A few years back every other post on this site seemed to be about the spine or "spline" of a rod blank. Today this topic has been abandoned in favor of the best guide spacing, right down to the millimeter.
I have never seen any credible, objective tests comparing the distance or accuracy or ANY performance feature of completed rods with differing spine alinements or guide spacing? Are these subjects matters of faith rather than proof?

There has never been any data to back up the idea that spine has anything at all to do with casting accuracy or distance. There has been much data to suggest otherwise, however.

Guide systems, spacing, etc., indeed have something to do with casting distance. Of course, at some point, there is a maximum distance that a given rod can achieve with a given casting weight. In my own work, I've found if you take any of the modern guide systems and tweak them about as well as you can, you won't likely find more than perhaps 1% difference in your maximum casting distance between the various systems. There is more to casting than just overall distance of course. Different systems may handle different line types better, or be more suited to a particular fishing style. I think that's where most any difference you'll find will be.

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There are the mass mfg's of rods for the market and close is good enough for them when it comes to building so they use the straightest axis vs the spine key word is close then you have the builder that looks to build better balanced rod so they take the time and find the spine and start from there depending on the type of rod they set the spine to closely match the rated action/ power of the rod making a well balanced rod that is hand stable so it doesn't torque in the hand left to right when fighting a fish or using heavy weight lures keeping angler fatigue to a minimum.
Then comes the guide placement with the new tech for guides has changed the old norm of cone of flow that worked for most and is still used for low end mass produced rods the higher end rods are changing to the new concept use of guides smaller and more running guides along with going to spiral wrapping casting rods all this is is about taming the line flow from the reel out through the guides achieving flat straight line flow and improving casting distance and overall weight of the rod.
guide placement done with general layout worked but there is the want to be perfect so comes in the load test for final placement to achieve the best handling rod you can build.
you can use all the different guide placement data and get close including the new Gps system and you will be close to perfect but in the end a load test will give you the exact or perfect guide placement most want to get, and you achieve the rod that is balanced gives the best casting distance and minimal user fatigue.
So with all this said the data for building rods changes from blank to blank and builder to builder with the use of guide choice the
Data as to what is best is minimal at best as there are no 2 rod that are the same close but still have small differences, that is why for mass produced rods close is good enough, vs hand building one at a time achieves the best results. with the choice of parts you choose to use

The best day to be alive is always tomorrow !!
Think out side the box when all else fails !!!
Wi.

THis is a post I made sveral years ago after we test casted 4 same model blanks with 4 different guide layouts:
Test CAsting Results
By Billy Vivona on Tuesday, April 24, 2012 at 1:00pm

Thanks to all of the 25 guys who showed up Saturday morning/afternoon for this event, I hope you all had a good time and learned a little bit in the process. I had a great time shagging flies for a couple of hours, lol. Good selection of food, lots of blanks and rods to pull on, and good company, gorgeous weather – couldn’t have asked for a better day.



Blank: Fiber Star composite 1266 10’6 2 piece ¾ - 4oz Butt: .65 Tip: 9 weight 6.5oz

Set ups: modified COF, SV Concept, K frame concept, LC Low Rider

Lure: Tennis ball with 2oz sinker stuck inside = 4oz



Builders: SurfisherMike & Surfmaster250 collabrated on all the guide set ups and spent a few weekends casting each one to find what they felt was the proper set up to maximize casting distance while still feeling “right” when fighting a fish.

Casters: SurfisherMike, Sudsy, Charra, JohnScag – each caster made 20 casts, 5 with each set up.



Results

- The LC set up as expected threw about 7% less than the other 3 set ups. This was set up similar to the

St Croix mojo factory rod, but we put the stripper 4” further away from the reel seat.

- The other 3 sets ups were within 1.25% of each other

I've been wanting to post this so here goes. With graphite golf shafts we used the bearings in pvc until John Kaufman built a laser light to fasten to blank tip Having blank secured in frequency clamp (generally 5") one would twang the shaft parallel and watch the laser, as the blanked slowed an oscillation would occur. By rotating the shaft in small increments the light would flow perfectly, exposing the Spine or hard side. I gave this a try using my AT Power Wrapper. Frequency equipment still being in storage. Well I was able to locate the spine using this method. FYI

The thing is, so what? The lever arm effect of the guides trumps any spine effect under load. And there are other factors more important that spine in terms of what we actually do with a rod.

You may also find, and likely will, that with guides mounted off-spine, you can repeat your frequency test and the rod will no longer oscillate on the same primary axis.

And there is always this: [www.rodbuilding.org]

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Phil,
I generally do both - i.e. the spine check and the straightest axis check.

About 9 times out of 10 - they are at the same location on the blank.

But, suit yourself.

Be safe

A rod's performance depends not only upon its components and construction but upon the rod's user, the type and size of the reel being used, the diameter and stiffness of the line being used, the weights being cast, and the size and strength of the targeted fish. A custom rod builder will identify these requirements and make the necessary compromises to create the "ideal" rod for its specific use.