Is there a standard way to measure rocker and if so what is it?
This was taken from Surfline's How To Shape guide: "You can use an aluminum beam to measure rocker by putting a pencil dot on the stringer at the center point of the board. Place the beam lengthwise down the stringer and measure the nose and tail rockers with a T-square." Make sure to balance the beam vertically (on edge) so that it won't dip towards the ends, and also make sure to measure with the T-sqaure held vertically rather than perpendicularly to the blank.
That's great but how do you get consistant results? It seems to me that those numbers would be completely dependant on how the board was sitting in the racks. Even if the racks are level with eachother the thickness of the blank and its position on the racks could make the measurements vary greatly. Any idea how to make this more consistant?
AWL, You push down with a finger on the rod at the center line.
Rocker measurements are a tough call. I've set the board belly down on a straight edge, let it find it's own balance point and measured up from the edge. Of course, a glassed board with fin(s) and/or box(es) will balance differently than an a shaped blank in progress. Board thickness taper and how it sits on the racks will affect the balance point if you try to measure belly up. Once you figure out a way that works for you, stick with it and don't trust what the shaper has written (if anything) on the stringer - remeasure using your method.
Thanks for the help guys, I appriciate it.
There is only 1 line and 1 line only that is tangent to a point on a curve. If you put the straight edge on the mid point, it does not make any difference how the board is tilted, your measurements will be the same.
Lee is correct... the problem I've had is that the straight edge doesn't necessarily balance level at the mid point by itself. That's where I get into trouble... If I force the straight edge to a level position at the midpoint, the thickness and positioning of the blank on the racks becomes an issue when measuring at the ends. What I mean is, if the tail thickness is increased by say 3/8" along the deck, wouldn't that alter the "rocker" measurement when taken from the bottom with a straight edge? Or if the blank is shifted forward or backward on the racks, wouldn't that affect the height at various points along the bottom if measured from a level straight edge? To be honest, I'm not that technical of a shaper that it would make much difference but in theory???
If you hold the beam on the midpoint, the measurements will be the same regardless of the "angle of the board". Of course if you shift it too much the beam will slide off the point and then you are screwed. You can bungie the thing in place or just rock the blank until the beam balances. The only reason I level the beam is so I can use two hands for other things. That is the beauty of a rocker jig like Pleskunas'. Just get a long piece of aluminum stock, drill holes every 6 inches and insert dowels. I hold them with set screws. Its still pretty crude and there is a lot of eyeballing. If I can get it within 1/8", I'm doing pretty good. I use the jig more for reference than a "tool". I just don't make enough boards at the same length, rocker, and design to try and get it better than 1/8".
Bagman showed me the lazer marker trick the other day. It works like a charm. Just measure where the little red dot hits the tape at either end of the board and subtract the thickness of it's height off the bottom of the board and you're right down to the last 1/128". I have a 12 foot 2x2 that's dead straight that I use. I just mark the center of the board and go from there. That's accurate enough for me. Gone Surfin', Rich
Sort of shedding light on the whole problem eh? I like it!!!!!