controlling arc length of a sweep

[kgatzke]

Why have you made this so difficult to accomplish?

I want to control the length of a sweep defined by a path consisting of a single arc.  I want one end of the arc to remain fixed.  I want the other end to move towards and away from the fixed end ALONG the arc so the radius remains fixed.  I tried parameterizing the arc length.  I can only get a reporting parameter.  I tried reference planes controlled by an angle parameter.  I got a constraint error.  I tried reference lines.  At first the parameter would always move the pinned line (really?) and then I followed the advice of this post but the arc hops around (at least the radius remains the same).  I tried aligning the fixed ends of the arc.  I got an overconstraint error on the sketch.

There has to be a way to do this.  Your programmers aren't so daft they concluded no one would ever want to control arc length.

SO HOW DO I DO THIS?

[BIM.Consultant · Accepted solution]

Check attached family. If you need any clarifications please ask.

[Alfredo_Medina]

I think @kgatzke wants to drive the arc by the length, not by the angle. Maybe the family requires the addition of a formula that receives input for the desired length, and, based on that length, the formula outputs the required angle.

[kgatzke]

Angle works for this use, but length would be better since it gives me something that can counted towards material takeoffs if I needed to go that route.  I don't in this instance.  The angle method described above works, though not with the subtended angle.

There's a trick, though.  I was having constraining problems because I kept trying to align the endpoint of the arc to the line/plane/etc. which resulted in constraint errors.  I tried extending-to the plane and that worked parametrically.  I did not expect that or try it sooner because I assumed extend-to was a one time thing and wouldn't stay joined.

[Alfredo_Medina]

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@kgatzke wrote:

Angle works for this use, but length would be better since it gives me something that can counted towards material takeoffs if I needed to go that route.  ...

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OK, so just in case you need to control the arc by the arc length, this is how it works:

 You enter a value for the desired arc length (AL) and the formula calculates the angle (B), as shown below.

The formula for angle B is = AL * 180 / ( pi() * R )