This wasn’t (as far as I can tell) cheap finger jointed knotty wood. It was some furniture maker who thought “well, this part needs the grain one way and this other part needs the grain the other way, and I have a finger jointing machine, so I’ll finger joint it!” Even if they somehow found a shop that stocked sheets of finger jointed wood with a 90 degree grain rotation across the joint, it would have been an incredibly inefficient way to produce the part in question.

But they didn’t think very hard — see my other comment. I don’t think a single solid piece of hardwood would have performed a whole lot better. Either metal reinforcement or plywood or much more carefully considered joinery was needed.

The glue will probably be the strongest part of it, but finger-jointed hardwood isn't that terrible. Any decent wood glue is crazy strong.

The problem with knots is that they resist drilling and screwing. The problem with new growth is that the pith is the weakest part of the wood, and new growth has the most pith.

Still, it's not a weak and terrible pos wood-like material like 1990's MDF, it will probably be ok for most uses as long as the grain direction is respected in regards to shear direction (typically you want the grain direction to run perpendicular to the shear forces) and everything is properly braced.

That sounds like hardboard? Hardwood is natural.

The chairs had four legs, each of which radiated out horizontally from a central point (they were swivel chairs) then turned downward to the floor. The legs were about 1/2” wide, maybe a bit more. They were maybe 1” tall (vertically in the horizontal section and horizontally in the vertical section).

So the grain needed to run horizontally in the horizontal part to support the bending load. It was probably best for the grain to be vertical in the vertical part, although that was maybe less critical: that section was mostly in compression. It probably also looked better that way.

In any case, the actual construction put a finger joint in the horizontal section just past the turn, so a tiny bit of vertical grain wood extended horizontally over the turn. And several of the legs cracked just along the side of the finger joint, and one failed completely after about a month of gentle use.

The design plausibly could have worked if the joint went diagonally through the turn or was below it. But plywood is strong along both in-plane axes, and the legs could likely have been cut in single pieces from sheets of plywood with strength to spare.

Attractive plywood, even from hardwood species, is readily available. The plies are visible along the cut edge, but this is actually a style people like, especially in Scandinavian furniture. Even IKEA sells some nice chairs with plywood elements, at entirely reasonably price points.

I think he meant "place" as in literally "the location on the furniture" rather than the (very reasonable from context) interpretation I suspect we both had that it mean "place" in the geographic, or at least climatic sense. Which is itself important as certain woods deal with extremes of humidity better than others. In a temperate climate, just about any old wood will do, but somewhere that is very dry OR very wet, woods like mahogany and teak are best.

Teak especially is so good at dealing with water that it was harvested to near extinction in the 19th century just to build ship's decks and cabins out of it.

I don't think that amluto is saying that the hardwood itself is inappropriate, or is necessarily ever inappropriate. I think they are saying that the specific joinery in their example was form over function, to the point where the joint was a critical point of failure.

Having done a bit of woodworking as a hobby, I would say that hardwood could be inappropriate if it is used for an element that is purely structural, internal (and thus will be hidden by external features) and there are cheaper alternatives that are just as good, or stronger materials available and we are talking about a critical structural element.

That's a pretty abstract answer but it's always going to depend on the specific project. Sometimes a piece of furniture has no hidden internal structure, or the appeal of the furniture is that it is all bare wood and you want it made entirely out of a beautiful "furniture grade" hardwood. For certain upholstered furniture, such as many sofas, using expensive materials for inner framing could not only be superfluous and add unnecessary cost to the piece, but in certain circumstances there may be better materials available even if you could make a perfectly adequate structural support that will last a lifetime using expensive hardwood and the right joinery for critical stress points.

I read amulto's point as being "expensive material and fancy joinery doesn't matter if you have a weak design."

Plywood is amazingly structurally sound, because it's got grain going all which ways.

Especially when thin, wood is surprisingly easy to break, and it doesn't handle being pulled on very well at all.