Why are records still warped?

Moonglum,

Your "dynamic changes in VTF" are what TTW and I referred to as suspension movement... I think! Maybe you're talking about something different, such as the platter slowing down as the stylus goes up the hill due to an increase in friction between the stylus and the LP due to an apparent increase in tracking force and the platter speeding up as the stylus goes down the hill due to a decrease in friction due to a reduction in apparent tracking force. I don't know what you meant, I'm just thinking of other ways that warps can mess up the sound.

Dear Ketchup,
Although I'm not a mechanical engineer it's an effect that relates to the mechanics of the tonearm design and the position/height of the pivot relative to the stylus? An analogy I use to help me guess which way the force increases is what happens when a tonearm is balanced.

If you balance the arm then briefly push the "stylus end" downwards the arm will react with a restorative force which eventually restores the arm upwards back into a balanced horizontal position. (i.e. analogous to less VTF).
By the same token if you lifted the "stylus end" then released it would fall due to a similar restorative force, eventually settling in the manner of a damped oscillation. (Otherwise the arm would defy gravity and stay exactly where you released it?)

(I believe) the behaviour is the opposite of what you'd expect if you viewed a declined or inclined tonearm playing an LP? Typically, warps encourage increased rather than decreased VTF.

Qualified M/Eng's might volunteer to offer their insights. ;^)
Cheers,

..To elaborate further you can use the VTA calculation/rule-of-thumb promoted by MF & others to work out roughly how much of an increase will occur due to the height of the warp...

(As a rough "guesstimate" you could be looking at a few hundredths of a gram or more, so in theory it could push the suspension slightly beyond the cart's Specification)

Hope this helps.

"Here's a heartening story for the OP : I often accumulate new LPs but don't play them with the intention of getting them cleaned first. Yesterday I took a chance and played one that had been stored, uncleaned from new since 2013. Opening it for the first time, it was "ruler flat", no discernible warps. Hole and label registration were very good. The LP played as if it had just been scrupulously cleaned. Noise floor was inky black. Transient peaks tracked perfectly and cleanly throughout the entire record. This 180g was a triumph of LP manufacture that harked back to the halcyon days of the 70s & 80s when no one had even heard of MRA and uncleaned LPs bought new still sound perfect today."

Emboldened by my own experience (above) I've started playing new LPs without cleaning them. After warming up the stylus on a 2nd-hand LP, the next two that I tried were "For Your Pleasure" (Roxy Music), 1x180g LP, and "The Raven That Refused To Sing" (Steve Wilson), 2x180g LPs.
To my pleasant surprise all three of them gave the same result as above. Each had a nice glossy black patina.
I paid particular attention to the quiet/silent passages on the Steve Wilson because it had a bit more dynamic contrast than the other album.
Even though I listen at levels of 85db or so - measured at a distance of 5-6m there were no clicks or pops just inky blackness. As a double-check I stepped into the near field during quiet sections and got the same result.
The run-ins and run-outs were also smooth and untroubled.

I sense the beginning of a grand experiment to see how many new, uncleaned, LPs I can play & obtain such gratifying results from before I crash-and-burn on an MRA-riven one! ;^)

Funny in the 70s I would buy a record for $5 bucks .Now there $50 an can be warped...no thanks .