Do wooden arms warp

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.

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.

A guy I knew from school was an Air Force Lieutenant who volunteered for an experiment at the medical research facility at Wright Patt AFB in Ohio, the experiment was to see how long he could stay in a heated chamber before signaling the experimenter to be let out. Dressed in street clothes he was in the Chamber at 425 F for 45 minutes. No big deal.

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.