Radius of cutting stylus' edge

[statfi]

What is the radius of curvature of the cutting edges of new and used cutting styli?

[Aussie0zborn]

Do you have any documentation from Micropoint USA or Adamant Japan?

[boogievan]

The radius of curvature of the new Micropoint stylus tip is 3 - 4 micrometers.

http://www.discolathe.com/.pdfs/cutting%20styli/ruby_stylus_B.jpg


Whereas, the 'cutting edge' is considered by Micropoint to be 'the intersection of the stylus face
(or 'mirror') and the burnishing facet'.

http://www.discolathe.com/.pdfs/cutting%20styli/ruby_stylus_D.jpg

[statfi]

Thanks so much!
Does anyone know the radius on the cutting edge between the face and the burnishing facet, perpendicular to that edge for new and used styli? In http://www.discolathe.com/.pdfs/cutting%20styli/ruby_stylus_D.jpg it is shown as a slightly obtuse angle with an infinitesimal radius which presumably is finite if you look closely enough.
Are there geometrical criteria for replacing a cutting stylus?
(Tangential topic) Some London/Deccas had a peculiar, endemic, pervasive noise on their otherwise superb sounding LPs. What was the cause of that noise?

[dmills]

There are some detailed drawings in the AES Disk cutting anthology of the (IIRC) Capps styli, and I think there is at least one drawing in "Basic Disk Mastering" by Boden.
You got someone able to make these?

[boogievan]

Here's a scan of Adamant's spec sheet for their stereo-cutting (as opposed to CD4) Neumann stylus that Larry included in his compendium.

http://www.discolathe.com/.pdfs/cutting%20styli/Neumann_stereo_Adamant.jpg

[boogievan]

As you can see, Adamant didn't provide a 'radius of curvature' for the cutting edge, either. It's probably because it's not a curve, innit?
It's simply a corner on the mirror that starts the flat, beveled surface which has non-zero length. Ideally, it's a line, this 'corner'. Whereas the tip is deliberately polished into a circular shape, therefore, having a 'radius'.

Notice, also, how Adamant allow a full, +/- 1-º tolerance about the 20-º angle target for their stereo styli's burn. facets (see the letter, Beta, in their own drawings), whilst Micropoint (who also for a while sold their own brand of master lacquers) claimed that the resuults of their experiments showed the ideal angle for the beveled edge to be 22,5º...

Significant deviations, they claim, depending on which direction, cause either increased noise, or waveform deformation.
http://www.discolathe.com/.pdfs/cutting%20styli/ruby_stylus_C.jpg

The length of the 22,5-º bevel which begins at the cutting edge is supposed to be as short as possible without causing immediate destruction of the facet upon being 'dropped' into the heavy paint. So, if you're about to manufacture cutting styli, I'd use the Micropoint figures for styli made of good-old 9-Mohs Al2O3 and facsimiles thereof, and use the Adamant figures if daring to bruit, lap, buff, saw, and polish from pure C... There are no infinitesimally subtle rules beyond these - facets of custom lengths were tried, including the 'feather edge', shown in figure S 10:
http://www.discolathe.com/.pdfs/cutting%20styli/feather_edge.jpg




Is Tod here?

- boogie

[statfi]

Thanks so much! This answer hits a number of nails on their heads.
My question was misguided in the sense that the burnishing facet reduces the relevance of the question substantially if not to zero.
I am an applied physicist and metrologist who listens avidly to LPs. I come from the perspective expressed in https://www.nanoandmore.com/afm-tip-shape-effects#:~:text=1).,accurate%20imaging%20of%20steep%20slopes.&text=tip%20with%20important%20parameters. People put enormous effort into making AFM tips "as sharp as possible", but recognize that a zero radius of curvature is unattainable, on the one hand, and wear causes further deviation of that ideal, on the other. I am interested generically in the fidelity of the motion of the playback stylus to that of the recording stylus. The answer correctly points out the obvious fact that the burnishing facet has more effect than the edge radius on this fidelity. However, I would still like to know what we know about how a new cutting stylus differs physically from a worn one that needs to be replaced. So, what makes a worn recording stylus worn?

[boogievan]

Breaking (off) jaggedly is a common mode of failure after too many hours or (G_d forbid) touching the alu substrate beneath the thin layer of paint on the blank record. I scanned images of broken pickup styli that appear in the AES anthology of Disk Recording (Vol. 1. Groove Geometry and the Recording Process). They resemble the broken tips of cutting styli - other than having much larger-radiused tips.

http://www.discolathe.com/.pdfs/cutting%20styli/radii.jpg

The size of the radiused tip affects its strength. This is reminiscent of the earlier statement about the length of the burnishing facet. To make them strong enough to last for close to 20 hours, with heat, during cutting, the burnishing facet length is kept above 0 in length at about 16.5 hundredths of one thousandth of an inch (a.k.a., ~ 4,2 µm, according to a (vintage) MicroPoint bulletin).

