A behind the scenes look at film and television Prop making peppered with everything else creative we do!
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 ASPIREsoftware, 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.
While were working away on our various NDA jobs, we also started a new job for a film.
I do believe the title is "A Christmas Horror Story"
One of the items they need is Santa's crosier. This however will be a gold crosier of death.
I modeled this up in Hex for the art directors approval, based on a couple of quick sketches they supplied me. Notice the Christmas tree spike at the top? That's what I'm talkin' about!
I imported the model into Aspire for machining. I set the model in the center of the working plane, as I plan on machining this side, and a mirror copy for the back. I decided not to double side machine this as one part, as I wasn't quite sure which direction we would be going when it comes to casting them.
Were casting them, as they need a hard version, and a softer rubber-ish one. I'm also going to cast the tree at the top of it separately, which is why it's not included in the Aspire model.
We're cutting this from 3/4" 30lb HDU. I didn't run a roughing pass, even though I was cutting with a 1/16" tapered ball nose cutter, with a 5% stepover. Total time per side was only 22 minutes.
The final pieces fit perfectly, as usual! Tomorrow I'll get it primed and sealed, ready for ripping a mold!
With the second layer component now visible, and selected in the working window,
I used the create vector boundary tool, then offset the vector outwards by the same .300" offset.
In cases like this, I would toolpath this vector before-hand, and have our Techno cut the flat shape, having it on standby for gluing on. Or, you could just cut a rough block of 1" at this point on the saw.
We're going to assume I've now glued the second layer of material to the first layer that has already been machined.
The next step is to draw a box around the entire object. We'll use this to create a "false bottom"
Using the new box vectors, I set the height of this new component to 1.7" inches. This is approximately .250" below the actual surface of our real world material block on the cnc.
Make sure to set it to "MERGE"
The reason I do this, is to completely remove the danger of the cutter wanting to plunge all the way to the table surface, where the geometry of the model permits. Largely between the leg area. Without this block, I would crash the collet into the model, due to the shorter tool length were using.
You can see in this image where the seam is, and that the tool will completely machine over it, but just down to the block component.
Now we can turn on the second layer slice, and get ready to toolpath!
We now have to adjust our material setting. The first layer block was 2", we then glued a 1" block to our first slice, so the new material thickness becomes 3" total. Make sure you leave the Z zero at the bottom still.
With our 2nd layer offset vectors selected, I simply calculate a new roughing and finishing pass.
This machines the second layer, and removes any of the glue that may have oozed out during laminating the 2 layers. Keep in mind, the glue has to be dry. Usually we use a CA clue with HDU, so the dry time is pretty fast!
You can do this indefinitely, adding layer by layer. Without having to buy longer and longer cutters, or machine separate slices, and glue them up, trying your best to line them up together.
I do this all the time, and it certainly saves a lot of post finishing. Just be sure to adjust your material block height in the setup window for each layer.
Not rocket science, and I'm sure I'm not the only one doing it this way,
but hopefully it might help someone who hasn't done it before!