I am sure there is a very basic answer to this, but I can’t seem to find it.

I need to draw a perpendicular line at a fixed point on a curve. There is the “Line perpendicular to a curve” function which keeps the line perpendicular to the curve, but I can’t work out how to fix the start point of the line to a specific point on the curve eg. 300mm from the start.

So if I need to draw a 500mm line perpendicular to the original curve, with a starting point exactly 300mm from the start of that original curve. The 500mm part is easy to input, but I can’t find a function to control the start point.

not sure if any of the options of _line can do this.

to find the precise point

_divide the initial curve by _length
click on the curve / arrows if the direction / start / endpoint does not match.

to draw the line

start drawing a standard _line
pick the startpoint.
use the objectsnap _PerpendicularFrom
(pick the curve again, pick the startpoint again)
now you should get a temporary guide perpendicular to the curve.

alternative to the _PerpendicularFrom Snap
you can also turn on Smarttrack, it should show a guide “onPerp” after you picked the first point.
(smartrack is a Button/field at the top of the window - Gridsnap, Ortho, Planar, Smarttrack )

check the help for above commands to get even more background info.

Thanks for the answer, but still can’t seem to set a start point on a curve.

As a work around is there a way to add a point on curve at a fixed position. I can’t seem to find that either. I could then add the perpendicular line fro that point.

Maybe search for some Tutorials about object snap ?

if you want to snap (=precisely get a point) on a curve i recommand to do some construction, like above divide the curve to get a point, then snap to that point.

alternative - you can use the
_NearSnap
with not the biggest amount of precision.
NeatSnap is a big source of unprecision, don t turn it on persistent. Use it with caution !!

Heh - on the fly this is not exactly straightforward… probably easiest is to mark the point using SubCrv > Mode=MarkEnds and give it the length you want. This can be done on the fly within the command like so, but I am not sure it is worth it:

Start Line > Perpendicular > PointOnCurve… but instead of selecting the curve, type SubCrv, then select the curve and then type in your distance and snap to the end of that sub curve.

Thanks for everyones help with this. Seems more complicated that I thought it would be. Fundamentally I think I need to learn the program better first, but thanks for everyones input.