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How to set SRA after determining true vertical?

Here is a picture of a stylus with zero rake angle:

http://members.cox.net/nsgarch/SRA@%200.0%20deg.jpg

Since all modern styli are symmetrical in the x and y plane about the verical z axis, the tapered stylus and its reflection will make a perfect "X" when vertical (z axis perpendicular to the groove) and viewed from the side.

This condition is established by raising or lowering the tonearm pivot post. Once you find this point, and assuming you have a typical 9" tonearm (about 230 mm from pivot to stylus) then each 4 mm you raise the post from the zero
SRA point will apply one degrewe of SRA to the stylus.

A test setup is shown in these two pics:

http://members.cox.net/nsgarch/SRA%20setup1.jpg
http://members.cox.net/nsgarch/SRA%20setup2.jpg

Equipment includes:

a mini Mag-Lite flashlite,
a first surface mirror from old SLR cameras -- easy to find at photo repair shop)
a 50X pocket microscope
bean bags

Don't forget to first remove antiskate and set VTF.

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128x128nsgarch
gregadd
574 posts
 
Nsgarch- you make a convincing argument. your shovel and chisel anology could be true but they move in only one plane. the cutting lathe moves in two planes. I believe your analogy would be true if the cutting head were like a jackhammer titlted forward. Then each groove would be cut from the top with the resulting angle of the jackhammer. Not so when the cutting head is moving in two planes.

Like I said I definitely hold the minority opinion.
BTW thank you for such a gentlemanly rebuttal.
nsgarch's avatar
nsgarch OP
2,524 posts
 
Greg, actually, the chisel, or spade-shaped cutter, can only move in one plane. It's a plane that lies across the two "spade" edges. It moves diagonally (up left or right or down left or right) but remains constrained on that plane. It's movement is created by two electromagnetic drivers on each upper corner of the cutter blade. It can cut a signal (wiggly undulations) into either groove wall while cutting a smooth groove wall (no signal) on the other side, Or it can cut signals, even different signals, into both sides of the groove at the same time.

I wish I could find a decent diagram somewhere to post. If not, I'll try and whip something up and post it.
gregadd
574 posts
 
cutting in one plane would dig a hole. to make a 45 degree grooved trench you have to move in two planes n'est pas? maybe I stated it wrong.
nsgarch's avatar
nsgarch OP
2,524 posts
 
Greg, yes you simply stated it backwards. The cutter head stays in one plane but moves in two directions.

Imagine you have a nickel on your desk. Imagine that's the cutter head looking from the front. You put your finger on the nickel. You push it up and down, left and right. But it still remains in one plane -- the plane of the table.
gregadd
574 posts
 
I am thinking the cutter head acts more like a plow vibrating fom side to side. thus the record rotates under the cutting head as the head plows ahead vibrating either to the right or left, thus there is no downward cuttiing motion. that is why I prefer the vertical position.
I think I 've made enough empiracal arguments it's time to do some research.
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