Vinyl grooves and the friction heat

[magiccarpetride]

My recent experience with the Beresford Caiman DAC had whetted my appetite for the analog sound. The Caiman is indeed approaching, in many aspects, the high quality analog reproduction.

The trouble is, my old turntable got destroyed seven years ago in a flooded basement, and I haven't found a replacement yet. I've started thinking about it now, but before I do anything, wanted to double check one urban myth with the knowledgeable folk here: as the myth proposes, when the stylus hits the rotating groove on the turntable, the mass/velocity factor causes enough friction to heat up the vinyl which then melts and the heat warps and distorts the original grooves. Is that a fact, or fiction?

If it's a fact, how does that affect the quality of the reproduction? Our 'garbage in, garbage out' theory holds that, the moment you mess up the signal, what you get out of the speakers is, well... mess.

I've even heard that some audiophiles play their vinyl only once, while at the same time recording it onto a different medium (a reel-to-reel tape, or digitally). The theory goes that, when you're playing a virgin vinyl for the first time, that's the only time you're actually hearing the pristine, undistorted signal as it is embedded in the grooves. True?

[Alex_UK]

OK, now I'm convinced you're winding us up! I wasn't sure before... :)

[AlanS]

That thinking is a bit linear, maybe even tending towards the objective. I thought the first playing burned in the disk, rounded off any moulding imperfections or is that the stylus.

[magiccarpetride]

OK, now I'm convinced you're winding us up! I wasn't sure before... :)

Busted! Just curious -- what was it that gave me away?

[The Vinyl Adventure]

Eh... Is your fisrt post a joke or your second one magic alex

[The Vinyl Adventure]

I thougt it was a legitimate question!...
I don't see why a diamond won't eventually damage a bit of vinyl...

[Alex_UK]

I was in the scouts, I've tried making fires using a fire drill - believe me, it's not as easy as Ray Mears makes it look - the friction needed to create that sort of heat from a tiny diamond on a piece of vinyl is going to be a lot more than 33 or 45rpm I'm sure... I'd be very careful playing any 78s though, you might spontaneously combust! ;)

[AlanS]

I thougt it was a legitimate question!...
I don't see why a diamond won't eventually damage a bit of vinyl...

Yes but


the mass/velocity factor causes enough friction to heat up the vinyl which then melts and the heat warps and distorts the original grooves

is another story. Who is the author?

[The Vinyl Adventure]

Ha, oh yeh ... Passed me by that bit ...

[magiccarpetride]

I was in the scouts, I've tried making fires using a fire drill - believe me, it's not as easy as Ray Mears makes it look - the friction needed to create that sort of heat from a tiny diamond on a piece of vinyl is going to be a lot more than 33 or 45rpm I'm sure... I'd be very careful playing any 78s though, you might spontaneously combust! ;)

Hey, don't shoot the messenger! I'm just relaying what I've heard out in the wilderness. Wanted to run that by you, just in case it may not be an old wife's tale after all.

And oh, by the way, Magic Alex from the UK, it is one thing trying to set fire to a piece of hard wood, and another thing warming up a piece of pliable plastic so that it warps a bit. Different pressure points, wink-wink, say no more, know what I mean? ;)

[Alex_UK]

Hey, don't shoot the messenger! I'm just relaying what I've heard out in the wilderness. Wanted to run that by you, just in case it may not be an old wife's tale after all.

And oh, by the way, Magic Alex from the UK, it is one thing trying to set fire to a piece of hard wood, and another thing warming up a piece of pliable plastic so that it warps a bit. Different pressure points, wink-wink, say no more, know what I mean? ;)

Well you actually used the word "melts" in your original post - not "warps a bit" - according to this site (http://www.instructables.com/id/Hot-Wax-on-Vinyl/) you need 200 degrees F which is a lot more than "warming up" in my book ;)

I haven't made any measurements or have the capacity to do so, but I severely doubt this could happen - can you point us to some research or links that suggest it does? I had a quick google but couldn't easily come up with much.

[The Grand Wazoo]

You don't need to apply much heat to a record to make it pliable. Did none of you ever make ashtrays from ~Shakin' Stevens singles?
Heat is a product of the application of pressure. The contact area of a stylus is minute - what does a tracking force of, say 2g convert to when exerted on that sort of point force in kg/m2?

[magiccarpetride]

Well you actually used the word "melts" in your original post - not "warps a bit" - according to this site (http://www.instructables.com/id/Hot-Wax-on-Vinyl/) you need 200 degrees F which is a lot more than "warming up" in my book ;)

I haven't made any measurements or have the capacity to do so, but I severely doubt this could happen - can you point us to some research or links that suggest it does? I had a quick google but couldn't easily come up with much.

The only 'research' I performed so far was while I was in high school and left my copy of Jethro Tull "Stand Up" LP sitting on the turntable, while the sun was blazing through the window. Next thing you know, the LP got warped all out of shape and was useless for playback.

That happened rather quickly, which points towards the conclusion that you don't need that much heat to bend the vinyl out of shape.

