How to Create Paraboloids With FreeCAD 0.17 for 3D-printing Solar, Antennae, Microphone or Other Projects

Introduction: How to Create Paraboloids With FreeCAD 0.17 for 3D-printing Solar, Antennae, Microphone or Other Projects

This Instructable will use FreeCAD's v0.17 new tool for drawing parables in sketches.

There are ways to do this with older versions, but are far more troublesome than the way I show here.

Step 1: Install and Run FreeCAD 0.17

Download and install FreeCAD 0.17 following the instructions in this link:

Once v0.17 is installed, open it and click "create a new empty document."

Step 2: Create a New Sketch

Select the "Sketcher" toolset from the drop down menu and click the "create new sketch" button. FreeCAD will then prompt for the sketch plane orientation. I chose XY for this drawing.

Step 3: Select the "Arc of Parabola Tool"

Select the "Arc of parabola by focus, vertex and endpoints" from the conic curves drop down button and click it.

Step 4: Select Your Focus Point, the Vertex and the Endpoints Coordinates

First click will set the focus coordinates, second click will set the vertex and the last two clicks the two endpoints (you can change the coordinates of all of the points later.)

Step 5: Set the Distante From the Focus to the Vertex Points

Using the horizontal distance tool, set the distance from the focus point to the vertex of the parabola. In this case I want the focus point to be at 20cm from the vertex.

Similarly, using the vertical distance tool, I set the vertical distance from the vertex to the endpoint at 150mm for a 300mm dish. If this were a solar reflector, it would concentrate a power of about 75W at a ratiation level of 1000W/m2.

Step 6: Adjust the Other Endpoint and Fully Close the Sketch Drawing

Set the other endpoint on the horizontal axis and then, using horizontal and vertical lines, close the drawing.

In a later step, I will perform a revolution to create a solid, so I only draw a half of the parabola. If it's not a closed figure FreeCAD will complain with error messages.

Leave the sketching mode by pressing escape or clicking the close button on the left panel.

Step 7:

Select the recently created sketch and then click the "Revolve" tool from the "Part design" menu. FreeCAD will complain with an error, reporting that first a "body" must be created. Select the sketch in the left panel and click the "Create a new body and make it active" button from the "Part design" menu. Then try the revolve tool again.

Step 8:

In the left panel check the "From different parts or free features" option and then click the sketch in the area just above the options. Then click the "OK" button.

In "Revolution parameters" select "Horizontal sketch axis" and then the "OK" button again.

Step 9: Now You Have a Reversed Paraboloid

Of course, you could have designed a concave solid in the sketch by closing it backwards, but I find this way useful to "carve" paraboloids in arbitrary solids and at any angle.

Step 10: Now Use the Convex Paraboloid to Cut From Other Solids

In this example I'm cutting from a solid block to obtain the result I was looking for. Then I can shape the resulting solid to fit the requirements of the design, the size of the printer and many other factors.

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    2 Discussions


    9 months ago on Step 7

    Thank you so much for explaining this error! I've been fighting it for so long and thought I was designing parts wrong or something. Thank you!!!


    Question 1 year ago on Introduction

    Hello I have a 3.6m dish antenna with an f/D of 0.5 and I want to extend it to 5m with an f/D of 0.36. This means leaving the focus at 1.8m. I will extend it by making some aluminium profiles with a 5cm overlap on the existing ribs. I will also add some rear supports. I need to get these profiles laser cut and I will need a CAD drawing in a recognised Vector format in order to get some quotes.

    So that is the background. I will only need a segment of the parabola which I have plotted in Excel. First problem that I have encountered is resizing the work area in Sketches so that it is big enough. I have added a sketched image of what I am trying to achieve.

    I need to add some cut outs and mounting holes as well.

    The learning curve for a none CAD user is steep.

    Step 1 make the sheet big enough for the full single radius (say 2.8 x 1m)

    Step 2 Set an appropriate grid

    Step 3 Enter the parabola maybe X-Y co-ordinates from my excel file can be used or the polynomial?

    Step 4 Create a suitable 2D polygon

    Step 5 Add some cut outs to reduce weight and wind load - a lattice type construction

    Step 6 Add holes for pop rivets

    Step 7 Save in a well known format for the laser cutting companies

    Step 8 Save up some money :-)

    I would be grateful for any tips at all. I have installed FreeCAD V0.17