and as you can see, we have a nice clean white background and a dark object.

Some of the problems caused when reverse-engineering objects are usually surrounding the acquiring of the image, for example, using a poor quality camera, taking a photograph at an angle, therefore, skewing all of the dimensions, and also little issues like camera flash or having an object which is on a busy background. So some simple steps to make sure you have a nice, clean image for conversion. It’s gonna make your life much easier if you are to do this repetitively. So we have a clean image here of this gasket, and with Scan2CAD what we’ll need to do is first treat the image to make it suitable for conversion, and then convert to vector, which can be saved out to DXF, DWG, or G-code file format. So that’s super simple with Scan2CAD. We can treat the image in two ways: We could use the usual clean raster image tool, where you can threshold the image and so on, or we can use our new grab-cut tool. So we go to “edit” then “grab-cut.” And this is designed specifically for converting physical objects.

So firstly asks us to select the part of the image that has the object. I’ll say, “Use whole image,” and confirm. And now Scan2CAD has read through the image, looked for parts that it thinks would be the physical object, and isolated it and changed the rest to a black background. So it’s already actually done what we need in this case. If it hadn’t, we could select backgrounds, draw in the elements that we… Tell Scan2CAD is a background then click “run.” However, as you can see, this is all done automatically. So we just click “next” and “okay,” and you can see now we’ve converted the image to a flat image, which is more suitable for conversion. I do see a couple of issues. There’s a white dot here; it’s probably caused by some dust or something on the object, and Scan2CAD is seeing that as a whole. So let’s clean that up. Now we’ll go to the “clean raster image,” which is threshold. We’ll check “remove speckles and holes,” and you can see that that speckle has now disappeared in the preview. And I can see some jaggedness around here as well, so we might as well just click “smooth” to smooth out the lines.

We’ve now got an image which is suitable for conversion. So to convert this image, we go to the “convert raster image” tool, and in this case, if you’re converting for manufacturing purposes, you’re probably always going to use the outline conversion method. So select “outline,” and let’s just hit “run” with the defaults; the defaults are there to give you the best starting point. And you can see the preview of the conversion in the window here, and it looks really good. We’ve got a nice, clean vector outline of the shape. You can compare that to the raster image in the raster tab in the preview. You can even see both together, highlight the vectors so you can see this pink outline now for the vectors. Now, if you want, we can go ahead and change the conversion. For example, you can choose sharp, where it really follow closely the pixels of the image. But note that by definition, a pixel image is a pixel-based image; therefore, you’re gonna have some jaggedness if you go super sharp. That’s why you wanna go somewhere slightly on the smoother end.

And you can also choose the vector outputs; for example, if your machine only supports polylines, so you can select that. However, we have it default here… Defaulted here, as you can see, to lines and arcs. Let’s click “okay.” We’re gonna say “okay.” We can see the results now in our canvas, and we see now that, before, we just had a raster tab, and now we have a vector tab showing the conversion. We can see both together. So you can see the results, and you can even just go ahead and make some simple vector tweets if you wanted to. If you’re happy with the results, all you have to do now is export the file. So we go to the export button. And let’s just name this “gasket,” and from here, you can save as DXF, DWG, and so on.

Ah, but there’s one final thing that we didn’t do, which is to input the scaling. Scaling should be inputted before you export the file. To do that, we go to the measure tool. And let’s say, for example, we know the full diameter of this is, let’s say… Let’s say the width of the whole gasket is 30 centimeters. So what we’ll do is we’ll measure from this point to this point. Just as an example. You can see that Scan2CAD has measured that distance in pixels. And what we are gonna do is click the calibrate button. And in our example, we’re going to say that this equals 30 centimeters, so we say “30,” change units to centimeters, click “apply,” and now the whole drawing, this vector file, whether it’s a DXF, DWG or CNC file, now has a correct scaling when it comes to manufacturing. So now is the right time to go ahead and export the file. You could just say, “gasket.” Save as your designated file. You can see here the different G-code file formats, should you require that. DWG as well and DXF. Click “save,” and you’re good to go.

So that’s a quick overview of how to use Scan2CAD to reverse-engineer an image of a physical object for manufacturing purposes.

Fortunately, programs like Scan2CAD can help make this straight-forward and much less confusing than it has to be. Although the steps taken can be quite involved and might take a little time to understand, it’s one of the best ways to digitize and recreate a product part that’s difficult to find or procure otherwise. Today, we’ll go through some of the more complicated steps in using Scan2CAD and help you convert your physical objects to vector files that you can easily use for reverse engineering. High-quality CAD and vector files are immensely helpful during reverse engineering, and Scan2CAD is the easiest way to produce them.

A reverse-engineered 3D scan of a machine part

A reverse-engineered 3D scan of a machine part Source

Step 1 – Scanning or photographing the object

A low-quality scan of a machine blueprint

A low-quality scan of a machine blueprint Source

It is imperative that before we digitize an object using Scan2CAD, we get a high-quality raster image that is suitable for automated conversion. Ideally, the preference is to use a high-quality scan of the object. The settings for a good scan are as follows:

  • Make sure to set the scan file format to TIFF or any other similarly lossless file format. JPEGs will typically have some details lost in the scanning process since it isn’t a lossless file type so try to avoid this file type if you can.
  • Set the DPI at the range of 300-500. Anything lower than 300 DPI will give you a low-quality and often pixelated scan and anything higher than 500 DPI will give you unnecessarily large file sizes with no additional benefits.
  • Monochrome or black and white scans are best for the purposes of Scan2CAD automated conversion. You can use grayscale scans and colored scans as well, but these will still inevitably be turned black and white on Scan2CAD before being converted into vector files.

