When I lent my services to a collegue who was working on a film about 12 years ago, I was introduced to the world of cnc. I remember watching this huge machining centre milling out a slab of mdf and turning it into a fantastic set of gears. I knew that it would have taken me hours to achieve the same thing with traditional power tools. I decided then that I would invest in a cnc router for my own business Oxenham Design. At that time I could turn on a computer, but even to check email seemed like a crazy set of operations. I persevered and learned every piece of relevant software I could get my hands on. I am now fortunate enough to be using Vectric's ASPIRE software, and Techno cnc routers, which has helped us to create some amazing projects, both in part, or in full. I thought that this blog would be a great place to share "behind the scenes" adventures with the software, materials and equipment we use, as well as the projects we build.

Tuesday, 1 May 2012

They Lie, Size Does Matter!

But only when it comes to brains!

The roller coaster car got it's electric orange colour applied this morning. 2 coats covered extremely well, even though it was as bright orange as it was.
Tomorrow we will get the lap bar on and final assembly ready for Thursday delivery.

We also started the big brain that will be shot in a bell jar. The jar is HUGE. Well it's huge for a bell jar to me anyways! It stands 20" tall and about 9" in diameter. Filling it will take a rather large brain. A normal size brain model from a medical supply place is pretty small, and would look puny in this colossal jar. So we're making one. We are lucky to have complete control on this job, whatever we like, we can do. They are shooting this 2 ways. One way will have the jar and brain upside down and filled with a liquid of some kind, and they'll flip it in post, and the other way will be the right way up with no liquid. I could have sculpted a brain out of the many weird products we have here by hand, BUT all those materials would be solid and opaque, and that's pretty boring I think. I want it to GLOW! So I found a pretty cool 3d model brain on line and downloaded it. I usually do that first for generic things. Why model it if one exists already.

This is the brain after I did some sculpting in Hexagon. I like that it now pulls down in the middle.
I quickly found out that the original geometry wasn't all that great to begin with, and after the sculpting, it was a real mess. It looks good, but it's a mess. And all this messed up geometry means Hexagon doesn't want to split it how I want it to. I can't bring this into Aspire the way it is, as all the undercuts would be filled, and not to mention it's thicker than any one material I have. Long story short, I need to slice it. After thinking about it, I decided on a new approach. I would strategically place cubes around it, then remove the cubes in Aspire, leaving the portions of the brain I need.

Here I added a center cube rectangle in the dead centre. This gives me the left and right brain halves. When I import this into Aspire, I'll sink the model into the zero plane so the brain part is the only thing sticking up.
The brain is symmetrical, so I only needed to mirror the other side, instead of  importing it twice.
I continued to work my way around the brain with the cube method. Now it was important that the cube faces be touching, not overlapping. This would keep the brain pieces working together properly.

Here's how one piece looks when I'm importing it in to Aspire. All the cubes come in, with the brain and I'll just trim them off after they've been pasted down.
After trimming the cubes off, I'm left with the portion I need.
Now for the fun part! I don't want to machine this as the final piece. I want to make a mold. I said before that I wanted it to glow, and we have clear casting resin in stock that hardens up in around an hour. I could have machined the brain as a 'positive' shape, and made a rubber mold. But this would have required waiting overnight for the mold, then we would have had to make a "jacket" to support the rubber mold, then the couple of hours for the resin to harden up. We just don't have the time on this, it shoots on Thursday.

 So instead, I machined the brain as a negative component, and I used styrofoam as the mold material for machining. The casting resin will bond really well to the styrofoam, but that's not really a concern, as we are going to bust it off in the morning, and clean-off any styrofoam bits with lacquer thinner. This wont hurt the resin at all, as it's a urethane and very durable. I made sure that the styrofoam blanks were lined up exactly along the Techno cnc's axis.
Making sure the blanks were aligned to the edge of the material made the task of trimming the mold parts on the table saw very easy!

After all the parts were trimmed on the saw, I heavily coated the gluing surfaces with Super 77 spray contact cement. I used alot of it in hopes to create a seal so the resin wouldn't poor out the seam joins.
It's a little hard to see in this pic, but this is the result of all the blocks glued up, leaving the open 'brain cavity' mold.
We mixed up the clear resin with some tint in it to give the brain a fleshy, translucent colour, rolling it around to coat all of the inside. After it became solid enough, I drew veins all over it, in hopes that they would  show through faintly when the light is added.
We added one more layer of coloured resin, then backed it up with a few more layers of just clear. I don't want to opaque it out totally. The resin does get quite hot, especially in an insulated mold like this one. I'm hoping that the first thin layer was enough to protect the styrofoam from melting under the heat. It should be o.k. but I won't know until I crack it out in the morning.
Let's hope!

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