[magiccarpetride]

You don't need to apply much heat to a record to make it pliable. Did none of you ever make ashtrays from ~Shakin' Stevens singles?
Heat is a product of the application of pressure. The contact area of a stylus is minute - what does a tracking force of, say 2g convert to when exerted on that sort of point force in kg/m2?

As anyone who went to school knows, pressure increases with the diminishing surface of the point of contact. This is why we use a needle point if we want to pierce through something hard.

Don't know the details off the top of my head, but apparently a spinning disc carrying a needle in its grooves does endure a lot of pressure. The contact area is minuscule, which, according to the laws of physics, translates to a lot of force (small contact area combined with velocity/kinetic energy).

Sidebar: Don't know what's with me today -- I feel very brainy, even though I promised myself not to be that way ever again! :scratch:

[Alex_UK]

The only 'research' I performed so far was while I was in high school and left my copy of Jethro Tull "Stand Up" LP sitting on the turntable, while the sun was blazing through the window. Next thing you know, the LP got warped all out of shape and was useless for playback.

That happened rather quickly, which points towards the conclusion that you don't need that much heat to bend the vinyl out of shape.

I don't disagree, I've seen a rather fetching flower pot made on a gas hob in a flash, but I'm still struggling to understand the "math" which TGW has eluded too - 2g of pressure doesn't sound a lot, but maybe? :scratch:

[AlanS]

If you play a disk on a record player with a worn spherical stylus/needle/what is tracking weight you loose detail within a few plays and gain noise. Use a turntable/good arm/quality shape stylus and you can play a disk 10s of times before audible harm is done.
Whats this got to do with heat? Groove wear is caused by poor complementary shape of stylus to groove. The greater the interfacing match of stylus to groove the lower the load/stress/wear.

[shane]

A stylus tracking a groove will get pretty hot, but the thing to remember is that the actual mass of hot diamond is very small, and the vinyl is going past very fast and does not experience significant heating.
Vinyl damage caused by a stylus is due to the stylus acting like a lathe, rather than any heating effect.

[Themis]

Vinyl damage caused by a stylus is due to the stylus acting like a lathe, rather than any heating effect.
My thoughts, exactly. ;)

[DSJR]

Vinyl's also slightly springy, so should recover a few seconds after being played. The worst thing for a record is a worn stylus!

[The Grand Wazoo]

It occurs to me to wonder, not what the stylus does to the vinyl, but how the stylus can exhibit any wear at all, given that it's made of the hardest naturally occurring substance known to man and that vinyl is very soft – easy to scratch with your fingernail. Given this, why don't styli last much, much longer?

I had a bit of an old think about all of this. I did some googling and I had a bit more of an old think. This is what I learnt and what I thunk.

Relative Hardness
So, I took a very brief look at the science of measuring hardness. This led me to 'Mohs Scale' where there are 10 reference points based on 10 different naturally occurring minerals, ranging from very soft rock (talc) to the hardest (diamond). The test is simple – take a piece of rock from the list in one hand (your 'Reference Rock'). Take your 'Rock of Mystery' in the other hand. Then you scrape one against the other. If one scratches the other, then it's the hardest one and vice versa. If they are both scratched, then they're the same hardness. Keep trying all the different Reference Rocks till find one that is a 'Mutual Scratcher'. If you fail in this fine endeavour, then you keep scratching stuff till you find 2 minerals that are adjacent on the scale – one that your 'Mystery Rock' scratches and one that it doesn't. That means your 'Mystery Rock' gets a half mark – there are no other subdivisions than halves.

This is the scale, but as it's linear and the actual hardness of things is not, I've added the figures for absolute hardness.

Mohs Hardness Scale and Absolute Hardness Scale

1 (Mohs)– Talc – 1 (Absolute)
2 – Gypsum - 3
3 – Calcite - 9
4 – Fluorite - 21
5 – Apatite - 48
6 – Orthoclase - 72
7 – Quartz - 100
8 – Topaz - 200
9 –Corundum - 400
10 – Diamond - 1600

So this means that vinyl, which, as we all know, can be scratched with a fingernail must be less hard than a fingernail. I have it on good authority that a fingernail is a 2.5 on Mohs scale. If we look at the scale, we see that this point lies somewhere between gypsum and calcite. I'd think the figure of 2.5 must be about right as nails are mainly made of calcium which is a major component of gypsum. We know that we can scratch gypsum because that's what plasterboard is made of. If you look at the absolute hardness of calcite, you see that at 9, it's 3 times harder than gypsum & I think we'd struggle to scratch something that hard.
So if we can scratch vinyl with our fingernails, and I know it's harder than gypsum, then it must also be a 2.5 on the scale.

This means according to the absolute scale, that a diamond stylus must be something like 266 times harder than the record it tracks. That's pretty hard, so why does it wear out?

Distance
So the next thing I turned my mind to was to try to work out the actual mileage that a stylus does by the time it's worn out.
I had to make some assumptions here and I got some figures from some websites that I can't be bothered to mathematically verify.

