Do wooden arms warp

Tonywinsc- Try reading what Vetterone wrote again, s l o w l y

If there were better available, I would be using it. It certainly would cost less and save many hours to make a metal armwand than a properly prepared wood armwand.

Oh wait, I wouldn't want to confuse a conservative with the facts...

I am but lowly wetland scientist, not a material scientist, but after some initial skepticism, I am now quite convinced by both theoretical and empirical evidence that wood's "instability" need not automatically disqualify it from being used in a perfectionist analog set-up:
Theoretical- metal also is dimensionally unstable and has a coefficient of thermal expansion that can be quite a bit higher than certain kinds of wood. Same is true for some ceramics. Assuming that the wood is properly dried, we see the following coefficients (units are 10 minus 6th inches change per inch length per degree F), rounded to the nearest whole unit:
Aluminum 12
Brass 10
Copper 9
Steel 8-10
Stainless 6
Magnesium 14
Glass 5
Glass fiber/plastic 14
Porcelain 4
Titanium 5
Fir 2
Fir (cross grain) 17
Oak quarter sawn 30
Diamond 1
So if dimensional stability in terms of temperature change is the most important parameter, then diamond would be best. It's cheaper than unobtanium but it's a bitch to machine ;-)

The issue with respect to humidity is much more complex. My only comment is that I believe some wood tonearms are "stabilized" by impregnating the wood w resins or epoxies, not just by sealing the outside with a varnish or polyurethane finish.

Empirical- Others have noted that several of the finest tonearms wands are made of wood. We also see Lewm's report that his 2 wooden tonearms are dimensionally stable enough that over the course of 2 years, their alignment, when measured using the most precise (and most expensive) alignment jig currently available, has remained on the gnat's a$$ (my words not his). We also see that the physical properties of cartridges vary enough over time that in a highly resolving system, it is possible to hear changes in the sound with changes in VTA, VTF, and AS that are far less than anyone would previously have suspected.

As with most of these complex designs, esp. w transducers, it comes down to establishing design goals, optimizing the design to achieve those goals, and properly implementing the design. And then of course there is the subjectivity that the listener/user imparts to the process. So there will almost never be a single "best" material or "best" drive mechanism, or "best" stylus profile, or "best" circuit topology, etc., etc.

To get back to the OP's ?, the simple answer is that yes wooden tonearms can warp, but it appears that a properly designed, properly manufactured, and properly maintained tonearm wand can be made from wood, without warpage being a major constraint on its performance. However, I don't think I'd want to buy one if I lived in the Amazon ;-) Although now that I think about it, constant high temp and humidity is probably less harmful to alignment than the changing New England weather.

Tonyw- 300-400 psi seemed awfully low so I did the math. Someone please check it for me, but here is how I did the calculation:

According to Audio-technica's cartridge glossary @ http://eu.audio-technica.com/en/products/cartridges/glossary.asp#microline, a line contact stylus typically has a contact area of 50-75 square micrometers. Using the upper number, that converts to 0.0000087 sq. in. 1.8 gm VTF convert to 0.0634 lbs. So psi is 0.0634 lbs/0.0000087 sq. in or slightly over 7287 psi.

It's beyond my skill set to convert that to a temperature differential but if its a linear relationship, and if your other math is correct, then we are looking at a temp change of over 400 degrees. Of course, the total contact area is tiny and the mass of the surrounding vinyl quickly dissipates some of the heat so the vinyl does not "melt" or "burst into "flames"

And yes, there are some who say that the pressure and temperature stress is sufficient to cause the vinyl to deform; even advocating that LP not be replaced without some time to cool and rebound to their original shape.

And that's why I'm not an engineer, Al ;-) The actual verbiage copied from AT's web site is "Line Contact tips are also known as “Shibata”, providing a contact surface between 50 and 75 μm2". ZYX web site shows following spec:
3micro m x 60micro m
which I would interpret as having a contact area of 180 square micrometers.

If you look at Zev Audio's site @ https://sites.google.com/site/zevaudio/turt/stylus-shape-information
you see that line contact styli have a contact area of 47-62 square micrometers. Interestingly, elliptical styli have a much smaller surface area (21 square micrometers) and so would result in 3-4X the pressure and thus potentially even higher temperatures.

I haven't gone back and done the math but it's possible that TonyW (or his source) used the radii of one or more styli to compute the contact area. However, this is not correct. The contact area is not the same as the stylus dimensions.

Of course, this is way off-topic. My apologies to the OP.

Ilikmangos- thx for bringing some real world experience to this discussion.

Geoffkait- I was originally trained as a biologist and I'm a pretty good cook, so my bull$hit detector went off big time. Apparently the high temps cooked your friend's brain;-). It took about 5 millisec for Google to find the actual test results paper of the Wright Patterson experiments. The highest temp any of the men were exposed to was 158 degrees!

Geoff- if you look at the graph in the appendix of that paper, you will see that the temperature vs humidity effect is acconted for and when you extrapolate back to 0% relative humidity you can see that the maximum 45 minute tolerable temp is a tad over 160 degrees. And I'd be hard pressed to believe that they would subject the officers to something they had not tested on the enlisted men first. Remember that an internal temp of 165 degrees is well done for a piece of meat, which of course is what we are. To say nothing about heat stroke, which is classified as a medical emergency and occurs when your core temperature exceeds 105 degrees. Sorry, I ain't buyin.