This set, following the numbering system that Old Street Tool recently made uniform, consists of even numbered planes 2-18. A #2 cuts a radius of 2/16" (1/8") a #12 cuts a radius of 12/16" (3/4"). (The numbering system changes [for good reason] above this point when the planes start increasing by 1/8" instead of the previous 1/16".)
A half set of planes often consists of these evenly numbered planes. To round out a half set and make it a full set, you would include the the odd numbers: 1-17. These planes cut radii of 1/16, 3/16, 5/16 and so on.
Blogpost starts here:
I often speak to people who think a half set is a good place to start. After all, it is one half of set.
For me, a half set is unnecessary. To the scale I work, I won't likely use the 18s (R1 1/2"), 16s (R1 1/4"), or 14s (R1"). I certainly do not need the 17s (R1 5/16"), 15s (R1 3/16"), 13s (R1 1/16") or 11s (15/16").
HOWEVER, when you get down to the low end of the range, THINGS CHANGE.
For example, a #12 (R12/16") cuts a radius that is 20% larger than a #10 (R10/16")
dIt's very different, but still pretty close.
A #11 (R11/16"), however, cuts a radius that is just 10% larger than a #10 (R10/16") and approximately +9% smaller than a #12 (R12/16")
Let's look at the low end of the range now.
A pair of #4s cut a radius of 4/16" and are 100% larger than the #2s that cut a radius of 2/16".
A pair os #1s cut a radius of 1/16" and the #2s are 100% larger than the #1s. This is a big difference.
At the low end of the range the difference between the the hollows and rounds is large and, perhaps, desirable.
A pair of #3s cut a radius of 3/16" and are 50% larger than the #2s that cut a radius of 2/16". I want a pair of #3s included in my ideal set.
My ideal half set of hollows and rounds would consist of the following pairs: 2, 3, 4, 5, 6, 8, 10, 12 and, if I had to choose a 9th pair, 16s. (I'd likely be completely content without the 16s.)
What I'm trying to say is twofold. (1) The odd numbered portion of the set is drastically different at the low end and potentially desirable. (2) I made a pair of right handed 3s when they were supposed to be left handed so you had better send me an email (email@example.com) stating that you want them before they get stamped with my owner's mark. I really want to keep these [SOLD].
All of that being said, you can make a lot with one pair and exponentially more with two.