Do wooden arms warp

Someone please check it for me, but here is how I did the calculation...

Michael (Swampwalker), thanks for (as usual) bringing some level-headed and intelligent perspective to this thread, as was evident in the conclusions you stated in your earlier post. But upon checking your math I see what appear to be a couple of incorrect calculations.

75 square micrometers/square microns = 1.16E-7 square inches.
1.8 gm = 0.0635 ounces (not pounds) = 0.00397 pounds.

0.00397 pounds/1.16E-7 square inches = 34224 psi, much higher than even you had calculated.

Although offhand I'm not totally certain that the 75 square micrometers is really that, or if it should be 75 micrometers squared = 5625 square micrometers, which corresponds to the square inch figure you used, and which would put the psi just slightly higher than what Tony had indicated. Can anyone else confirm that (as I suspect) 75 square micrometers is a reasonable figure for contact area?

Also, without doing further research I too have no knowledge of how to convert that to a temperature rise, or if Tony's assumption of a 0.22 coefficient of friction is accurate. FWIW, though, I recall that some time ago an article by Robert Harley in TAS cited the same 500 degree figure that was mentioned above by Vetterone.

Best regards,
-- Al

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.

In questioning the OP's opening post, It is not necessarily that all wood warps. In most any wood, a warp can be induced, but, in old, very well seasoned woods, the main reason for warpage is internal tensions within the wood. These tensions exist , mainly due to environmental conditions which the tree was subjected to while still alive, like living on a windward slope, exposed to high winds, uneven weight due to the tree leaning, tensions set due to heavy branches, and countless other individual circumstances.

Most likely, any wood that has been correctly stored and seasoned for many years, yet is still warping, either it is due to internal tension, or it is a species that is less stable.

In the case of Ebony, or Cocobolo, or similar extremely dense, and/ or resinous woods, no matter how long they have been seasoned, it is a good idea to let them rest again after rough milling to a dimension close to the final dimension, as moisture will only move through solid timbers of these species to a degree and no more. When they are cut into, they need to season some more so that the exposed bits can come to equilibrium.

Yes, it is very possible to make an item like a tonearm wand that will predictably hold it's shape, and not warp. The main factor is how carefully the piece is made, mainly in 'working with the wood' and not against it's nature.

I am a life long woodworker, and have extensive extensive experience with many different species of woods. I have built nearly 1600 plinths for the LP12, the Garrard 301/401, and the Thorens TD124. I made the armwands for the Teres Illius tonearm, and have been working on a tonearm design of the past several years. I also build instruments as a hobby.

Wood is a great material for a tonearm wand, what separates the end results, are exactly what wood is chosen, species, grain orientation, age, moisture content, how it is worked, and how it is finished.

Some woods are more susceptible to continuous change corresponding with environmental changes than others. Some wood species, if there is no internal tension, are very stable after the sap moisture in the wood has come to relative equilibrium. Changes in relative humidity have less of an effect on some of these woods. Internal tensions can be mostly sorted out in the wood selection stage, and can be very effectively further checked in the preparation stages of turning the wood into arm wands, or whatever.

Quality instrument makers prepare neck blanks by rough milling, and then storing them. Then years later, roughing out the neck shape, cutting the neck top plane, and neck sides, then leting the blanks 'rest' again. After some time, if the blank has proven itself to be stable, it is finished into a neck. This is a relaible method for taking the factor of warpage out of a wooden item like a tonearm wand.

Vacuum wood stabilization is very effective in checking wood movement, as well as increasing the damping factor in a given wood. To someone above who questioned the 'integrity' or 'ethics' of stabilizing wood, or whether or not stabilization with vacuum impregnated polymers turns the wood into plastic, no, it is still wood. And how many metal arms out there that employ some sort of damping strategy to reach a desired end result? Many top instrument builders say that the finish actually does more than just protect the wood, that the finish is part of the synergy that comes together in tempering an instruments 'sound'. The changes that occur to a piece of wood that is vacuum stabilized, still leave the treated piece of wood well within the range of mechanical characteristics that make wood a desirable material to work with, only more stable, and perhaps with more desirable sonic characteristics, in the case of a tonearm wand.

I have one of those Cherry tonearms that were sold here on agon, it was given to me by a customer who I built a deck for . It IS warped. However, it is clear from looking at it, that very little was done to prevent warpage. It is not stabilized, and it is not shaped in a way that would tend to prevent it from warping. To compare those Cherry tonearms with a Reed, or a Schroeder, is like comparing apples and oranges, it has no relation.