A number of people have done this but I can't quote any details. Try searching thread titles for something like Atlas Feed Rate. Or if you just want to slow the feed rate down 2:1, you can also introduce a reduction on the change gear bracket. For example, put a 20T gear behind the 40T Sliding Gear (it will no longer slide) and add an idler driven by the 20T that's large enough to drive the rear 48T gear that drives the QCGB, without the 40T touching the front 48T. There was a thread a few months ago on doing this. Except that I seem to remember that he used one of the 48T in place of the 40T with a 24T behind it. And used the 24T to drive the remaining 48T. I don't recall what he used as a spacer in place of the front 48T.
