Tuesday, August 15, 2023

Reverse Engineering Challenge - Calipers or Scan

Some months ago, I was asked by a colleague, that knew I had some 3D scanners, if I could help him create a replacement part for a vintage Cadillac Allanté.

Reverse Engineering:  Using Calipers

Unfortunately,  none of the scanners available to me at that time were really up to the task.  So, I agreed to use Moment of Inspiration to recreate the part for him.

I used two methods for reverse engineering the part.  The first step was to take photos of the part from every direction.  I was able to bring these photos into Moment of Inspiration to use as guides.

 None of these photos could be completely relied upon for accurate dimensions because of the distortions due to proximity and angles when using a handheld device.  But, they were useful to help ensure I was at least close to the original as the part was designed.

Digital calipers were used to obtain accurate dimensions.  But, even here, there were some difficulties because of the location of some of the holes in the part and because the original part's features were not consistent.  It looked like the part has been modeled in clay or wax to create the original mold for the part made from some unknown resin or plastic.

Fortunately, we had the original part for comparison for with a few iterations we were able to finally arrive at a 3D printed part that accurately represented the original in a useful form.

While the final result was accurate and useful, the amount of cost, in terms of time expended, was probably WAY out of proportion to the cost of the original part were it available.  But, the part was no longer available commercially and impossible to find even as a used part.  But, being critical to the operation of the Allanté,it was the only available option if I was going to be able to help my colleaque.

But, what if I had had a different scanner available?  What might we need and how might it have been helpful? 

Reverse Engineering:  3D Scanning

3D Scanners cover a very broad category with prices ranging from a few hundred dollars to many tens of thousands of dollars.  And, the technologies used by various scanners also cover quite a range from white-light to lasers.  Any scanner tackling this job has to be able to accurately capture small objects.  This part measures under 50mm in all directions.

Cadillac Part Dimensions

But, the greatest challenge to any scanner are the hidden cavities, strange undercuts, fillets and holes.

I am not sure that any 3D scanner, of any price point, could completely scan all of the features of this part.  But, could a high quality 3D scanner have been able to be helpful in speeding up the process.  And, if so how?

The first requirement would be high accuracy.  flat features would have to be flat and the general shape would have to be accurately captured so that ALL features were accurately located.  If the output of the scanner could be brought into a CAD program, features hidden from the scanner could be added.  All that would be necessary from the scanner would be accurate capture of the location and size of the entrances to the holes.  The more well defined the edges, the better.

To be a success, a scan does not have to 100% identical to the original in every aspect.  It only has to cut down on the time it takes to reach the point where a replacement part is 100% functionally identical.  If we can use a scan to accurately create the basic shape and locate holes, etc., enabling us to bring that shape into a CAD application for finishing, then that qualifies as a successful scan.  

At the very least, attempting to scan this part would be an extremely useful learning endeavor.  It would most likely require some novel placement of a turntable and, perhaps, some 3D printed props, or clay, for holding it in positions for capturing the undersides of various features.  

If anyone has a scanner and would like to give it a try, here is a link to the .STL that could be printed on an SLA printer for scanning.


 I'd love to hear about your scanning attempt.

By the way, it is possible to convert .STL files to .STEP files and bring them into Moment of Inspiration for editing.


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