Elliptical?

[Bran Kulez]

I recently bought a used machinists inspection microscope to view the various styli I own up close. One thing I noticed was that most of the so called ellipticals seem to be conicals with the front and back ground flat. Most of my cartridges are Shure, and the styli with bonded tips, as opposed to "nude" tips, all look like the following photo. This is true for OEM Shure as well as JICO. Does grinding the front and back off of the tip make a difference? (I don't have any way to photograph them that close so I lifted the following photo from VE)

[dlaloum]

There is a long thread here viewtopic.php?t=22894

This is possibly the best source of stylus shape information anywhere!!!

The end result of grinding away the front and back is the the very tip of the needle - the bit in contact with the vinyl, ends up having an oval (eliptical!) cross section.

Lots and lots of info in that thread!

bye for now

David

[Bran Kulez]

I couldn't find anything in the thread regarding my original question which is, "does grinding the front and back off of a conical, (if that is what one gets when buying a middle of the road elliptical), make any difference in sound quality or record wear?"

All of the information assumes that the stylus shape is "elliptical" or "oval" as you mentioned. But in terms of solid geometry, slicing off opposing sides of a cone does not create an ellipse (or oval). The contact radius in horizontal section is still whatever the original cone radius is.

The following sketch shows a .7 mil conical tip with a .2 mil x .7 mil elliptical superimposed in horizontal section. The dashed lines represents the portion ground off of the stylus tip to give it "elliptical" dimensions, as I see it :

[kelvinMunson]

You need to look at that in 3D. Basic school geometry........

In mathematics, an ellipse (from Greek ἔλλειψις elleipsis, a "falling short") is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis. An ellipse is also the locus of all points of the plane whose distances to two fixed points add to the same constant.

The flats are ground so that the contact area with the groove is the generated ellipse.

[dlaloum]

I understand what he is saying - if the side radius of the circle being "cut" is 0.7mil, then cutting the front and back will not change the side radius in the least... it will result in a side radius that is still 0.7mil while the front and back radius will increase based on the positioning of the eliptical cuts.

To achieve a 0.4mil x 0.7 mil eliptical (the most basic sort) - you need to start with a 0.4mil conical - this would be too narrow across the groove, so to "raise it up" you grind away the front and back - so the major radius is now 0.7mil whereas the minor (side) radius remains 0.4mil - now you have a 0.4x0.7mil eliptical... (mind you I'm just guessing - someone who has read the patents on the manufacturing methods for the styli should be able to shed more light on this!)

bye for now

David

[markcass]

Hi

I think a lot depends on the degree of finishing after the flats have been cut. Polishing of the tip rounds the "corners", reducing the contact radius to a greater or lesser degree. The more refined ellipticals have sometimes been called "swept ellipticals" because the polishing process generates a smooth contact shape. This can extend the vertical contact radius so that the stylus tends towards a basic line-contact form.

Shure used to call their basic elliptical styli "bi-radial", which perhaps gave a more honest description of what was on offer!

Mark

[Bran Kulez]

kelvinMunson wrote,

You need to look at that in 3D. Basic school geometry........

I sketched it in 2d but am thinking in 3d. Take a look at the photo in the first post. Any ellipse created by your definition has no bearing on the actual contact area of the stylus. Basic common sense........

[Zeppelinn]

I sketched it in 2d but am thinking in 3d.

Hi Bran,
You raised very interesting question!
I also thought they do the final job by fine polishing the tip. However at the picture below the two cuts are visible with clear edges (please note it's the same needle as the one at the first post).



UPDATE: Probably the trick is that the cuts are not the same. The back cut (right on the pic) is "deeper".

[Ldg]

To achieve a 0.4mil x 0.7 mil eliptical (the most basic sort) - you need to start with a 0.4mil conical - this would be too narrow across the groove, so to "raise it up" you grind away the front and back - so the major radius is now 0.7mil whereas the minor (side) radius remains 0.4mil - now you have a 0.4x0.7mil eliptical... (mind you I'm just guessing - someone who has read the patents on the manufacturing methods for the styli should be able to shed more light on this!)

No, that plain doesn't work !

Bran K raises an excellent question, and I don't know the answer. But I think it has to do with that the cone shape is not mounted on it's principle axis, it is mounted at a pronounced front-back inclined angle. You can see this when looking at an eliptical stylus from a side angle. This is the only way to obtain an eliptical locus in the horizontal plane from a cone surface, AFAIK.

