wk9 | molding and casting

Assignment :

• design a 3D mold, machine it, and cast parts from it

Download : stl & rhino model - balljoint & mold

My notes :

27 march 2014 | introduction Rhino

For this design I want to have some specific measurements.
And since Blender isn't capable of that, I will try out Rhino.

After installing it on my laptop. I started out with watching some YouTube's
to give me a impression about the general layout of the program.

- What I really like about Rhino, is that you have a GUI interface,
but beside all the button's there is a good shortcut system (with a properly working autofill).

- Rhino have 4 view ports, 1 in perspective and the others 3 are flat views of you design.
You can change those to you liking. (double click on the left top corner to get one big view).

- When done designing a shape, it's important to check in the properties menu (on the right or F3) if it's a waterproof.
(needed for the milling process later on).

- On the bottom of the screen there are a lot of snapping option's. Try different setting's to help you snap the right line.
And also the smarttrack tab at the bottom, can (sometimes) be helpful.

• join : to join object into one object. (for 2D objects)
• trim : to cut pieces of a object away (for 2D objects)


• booleanunion : merge & subtract shape's (3D object's)


• repeat the last step again : right mouse button


• hide and show command (like a layer option, to get objects out of the way).
• showselected : To select a hidden object back into view.


• offset : to offset a line


• loft : a 'plane' union between 2 non matching shapes, like a square and a circle.
• cap : to close a non complex open shape (to get it waterproof).


• explode : to detached a object into faces.


• polararay : To duplicate a shape several times in a radius

28 march 2014 | designing the mold Rhino

What I want to make, is a second version of my (cardboard) hinge design.
I want to create a ball and socket joint, so movement can be controlled 4 way's instead of 2.


step 1 : create a 3D design

step 2 : invert the design (create a mold of a mold).

1. the finished model
2. draw a box around you design and apply 'boolean difference' (A+B).
   draw a second box on top of you design (D). 'boolean union' the interior of the design with that box (C+D).
3. result is a split between the interior and the exterior.
4. add air holes and a 4 poring hole to the interior design, and to the exterior add a 'tube' shape (with a high edge).

The end result of this step :

step 4 : invert the design again (to create the mold for machining).

Turn both shapes upside down. And draw another box around it and apply 'boolean difference'.

step 5 : export selected as a .obj

Export the selected shapes and open the obj file in PartWorks 3D. Here you can edit the 3D toolpath in preparation for the shopbot.

31 march 2014 | machinable wax

After discussing witch my tutor, we decided to do the ruffing toolpath and the finishing toolpath with the same flat nosed tool. End Mill (o,125 inch)
A ball nose tool would do a nicer job in finishing the round surface, but we would also loose the nice sharp corners in the design.

Because the machinable wax is a soft material, securing it with screws like you would do with wood is not a option. In stead you clamp it down.

Also make sure the shopbot is clean (no wood dust etc) because the wax splinters can be re-used.
(So don't turn on the extraction.)

Sadly, the little air vent was to fragile and didn't survive the milling process.
To replace the broken one I carefully drilled out the hole (by hand) and put in a a small nail as temp replacement.

31 march 2014 | oomoo cast

Next step is casting oomoo into the wax mold. Oomoo 25 is a silicone rubber compound.

To know how much oomoo to prepare, I need to know how much volume my design contains.

Open up the original design (from step 1).

cubic millimeters can be converted to ml, and ml can be converted to grams.

Which is useful because we can measure that by scale.
So now I know how much oomoo I should prepare.

And after waiting for 75+ somewhat minutes ...

Repeat the same trick but now with a hydrostone cast.

I tried a couple of time's but sadly I keep ending up with bubbles in my cast.
After the second time I drilled 2 more air holes into the oomoo mold, hoping this would help.

I think I should have placed the air holes at the end of the little rings in stead of in the middle.

And as a second design flaw; the little rings are flat and should maybe have been slightly askew.
(Because air bubbles always travel to the highest point.)

Neil gave me the advise I should have some more patience while mixing the hydrostone.
Wait a few minutes, let it set a bit before casting the mix into the mold.

Tried again, and this time I got a cast with 4 complete rings, and used one tiny bubble.

Download : stl ball joint model