I have a openbuild 1515 with Dewalt router. it accepts up to a .25" bit but I am wondering if I can make my projects more efficient by getting a larger bit. obviously I cant put a 1/2" bit in a 1/4" collet. A) is there an adapter that will increase the collet size? I see reducers but not collets that increase the size. B) do I just need to get a more powerful router that will fit in the support collar on the Z gantry?
We wouldn't recommend it - but look into HSM/Adaptive stategies with 1/4" tooling. Moving faster, gets more done - without needing bigger tooling. Tweak your Max Rate and Accelerion values to get the maximum feedrates out (travel moves between cuts cost a lot of time in a job too) - and then optimise your toolpathing for max feedrates as well. Sometimes running very fast, and not so deep - gets a job done faster than trying to cut deep and moving slow for example. HSM/Adaptive is kind of the opposite, deep cuts, but using Trochoidal motion to keep loads low Large diameter tooling needs higher horsepower spindles, and that in turn needs beefier framing to resist the cutting forces (every force has an opposite) and also carry the heavier spindles without deflecting too much
Elaire Collets makes great precision collets. I have a Makita, but I own Elaire's collets for 1/8" to 8mm in both metric and imperial. They make a 8mm for Dewalt for about $20. Elaire Corporation - Dewalt Router Collets I mostly use the 8mm to rough out large 3D carves in wood where I am only doing a 40 percent stepover and have seen no adverse effects for how I am using it. Like Peter said though, slotting harder materials with an endmill that large may be a bit much.