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Using Fusion 360 to design a GMFC project

Fusion 360 is a great CAD program, and quite easy to learn. For now, it is also free for personal usage. I have already used it to design few models.

Here is a tutorial that explains how to design a “simple” shape using Fusion and then exporting it into a GMFC EXPERT (and PRO) project.

First, you need to start Fusion, and create a new design (File/New Design).

Using the view cube in the right, select the front view.

Then, create a sketch (Create/Create Sketch). Select the (front) plane to define the sketch on the front.

Now draw a hexagon using Lines. Then finish the sketch.

Now, we are going to create the second face. First, we need to create a second plane parallel to the first one. Use Construct/offset plane for this. Select the front plane which is the XY plane in the Origin section in the browser, and enter the distance between the two faces (here 60mm).

There is a new plane in the construction section. Right click on the plane and select “Create Sketch”.

Draw a circle on this face, and center it with respect to the hexagon.

Now we need to split the circle so that we can synchronize both faces. Here we want to divide it in 6 parts corresponding to each side of the hexagon. For this, let’s draw lines from between each hexagon opposite points. Change the type of the lines to “Construction Lines”.

The next step is to break the circle at the intersection of the construction lines. Use the break tool in the “Modify” menu.

Cut also the construction lines outside the circle, using again the break tool. Then finish the sketch.

Now, we need to construct the 3D view of the object, so as to check the final result. Select the “Loft” tool in the create menu, then the two profiles.

Here is the result.

Note that we could have split the circle in other ways. The construction lines are there only to ensure that all part are symmetric. What matters is that in the end there are the same number of segments in each profile.

Now we need to create a GMFC project from this shape. The solution relies on exporting both sketches into DXF files. Fusion does that, but it also exports construction lines which would require editing the DXF using a CAD program. My solution is to create a script for fusion that does the exportation while removing the construction lines.

First download the script. It is available here: http://gmfcsoft.fr/download/utility/ExportDXFSelection.zip

Uncompress the zip file in a directory. You need to install the script within Fusion. This should be done only once. Call the script menu using the “S” command. Then click on the green cross and select the installation directory. “ExportDXFSelection” should be now present under “My Scripts”.

Select “ExportDXFSelection”, and click on “Run” to launch the script. A windows is displayed with the number of sketches selected.

Select the sketches you want to export, then click on “OK”. A new pop-up window appears for selecting a directory where the DXF are saved. There is a file for each sketch. The name is constructed by concatenating the design name and the sketch name.

Then for each sketch, the script displays the bounding box, i.e., the limits of the sketch.

Finally, the script displays the delta in X and Y. This information is critical for correctly positioning both profiles when creating the GMFC project.

Now, we can create the GMFC project. Start GMFC, open the panel parameter. Select “Different root/tip”.

Enter the DeltaX value in the “Sweep back” field. Add the DeltaY value to the root “Basic Height” and enter it in the tip “Basic Height”. Enter the distance between the plans into “Panel span”.

Import both profiles using “File/import DXF”. For more details, follow the tutorial at https://gmfcsoft.fr/blog/?p=879.

Enter the alignment mode. We need now to assign the same number of cutting points to each corresponding segment at root and tip.

Double-click on a segment and set the number of points.

Voila, you are nearly done for the design part… now you have to cut the shape.

Note that this project induces a lot of sweep back in X and Y… I used a 100mm wedge for cutting the shape. Fortunately, my Y axes are large. Here is a video of the cutting…

This tutorial is for GMFC EXPERT. If you are using GMFC PRO, you need to transform the DXF files using a CAD tool. Split each segment into the desired number of lines, then finally merge them into a polyline.

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GMFC 4.0.3

It time to release a new version after more than year. I consider version 4.0.3 as a stable one. Please upgrade to this one.

