Hi there!
Today I’m going to share my knowledge of making good wood selections for making yoyos.
This information applies to making three piece yoyos (two halves and an axle). I will be focusing on selecting the wood for the yoyo body - not the axle, because that warrants a separate post entirely.
Wood is a Hugely Variable Organic Thing
There are a huge amount of factors that affect how a sawn, kiln dried piece of wood will be. These include the age of the tree, the location, the soil composition, the annual rainfall, and whether the tree has suffered any other kind of environmental stress (natural disasters). These are largely unknown the end purchaser. Even still, informed selections can be made.
Hard and Soft Woods
When selecting woods for making a yoyo, as a general rule, hard woods yield far better results than soft woods. This is because with softwoods, the early wood rings (spring growth) have significantly lower density than the late wood rings (autumn and summer growth). This creates a lot of density variance that can cause yoyos to be very vibey to extremely wobbly. Rarely have I ever made a softwood yoyo that turned out well no matter the size or design.
On top of this, they damage from play a lot easier and are more succeptible to mold or insect damage. However, if your yoyos are sustaining this kind of damage, you are sorely neglecting to play them.
In short; avoid softwoods. Yes - even the really pretty ones.
Hardwoods
Hardwoods are the right choice. Their earlywood and latewood density has less variance, yielding smoother and more consistent results. But what about the overall density?
Specific Gravity
Specific gravity refers to the desity of the wood compared to the desity of water. The specific gravity of water is 1, therefore a .75 specific gravity of a piece of wood means it has 75% the density of water.
Typically, the correct specific gravity of a wood density for making a fixed axle around 58mm in diameter and 34mm widr is about .65-.75 at 12% moisture content. You don’t need to worry too much about the moisture content if you are buying your boards from a reputable store as it will almost always be kiln dried and contain an appropriate moisture level. If you are sourcing ‘ditchwood’ that you have spied on the side of the road, the moisture content could be anything.
Which Woods have the Right Specific Gravity?
I’ll save you the trouble of looking it all up: Rock maple, white oak and walnut.
Of course there are a lot more woods that are suitable on paper and may yield a good yoyo, but seriously, white oak and rock maple are consistently the best. Walnut gets an honorable mention, but being on the softer side, it can sometimes yield very light yoyos and be succeptible to wobble.
Everyone Wants Purpleheart and Wenge (Murderwood)
‘Can you make me a Bloodcell in purpleheart?’ is a question I get asked often. There is a reason that I and just about every other wooden yoyo maker rarely use it; it simply yields yoyos that are too heavy at a conventional size (not to mention expensive). I also doesn’t help that they can be a b****** to work with too. Purpleheart has a specific gravity that is close to 1 and wenge is similar in that regard. However, most pieces I have have had an even greater specific gravity.
Wenge? Well that wood simply wants to kill you when you are working with it. It affects your central nervous system and the splinters can potentially give you a blood disease. I tell you this so that you can take precautions when you find a fancy piece of wood. Always look up information about the safety of working with the wood before doing so.
Flatsawn, Riftsawn, Quartersawn…
When selecting a wooden board, it is important that you buy one that has been sawn in the correct orientation. Flatsawn is what you are looking for as it produces the best results. You can see in the picture below that there is an arc from one edge of the board to the other. This is what the endgrain of a flatsawn board looks like:
You can tell when a board is riftsawn or quartersawn because the grain runs at a 45 degree andgle or higher and quartersawn around 90 degrees (see below). Avoid these, as they don’t produce consistently smooth yoyos.
Check Over the Wood Carefully
Look over the entire board very carefully for knots, resin voids (they look like a dark gash) and any weird, curly grain. Do not fall in love with curly grain, while it can produce good yoyos more often than not it produces wobbly yoyos. Also check each end of the board. One end may appear to be flatsawn and the other side more rift or quarter sawn. Try to find one that looks flatsawn both ends.
It’s also important to avoid a board that has both heartwood and sapwood in it. If you notice when looking at it that there is a clear distiction where one part is darker wood and the other light, you have a board containing both sapwood and heartwood. These two kinds of wood vary a lot in density, and if you cut a yoyo blank that spans both, it will yield a very wobbly yoyo indeed. Check out the the white oak board below; you can see the lighter sapwood in it.
Choosing a White Oak Board
I have had some pretty wildy inconsistent boards of white oak. Some have been very dense and others lighter. I have found that if there are large dark rings in the end grain, that likely means its a very dense piece of oak. It may also have an almost shiny or waxy look at the end grain. Avoid a board like this because it will likey yield yoyos a lot heavier than you predict for white oak.
Look out for knots in white oak too. Make sure the grain on the face of the board looks straight and pretty consistent.
Choosing a Maple Board
Maple tends to be a very forgiving wood for making yoyos. As long as there isn’t any evidence on the face of the board of dark resin channels (they are considerably darker than the rest of the wood and sometimes even open) or knots, you are generally good to go. You can even get away in many cases using riftsawn or quartersawn wood with maple becuase the grain is so fine and consistent. Maple is king for wooden yoyos.
Where to Cut the Blanks
Cut your blanks as central to the flat sawn peak section of the board that you can (The highest point of the arc should be the centre of your blank). It can still work if you are not entirely dead centre, but as central as you can gives you the best chance of success.
Alternatively…
Feel free to ignore all my advice and use absolutely anything you fancy! It is important to love the wood you are working with. Experiment and see what works for you. Everything is an opportunity for learning. 
Check out the Wood Database website when you find a wood you like in the store. It can tell you very imporant information before you buy: https://www.wood-database.com/
There is certainly more that can be said, but this should be enough for now.
I hope this post was helpful!