@Alex,

Thanks a lot for the photo and explanation. I now fully understand what the two pin means.

@antss I'd eager to learn and explore all possible solutions.

If I have conservation, my only concern is:

If the distance between the bit and the line connecting the two pins is fixed(we call it

*A*), the setback of the cut slot to the edge depends on the shape of the curve. If it's convex, the setback will be shorter; if concave, longer. And the more curvature, the more difference.

As the change of the curve is consistent, I have no way to change the distance

*A* accordingly. Therefore I will end up have a slot that never parallels to the original curved edge.

PS. I told a lie that I actually need to have the slot 6mm off the edge, in lieu of 30mm. So precision will be required and freehand is not an option here.

Can I summerise:

Two pin method give bests control, but is more suitable for a curve with unchanged curvature, when precision required.

@Michael Kellough @Gregor, Thanks, I will go for the Lee Valley one.