And what does that radius 31.1 at 18inch off tail mean?

Thanks a LOT. this is giving me a big headache…

EDIT: i want some curvature in the back half of the board, but i dont read in boardcads help files whether the line needs to be higher to represent more curvature, or whether curvature line must be very curved at the last half of the design. IE: last 36 inches, the curvature line is pretty flat. That is wrong right if you want curve in it, right? How can i do this?

Keep in mind that these programs are based on algrithisims that create a foil flow between three points. The idea is to use “guide points” to indicate the desired flow, but not hard “points”. This will allow the program to create the desired flow. To modify that flow, one would use the tangent curve modifiers to “stretch” and change the flow of the curve to closely match the desired flow near or on the guide point markers. If you insert a bunch of hard points, your flow will become choppy, and not the curve your looking for.

I wasn’t questioning anyones intellgence, just wanted to make a point that sometimes its difficult to make the curve hit all points. Sorry if I made it sound any different than that…

Ken, no worries, i didnt take any you wrote as an insult or whatever!!

You wrote just technical stuff.

Do some people argue that it is better to cut and howire your own rocker instead of using a computer based design? What programs do the pros use? I mean, Rusty and Merrick. what program do they use? is it 3D?

I use a turbo cad program to lay out the rocker profile for the hot wire. Because it is a 2-d design, all is pretty simple…no need for any 3-D type programs. I just do the design and save it as a DXF file, and let the program determine the tool paths for the cut. The hot wire machine is technically a four axis machine, but in reality is a 2 axis machine.

When using the APS3000, I use the machine version of the APS program. The APS, BrdCad, and Sape 3-D are very similar programs, but do have some suttle differences. I am looking to upgrade to either Shape 3-D or another program that is in the works, which will improve the toolpaths for the cutter.

it may or may not be possible to connect a set of measurement point with a continuous curvature through the control points, atleast not with a small set of control points. If you add more control points that may only make it harder… We do have plans for fitting a curve to a set of guide points to the smallest error possible, but it’s going to be a while before it is in place. The discontinuity you have in the center can be fixed by either: 1) extending the center tangent 2) extending the nose tangent 3) extending the nose tangent 4) rotating the nose tanget. Thus you have quite alot of flexibility to fit the curve to the set of points.

A higher curvature graph means higher curvature, so yeah, you have some accelerated curvature in the tail, but only the last few inches. Extend the tangent at the tail to make it influence the rocker further from the tip of the tail. The radius is the radius of the rocker curvature at the given point in the selected unit. So 31.1" means that the rocker at that point describe a circle with a radius of 31.1" at that point. Atleast that’s the idea and the math behind it though it’s hard to test it practically…

Hope this helps.

Bdw. since BoardCAD is a Open Source Project, if anyone want to give us a hand with extending the help material, write tutorials, tips and trick or (even better) a few lines of code, please let us know. Even suggestions for future improvments and bug reports are appreciated.

Could you help me out with the board in the pic? You say i can fix the discontinuity - and i tried that, by extending the tangent on the left side of the centre, it just lowers the rocker at the tail, where my points dont match. so it worsens the situation [read: lowers rocker]. my naked eye does not see a lot of objection to a disconituity at the center curvature. It is nearly flat, so how can my curvature change on two sides of a point that lies on a near straight line? i dont see or get it.

i cant extend the nose tangent, for that rocker is good. so…

What do you mean by rotating the nose tangent?

t: it may or may not be possible to connect a set of measurement point with a continuous curvature through the control points, atleast not with a small set of control points. If you add more control points that may only make it harder… We do have plans for fitting a curve to a set of guide points to the smallest error possible, but it’s going to be a while before it is in place. The discontinuity you have in the center can be fixed by either: 1) extending the center tangent 2) extending the nose tangent 3) extending the nose tangent 4) rotating the nose tanget. Thus you have quite alot of flexibility to fit the curve to the set of points.

A higher curvature graph means higher curvature, so yeah, you have some accelerated curvature in the tail, but only the last few inches. Extend the tangent at the tail to make it influence the rocker further from the tip of the tail. The radius is the radius of the rocker curvature at the given point in the selected unit. So 31.1" means that the rocker at that point describe a circle with a radius of 31.1" at that point. Atleast that’s the idea and the math behind it though it’s hard to test it practically…WHICH IS WEIRD, CAUSE AS YOU CAN SEE AT 18 INCHES, NOT A LOT OF CURVATURE IS TAKING PLACE. WHEREAS AT 6 INCHES OFF TAIL, THIS NUMBER IS LOT LOWER, YET THE CURVATURE IS GREATER… SO I DONT GET IT. WHAT DO I MISUNDERSTAND OR MISREAD?