I needed some different endcaps to finish a project with tubes involved. As there were pretty much different sizes of them I had to write a highly customizable script in OpenSCAD to quickly print them without remodeling for each size or shape of cap. This prints with touching buildplate support for the hole of the cap and for the upper cap overhanging border. Some variations/customizations of the cap can be printed without support as seen in one of the examples. You can also make bottle caps, chair leg caps, walking stick caps, pencil caps, Lego heads, dishes, or even peg-tops!! This is an amazing flexible script and a perfect example of how powerful and easy OpenSCAD is. Don't be affraid if you haven't used it yet. Try it now following the instrucions below, you won't regret. You will learn a valuable tool. I've also uploaded a MakerBot customizer version here: http://www.thingiverse.com/thing:1654016 just in case.
Instructions: Just download and install OpenSCAD if you don't have it (its free). Open the .scad file. Edit the parameters at the top of the file in pure and clear plain text and see how the magic is done. Measure your tube and make your calculations. Comments and parameter descriptions included nearby each parameter. Press F6 and wait for the software to render the model. Press the STL icon and export it. Then use your favourite slicer to print your customized endcap. Easy, portable, quick, free, clean and powerful. Endcaps won't be a problem for you anymore !!
Enjoy it as I did !!