Composites

Milling the shape

The shape is imported as .STL in Vcarve for work with our brand new the ShopBot:

A first large tool is used to save time (still more than 20min), and then a second thiner tool is used for finition:

The final shape is smooth, and does not need any further work:

Preparing the shape

The shape obtained is first recovered with a polyethylene film (food conservation film does the job) to prevent the resin to stick to the shape. Then paraffine oil is spread on the film to make separation easier:

Preparing the epoxy resin

I followed the instructions on the bottle, using a scale and the weight ratio between resin and hardener 1:.47 (rather than the volume ratio 2:1): Initially I prepared only 32.3g of resin (+15.2g of hardener), but it appeared in the next step far from sufficient. I therefore prepared a second amount of resin (50g+23.5g).

Applying the resin

All sheets are carefully impregnated with resin, on both sides. The burlap used is rather rigid when dry, but softens when impregnated with the resin. It is important to add a lot of resin so the burlap is flexible enough to reproduce the shape:
After applying the resin on three layers of burlap, a second polyethylene film is layed on top of the assembly.

The assembly is finally put into a vacuum bag (for clothes storage), and a vacuum cleaner is used to remove the air:
The resin used is, in principle, harmless. However, we set the vacumm-cleaner under the hood.

The assembly:

It is important to clean rapidly and carefully the tools, especially brushes, before the polymerization; otherwise the brushes are to be trashed. However, it is not easy to find information about the proper solvent. (CH3)2O works, but this produces a large amount of secondary chemical waste, that has to be managed properly...

Or just dispose the brushes...

Final result

The composite shape is glue to the wood-shape because the polyethylen film was not tight enough. Next time, I will completely wrap the wood inside the film. It is difficult to separate the shape from the wood:

Here is the final result:

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