Ordering blanks with rocker adjustments

General Discussion
1

 

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**I've been ordering blanks with the natural rocker adjusted for a while now. This saves time when roughing-out the shape. But I've never been "schooled" on this aspect of shaping, so there are some gaps in my knowledge. My first question has to do with ordering rockers from a dissimilar blank. For example, I recently ordered a 9-4B with the rocker from the Clark Foam 9-5S (CF 9-5S BC). I understand that “BC” means “bottom centered” which to me means the bottom midpoint of the 95S rocker is indexed on the bottom midpoint of the 94B blank. Is that correct? What I don't understand are the terms like “deck matched from nose” or “ adjustments indexed to deck”. When and/or why would you make this specification? **

**Also, can anyone clarify a compound adjustment like 10'2"B -1/4" N -1/4" N24" + 1/4" T24" ? (noserider blank?) I understand it to mean “on a 10-2B decrease the nose rocker by 1/4” from natural starting from center, and then then decrease the nose rocker again by 1/4” starting at 24” from the nose, and finally increase the tail rocker by 1/4" starting from 24" up from tail.” Is that nose rocker curve so different from “-1/2NR”? **

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**Mechanically, how do they adjust rocker at the blank factory? I find more excessive stringer material on the bottom of my blanks than on the deck, so it would seem that the stringer with the pre-cut rocker is matched up with the blank's deck, right? **

 

 

 

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Deck rocker is where it starts

3

Adjustments are indexed on deck-side? So, -1/2"NR drops the deck rocker 1/2" at the nose, with a corresponding drop in bottom rocker by the same amount since there is no change in thickness? I know that what it says in the US Blanks Catalogue but it seems counter-intuitive. Why don’t they index the bottom? I’m thinking it may have something to do with how the rocker (deck and bottom) is cut into the stringer. Is anyone familiar with the process? 

4

TP;

This might help explain things a bit more.  In your blank:

10'2B 1 1/4" N translates to a 1/4" drop in the Nose understood to

be at 0", or the end point of the curve.  N24"  - 1/4" means that the flip

is taken out of the curve of the rocker in the nose by reducing the curve

at the point 24" up from the nose. (Or you could say that the curve will be

 "more gradual" in the first 4 feet of the blank on the bottom.  In the tail, this

means that the rocker is increased at the 24" mark creating a flip in the tail

from this point.  This is different from increasing the rocker at T(at 0") + 1/4"

which will work differently that an old school-type noserider. 

There is a slight difference in the deck rocker with these mods, but the stringers

are machine cut (usually CAD) so the difference in deck rocker numbers are just

to maintain the blank foil as the foam is flexed and glued to these dim's.  In blanks

that get softer the deeper they are cut (read US Blanks), deck rockers are important

 in machine cut blanks as most material is removed from the bottom to generate the

 thickness required and minimum foam removed from the deck for foam strength. 

You can see the deck rocker changes by changing the numbers, curve, etc. on programs

like Shape 3D lite on the bottom of a board and then viewing the deck rocker numbers. 

Always measure any blank, custom or otherwise if you are hand shaping as the can move

around during the gluing process.  Rocker sticks for bottom & deck have been discussed here

a lot lately and can really be useful.

I hope this helps, just my 2c! 

5

 

Thanks SD and ST. I understand how rocker adjustments increase or decrease the acceleration of the curve on either end. From the 2011 USB catalog (when all else fails, read the instructions...) “Unless instructed, all rocker adjustments will be made from the center of the blank.” To me, that means the curve is changed from the center of the blank to either the nose or the tail by raising the endpoint the prescribed amount. Continuing from the catalog “If the adjustment is made from a point other than center, the adjustment point will be part of the description.” To me that means the curve is changed from the point specified in the description (24” up from tail in our -1/4TR24 example).

So when the CAD guy adjusts a rocker profile for a stringer, he does what I do in AKU. He sets-up the bottom curve first and then pulls the deck line up or down to conform to the blank's thickness. He uses the adjusted profile to cut the stringer and then the stringer is glued into the blank flush with the deck. Am I close? Holy crap, how do they maintain the correct rocker when wedge stringers are used? 

 

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Blank rockers are indexed from the deck because they are glued top up.  Nonetheless, just like fruit the sweetness is in the bottom.