Perhaps it's then necessary to grind flats to form the base profile (remove the point), and avoid bulk fouling ?

If the contact area were formed from intersection of the ground flats, it would be a sharp line, so I just can't see this. It could be repolished, but that would be tricky, I think. Plus, it doesn't look like that. If it's not repolished, the original cone surface would form the contact area.

I'm very interested in the proper answer to the OP question. I think it might be insightful. I've read the Grado patent about three times and I still don't get it, perhaps I have some block !

[Ldg]

IF I were right about this, minor and major radii would be determined by included angle of the cone, and inclined angle front-back at which the cone is mounted. Purpose of the flats would be to debulk, and form the base profile. Surface of contact areas would be part of the original cone surface. Ground edges would play no part. Only repolishing would be deburring.

But it's just an idea, might well not be right.

[Ldg]

Well, I can't find any sign that the eliptical cone is mounted off axis, and I can't make the correct eliptical radii happen that way either. So I'm wrong about that idea. The Grado patent doesn't describe a method to make an eliptical either. Nor what the exact shape is. So I don't know !

[Ldg]

Intriguing, this is starting to bug me !

Here's what a 3rd party microscopy site says about elipticals :

.....The standard elliptical tip is made by first grinding the diamond to a conical shape having a spherical tip with a radius equal to the curvature across the major axis of the finished elliptical stylus. Narrowing the tip to form the ellipse is achieved by grinding a flat surface on the front and the back of the tip so that the profile is now "elliptical" when viewed looking directly at the tip along the axis of the cone.

Except.....that does not make an eliptical contact area. The contact surface would be either part of the original spherical surface (as appears in the microscope photos showing where the wear patches are), or part of a sharp line (but in the photos, the two grinds don't intersect). As Bran K points out in the OP.......

Here's the link, but personally I'd treat the content cautiously, though the photos speak for themselves. I've never seen wear patches that big either, BTW.

http://www.micrographia.com/projec/proj ... ny0300.htm

Personally, looking closely at an AT95E at x200 confirms that the grinds don't intersect. And have well defined edges and curves as though they have not been repolished.....and the curvature appears constant in both planes, as best I can see.

Er, are elipticals really just debulked sphericals then ?

[dlaloum]

Makes no sense - if the major radius was 0.7mil. then the end result would be a 0.7 x 0.7 + + mil eliptical.

For this method to work you would need to start with a conical which is of the proportions of the minor radius, and then the front/back cut would widen the major radius... so your starting point would have to be a 0.2 / 0.3 / 0.4 mil conical/spherical.... {?)

No polishing of the front/back cuts is required as these are not contact areas...

More information needed methinks

[Ldg]

Makes no sense - if the major radius was 0.7mil. then the end result would be a 0.7 x 0.7 + + mil eliptical.

Well it makes sense in that yes, the contact areas would be part of the original spherical surface. Unless the ground edges play a contact role, which seems very bad........

For this method to work you would need to start with a conical which is of the proportions of the minor radius, and then the front/back cut would widen the major radius... so your starting point would have to be a 0.2 / 0.3 / 0.4 mil conical/spherical.... {?)

No, it plain wouldn't work. The seperation between the contact areas would always be very wrong (0.56mil seperation for 0.4mil spherical, whereas should be 1mil seperation for 0.7mil radius), and besides those ground flats don't intersect with the major radius (which is vertical through the contact areas). So you can't enlarge the major radius of the contact areas by grinding front/back slats. By starting with a 0.4mil spherical, you'd just end up with a smaller version of what we already have, with wrong spacing, and still with spherical contact radii !

No polishing of the front/back cuts is required as these are not contact areas...

Agreed, but what about the edges ?.....they don't appear polished either, so presumambly aren't in play....(which is a relief because they aren't polished!) I think one can see from the wear spots that they don't reach the edges, and this suggestes the edges don't participate. I'd like to think so, they look hard and well defined.

Sreten reached the same conclusion here previously, BTW.

So it seems that the contact region of a common elliptical actually has 0.7mil x 0.7mil spherical contact radii ? Essentially a 0.7mil spherical with front and back surfaces cut away (debulked). Which, under the microscope, is rather what it looks like ???