I probably could have started a new threat on this but since we did get on gouges here is a question. When do you use a 1/2 Bowl gouge and when do you use a 5/8 bowl gouge. Does it have anything to do with the size of the bowl? I just realized that I have Doug Thompson's 1/2 and 5/8 bowl gouges. Rich
I will assume you are speaking of bar diameter and use bar diameters in my answer.
For the average turner it is personal preference.
Most turners in US use the 5/8 diameter bowl gouge almost exclusively.
Some production turners will use a 3/4 or 1" diameter gouge just to hog off wood faster.
Anyone with a 12" swing lathe or smaller is probably better off with a 1/2 diameter as they will stall the lathe less often.
I virtually never use a 1/2 diameter gouge.
I have a couple but I know I have not used them in ten years.
I use a 3/8" diameter to work tight places and for a fine finish cuts and hollowing small openings
The 1/2 bowl gouge can hollow a smaller opening than a 5/8 but the 3/8 can hollow smaller and hollow anything the 5/8 cannot.
I use a 5/8 gouge for virtually everything I do. Paired with a 3/8 spindle gouge I can can turn any outside shape.
For roughing the 5/8 gouge can easily take a 3/4 wide shaving.
In a finish cut it can take a 1/64 and smaller shaving.
The 1/2 gouges tend to be more pointy than the 5/8 and a lot of folks have harder time sharpenining a side grind on the 1/2 than they do on the 5/8. There is not much steel on the tip of the tool and people either sharpen it too much making the wings into catch makers or the sharpen it too little making it pointy.
I would also add that the wing is much less useful on a 1/2 than in a 5/8
Can't take as big a shaving and it is not as good on advanced the shear cut.