I don't plunge, or make signs. But way back when I was making small figure banks I would plow thru 1/2" plywood. Bit was a 1/4" shank, and 1/2" pattern bit, powered by an old Craftsman, either 1/3HP or 1/4HP or 1/2HP, somewhere in that range. Don't recall, but not much compared to what most here have.
Went thru with no problem, did go slow, and if it seemed it was starting to have a hard time of it, would stop for a second, then start again, slower than before.
Going by that, I would say your bit. And like was said, a picture would help, also the brand, style of bit, and whatever.
"It ain't what you're told, it's what you know." - Granny Weatherwax
Some days, the supply of available curse words is insufficient to meet my demands.
Call me a craftsman, artisan, or artistic, and I will accept that. Call me an artist and you will likely get a quite rude comment in return. I am not a @#$%ing artist.