Stylus Rake Angle

Atmasphere,
Surely the groove depth changes with signal? A right channel signal for example must cut into and out of the lacquer at 45 degrees. I can see that a heated cutting stylus will help the process, but then does that affect the final profile as the material cools?

Lewm,
The VTA is the angle from the cantilever pivot to the stylus tip relative to the record, which ideally should be the same angle as the equivalent angle a line from cutter pivot to the cutter stylus makes with the lacquer if there was no "give" in the material. Both can vary. Apparently there could be 10 degrees of a difference depending on the lathe.

But the cartridge is designed such that for an optimum downforce the generator is centred, and the resulting cantilever angle is the VTA. So the angle of the stylus relative to the cantilever is fixed and the two must vary together.

Now while the stylus might be set at 92 degrees, the cantilever may not be at the same angle as the the cutter. In which case there will be a distortion in the playback, similar to horizontal tracking error. Any adjustment to set VTA - the cantilever - to a particular angle will change the stylus rake as well, perhaps away from the average 92 degrees.

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You are mistaken. VTA has nothing to do with the angle of the cantilever. The angle of the stylus relative to the cantilever can vary wildly from one cart to another and therefore result in huge differences in cantilever/surface angles. VTA is set by the cutting stylus itself. Therefore there doesn't need to be a reference to VTA adjustment at all. It's done with as soon as the laquer is cut. The pertinent function to play back is SRA, the thing that follows. The fact that the cantilever angle changes with SRA adjustment is incidental.

Surely the groove depth changes with signal? A right channel signal for example must cut into and out of the lacquer at 45 degrees. I can see that a heated cutting stylus will help the process, but then does that affect the final profile as the material cools?

I used to hear about this thing called rebound associated with lacquers but yet to experience it. Yes, the groove wall is cut at a 45 degree angle, so if you were to cut an out-of-phase bass signal, the groove would indeed modulate up and down. Of course, the needle would not be able to track it, and such a signal fortunately does not exist in nature. If we encounter studio productions where out-of-phase information is a problem, we have a simple passive processor that takes care of it. So groove depth can be considered a constant.

Another way to look at this is if the cartridge body rises higher, that is a change in groove depth, if the needle simply traces a signal, the groove depth has not changed.

Atmasphere, Does azimuth vary from cutter to cutter and lathe to lathe? If so it would not surprise me.

Csontos, you said:

You are mistaken. VTA has nothing to do with the angle of the cantilever. The angle of the stylus relative to the cantilever can vary wildly from one cart to another and therefore result in huge differences in cantilever/surface angles. VTA is set by the cutting stylus itself. Therefore there doesn't need to be a reference to VTA adjustment at all. It's done with as soon as the laquer is cut. The pertinent function to play back is SRA, the thing that follows. The fact that the cantilever angle changes with SRA adjustment is incidental.

You need to do your homework and think more on this.

Vertical Tracking Angle is a cartridge property. The clue is in the word "tracking".
The fact that it may not be the same as the equivalent angle used when the record was cut, as you mention but fail to realise its relevance, is what can lead to distortion in playback.

Atmasphere, you said:

Yes, the groove wall is cut at a 45 degree angle, so if you were to cut an out-of-phase bass signal, the groove would indeed modulate up and down. Of course, the needle would not be able to track it, and such a signal fortunately does not exist in nature. If we encounter studio productions where out-of-phase information is a problem, we have a simple passive processor that takes care of it. So groove depth can be considered a constant.

I wasn't talking about out of phase signals, but left or right signals. I can see that a mono signal varying only in amplitude, side to side, will maintain a constant groove depth which doesn't vary, but stereo?

I'm not trying to make a point but just trying to understand the process and its implications for playback, as coming from a mechanical engineering perspective, I am familiar with lathes and cutting tools, and the issues involved in machining different materials. That's why I'm interested in knowing more.

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