Most of the changes are bug fixes:

  • Improvement in points selection in DXF importation
  • Bug exit spar cutting in separated pass
  • Bug get down surface for closed profile
  • Modification of foam management dialog, move of field C
  • bug postion, horizontal LE in cutting spar & lower surface
  • bug position table+5mm
  • bug pre-heating spar & lower surface
  • Time for stabilizing heat in test cut for foam calibration
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Foam Calibration Tutorial

If you want to get the best out of GMFC, you need to precisely calibrate the cutting speed and the kerf. Foam settings are fully specific to a given foam material. Foam settings are also specific to temperature and humidity. In my experience, foam settings are valid for a range of 5 degrees (centigrade) around the temperature in the workshop during calibration.

Calibration is done using the foam management dialog (GMFC/Foam management). Start by creating a new material. For choosing the name, I specify the type of the foam, the temperature and the type of the wire.

Calibration is achieved by cutting a slice of foam. The dialog allows to cut a stack of slices in a single block. Therefore, you need to enter the block height and the block placement in X0. Enter also the size (width, height) of each slice. The dialog shows how many slices can be cut in the block. Start cutting a slice by clicking on the “Cut” button. Between each slice, cutting stops so that you can adjust speed and heat parameters.

First, we calibrate the high cutting speed and heat. Expanded polystyrene can be cut up to 3-5 mm/s. This depends from the machine speed, and also from the heat (wire and voltage). You need a small piece of foam those edges were cut manually by a knife/cutter since after the foam is burnt, the surface becomes harder to cut in. Remember that GMFC cuts by radiance. So the wire must penetrate the block without dragging it. Specify the high cutting speed and adjust the heat so that the block does not move while cutting the slice. Also be careful to minimize the heat since too much heat increases the kerf and alters the shape.

When speed and heat are fine, you can evaluate the kerf. Use a caliper to measure the slice height after cutting. The kerf is equal to the difference between the measured value and the specified one. Enter the result in the “Root kerf” field. With a 0.3mm Nichrome wire, the kerf should be around 0.6-0.8mm (depending on the speed and heat). Note that in this dialog there is no kerf compensation when cutting a slice.

We now need to evaluate the kerf for a tapered wing those tip is smaller than the root. We already have the kerf at Root, we need to estimate the kerf at Tip. Enter a C ratio (length of Tip/length of Root) that is close to the kind of wings you will cut. C=0.8 works for gliders. C=0.5 is the limit. A smaller ratio induces too much deformation.

Let’s cut now a tapered slice. For this, check the box “Measure kerf at tip“. Enter also the length of the bock in Z and it’s position with respect to the left axis. Be precise since it directly impacts the slice dimensions. Cut the slice by pressing the “Cut” button. Measure the slice height at tip with the caliper and enter the result in the “Tip kerf” field. Note that the root kerf should still be the same.

Finally, we need to determine the low cutting speed and the associated heat value. Note that this does not impact kerf value which should be the same at this low speed. Choose a low speed between 1 and 2 mm/s. GMFC reduces the cutting speed when the wing/shape is high tapered which in turn induces a large displacement (and speed) at the axis level.

Et Voila, you are done. Click on “Apply and exit“…

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GMFC 4.0.2

Here is a new version for the beginning of the year.

There is an important novel feature that improves wire heat. When the wire sits on the table, its temperature is reduced by the table itself. Therefore, the wire temperature may be lower at the beginning of the cut. With this version, the wire raises up to 5mm above the table and waits for a given time before continuing the cut. In the table configuration, there is now two time parameters: one for un-gluing the wire from the table, and the time for temperature stabilization.

Parameters of the wire cleaning are now saved.

A bug in the non-detection of the GGC for Windows 10 has been corrected. Finally, few minor bugs introduced in version 4.0.1 have been corrected.

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Merry Christmas and GMFC 4.0.1

Santa was generous this year. He brought a new version of GMFC in his hood 🙂

Here are the novel features:

  • In variable heat mode, the maximum cutting speed is given by the max calibration speed.
  • The entry to the TE prologation and the round spar cutting speed are now indepedent from the profile cutting speed. This is a major improvement since dihedral in the spar or wing taper may severly impact cutting speed.
  • There is a new Xoffset option in the foam cutting dialog (PRO and EXPERT versions). This allows to quicky shape foam blocks at a given width.

Happy cutting between the turkey and the cake 🙂