Tonearm mount on the plinth or on Pillar ?

This statement is unexpected and seems counterintuitive, at least to me. Could you describe the tables measured? If you've seen photos of Halcro's TT101, do any of the measured tables reflect that level of isolation?

Could you please list all the tables, arms and cartridges and what they were sitting on Atmasphere? Photos would be good here.
And can you upload the frequency print-outs for each one?

Good that for you it's easy task. I think that your measure is not exactly what happens during playback because you did not use a recorded LP and we want to know what it's happening during playback in real day by day listening conditions.

Now,: speakers playing loudly?.  95 db, 90 dbs, 100 dbs?  why only playing loudly?  We need to have information as day by day real as we can not over diferent conditions.

We ran this experiment using our lathe. The reason was we wanted to install a 12" Triplanar on the machine so we would not have to move the lacquer to a different turntable once in place- to test, simply place the tonearm on the cut.

The easy way out was to install the arm on a pillar. We found out really quick that was not the best move. Now you have to understand several things here- first, the lathe is mounted on an anti-vibration platform that is rather massive, designed specifically for the lathe. That in turn sits on a custom table with adjustable points for feet. The entire arrangement has to be by definition rather dead, else sounds in the environment can affect the cut. What we discovered is that the arm mounted on the pillar was giving us more noise than the same lacquer played back on a Technics 1200 sitting nearby.

IOW, it was not suitable for actually telling if our cut was truly silent, set up in this fashion.

By coupling the arm directly to the plinth in which the platter bearings reside the issue was solved. Apparently even though a very effective anti-vibration platform was in use, it could not prevent the arm from moving in a different plane from that of  the platter (which is the failing of pillars generally speaking, per my first post above, should anyone care to understand the engineering principle in layman's language). This ultimately required that we machine an arm mount that mounted to the plinth rather than the platform. We made our measurements using the phono equalizer in a Tascam mixer board, read by an Tektronics 465 oscilloscope. I hope this gives you some idea of how easy it is to measure this!

As to sound pressure- we get about 90-95db of noise going on when mastering. The vacuum system is enclosed in its own chamber, but still makes noise when in operation. 

Now I understand this is bad news for some and as a result there will be those that think that somehow these principles don't apply to their machine. It is true that I did not make the measurements on anything other than our lathe, but if you think the engineering principle is somehow different, or that the lathe is somehow noisier than a conventional turntable (while at the same time somehow perfectly capable of turning out cuts that are so quiet that essentially the playback electronics are the noise floor no matter how quiet) you would be mistaken, check with Mr. Occam on that one.

It is of no consequence whatsoever that we used a silent groove for this test. A groove with modulation will still experience the same noise and colorations if the arm is anchored to a point that is able to move with respect to the platter.

This is not a difficult principle to understand; IMO the resistance to it springs out of the cost of some of the machines guilty of this engineering flaw- its an inconvenient truth (especially when you consider how much harder it is to make a plinth for the platter and the arm).  FWIW, the lathe is not a cheap machine either; if we were to put it up for sale in its present state (functional tested used stereo cutting system) it would be going for over $30K. If it were new it would be pushing 6 figures. Out of necessity it has far more precision in its construction than most turntables.

Now I want to make something very clear. I'm not saying a system with a separate pillar can't sound **good**. What I am saying is that if the arm mount is integrated into the plinth it will be lower noise and have less coloration, i.e. it will sound **better**.

I'm not sure that the cutting process tests can be transposed to the playback field.
After all.....you use direct drive and linear-tracking arm in the cutting process but you prefer to use belt-drive and pivoted arm for your playback.
Seems counter-intuitive to me......

Sorry Atmasphere,
I missed the point about the Triplanar and the Technics 1200.

I don't see how attaching the tonearm to the plinth can affect the 'noise'?
Surely the 'noise' is a function of the isolation, the tonearm pod mass, fixity, density and material selection as well as the tonearm rigidity.
There are some who are not fans of the Triplanar with regards to its performance in these areas.....but reaching conclusions about 'noise' when using different tonearms does not seem paticularly scientific nor conclusive.

Atmasphere thanks for that info. Something is not clear to me. Maybe it's just me. Did you actually permanently mount a tonearm to the lathe ?
     
You said.

What we discovered is that the arm mounted on the pillar was giving us more noise than the same lacquer played back on a Technics 1200 sitting nearby.

Just so I understand, you attempted this in order to make your business of cutting and testing playback more effective and efficient. I can understand that, and you have discussed the Technics SL1200 with Grado cart in another thread. Now you said in regards to the tonearm mounted in the pillar next to the lathe. 

IOW, it was not suitable for actually telling if our cut was truly silent, set up in this fashion.

So it generated noise, which in your line of work is how you pass or fail the discs that were cut. This is my understanding of what you are saying.   

But then you said.

By coupling the arm directly to the plinth in which the platter bearings reside the issue was solved.

So. Are you referring here to playing the cut disc back on the nearby technics sl1200 in your work environment ? or did you actually mount the tonearm that was on the pillar directly to the lathe plinth?

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btw - thanks for the great information on my question about the angle of the disc cut.

Pani (OP) sorry, but if I may digress for a moment...

It is consistent with the info I have received from talking with people that do this work over the years. The very important part of the information to me, is that the angle of the cut varies. The angle that the cutterhead is placed at when a disc is cut, results in an included angle in the final disc. This included angle must be duplicated with the reproducing stylus or distortion will result. I think everyone is ok with this right statement ..right ?

Now Halcro (Henry) said

I'm not sure that the cutting process tests can be transposed to the playback field.

The angle of the cut varying on the cut disc; applies directly to playback of the actual records we buy.   
 
Let us think about something.  
We all own multiple copies of favorite pressings. Have you ever noticed how lps from the same era, country and plant can sound different ?
The stylus life as Atmasphere said is based in hours. And when it is replaced it is never set up exactly the same again. And the cutting stylus puts that included angle in the disc. If that angle is not duplicated on the records we buy, you will get something on playback that is different than what was originally cut.  And it can vary with record. So to those that like to use a USB microscope to set up VTA/SRA .....?  thats another thread discussion. It does bring up importance of correct VTA on the fly (imo).  

So what .... 
To me it means the skill of the lathe operator is very important.  Imagine that same music being done on different brand lathes, different countries, different eras....
All the great engineering work that was done to capture the original recording on tape or file;  can be lost if the guy/gal doing the cutting is still learning how to do it. Sorry to ramble. Fascinating stuff.