I’ve been experimenting with many different varieties of wood.
The primary factors I’ve noticed I am able to consider when choosing what to use are: Appearance (obviously), porosity, and hardness.
I know there are other factors, but I have a hard time finding any comprehensive resources that help me quantify the qualities I care about. For example, if making a baseball bat, I am told Ash and Hickory are both hard and “impact resistant”, but where do I find any sort of quantification of these qualities? What if I want the same qualities but in an exotic wood?
Are there other factors to know about?
Not being a member of a woodworking community, these questions of plagued me… and search as I might, google has failed to yield what I need.
Do you have any specialized knowledge to share? Even better, any resources to these points?
Thanks 
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Regarding hardness, look for the “Janka” rating of wood. It measures the amount of force it takes to embed a steel ball half its diameter into the wood. So, the higher the Janka rating the harder the wood will be. There are probably hundreds of charts from different companies online, but they should all give roughly the same values.
Edit: One good site you can visit is http://www.wood-database.com/. Not only does it give specific information on a LOT of different woods, it also gives good descriptions regarding the various categories. For instance, if you don’t know what “Janka” is, you click on it and it will describe the test.
Janka seems to be the only real reliable and functionally useful rating system - but would you make a hammer out of glass? it’s plenty hard… This is what I’m trying to figure out… other physical characteristics to consider such as stability and durability… often I see just comments “very stable” “very durable”… okay what does that even mean? How does it compare to another species of wood???
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There is hard and there is tough. Try us.
As far as I know, there’s not a quantitative system set up for the other typical materials categories (brittleness, strength, et c.), much less for stability and durability. Unlike with metals, the wood can vary widely between different trees of the same species and even within the same tree. There are also variables that can affect the material qualities, such as moisture content, ring thickness, and UV exposure.
Unfortunately, working with wood is much more of an art than a science. The best you can do is figure out what conditions you will be exposing your project to and finding the best fit for it. For instance, you want a baseball bat to be relatively hard (but not too hard), with a tight and straight grain structure, so it can withstand impact without cracking.
Another thing that makes it more of an art than science is the fact that woodworking is highly visual. If you are doing a 3-D topographic map that will be placed on a shelf, you may want a wood with color bands, and you’d have to find a wood that was capable of holding fine detail without chipping. In that case, zebrawood may be best. If you’re making a simple 2.5-D sign that will be painted and hung outside, pine or poplar may be good enough since they are inexpensive.
Stability and durability, among other factors, are just too difficult to quantify without ridiculously large error bands. Ultimately, it’ll be a judgment call on your end based on what you want the end result to look like.
Of course, that’s assuming you’re not using them for anything where a professional engineer should be doing an analysis for safety. That goes down a VERY different path, which pretty much takes you away from the X-Carve. 
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When you think about it, even janka hardness is largely dependent on type or tree, and fundamentally is used as a “relative” rating system despite somebody applying hard numbers - none of us are driving steel balls into wood, after all.
Likewise, it would seem reasonable to have a relative expectation of different species - in that regard I don’t think it would be any more ‘art’ than a janka hardness rating.
If I take my purple heart and make a hammer of it, will the handle snap off? it seems ludicrous that I would have to actually make the hammer in todays day and age to know that it isn’t a suitable application of that species of wood - the idea that no knowledge can be shared and everything must be learned anew with each person seems to indicate a gap in the woodworking knowledge base - after all, this isn’t an issue of experience, practice, or feel, but general physical properties. I don’t have to make a baseball bat out of every type of wood to know that ash and hickory would work - they clearly have the physical traits that make them acceptable as evidenced by everyone who uses them already. Is it more or less suitable than using wenge? Why? How is this relative quality an unknown?
This is something one can discuss w/ the folks at the lumber yard (and if you’re not buying wood in quantity at a lumber yard you’re over-paying, or prioritizing convenience in a way totally foreign to me). That said, there is (of course) a website: The Wood Picker – WoodBin
Most woodworking beginner texts discuss this: Mountain View Hearth Products and here’s a discussion in the context of furniture: Choosing Wood at www.plesums.com/wood
Usually if you research a given wood species, there will be a discussion things which it has been used for traditionally:
- ash — baseball bats, best firewood
- beech — wooden planes
- hickory — tool handles, archery bows
- willow — prosthetic limbs
- yew — longbows
&c.
Some further links:
and see the links at: Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable
and also be sure to see: Wood Allergies and Toxicity | The Wood Database Potential Health Effects of CNC and Machining - #7 by spongefile - How To - Carbide 3D Community Site
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Perfect, this is the best i’ve seen for this sort of purpose. Thanks!!!
