Diagonals And Offset Tables

rwatson · Apr 15, 2014

jehardiman said: ↑

Ok, here is the solution to constructing a perpendicular finder.

Note that I have shown the construction exaggerated and on a changing curve to show how it works and bring out where a very very small error could creep in. In reality, you would not be able to measure it as long as Circle 4 & 5 are small compared to the radius of curvature of the hull which is why you need different size ones...tiny for drawings and large for the loft floor. You can construct the tool on a straight line or the radius of a large circle. Most ones for drawings are built flat and those for loft floors have depth with a gap for the batten so you can butt it right up against the sprung batten.
Click to expand...

Thanks for that diagram.

I think you may have left out important detail on 'The Tool' diagram - a hole on the centre of each 'circle' on the tool to place on the curve being offset.

I have included them as green dots, on a green line representing the frame line, to show what I am alluding to.

I have also included the orange 'wrong' triangle solution overlaid on it, with slightly wider centres for illustrative purposes only. I cant see any difference in operation for either tool, except that The Triangle has a much more convenient permanent 'pen' hole for plotting the inner point, whereas 'The Tool' will require manual matching of the dimension mark on the guide tongue.

Likewise, for the lofting floor, the two bottom corner points of 'The Triangle' tool can be shaped to be conveniently laid up directly against any guide batten.

jehardiman · Apr 15, 2014

rwatson said: ↑

I think you may have left out important detail on 'The Tool' diagram - a hole on the centre of each 'circle' on the tool to place on the curve being offset.

I have included them as green dots, on a green line representing the frame line, to show what I am alluding to.
Click to expand...

Nope, you have to use the TANGENTS, not the centers. Which is why I pointed out the possible very small error. You could strike a line from inside to outside and split the difference, but I have found that in drafting and even on full size ship lofting, the lines overlie each other (i.e. error >> 0.5mm in ~6" or 300 mm.

rwatson said: ↑

I have also included the orange 'wrong' triangle solution overlaid on it, with slightly wider centres for illustrative purposes only. I cant see any difference in operation for either tool, except that The Triangle has a much more convenient permanent 'pen' hole for plotting the inner point, whereas 'The Tool' will require manual matching of the dimension mark on the guide tongue.
Click to expand...

Again you misunderstand... the error in your method is shown in the attached graphic. You missed measuring the secant offset of the arc.

SukiSolo · Apr 16, 2014

I can verify that THE TOOL is also found this side of the 'Pond.

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Diagonals And Offset Tables

rwatson Senior Member

Attached Files:

PerpTool.jpg

jehardiman Senior Member

Attached Files:

tool2.png

SukiSolo Senior Member

Offset Tables And Lines Drawings