Creating a Frustum of a Cone with absolute measurements.

[northcoastrat]

I am having trouble creating the exact cone frustum I need. I have been trying to create a circle, either extrude it or use the follow me tool to make a cylinder, the re-scale the upper radius to make it smaller. The scale tool uses a scalar (relative value), however it would be much more convenient to use the absolute radius measurement that I have.

I am modeling the structure of redwood branches as a series of cone frusta. Each branch is composed of many frusta of precise but varying sizes and orientations. My overall goal is to create a script that can read x,y,and z coordinate data and radii for the base and top of each frustum and output a 3d model. I have minimal programming experience so any help on how to best approach the problem would be appreciated. I hope this makes sense.

[TIG]

The native Scale Tool takes a float by default - so 0.5 will scale by a half.
If you know the original size of the circle you can calculate the scale-factor needed to resize the frustum end to a required size... If you are eventually looking to code this process then the 'scaling transformation' you'll have to invoke will need to be derived this way...

BUT the native Scale Tool WILL also take dimensions - you must remember to add a units suffix...
So if you want to Scale something to an exact dimension type it in with say 'mm' afterwards...
e.g. you can use 50mm to scale it to be exactly fifty mm [irrespective of its original size], whereas using the unsuffixed 50 it will be made fifty times bigger than it was before !

[Jean Lemire]

Hi folks.

See this SU file for ideas:

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Cone frustrum.skp

[Dave R]

As to drawing the frustra in SketchUp, you could take advantage of Cardinal Points and the Move tool. You'd end up moving the points the desired change in radius. So if the radius is 1 inch and you want the new radius to be 3/4", move a cardinal point 1/4".

Maybe you could utilize that in a script to do what you need.