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Move End of Arc Perpendicular to Axis


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I've been somewhat struggling to understand how to create ramps using the Wire Helix tool and the Axial Sweep tool.  My difficulty seems to be determining the correct Length of the 764910257_WireHelixRadius-Cycles-Length-PerCycle.jpg.b75231ce265fb904b46501f41bf9bd24.jpg 

wire given the Radius and # of Cycles to achieve a certain vertical dimension.   Without a formula its more or less a trial and error to obtain the correct vertical dimension.  A semi-circle is fairly simple in that your cycles are .5 and you multiply the vertical height you want by 2 to get the Length.


What would be really helpful would be if the Tool Options for the Wire Helix had a Total Height option when the Wire Helix was created about Axis.

That said, SketchUP has a wonderful feature where you can Move the end of an Arc along an Axis perpendicular to the Reference Plane and easily set the height of the arc.  I'd like to recommend that FormZ add a similar feature to the Move tool so that the arc maintains it's curvature and raises an endpoint perpendicular to the Reference Plane.  This would make creating a curved helix path for a ramp a breeze.

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Oops!.  Disregard when I wrote "A semi-circle is fairly simple in that your cycles are .5 and you multiply the vertical height you want by 2 to get the Length."  That worked only for a specific set of circumstances.  My mistake. 

Edited by Paulji
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I use the scale tool in a side view to achieve this.  It should also be possible to show controls and then adjust the height of the wire helix Or to enter an exact height in the data field. I don’t have access to check at the moment. 

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Thankyou for your response.  I like that you use the independent scale tool in a side view to create a helix.  I hadn't considered that method.

I've given this some additional thought and looked at three methods of creating a helix.  In the end, I made two strange discoveries while using the Wire Helix tool. They are highlighted below in red.

First, I tried your method of using the independent scale tool.  Please let me know if your method differs from what I've described? 

Method #1 - Rotate (Side View) plus Independent Scale:

1. On XY-Plane create Arc 1: Origin (0,0,0) : X' radius (counterclockwise) to create semi-circle.

2. Select Left View from the Navigation Tools

3. Draw V-Line from Arc's endpoint. Enter desired Height: Z'

4. Select T-Form > Rotate:

  a. Select Arc.

  b. Define start point of rotation about YZ-Plane. Snap to endpoint of arc.

  c. Define angle of Rotation: Snap on Y-axis. Rotate yellow rotation symbol and snap to endpoint of V-Line (Height).

5. Select T-Form > Independent Scale:

  a. Select entity to scale

  b. Define start of scale by snapping to the start point of the arc

  c. Snap to high endpoint of rotated arc.

  d. Snap to endpoint of V-Line


Method #2 - Cylinder plus Derive Segment:

1. On XY-Plane Generate > Cylinder:

  a. Define Center Point

  b. Define Radius: X'

  c. Define Height

  d. Rotate Controls 180 degrees to create Half Cylinder

2. Select Navigation tools > Look at Face and click side face of Half Cylinder

  3a. Draw 1 > V-Line from bottom right to top left of side face. Insert Option ON.

  4a. Reshape > Reshape: Push Triangular face through Half Cylinder

  5a. Derive > Derive Segment: Select curved segment.


  3b. Draw 1 > V-Line from bottom right to top left of side face. Insert Option OFF.

  4b. Edit > Extend tool: Set Distance. Click both ends of V-Line to extend beyond Cylinder face.

  5b. Reference Planes > Define Reference Plane: Click on Half Cylinder face.

  6b. Modify > Slice: Select Half Cyliner. Select V-Line.

  7b. Delete top or bottom of sliced Half Cyliner.

  8b. Derive > Derive Segment: Select curved segment.


Method #3 - Wire Helix:

1. Derive 2 > Wire Helix: In Tool Options- Wire Helix:

    a. Check Wire Helix about Axis ON

    b. Enter X' Radius.

    c. Angle: 180 degrees.

    d. Length pop-up: Set to Total

    e. Length = Helix Height.

NOTE !!:  The formula for Length of a Helix (Helix Height)²+(2πr)²  ... however the Tool Options equates Length to the Helix Height !!  This is quite confusing to me.  Perhaps "Length" should be renamed "Height"   Any comments on this would be appreciated.

