Modelling a Bike – The Frame

Recently I’ve been modelling a road bike and thought I could share the methods and techniques I used, as well as the errors and solutions that I found.

I used the two straight cylinders as my starting point. I knew beforehand the required measurements of the frame and the shape of the two cylinders were fairly easily to create with two extrudes.

This is where it starts to get fun. Using lofts I could connect the cylinders with the nice frame shapes. Firstly the bottom loft. To start off the process you need to draw two profiles of the pipe you want. The start and end profiles. Secondly a guide curve or two are needed. The best option for this I found was two, as one could shape the curve of the top with a spline and a second running the bottom edge. I used splines to create the smooth curve. Make sure the splines are piercing the profiles at the relevant points of the profile.

Now one issue I had with this, is that if the profiles did not extend behind the two initial cylinders, as in outside the two, when it came to merging them all together at the end, the separate multi-bodies would produce the zero thickness geometry error. By having extend to the outside and having the merge results tick box clicked, the model will stay as one whole body and I can trim the excess material away later.

Here is mine in action:  

For the top horizontal structure, I used surface lofts. In a very similar fashion, I created two/three profiles along of which I wanted the structure to have a section view of. Then surface lofted these shapes. To make the surface into a physical solid, I thickened the surface to the required size.

The rear of the frame looks complicated. However there’s a few tips I suggest. If you want straight shafts that are horizontal, then I suggest creating a plane through the centre of where you want the shaft, you can easily create a line which one profile will follow. Draw a profile on one end and sweep it across. 

But if you require a little more fancy shape and a slight curve like I achieved here, a 3D sketch is needed. I suggest a spline with end points at the start and end of your sweep. Then use different views and orientations to position the spline as required.

Both these options can be mirror about a plane going through the centre of the bike. The other shafts are done in a similar fashion with a profile and a path to sweep along.

We have a good few bike fanatics at Solid Solutions so it was a nice challenge to model something familiar using a range of techniques to achieve the desired result with all the necessary subtleties.

Jack Murphy

Applications Engineer