What is the actual 'mileage' of a stylus before it becomes worn?

Linear speed of vinyl past stylus on outer grooves of an LP at 33.3 rpm - 510 mm per second
Linear speed of vinyl past stylus on inner grooves of an LP at 33.3 rpm - 210 mm per second (Interestingly, this is only 41% of the linear resolution).

This gives an average speed of 360 mm/sec.
For a 20 minute record side ( 1200 seconds): 360 x 1200 = 432000mm = 432 metres per side

The stylus becomes worn after, say 700 hours use = 2100 sides = 907,200 metres.
So, your precious diamond becomes kaput after it has effectively travelled a total distance (in the Kingdom of Grooveland) of 907.2 km.

Now, I wondered how far this was between two prominent places in the UK (my mind still works in miles, I'm afraid) so I took a look at a map with the knowledge that Lands End to John O' Groats is about 900 miles. I thought, well 900 km would maybe get you as far as Edinburgh, so I Googled it to see how far off I was. Can you believe that the distance from Land's End to Edinburgh is 907.67 km?
Now that was a pretty good guess I reckon – I was only 470 metres out!!!!

So you start to see that the distance you're dragging that little piece of rock is quite significant.

Pressure
I tried to answer my question from a previous post about the pressure for a downforce of 2 grammes, but couldn't find a figure. I did find this though:

Even though the tracking force of the stylus above is only 1.5 grams, this force is applied to such a small area that the pressure on the walls of the groove can be surprisingly high.

Measurement of the wear surfaces at higher power using an eyepiece micrometer gives a figure of 20 µm for the average width of the worn areas. Neglecting factors such as the elastic deformation of vinyl, the distribution of forces in a V-shaped groove and the accelerations at the stylus tip during tracking, simple calculation based on these figures gives a stylus pressure of 240 grams per square mm, or 340 pounds per square inch. The transient pressures exerted by a stylus tracing a heavily modulated groove during playback will of course be much greater, but beyond my ability to calculate.

340lb/sq inch - that's a pretty large force in anyone's book, and the last statement tells us that the force gets plenty bigger. I guess that you would also have to conclude that a new stylus would exert more pressure as the contact area will be smaller than for a worn one. This means that the rate of stylus wear will plot as a bell curve – fast wear at first, then as the worn area gets bigger, the contact area will increase &, therefore pressure and rate of wear will decrease. So the amount of time your cartridge is in a semi-kaput state is presumably quite long – but at what point does it become kaput – kaput?


Speed
Apparently, the wear on a diamond is related to the speed over which the friction occurs. We saw above that the speed averages at about 360mm per second. I don't know if this is good or bad!

Temperature
It turns out that diamonds have exceptionally good heat conduction properties – far better, in fact, than copper. This is very interesting indeed because it might lead you to believe that the heat generated on the groove wall is drained away quite quickly into the diamond (…. & up the cantilever?). So maybe heat isn't a factor at all. But the heat conducted up the cantilever could be having other effects – effects on the cartridge: Differential expansion of joined parts? Glue softening? Shortening the life of suspension rubber? ….Who knows!


All of the above is quite interesting, and I suppose it lets me understand the forces that lead to stylus/cartridge wear, but I don't think it answers my, or anyone else's questions.
Any more thoughts from anyone else?

[Alex_UK]

Great stuff Chris! (But I do think you should get out more! ;)) I guess a similar comparison could be Tyres vs. Roads - yes, tyres are much softer, and wear relatively quickly, but the road wears away eventually, purely based on the amount traffic it encounters.

[magiccarpetride]

If you play a disk on a record player with a worn spherical stylus/needle/what is tracking weight you loose detail within a few plays and gain noise. Use a turntable/good arm/quality shape stylus and you can play a disk 10s of times before audible harm is done.
Whats this got to do with heat? Groove wear is caused by poor complementary shape of stylus to groove. The greater the interfacing match of stylus to groove the lower the load/stress/wear.

For the purposes of this discussion, I'd like to postulate two types of wear and damage to the vinyl:

1. Damage resulting in audible pops and crackling noise
2. Damage resulting in distorting the pristine signal, embedded in the groove, the way it was shipped from the pressing plant

The damage #1 is much more clearly audible than the damage #2. But both exist, and are undeniable.

My original question was related to the damage #2: how serious can it get during the first ever playback?

[The Grand Wazoo]

Recycled vinyl = bits of 'not vinyl' embedded in the record = bits of 'not music' embedded in the music

[Barry]

It's not that the hard diamond will wear away the softer vinyl, nor is it that the 'friction' between the stylus and vinyl will cause the vinyl to soften. None of this will occur if the load applied over the contact 'footprint' on the groove wall is low enough. Unfortunately, as Percy Wilson and others have shown, using playing weights greater than 0.5g will stress the vinyl beyond the elastic limit, that is, the groove wall will not return to its original shape after the stylus has passed.

Don't blame me if I have now given you all sleepless nights!

Regards