I was playing around with new FileMaker 14 features and discovered that button bars works great for gantt charts. I've created a little demo file. It's half baked, but thought I would post it on here and see if the community can develop the idea a little more.
Button bars are great for re-sizing and conditionally hiding button bar segments can change the range of the gantt chart. Hopefully this can help out a few developers. Let me know what you think.