Lyrec Synchronous Motor SM 8/3 A

[leo gonzalez]

yes, hello mossboss.

i apologize for deviating the subject of the topic which was the lyrec motor itself.

i also replaced the start cap. when i got the system last year, the motor still had the original 1950s cap. belive it or not!

i found a 21uf cap that seems to be just fine for it. noise while synching decreased and it's easier for it to engage too.

i also have on my schematics those caps before the starting cap. rubbing my head asking why. i haven't put them on my lyrec.

about the direction of chip suction, havent tried that. chip suction from the front sounds like ideal but as i see it difficult in practice with the 3dII. i have the advance ball knob right in front.

we are putting a central vac system in the studio and then the variac is going to be essential. if not im gonna have to take the head out of the chip jar!

leandro.

[tubefan]

The way the Neumann lathe uses the Lyrec motor is through a mechanical low-pass filter. The Lyrec produces 120 or 100 Hz torque ripple, and this filter is tuned to filter the ripple out, so the high frequency cut-off might be in the 0.5 Hz or 2 Hz range, I haven't measured one recently. It's a mass-damper-spring system, the mass is the platter's mass, the springs go between the inner and outer cups of the bearing, and the oil film sits between the inner and outer cup and forms the damper. The Lyrec drives the outer cup via a shaft from the bottom, the inner cup drives the platter through the spring/film system.

An oil bearing with thick oil would get you some filtering, but perhaps not enough filtering. Best would be to duplicate the bearing assembly of the Neumann or Lyrec lathes (lyrec had a much heavier platter so the system was a bit different)... Or use the original Scully system, the set of belts and flywheels does sort of the same thing...

[blacknwhite]

The way the Neumann lathe uses the Lyrec motor is through a mechanical low-pass filter. .. It's a mass-damper-spring system, the mass is the platter's mass, the springs go between the inner and outer cups of the bearing, and the oil film sits between the inner and outer cup and forms the damper. The Lyrec drives the outer cup via a shaft from the bottom, the inner cup drives the platter through the spring/film system.

I don't understand the Neumann springs.

Wouldn't the use of springs introduce speed variations? When the variable-depth cutter goes deeper, won't the blank disc slow down first, and then speed back up as the spring tensions?

[mossboss]

Hey Blackie
The spring is between the inner and outter bearing cups so as to keep certain tension on them end float and all that, the film of oil gets formed as the motor rotates in some ways it acts as as a pseudo "damper" or a "dash pot"
It does not drive anything if you download flozkies schematics and look at the mechanical drawings you can get the idea
Cheers

[blacknwhite]

Hey Blackie
...if you download flozkies schematics and look at the mechanical drawings you can get the idea
Cheers

Sorry, can't find my way to the mechanical drawings of the Neumann... can you point me in the right direction? Very, very interested. I bought the "neumann manual" being sold on eBay on Cd, which shows an actual photograph of the turntable from underneath with the springs, but it doesn't explain what is connected to what; I had assumed the springs helped drive it; I didn't know they were just for keeping it centered. I see a rubber lug; guess that does the driving between inner & outer oilcup?...