Assignment 14: Composites

As the composite object I decided to make a drinking water bowl for birds. And finally I also came up with the idea for "make something big". A bowl stand made of 12 mm plywood.
The diameter of the bowl is 32 cm and the height is 4 cm. The height of the stand is 68 cm.



For the bowl I designed two molds: concave and round.


The thickness of the stock piece is 50 mm, the height of the bowl shape is 40 mm, and there is a 10 mm deep, moat around the bowl to cut it loose from the stock. A round stock would have been better and faster to mill!

I used fabmodules Smoothie to calculate the toolpaths:


Note:
Mach3 program that we use to control our milling router didn't recognize gcode G04 S5 generated by fabmodules, and I had to edit it to G04 P5.
;G-gode for Smoothieboard/sentierBattu
G17
G21
G90
T1M06
F2400.0000
S106.25
G00Z2.0000
M03 F106.25
G04 P5
G00Z2.0000.....


I then used our home made milling router with 6 mm round bit to  rough cut the mold. The spindle speed was much slower than with plywood, maybe 3000 - 4000 rpm.


The rough cut mold came up fine. When we started the finish cut, we noticed that the tool path is otherwise nice, but it did not really touch the material. For some reason, the rough cut went 5 mm too deep and left nothing to cut for the finish cut.



Therefore I sanded the mold to make the shape smoother. I didn't sand all the grooves away, and in hindsight, the folds in the final bowl make it tougher.


The composite making process:

I used Super Sap high bio-content epoxy resin and hardener. They come in two different size containers with scaled measuring/dispensing pumps. Mixing the two components is easy: pump as many times with the bigger pump from the bigger resin container as you pump with the smaller pump from the smaller hardener container. This product has 25 min. pot life and 4 hours tack free time (not sticky).



The fabric is natural jute.


When making the composite I laid the following layers on top of each other:
- mold
- food preserving plastic wrap
- 4 layers of fabric soaked in resin
- perforated food preserving plastic wrap
- fibre planket
- food preserving plastic wrap

Then we vacuumed everything in a vacuum bag for storing clothes.





I revacuumed the bag two times after the initial vacuum to make sure the composite becomes firm. And did it? See for yourself! Just 4 layers of fibre make it tough enough to stand on.


I will smooth the edges of the bowl before I give it to the birds.

Files:
123DDesignConcave
123DDesignRound
Concave mold
Round mold

Home