Here is a bit of a raw version about how I made a plastic bearing holder for a sliding door. My dad asked me if I could make him one with the Printrbot i bought for the school I teach. Since I thought it would be a good practice project to learn to use the thing and to learn using the 123D apps. My pupils work with iPads so I tried to do it completely on my iPad. That however wasn't possible due to some restrictions in the app, especially concerning precise measurements. I printed the part in ABS but found it a bit brittle and might try it in nylon later.
The steps I've used can be transferred to any other small broken part off course (Since i didn't take pictures off all the steps i mixed it with some of doing the same for another part)
Step 1: Meassuring
I measured the part with a digital calipers and notated these measurements. The note you see here is from another part though. I lost the one of this one.
Step 2: Using 123D Design on an IPad
Here I'll show you some screenshots of the designing in the 123d design app.