HOW TO MAKE [ALMOST] ANYTHING_MAS.863
This weeks assignment was to design and fabricate a 3D mold and produce a fiber composite part in it.
Having never worked with resin before and still getting my sea legs with the milling process, I decided to work with two simple bowl shapes to mill.
Masteram, my old friend. Everything went really smoothly this time and I spent only about 20 minutes setting up the file. Thanks to TA Max for setting up the template for us. Here you can see a few screen shots of the different settings I used. I really only needed one toolpath for this job since foam is so easy to work with.
One of my favorite features of mastercam is that it runs a simulation of how your part will mill. Here it reveals any collisions or other issues that you might run into during the milling process.
The entire job took about 15-20 minutes. Everything was looking good until the machine went to change tools.
Fortunately, I was closely watching the machine and also would have a hard time missing the smell of melting foam. Here's what happened - the bit was shorter than the library indicated. Since it was only 1.75" long and it was trying to cut material that was 2" deep, the bit holder hit the top of the foam. Fortunately, it did not damage the bowls. I was able to just stop the machine and remove them.
Here you can see what the error was in Mastercam. We had the overall size of the bit at 2.125" long, but in reality it was only 1.75" so it did not show any collissions. The image on the right shows the simulation of just that toolpath - no collisions detected.
Bowls! almost. On the image on the left, you can see where the tool hit the top of the bowl - due to the resolution of the burlap, I'm not concerned about this and I could easily sand it out if necessary. The brown dust at the bottom is from where I cut into the MDF sacrifice board on the table. Sorry Chris. I went back to check my file and it appears that I did not put a check surface for the first toolpath (meaning the bit cannot go beyond that plane). Although, it looks like many of my colleagues had a similar problem with the MDF even though they did remember to set a check plane.
I've worked with foam a number of times in the past and I normally refuse to sand it as it tends to do more harm than good. Once I coated teh foam with a layer of gesso and let it dry for a few hours, I felt more comfortable sanding it and cleaning up the edges. Once i got to doing the resin lay ups however, I realized that this step may not have been necessary since the burlap is so... rough.
I also added little stands to the bottom so the burlap can drape over the entire mold and I can clean it up to get smooth edge later. I ended up taking the stand of the bowl on the right (with the square base) because I was told it might get crushed in the vacuum bag.
safety safety safety! There aren't many photos from the resin process since I had on my PPE gear. - two layers of gloves with the bottom layer taped to my tyvek jacket. Oh and safety glasses. All work was done under the vent hood.
step one, cover bowls with foil and smooth. Spray with mold release.
step two, we didn't have any breather sheets, so I had to poke a bunch of tools with this super medieval looking tool.
step three, coat burlap with resin (both sides) and layer three sheets over the bowl form.
step four, put breather and fluff over the sheets. This layer squeezes all the extra resin out in the vacuum and is absorbed into the foam.
I had trouble getting the vacuum bag to seal, so I ended up reducing the opening size with duct tape (on both side of the bag) and resealing it. This worked super well - I probably will just start with this if I use these bags again. The opening was larger than the seal, so it was challenging to get a good seal.
In the bottom left image, you can see the resin squeezing out of the burlap. This is the bowl with the square base.
As soon as the bag sealed, I could see that one of the bowls had deformed - I couldn't tell if it was just the fabric coming out of place or if the foam actually crushed. I decided to leave it as is because for one, the damage had been done, and second, I kind of wanted to see how it would turn out.
It turns out, it didn't actually deform the foam, but it did rotate in the bag and didn't really make the shape that I was intending to make...
Here's how it came out of the vacuum bag. Hard as a rock.
I decided to work with the bowl with the square base because the other one did not form correctly - also it has the foam stuck inside of it so I decided to leave that one as a learning experience for now.
The foam came out of the square-base bowl fairly easily. Getting the fabric and fluff off the burlap though was a challenge of its own.
Here's the naked bowl before I took it to the band saw. It's super strong - here's a picture of me standing on it.
I was nervous about sawing and sanding the resin, so I wore a mask while I was working.
Since the extra burlap was both super wavy and rigid, I had to move the bandsaw guard up super high to be able to cut through the thickest pieces. Also, I had to move really slowly since the bottom of the form wasn't flat. Once I was able to get the big chunks off, I was able to move the guard back down to a safe position and do the detail work.
You can see in the bottom left image that there was a bit of a lip on one of the edges. In order to cut this off, I had to shave away at the boundary of the bowl edge, making it a little uneven. I tried sanding the edges down to reduce some of the tooth from the bandsaw, but it turned the edges white, so I wasn't really thrilled with the results.
And voila. Here are a few photos of the final product.