Today I am going back in time with the chopper project and I want to show you the 3D model of the rolling chassis and share some thoughts about the fabrication process of the frame.
As you can see in the photos, the rolling chassis is almost ready from design point of view. The remaining things to add is the top motor mount, the forward control mounts and rear brake mounts. The fender was redesigned in Inventor and now it includes mount holes to attach it to the frame. The fender clears the rear wheel at 1 mm and I am planning to use 0.5 x2 mm miniature hex bolts from
Scale Hardware to attach it to the frame. The bolt head is only 0.46 mm in height so it should clear the wheel.
Back to the frame, it will be made mainly in 3 mm brass tube and the sections will be silver soldered together. All the bends have a 10 mm radius and to bend the tubes I started building a miniature tube bender. Fortunately, I found a nice CAD plan on the internet and only had to adjust the dimensions, use nuts & bolts I have around and remove some parts that I feel I don't need.
With the Inventor parts exported to CAD format, I went to a local water jet cutting workshop and they cut the basic shapes in no time (it took them 7 mins to cut all the parts). Unfortunately I found that due to the small dimension of the parts, the accuracy of the cut pieces is not that good. The water jet leaves a rough and uneven edge, which has to be milled or filed flat. This will reduce the dimension of the finished part with about 0.2 - 0.3 mm on each edge. So I had to enter the new dimensions in the Inventor solid model to get the actual size. So do take into account this aspect if you plan to use water jet cutting on small parts - you may need to rescale the parts a bit. However, the benefit in time is worth it.
Now it's time to finish the parts...