You are correct that the conical tip of the simplest pickup stylus won't be able to trace the path of the quill-like cutting stylus' tip -albeit 'radiused' - since the cutting stylus tip radius is only 12 hundredths of one measly thousandth of an inch wide, while the pickup stylus' radiused tip is a whopping 7 or so thousandths of an inch - when new. When old, that pickup stylus tip has probably gotten bigger. Same with the cutting stylus' very small tip. Note that this enlargement of the radiused tip is one of the symptoms of the need for stylus replacement, cited in this scanned doc. from Larry's compendium (Basic Disc Mastering) (shared, with thanks, for academic purposes)

http://www.discolathe.com/.pdfs/cutting%20styli/replacing_styli.jpg


The indicators for the need of stylus replacement are heard as well as seen. You can hear if the surface noise increases despite the application of stylus heat or, alternatively the sound gets muffled...indicating the enlargement of the burnishing facets that burnish too much, now...

I've seen the 'needle' and the damage done in a normal 20x stylus-inspection microscope (used for aligning styli in the cutting head's tapered chuck). The edge of either side of the 'v' shape (of the mirror, which, during engraving, is facing the incoming disk land) may look jagged, or, the tip, itself, may have broken off. There can be no doubt when irregularities are visible at only 20x...

Even the drawing of a feeler's 'radius of curvature' at the nanoengineering website is at the 'tip' of the instrument.
http://www.discolathe.com/.pdfs/cutting%20styli/radiused_tip.jpg

servus,
Boogie van Boogievan

[statfi]

Thank you! My comparison was between the *tip* of an AFM stylus where there is a 2D radius and the (45deg) *edge* of a cutting stylus where there is a 1D radius. I.e., I was not comparing tip to tip. Apologies!
Referring to http://www.discolathe.com/.pdfs/cutting%20styli/replacing_styli.jpg, what do you suppose is happening geometrically to the cutting stylus when
1. the cut is no longer shiny and smooth
3. the noise level is too great
4. high frequency response falls off
Also, re. "wear will generally show up on the edges after ten hours of cutting", *I* would expect the worn edge to become blunted as well. Should I equate your "jaggedness" with their "wear"?

[boogievan]

I should think the edges (and tips!) I've seen in the mic, jaggèd, were mostly due to sudden breakage along random faults, whereas the term, 'wear', sounds more like gradual and possibly even smooth deformations of the original silhouettes. Though in some cases, smooth, such wear results in changes to the length and/or angle of the facets and/or the roundness and size of the tip - the parts of the stylus that touch the lacquer - and these dimensional changes, alone, can increase noise, attenuate high frequency detail (as in, 'make muffled-sounding') or, conversely, could result in increased sibilance, if deformations and/or breakage were to result in the effective deletion of the burnishing facets, altogether, or waveform deformations caused by a now-decreased burnishing facet angle on either or both sides. It's without any b. f.'s with heated cutting that sibilance is excessive, yet with too great a pair of such facets - or at too great an angle (i.e., more than 22,5º) that one, now, loses clarity, due to over-burnished groove modulation. I recommend close reading of the two paras, Cutting the Groove and Burnishing Facet Size, for insights into what types of stylus damage result in what sound effects (hiss, noise, dullness, etc..), since it's not just physical distortion of the stylus, but its heat, and the vagaries of the lacquer formula that was flown (or reflown!) on that particular disk.

http://www.discolathe.com/.pdfs/cutting%20styli/ruby_stylus_D.jpg

If you're used to looking at your groove with around 150x magnification, you can focus on it in such a way that should at some point reveal the very narrow 'center line' that at all other focus-settings is invisible. But when you do tune in on it, it's clear that the stylus tip is as normal. But groove-plaguing can result from surface irregularities that are not even visible at 600x (which is the kind of magnification used, for example, by Mr. French at JRF Magnetics when checking the head gap of a 1/2" 2-track (Ampex / 2 mm guard band) repro head, and I believe Mr. Gross, of NiPro Optics, has this kind of mic on hand - yet, speaking of Nano Engineering - according to Spiro, the electroforming process is capable of reproducing surface details of only 13 nm. Indeed, NiPro's electroformed telescope mirrors are reflecting optical wavelengths.) So, while many types of wear and breakage are going to be visible at only 20x, you might have to use auditions of the pickup (in the test cut radii of a master lacquer or the master cut on a nickel mother (or stamper, if you've such a player)) because the pickup cart and the human ear can resolve more detail than the human eye and light microscopy can - the ear having 11 times the resolution of the eye, iirc - to decide whether or not to try a new stylus, and if the new one doesn't create the problem that the old one did, even though you might not have diagnosed the flaw, you've nevertheless solved the issue, innit? Often the appearance of the work done by a flawed stylus may show signs of abnormalities - either obvious or subtle.

- boogievanagain ∞

[statfi]

Man. Thanks! Goldmine.

From where is ruby_stylus_D abstracted, so I can read the rest?

It gives a direct qualitative answer to my quantitative question: "the stylus cuts a groove length of 1.4 km long, slowly wearing out and *dulling* the cutting edge". Is it reasonable to interpret "dulling" as increasing the small but finite radius of the stylus.

[boogievan]

The micro-point Recording Styli brochure is attached to this reply as a .pdf.

I'd agree that each 87-mile cutting-hour of 'wear' cited in the brochure results in a gradual 'radiusing' of the cutting edge unless there's sudden breakage when it looks, in the mic, jaggèd.

[statfi]

Fantastic. Thanks so much! I have learned a lot. E.g., breakage is the main mode of failure with age.