2. Select Z-Axis on the XY-reference plane axis or vertical segment.

3. For some unknown reason the starting base of the Helix is not on the XY-reference plane but is some distance above the reference plane. You must move the starting point of the Helix along the Z-axis to the reference plane with the Move tool. 

4. You can check whether the Helix height is correct with the Measure > Measure Distance tool. Set the "Also Measure Perpendicular" in the Tool Options.

By far the Wire Helix method is the quickest way to create an accurate helix for a semi-circular ramp. The other methods work fine however they involve more steps than I'd like. 

I still hold the opinion that a feature added to FormZ where the Move tool could raise an endpoint perpendicular to the Reference Plane while maintaining the arc's curvature would be useful because of its simple and intuitive.  


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Hi Chris,

Yes. When creating a Wire Helix about axis wherever one clicks becomes the origin or base point (of the controls) for the Wire Helix. 

I'd strongly suggest that this behavior be corrected so that selecting an axis behaves like the other Wire Helix tool options regarding its starting point.  The reason is simple.  There is really no way to know where you are when you set a Click point on an axis.  I've attached a short video to explain.  Whenever you select an X, Y, or Z-Axis, the axis highlights.  If you select the Z-Axis and move your cursor along that axis, the Input Palette does not change.  The Z coordinate remains 0.   If you move your cursor along the X or Y axis the Input Palette coordinates reflect the cursor movement however at coordinate 0 the highlighted axis changes to a different axis.  If you attempt to use the Input Palette to enter a 0 coordinate for any axis it doesn't execute the command, you are forced to click on the axis.  See attached.  

Since the tool prompt only asks: "Select axis of reference plane or a straight segment"  one would assume that either by selecting and axis of the reference plane or by selecting a straight segment the operation would be the same for both selections.  They are NOT.  Selecting any point along a straight segment ... even if you select the last endpoint of the segment (ie. not the initial start point of the segment), the start point of the controls for the wire helix begin at the initial start point of the segment and follow the direction of the segment.  So my recommendation is that the Wire Helix tool be changed so that if you select an axis, the start point for the helix be the 0-coordinate the axis selected.

When you select the Wire Helix along Path type, wherever you click a point along the path and the Helix controls begin at the first endpoint of the path.  The helix wire then follows the path's direction.   There should be a consistent operation between Wire Helix about axis type and the Wire Helix along Path type.  

The manual states: "The axis can be a Cartesian axis or a segment of an object"  The Cartesian axis of an custom or arbitrary plane can also be used.  The problem with using an arbitrary plane is that only the X and Y axis are indicated.  The Z axis is not. See attached. 1026711571_HelixAboutArbitraryAxis.jpg.39bf711c5a2d676c5031a078c8303e57.jpg

Would it be useful to be able to see the Z-axis?  I don't know.

In retrospect, if the Wire Helix tool only offered the Wire Helix about Axis type, then the Helix tool should have defined the LENGTH as HEIGHT.  This would have been in keeping with the definitions used with the Cylinder and Cone tools.  They ask for the Height not Length.   Since however the Wire Helix tool includes the Wire Helix along Path type, there is no way to define the HEIGHT of a 3 dimensional complex path. One must ask for LENGTH.   It would be helpful if the Manual contained a sketch describing the meaning of LENGTH via a diagram similar to the diagram shown in Kenth Agurell's book, "FormZ Desktop Companion: The Modeler with Renderzone version 4, p.42" See attached.1037033053_FormZCompanion-KenthAgurell_HelixAxis.thumb.jpg.deee707995c6aa98edd92659208df014.jpg

Wow!   If anyone knows how I can shrink these images so they don't look like billboards please let me know.

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Not that this is a complete fix, but you can set your grid snaps.  If you set them large enough, you don't have to get too finessed when clicking.

But, yes, it does appear that the controls of this could be more nuanced. 

In, my mind though, when applying to a segment, it should behave as it does.  To me, that is a tool built for a specific purpose.  When applying it to the axis of a plane, it is a little more arbitrary.  So, kind of get that too.


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