sketcher-help

[ProMan]

I have some problem with sketcher.please help: 1-How can I snap an end point of a line to a spline? I can only snap to lines, arcs and spline endpoints (not to the curve itself) 2-i also want to add a tangent relation between a line and a spline but I cant. (again not at the end point)

[JoeVarghese]

Hi, I hv not tried this. Probably, u can create two sketches. 1. Ur spline in the first curve. 2. Take referance of this curve in the second and both ur problems may be solved.. HTH Joe

[ProMan]

not the second one

[DavidButz]

Depending on what else controls your situation, there are a few ways to deal with this. For example, create the spline as a separate curve, as suggested. Then create a second curve, do a Use Edge to copy the spline, place a Sketcher Point on the curve, trim away the curve to one side of the point, then create a line tangent to the end of this second truncated version of your spline. Good luck, David

[DavidButz]

After thinking about it for 10 seconds, I went back to check; I had no problem creating a line tangent to a spline directly in either situation: starting at a point on the spline, or starting from elsewhere and coming to the spline. Did you pick the spline as a sketecher reference (Sketch/References) before sketching the line? David

[ProMan]

thanks David, i gave it a shot once again and had no problem DRAWING a line tangent to a spline (which i brought to another sketch using "create an entity from an edge"), but if the line is not DRAWN tangent and you want to add tangent relation after drawing the line you cant! this is ironic.

[DavidButz]

It's really not too suprising that what you are looking for is not available. Unlike the case of line-tangent-to-circle, there is an indeterminate number (including zero) of possibilities for tangency to a spline from a given point. Furthermore, with the constantly varying curvature of a spline, one would tend to get rather unexpected, probably unwanted, results because the tangency point would often move a considerable distance. I don't think the other option (maintaining the length of the line and swinging its end) would be much better. One technique that can add some flexibility is to place a sketcher point on the spline and a centerline through the point tangent to the spline. Then you can move the point to swing the tangency projection, and start your "real" line away from the spline on the centerline. David

[DavidButz]

Forget the sketcher point in the last suggestion; you can just make a tangent centerline and swing it by grabbing it directly. David

[ptc-1181807]

Actually, there's several ways to do this. If the spline exists, you can snap lines to the endpoints, and it will allow you to pull the line until it shows the tangent constraint. If you place the line and it isn't tangent, you can modify either the spline or the line afterwards and add the constraint. Also, a neat way to adjust the spline is to select it, right-click modify from the pop-up, and select the bottom left box from the dashboard. Hovering over the correct box will gove the message: "Switches to control polygon mode. Control points drive apline definition." when you select this, you get a bunch of purple, phantom lines, the white nds of which (NOT points on the spline itself) can be pulled to modify the spline. While in this mode, you can then add colinear or tangent (or perpendicular, etc.) constraints to any of the purple lines including (and especially) the spline ends. I stumbled across this recently while creating sketched splines in the "area control" thread I posted, and it's a great way to control things. Good luck.