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, 12 November 2013

Plastic Bears and MDF Woo-hoo!

While we were working on wrapping up the Zelfs job, we were also right in the middle of our Build a Bear machine prototype.
We were working with another company on building the prototype, so it wasn't totally our job from start to finish. This machine will be a 3' tall portable machine, that can easily be transported from one event to another. If you aren't familiar with Teddy Mountain, basically you buy a stuffed animal skin, and stuff it yourself with the fluff, and add all kinds of accesories like hats and clothes. This machine will get used to blow the fluff inside the empty skins.
The project started with a lot of meetings regarding everything that needed to be incorporated into the molds. We were supplied a set of castors, a telescoping suitcase style handle assembly, and the dimensions for the mechanics. The other big part was the shipping box that it needed to fit into. The size of the box was already determined at 2'X2'X36" tall. Apparently this is the most practical size for 'product to skid' ratio for shipping, as they get 8 cartons to a skid. I spent some time modeling the bear character above for the initial concept approval. With lots of back and forth emails, the front got signed off on.
The other slight complication to the build is that they want multiple different characters over time. BUT, they want to use the same backs for every machine. So ultimately, they only want to have 1 mold for each new character fabricated. A large task, but still quite solvable! I didn't quite now how at first, but I knew the answer would come while I worked away on the 3d model! I won't bore you to much with the initial 3d modeling in Hexagon!
With all the modeling finished in Hex, I brought the 3d model into Aspire. This is where I'll do the stuff that's too tricky to do in Hex. Aspire does an amazing job at adding the much needed draft angle that will be required to vacuum form the shells. You'll also notice I left the curved "tube" inside the bear. Once the piece is vac-formed, this will get trimmed out, and should fit the actual tube that's going in the chest perfectly.
I also punched in all the places that would get the final decals on the finished part. The reason for the punched in areas, is to help protect the graphics from getting caught and peeled off over time. It was way faster to do this sort of thing in Aspire, then any other software. The other addition done in Aspire, was the 2 bottom tabs that will counter-act the 5 degree draft angle on the whole model. These will let the machine stand straight up, without rocking back and forth. I added these as a separate component, so they wouldn't be affected by applying the draft on the imported model.
Once everything that was needed was added to the model, I sliced it up into 3" slabs. I'll be machining this from 4 pieces of 3" thick MDF. I didn't actually have to laminate these slabs up, the company that hired us supplied all the slabs at the size I requested them. NICE!
The material got delivered slightly over the 3" thickness the model was sliced to. This actually suits me fine, as I can mill off the difference for a perfect slab thickness. I also ran a second finishing pass at 90 degrees to the first one, but limited the toolpath to just the very edges. This saved a total of 10 hours machine time, versus wastefully cutting nothing at the top of the slab during the second pass! All of the slabs were rough and finished passed with an extra long 1/2" ball nose cutter. As I don't have a tool-changer (What's that Techno cnc? Why sure, I would LOVE an automatic tool changer:)
I try to keep my tool changes to a minimum whenever I can, so using the same cutter for both tasks, as it saves me the work of changing out the cutter.

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