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Comment by brador | Hacker News Reader

Why isn’t panzerholz wood used everywhere? What is the article missing?

Same reason we don't build bridges out of titanium: panzerholz is more expensive than normal wood, and normal wood is good enough for most applications where it's used.

Titanium's strength is in its weight: steel's Young modulus is almost twice as high, so you'd have to build rather large bridges to compensate. Titanium is useful where weight is a concern, like things you launch into space. Steel is perfect whenever weight isn't a concern and sometimes still works really well because you get so much strength out of so little which is why there are so many fans of the thin, shock absorbing, steel bike frames.

Titanium's advantage is imo not so much its weight, as aluminium is better still in that respect. Titanium is mostly better where corrosion and temperature resistance are important. Relative to weight, high grade steel, titanium and aluminium are about equal in tensile strength.

> Relative to weight, high grade steel, titanium and aluminium are about equal in tensile strength.

Scale of the artifact is also a variable if size is a constraint.

> Titanium is mostly better where corrosion

Until we mix metals and have galvanic corrosion, where an Al + Ti system corrodes exactly where the metals touch.

It's not titanium that will corrode when you have an aluminium frame bike with a Ti bolt at the bottom bracket.

Those steel bike frames don't have much in common with the steel used for structural steel. They both are iron alloys with added carbon content, the similarity stops there.

Similarly trying to compare "titanium" to "steel" is dumb. No one uses pure titanium for structural purposes & there are hundreds of common steel alloys.

> thin, shock absorbing, steel bike frames

Please stop repeating this FUD. The notion that a rigid steel frame provides measurable shock absorbtion over the supple, air-filled, rubber tires is mind numbingly stupid.

Steel bikes feel “better” and “springier” than aluminum bikes. Objectively, they last longer than aluminum bikes.

What exact differences in physical properties or construction leads to this, I couldn’t tell you, but you can pick up an old steel bike frame for cheap and experience it yourself. Well-made steel frames are much lighter than poorly-made ones, so I would recommend finding one of the good ones.

So long as that "feel" is just that, there's nothing to talk about.

Unless of course you tried two of the exact same bike with the only difference being the frame material, in a blind test. Then we could talk.

But most likely, you tried two completely different bikes, felt some difference and arbitrarily decided it must be the frame material.

No, I tried probably ten or fifteen of each type over a 35 year period.

There are a bunch of factors, including tube thickness, alloy (I’m sure that when it comes to steel this matters, I think it doesn’t matter with aluminum), and frame geometry.

One thing I can say with absolute certainty is that, if you are using rim brakes, aluminum wheels are so much better than steel wheels it’s not even a conversation worth having. This is because aluminum wheels, unless they are painted, will have a nice aluminum oxide coating. This is effectively a ceramic and the coefficient of friction with rubber brake pads doesn’t change when the rims are wet, say on a rainy day. Steel rims lose all friction when wet.

Because I have been around for a while and made a lot of “experiments” (mistakes), I know some things. I’m happy to share what I know with you.

The limiting factor in most structural uses of wood is stiffness not strength.

You could build your floor joists out of scaffolding boards, but they'd bend unacceptably.

Stiffness is basically a product of geometry rather than strength. Making your wood stronger doesn't help you if you need it to be stiffer.

As you can see from Figure 3a at the top of the third page of the paper, this densified wood is about ten times the stiffness of natural wood, in the sense of Young's modulus. Stiffness is basically the product of Young's modulus and geometry, not geometry alone.

Does it remain so stiff for decades, as would be needed in construction? Many wood treatments' effectiveness fades after time.

I'm curious about that too. See my comments at https://news.ycombinator.com/item?id=44027557 for more.

Thanks, I actually just read that and replied there as well. I didn't even notice it was from the same person.

You've been extremely informative and helpful, thank you.

Thank you! I am not a specialist in the area so I may be overlooking something important.

My assumption is that it would. Steam-bent wood stays bent once it cools and the lignin sets. It's a lot like thermoforming plastic.

There's another advantage of putting wood through a heating-and-cooling cycle: you remove internal stresses that cause it to twist.

Oh man if that's true I hope it replaces dimensional lumber for floor joists. I'm not sure which psychopath invented span charts for home building, but it's extremely rare I'm in a non-slab house where the cabinets and such don't rattle from just a normal person walking across the floor!

I ended up putting beams in to half the span across my own house because it got so annoying(I want to say they are high grade SYP 2x10s @ 13 or 14')

I-joists + glue and screws are just fine if you want to avoid deflection.

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