Hello
Would anyone have some advice on making 1/4 holes for a crib board all the way through 1/2 Lexan
What would be the best bit and bit settings?
I would suggest a slightly (or much) smaller endmill which has single flutes, and a coating — perhaps:
and the “Hard Plastic” settings in Carbide Create.
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Another option might be to use a 1/4" stubby drill bit.
Use the drill toolpath and peck w/full retract to clear the chips.
Waste board under the Lexan to account for the drill tip.
EDIT: yea sorry not the best idea 
, endmill is definitely better way.
Note for drill bits that you need to select one which can be spun safely at the speeds which a trim router/spindle will turn at.
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I would use a .125 Oflute, as Will suggested, a profile path cutting inside, and a spiral ramp if your software supports it. I cut holes in acrylic often.
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If drilling, I would recommend a mill drill designed for higher speeds.
I think the ideal tool would be a 3/16" single O-flute. “Hole Milling” using a inside contour at full depth with a shallow ramp to create a helical engage.
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As Will said above, a standard drill bit isn’t rated to turn and drill at such high speeds. Most drill bits need to turn/rotate under 1000 rpm’s. Interpolation milling would be the best option. Make sure the endmill is bigger then half the diameter of the hole to be milled/drilled. Make sure that what you are interpolating has sufficient cooling and chip removal. Cutting plastics this way can cause heat ups with the plastic chips, which in turn, cause melting, or fusing together chips.
Tod said it best with the helical engagement so the endmill doesn’t just plunge directly into the hole. If you cant figure out, or cant program the spiral cut, then reduce the depth of cut per pass so you can reduce heat and insure good chip removal.
Remember, heat is your enemy when it comes to cutting plastics.