When a scan of the object isn’t possible, photographs can also be used for Scan2CAD given the right setup. Here are the settings for taking a photograph for conversion on Scan2CAD:

If you’re converting an image of a physical object it’s important that you acquire a suitable image in the first instance. Here are some key tips:

  • Just as with scans, make sure to set your photographs to lossless file formats.
  • Set the object against a background with a contrasting color. Specifically, place a light-colored object in front of a uniformly black background and place a dark-colored object in front of a light background.
  • Ensure that the camera is parallel to the object and is pointed at it directly. This is to prevent any prospective distortion to assure that the resulting photo is an accurate depiction of the actual dimensions of the object. Ideally, you could take a picture of the object from far away using a telescopic lens.
  • Set the lighting so that the object has minimal shades and is not obscured or covered with shadows. Any shades and shadows picked up by the photo will be included in the output when Scan2CAD runs the conversion process.

After acquiring a high-quality raster image, take the extra time to double-check the image and to edit out any unwanted speckles, distortions, and image noise. Re-do the scan or photograph if you have to. Scan2CAD does have some editing tools you can use for any last-minute edit, but it’s best to use dedicated image editing software to really clean up your raster image before converting.

Step 2 – Converting your image to a vector file

Vectorized spanner on Scan2CAD

Vectorized spanner on Scan2CAD

The next step involves opening your raster file on Scan2CAD and proceeding with the actual conversion process there. This basically involves doing last-minute edits on your raster image, optimizing the vectorization settings for your image, optionally making last-minute edits on your output vector, and then saving the file. Here are the specific steps:

  1. After opening up the file, choose the Edit > Grabcut tool. In the dialogue box that opens, either click on ‘Use whole image’ if you want to convert the entire image or click and drag to create a rectangular selection detailing the area you want to convert. Then on ‘Confirm selection’.
  1. Scan2CAD will automatically take out the background but in cases where you want to do it manually or if Scan2CAD missed some areas, click on ‘Background’ and scribble a line or two on areas that are supposed to be backgrounds. Click on ‘Run’ to execute any changes and then ‘Next’ to finalize.
  1. The next screen brings you to the finalize object and here, you can choose to use the ‘Smooth’ slider to smoothen any jagged edges in the image. Click on ‘OK’ once you’re happy with the result.
  1. Additionally, if there are any other small cleanup actions you want to take, you can click on the Clean Image dialog box located at the top left of the screen. If the option is available, tick the ‘Threshold (Black & White)’ option under ‘Color Reduction’. This turns your image black & white and makes it suitable for conversion. If the option is grayed out, that means your image was already black and white and no longer needs to be monochromatized which is the case if you’ve already used the Grabcut feature.
  1. Although at this point, any major edits should have been done beforehand, there are also additional options under ‘Clean Image’ that you can use to do any small last-minute changes.
  • Remove Speckles & Holes: for any small clusters of pixels of white or black that need to be removed from the image
  • Thicken Lines: for any barely legible lines that need to be thickened
  • Smooth: for ‘jagged’ or pixelated lines that need to be smoothed out

Click on OK if you’re done with the ‘Clean Image’ dialogue after this.

  1. Other than the options under ‘Clean Image’, you’ll also have editing tools available on the left side of the screen. Most notably, you’ll be able to use the following:
  • Several ‘draw’ tools: separate tools for creating new raster lines in the drawing.
  • Draw text: to add raster text into the image
  • Erase: to take out any unwanted parts of the image
  1. If you’re happy with your edited and cleaned up image, click on the ‘Convert raster image’ tool . You’ll want to choose the ‘Outline’ option under ‘Vectorization Method’ and then click on ‘Run’ to generate a preview.
  1. You can then cycle through the tabs of both the original raster and the converted vector as well as a tab with both to see if the resulting vector is accurate enough for your tastes. The ‘Highlight vectors’ option can help you see the vector objects more easily. You can play around with the Vector definition slider if the preview is too jagged or too smooth; just be sure to click on ‘Run’ each time you make a change to generate a preview of your changes.
  1. Click on ‘OK’ once you’re happy with the preview to finalize the vector conversion.

Step 3 – Check and optimize the converted vector

Although it may be tempting to just run with the produced vector after using Scan2CAD’s raster-to-vector conversion, it’s always important to double-check the result and do any last-minute edits that need doing.

The draw, text, and erase options that were available to edit the original raster are also perfectly well-suited for editing any vector objects. At this point, make sure that the lines of the vector are perfectly straight, the angles are correct, and make sure that any bezier curves are converted into arcs or polylines for optimal compatibility with CNC machines. Scan2CAD also has a nifty ‘Convert vector image’ tool to do these optimizations for you.

Once your vectors are all optimized, all that’s left is to click on the ‘Export’ button at the top-right and set your file name and format.

Conclusion

Although do bear in mind that a discerning eye and careful double-checking is always integral when it comes to these kinds of processes, reverse-engineering doesn’t need to be any more intimidating than it has to be. Especially when you have Scan2CAD to do most of the heavy-lifting when it comes to reverse engineering and digitizing physical objects. 

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