CHAINSAWBefore I discovered this forum, I carved a couple of bowls out of a big piece of quite old, dry, hard beech, using the limited number of tools I had to hand - which included a small, cheap Ryobi chainsaw.
I came across a video on youtube of some chap somewhere exotic (Philipines/Mexico/... I don't recall) who used to carve bowls by hand but then got a small chainsaw. He cut a grid pattern into the flat top of the bowl to ease removal of the wood. So, that's what I did to start with.
I can't recommend it though. Chainsaws are expensive, noisy, dangerous, smelly, polluting things that need a lot of attention and maintenance, and leave chain oil all over the place. If you go that way, make sure you wear all the expensive safety gear and know how to use it. Also, how long does it take to: get the gear on, the chainsaw out, sharpen the chain, fuel & oiled up & clean-up afterwards (clean the bar groove & drive sproket area, grease the end-sprocket)?
HAND TOOLSWith reasonably green wood, it took me only
20 minutes of so to hollow out my most recent big round oak bowl (it too was an 18" blank) using a dinky little 600g Hans Karlsson cup adze. You could probably do it even quicker with the slightly larger 700g HK adze or the bigger, heavier Gransfor Bruks adze - but it felt quick enough to me and gave me good control of the process. And the blank was oak (dense & heavy) and several months old too (so perhaps not as soft as it would be fresh). Images here:
viewtopic.php?f=26&t=2389I split the log using Pa's old splitting wedges (about £7 if you shop around, less at car boot sales) - I'd sharpened one especially for this purpose - and a 10lb sledge hammer but that is unnnecessary, I've since bought a small 4lb lump hammer to do the job instead. I enjoyed doing it and it gave me excellent control of the split (the log had some defects so I needed to split carefully). I spent a lot of time carving the outside of the bowl (unusual, it was always the inside that took the time before I bit the bullet and bought the adze); I should probably have spent more time with the axe on initial shaping.
EPILOGUEMy chainsaw is in the shop currently, having a new starter mechanism fitted, again.

(On the positive side, being rather cheap & plasticky, the parts are also somewhat cheaper than the more highly regarded brands). My hand tools on the other hand are all in working order and a pleasure to own & use. I just strop them after use to maintain/enhance the edge. Chainsaws have their place but there are better ways to carve bowls.