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Group,

I performed a quick calculation using equations developed by Hertz (sphere to sphere contact) to calculation how much pressure the stylus applies to an Edison Diamond Disc record for :

1. Edison Diamond Disc Phonograph

2. DJ style of Stylus with 0.7 mil spherical shape and 2 Grams of weight.

3. 3.75 mil "Expert" stylus with 4 Grams of weight.

The results were very interesting! I used the material properties of Bakelite for the Edison Disc Groove and Diamond for the stylus. The PSI (pounds per square inch) values are the "point contact" force which in turn is spread
over the contact area.

Results:

1. 0.00166 sq inch contact and 72,566 PSI
2. 0.00015 sq inch contact and 93,583 PSI
3. 0.00046 sq inch contact and 19,902 PSI

Conclusion : Although the actual force is spread under and around the contact area, the calculations shows that the Original Edison Design was somewhat better than using a LP style and low gram load. The reason is because of the
non-linear relationships in the Hertz equations.

If anyone has other results please let me know.

Marc

This is fantastic, and I have wanted to see something like this for years. Can you please try doing it for steel needles/shellac? Obviously you will need to use a few more assumptions, but if those assumptions are consistent (shellac hardness, primarily) the tracking force and tip size variables should provide enough contrast to tell the story adequately.

PeterF

To be clear, are you looking to find the force from the steel needle before it takes the shape of the groove ? If so, I would ask if the steel needle as new has a 2.5 mil radius ? This is a number I have read about.

I have one picture of a steel needle after it has taken the shape of the groove, and its not pretty! Some of the needle is riding on the groove edge while the rest is in all of the groove.

Marc

I’m mainly interested in the comparative pressure that each different stylus exerts. Ultimately I’d like to see if any conclusions can be drawn regarding wear. As for the soft steel tips, we probably need to look at the surface areas for both the beginning and the end of the record side.

PeterF

O.K. I'll see what is available for soft steel and shellac with regard to initial pressure before the record turns.
Do you have any stylus force numbers ? I do not have anything but Edison Phonographs to measure here.

Marc

The weight of the soundboxes is something between 120 and 180 grams.