This week I made a box (of unknown purpose) using canvas and some epoxy resin.
Design
I used TinkerCAD and Aspire to create the design files for the mould. I started in TinkerCAD, and created a box ith rounded edges. This was a multi step process, starting with some cylinders and creating a frame with them. I then moved on to place boxes to act as outer panels. I filled in the empty space with another box and inverted the box and made the box into a hole type object.

I then made a larger box with similar thickness to my material and centered and merged the two pieces to create a mould. I did this because Aspire creates toolpaths for the positive object, not the negative.

I then moved the files to Aspire, first starting with changing the job settings to fit my material, a 48" by 12" by 4.5" block of insulation foam. I also set the origin to that of the shopbot, the lower left. To import, go to File>Import>Import Component/3d Model.

In the import options choose the settings shown in the image below. If you choose the wrong zero plane, the model will not be completely included in the toolpath or will cause problems on the shopbot. I would also reccoment not discarding data below the plane, just in case.

With the model imported, move the resulting image around in Aspire to find a good location to put the mould. I then saved the file and moved the file to the shopbot computer, which had specific settings for the bit and material. On the SB computer, I imported the file back into Aspire and created two toolpaths using the specific settings for our shopbot, the foam, and the bits I was using. The settings I used are shown below.

I calculated and saved both of the toolpaths to the shopbot format and sent the files to the shopbot using the procedures I describe here. I then waited for the shopbot to finish. The roughing path digs the basic shape of the box layer by layer. Some material is left over that is easy to clean up.

The finishing path moves back and forth to clean up the edges of the box. This takes the longest of the two, but produces the best finish. In the process of doing the finishing, the head ended up hitting the material a little. This was unavoidable, since my model was very deep.

To remove the grooves you see above, I sanded the inside with some sandpaper. The grooves are from the rounded bit I used. I could then move on to adding Gesso to the mould. Gesso helps seal the mould to prevent, alongside release agent, the epoxy from sticking to the mould and improves the finish of the end product. Gesso can be applied with a normal paintbrush and looks and is very similar to white paint. You need to apply multiple coats for the best effect. In between coats, the Gesso needs to dry, and we've found that since Gesso is water based, the heat of the sun is effective at drying it faster.

After applying Gesso, I could now vaccum form the mould.

Forming
The forming process took a long time to do (overnight) but produced great results. The first thing I did was a dry run of the forming process without any epoxy, to test if the method most of us initially chose (large layers of burlap) would work.

I learned that I needed to use layered strips to allow for the burlap to fit the form of the mould without stretching too much. After learning this, I moved on to the wet run using this method. To start, I sparayed my mould and the perforated film with release agent. This would make the finished product easy to remove from the mould and from the bag, and not stick to either.

I then mixed the epoxy and then began laying out the layers of burlap, applying epoxy to each layer. Next, I placed the sparayed film down onto the mould and layers of burlap. The breather layer is then placed on top of the film (which protects the fabric from integrating with the mould). and the whole mould is moved into the bag. To save time, we placed multiple prepared moulds into the same bag.

The bag was then vaccumed out. the pump was run for about two hours to allow for the layers of burlap and other layers to conform to the shape of the moulds. The moulds were then allowed to sit overnight in the vaccumed bag to allow for the epoxy to cure into that shape.


After waiting overnight for the moulds to cure, it was time to remove the moulds. It turned out that I needed to destroy the mould to remove the finished composite. This issue was probably a result of me not adding enough layers of Gesso to the mould, resulting in the release agent not working properly. Next time I will be sure to add enough gesso to the mould.
Next time I could also design the box with a draft angle on the walls, so that it would be easier to remove the finished product. The straight up and dowm walls may have made the removal of the composite difficult.
I cut the composite out on the miter saw and sanded down the edges of the composite. I'm sure that the dust of the epoxy is not desirable to breathe in, so I would reccomend a face mask to avoid breathing in the dust particles (you should do this when you are sanding any material anyways).

In the future I would make the box a little more shallow, so that the shopbot would not bump into the edges of the mould as often. I would also add a draft angle to the mould so that the composite would be easy to remove without breaking the mould like I did.

Files
epic_hango.stl - 3D model of the mould
Box.crv3d - Aspire File