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Part 2: Using Surfacing
Welcome back to the series! Let’s do a quick recap. I’m reverse engineering a motorcycle peg for a BMW motorcycle. The peg isn’t easily found off the shelf and so this gives me the perfect opportunity to test out my SOLIDWORKS skills and our Metal X 3D Printer. Now, most of the surfaces aren’t easily modeled but we took care of that in Part 1 of our series where we used standard 3D modeling to capture the straight structures that would hold the pin and attach to the bike. Today, we enter the wide world (well actually wide flat world) of Surfacing!
Before I begin, I’m curious if any of you have come to DesignPoint for our Surfacing class? If you haven’t stopped by yet, please think about adding this to your repertoire. Personally, it has expanded my abilities with SOLIDWORKS. This project is actually like some of the examples and exercises that we work through together as part of the 2-day class. The only difference is that this project is not guaranteed to work and hasn’t been done before…but that’s where things get really fun so let’s get started!
Using Pictures and Dimensions
Usually when someone decides to reverse engineer something, they invest in a fancy 3D scanner to get the critical data they need. What if I told you that this isn’t always necessary? One of the most universal tools known to man is the cellphone, and I was able to gather all my design data simply by taking a few pictures!
Another super important tip –create some point of references for yourself. I was able to take an overall length of the part and add a construction line as a guide for locating and scaling the picture. These pictures are going to be guidelines for our sketching. We’re going to outline the shape using splines and interpolate the results together using Project Curve. This will allow us to have flowing 3D geometry when we start working with surfacing.
In order to capture an optimal shot, I rested my cell phone in a stable spot and made sure to have a clear, clean, and solid surface. I chose to look down onto a white table and I held the object in place with my hands. After capturing my images, I brought the pictures into SOLIDWORKS sketches using the Sketch Picture tool. By the way, you’ll notice that my pictures are a little off kilter. This was an adjustment made to align the picture with what we already had modeled both in scale and orientation.
Are We There Yet?
With surfacing you must do many more steps to reach your goal than with solid modeling. It’s almost like origami where each fold matters but it only takes shape with the final step. When working with surfaces you have to use the 3D lines to create bounded areas. You can then loft surfaces for each bounded segment that match up with each other. When you have a fully enclosed area, that’s when you can Knit the surfaces together and create a solid. Remember that any gaps will cause the solid to fail so try to keep your shapes as simple as you can and reuse sketches to keep your edges consistent. If edge lines are reused, then they are automatically closed and you can move on to the next section with confidence. Once all the pieces are in place you can finally make the result that you were after from the very beginning.
Symmetry and Mirroring
Another helpful tip you can use to your advantage when doing surface modeling is symmetry. If you have symmetry from left to right, then the middle can be used as a reference and a flat place to create geometry that completes the surface enclosure. Once the solid is created (either by the Intersect tool or Knitting), then it is easily mirrored using the Mirror Bodies option. This creates a fully realized solid and the two halves are linked (if any changes happen to the original then it is immediately propagated to the other half).
When the individual solids have been Combined into one, we can smooth out some of the rough corners with fillets and any smaller features that need to be added. Now that I’ve actually completed the project, I can strongly recommend that you wait until the end to add fillets. To be frank, I didn’t and I regretted it. In the next part of the series I’ll dig into some other obstacles I faced.
I still need to have the actual pad modeled and fitted to the top of this motorcycle foot peg but that too will have to wait till our next installment in the reverse engineering blog series! Thanks for following along!