I have previously used Four Small long screws to hold my Helix in place per level. One at each direction + for the four soldered-up segments.
>> I now see where this was possibly not 100% Correct/Best > Based on Expansion Humidity and the rigidity of soldered Kato Unitrack.
Instead?
As read in another Post here...
One may not only be enough but best = So at least my Helix in Four Kato Unitrack Soldered Segments can expand/detract along all four lateral axis.
Further, for side to side expansion along the 180 degree curve at each end?
I am further segmenting each 180 degree Curve into Two - 90 Degree segments....and nailing down neither.
==> Only one screw on one side on the straight.
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At least with Kato Unitrack in N Scale...Thank you.
Didn't consider it at first but Yes, I now believe one screw per level may be the best compromise.
Thank you for the discussion and shared experiences.
Mark

it was fairly easy to create 30" companion radius to the given 28" Kato Radius by cutting the Unitrack with a Razor Saw.
A further note, I first started a Helix using Kato V-16 kits but found their 19" radius, even in Super Elevation Not to be wide enough for some of my best Steam Locomotives. If you are limited in space or only to ever run Diesels or Short to Medium Steam then a Helix made from V16 kits might be good enough.
> Not yet sure about Kato/Tomix/Con Cor Bullet Trains; such as the Aerotrain or Zephyr?
> I have read that such trains may need a 36" radius.