Drawing a Mug Handle Mold in Fusion 360

Lilly will take you step-by-step through the process of drawing a shell mold that can be 3D printed and used to cast a plaster mold for slip casting perfect-fitting handles.

E. Processes

https://digitalfire.com/videos/MugHandleReview.mp4

1
You are looking at the two halves of a mold. Plaster is poured into these to make a working mold for slip casting a handle that precisely fits the side contour of a mug. But it could also be a teapot or a pitcher.
Let me show you how flexible this can be in Fusion 360. I have parameters set up for the diameters of rim and foot. Changing these automatically changes the 3D model shape.
I can also change the shape of the mug or handle in the main sketch and the 3D model will adjust.
2
Here is the sketch again (without dimensions and points). A priority was keeping the number of steps to a minimum while still having enough parametric functionality to adapt a handle to a wide range of shapes and sizes. A number of details are important.
-The initial drawing has most of the complexity. It is important for the profile and box to be on the same sketch since they interrelate so much.
-Certain lines are offsets, they must follow their parent lines, I don’t do anything to break the link.
-The curve describing the mug contour was drawn with the spline tool, the others were offset, then its endpoints were joined to the horizontals.
-At least one of the handle endpoints must cross the box.
-The 13.5mm holes fit our natch system.
-It’s tempting to bevel some corners, but don’t do that here. Do it later in 3D.
3
Let’s trace the steps on the timeline. I will describe them conceptually so you can do this in any CAD product.
First, I created the initial sketch on the YZ plane. Then I created two planes perpendicular to the ends of the handle center line and then sketched the oval cross section on each (with 0.8mm insets).
4
I then extruded the 0.8mm walls of the box upward by 20 mm, and the bottom downward by 0.8 mm (excluding the holes for the natch clips).
5
Next, I revolved part of the 0.8mm thick part of the contour 35 degrees (using the join operation). This creates a mold wall that exactly matches the outer curvature of the mug.
6
Next, I lofted between the two cross-section profiles. I did this along the handle centerline (first solid and then using the center circle to hollow it).
7
To remove the unneeded part of the box I revolved the inner mug profile using the cut operation.
8
I then split the body front and back of the box (using its rim and base as the cutter). Then I removed the unneeded parts.
9
Next, I made the slip spares using the 2mm wide part of the curves (the horizontal lines define the bottom and top). I revolved by 20 degrees, in both directions, to create two new bodies, and then pulled these away 20 centimetres.
10
With the camera is in orthographic mode, I drew two ovals on the XZ plane (with 1.2 mm insets).
Next, I extruded the pipes to join with the mounts and then hollowed the centers.
11
Next, I bevelled the handle joins (inside and outside). The outside bevel keeps the wall thickness consistent, that eases mold release.
12
Finally, I beveled the top and bottom sharp corners (inside and outside). This helps prevent breaking the otherwise delicate plaster corners.
13
To finish it is just a matter mirroring this, 3D printing both, inserting the clip and embed pairs in the holes, filling them with plaster and using a heat gun to remove the print after the plaster has set.

This mold-making technique I have wanted my whole life

I wanted an easy way to make molds for slipcasting handles that mate perfectly to any shape mug (or pitcher, teapot, etc). I want to pair cast with thrown or jiggered elements and join them using just slip (even when the clay is stiff). We have developed a flexible CAD design that makes 3D printing of case molds within the reach of even hobbyists. It requires so little tooling it can be done in a kitchen using spoon mixing and a paper cup! These PLA shells, for example, print quickly to only 11g and they peel away from the plaster with a heat gut to give fine detail and perfect fit. Multiple cycles of redesign and print are practical, achieve just the right shape and fit. Cast handles can produced in quantity and stored in a damp box, removing one of the biggest hassles in the production of handled ware. Your ware will have designed handle, not a stuck on wet noodle.

By Tony Hansen
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