Scaling a spline

Caspar

I'm trying to scale a spline (and image) about an origin/base point so that the red point of the spline passes through the yellow point. I'd like the spline and image to resize about the origin without distorting when I subsequently move the yellow point. Can't think of a way to constrain the spline or image to achieve this!

Jake_Rosenfeld

It's possible that the Measure Distance custom feature could help you here:
https://cad.onshape.com/documents/572b968ce4b07aad125dbaaf/v/08093fef6c4d4f330f24dd19/e/b40df94c5081948fe8195e81
This custom feature lets you pick two entities and stores the min or max distance between them into a variable.

The workflow could be something like:

1. Extrude a surface from your sketch
2. Use measure distance to find the distance between the extents of your (now extruded) spline
3. Use measure distance to find the distance between the two reference points
4. Scale with a scale factor of #DesiredDistance / #CurrentDistance

Then you can change the original sketch and it will always update accordingly.

How to use custom features (see 'Start Using Custom Features' video):
https://www.onshape.com/featurescript

Part Studio variables:
https://cad.onshape.com/help/Content/variable.htm

Jake_Rosenfeld

@Caspar

You can dimension the image using the standard dimension tool on one of its bounding box edges, but most likely you will have to redraw the spline (as it will not rescale with that dimension).

If you're happy with your spline and do not want to redraw it, you could leave the sketch how it is, extrude it (either as a surface or a solid) and then use the 'Scale uniformly' option of the transform feature:
https://cad.onshape.com/help/Content/transform.htm

Caspar

Thanks Jake
I was hoping that I'd be able to scale all the elements between two defined points, not dimension the sketch (or apply a scale factor to the surface) as this would only be approximate and wouldn't update if other elements of the drawing are moved.

I also tried offsetting the spline but couldn't select the top of the vertical line as the 'through' point.

Jake_Rosenfeld

It's possible that the Measure Distance custom feature could help you here:
https://cad.onshape.com/documents/572b968ce4b07aad125dbaaf/v/08093fef6c4d4f330f24dd19/e/b40df94c5081948fe8195e81
This custom feature lets you pick two entities and stores the min or max distance between them into a variable.

The workflow could be something like:

1. Extrude a surface from your sketch
2. Use measure distance to find the distance between the extents of your (now extruded) spline
3. Use measure distance to find the distance between the two reference points
4. Scale with a scale factor of #DesiredDistance / #CurrentDistance

Then you can change the original sketch and it will always update accordingly.

How to use custom features (see 'Start Using Custom Features' video):
https://www.onshape.com/featurescript

Part Studio variables:
https://cad.onshape.com/help/Content/variable.htm

Jake_Rosenfeld

I should also mention @konstantin_shiriazdanov 's "Measure Value" here.  It has additional types of measurements besides distance and is very useful:
https://cad.onshape.com/documents/77baa8153589a7fc5f289829/w/cffd0f2a7077380d5378a885/e/d3174bf5315e6aafcb889367