How best to eliminate LP warps

@terry9, Yes, the Koetsu is a PITA. You do it by placing the tonearm down on a mirror with good light from both sides and your eye or a USB camera directly in front. This technique quadruples your accuracy. The stylus and it's reflection form an hourglass. You simply adjust azimuth until the hourglass stands up perfectly straight. It hardly takes any practice once you get the set up down.

This insistence on using hearing to make accurate adjustments on turntables is bordering on the absurd. Human hearing is in no way shape or form calibrated. It is like trying to use a screwdriver to remove a bolt. Wrong tool for the job. You do yourself, your stylus and your records a gross disservice by doing it that way. I do not mean to be harsh but it is important for everyone to understand this. If you insist your hearing is sufficient for the job than your ego is taller than the rest of you. You will not really hear a difference until your stylus is way out of line. 

@terry9, I for got to answer your question on USB microscopes! Sorry about that.

There are many hobbyist scopes out the $50 to $100 price range that are good enough for azimuth and VTA adjustment but not stylus wear. The real problem is positioning the scope so that it's aim is right and it has to be absolutely still or you will get sick watching the image. It takes a bit of creativity to get the job done. For an all around brilliant scope that you can use for stylus wear and has a staging system specifically for turntables the WallyScope is the one and only scope for the job and at last count it was $1250.00 which makes it a luxury item for most people.  

For $100 and some velcro you can get the job done for azimuth and VTA. It is also a lot of fun and USB microscopes can be very handy for a variety of jobs.

Yeh adjusting azimuth ..is something that takes some time to realize how many factors there is..

For example you can dive into the rabbit hole and use for example a azimuth fozgometer or like I did with a digital oscilloscope.

There is many ways/methods to adjust one and each parameter..

Ok here is the kicker if you use one of the tools mentioned above with a calibration LP disc (just a good one of those are pretty pricey in my book) you adjust it perfectly to that individual disc.

But how is a calibration LP disc manufactured? Yes you guessed it. it is manufactured as a LP is usually done. Hopefully with some more care in the setup of the lathe that includes setup of azimuth with the sapphire cutting needles on the lathe that will cut into the lacquer.

So more precise you have just adjusted your azimuth to match the azimuth that the sapphire cutting needle HAD during the initial production of the mold for your specific calibration LP disc..

If you get different manufacturers/labels of calibration LP discs they will not be perfect if you measure those. 

Why.. yes you guessed it there is still some small variance in azimuth setup from sapphire cutting needles setups from lathe to lathe and time to another time.

My approach is when knowing that is to set it perfectly straight like mijostyn have explained.

The reason is to not adjust it after a/one specific lathe cutting occasion, only.

The second reason is that all of the different albums we own has its own lathe azimuth adjustment when they're cut. So the idea is that with a straight setup you will on average over the whole collection be OK. And not be better on some and then worse on some of the others..

In assumption that the cartridge manufacturer has mounted the diamond, canteliver and so on straight..

But the super best way is to get azimuth as good as possible is using one of the tools mentioned and getting different calibration LP discs from of different manufacturers and labels and take a average then maybe you are still little better on it on average.. and probably adjusted also for deviation from the cartridge manufacturer..

Anyway that is nothing that anyone is doing maybe one individual on 2 billion people may or can do that. 🤣

But adjusting VTA/SRA is a different story and has physical properties during cutting. And depending on your stylus shape and so on there is more or less ideal ways to make that adjustment.

@mijostyn

"You simply adjust azimuth until the hourglass stands up perfectly straight. It hardly takes any practice once you get the set up down."

It seems to me that the adjusting eye or lens needs to be perfectly normal to the cantilever, which means simultaneously adjusting two right angles. I doubt if anyone can do that without an adjustable, stable platform, repeated accurate measurements, and statistical analysis.

Whereas anyone can listen to a dozen challenging, flat, LP’s and set for the ’best’ sound and take measurements. Then throw away the two top and bottom measurements, and set to the mean or the median as indicated. At least, anyone with accurately calibrated azimuth-on-the-fly and a statistical background.

YMMV

Actually, this whole discussion leads me to the conclusion that we are chasing a ghost. As @optimize notes, there are irregularities in LP manufacturing, whereas we are treating the LP as identical precision instruments that just need to be set up via the cartridge.

Instead, we should be looking for a tonearm that can be easily and finely adjusted on the fly to suit each LP as it is played. Preferably, the tonearm should have a precise measuring system built into it’s adjustment mechanism, so that these numbers can be noted on the record sleeve, and the adjustment made in two or three seconds prior to each play.

And, of course, we should remove warps and dishes from the equation, coming back to Lewm's point.