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Here are the first shots of this project. Note that this model is twice the size of my EVA Pod kit. This is 1/6 scale (13 inches in diameter)



We start out with two identical vacuformed 13-inch hemispheres. Since we know what the diameter of the earmuffs are, the first thing we do is plot that diameter onto the surface of the hemispheres using a pencil held rigidly at the proper height. This 'height gauge' is drawn around the hemisphere, marking where the cut will be made.



The cut was made using an abrasive wheel in a dremel tool. The opening will be sanded flush on a sanding board.



Here you can see the size difference between the kit version (right) and the 1/6 scale version. We will be detailing the large earmuff soon and I'll have photos of that later. The basic shape was turned on a lathe and then the grooves were cut on a mill. The plastic dome is a 4.5 inch hemisphere from Plastruct, cut down to fit.



Here you can see how well the earmuff fits the opening we cut. This earmuff master is a little thick at the base. This will be removed when we make the mold, sometime next week.

The small Pod was done in SLA, but the Aries was not. The masters for the large Pod are being built by hand because they are simply too large for the tank I had access to and because the amount of hand finishing required for the small Pod was what held up the darn thing so long. I do have one part that was done by SLA and I'll be putting a shot of that up soon.

SLA and 3-D Waxprinting are useful for a lot of things, but if there is a lot of detail, like the stuff under the window on the Pod, then its pretty much a waste of time. The 'grow pattern' has to be sanded out and small details have to be replaced by hand. Since the Pod is a sphere mounted in a cradle, the basic shapes are fairly easy to make by hand. The only hard part is the window bezel. I'm not looking forward to that at all!!

Scott

The moment we've all been dreading is here. I have to make the window bezel for this thing. And it has to be done by hand since growing it is no longer an option. But, that's fine. I've already got the whole thing planned out and I know exactly what to do--

I'm going to build it backwards.

What I mean is I'm going to build the 'negative' of the window bezel, not the bezel itself. The big problem with building this piece, as you are about to see, isn't the shape. Its all those tapered slats that make up the surface. Since it would be nearly impossible to do that cleanly, I've decided that it would be easier to build the grooves between the slats-- they aren't tapered! To do this, all I need to do is create the finished bezel shape and then generate the negative of it. In other words, I'm going to make a shape that would be the inside of a mold if I had the part to pour rubber on. Since I don't, I have to make it. Confusing? Hang onto your socks!!



I cut a piece of plastic to represent the window itself. This and the outside edge of the opening represent the two things that define the shape of the bezel-- the outer, compound-curved surface it is mounted into and the flat, eliptical window it frames. Once I had figured the proper depth into the model the window was mounted, and its angle, I made a spacer and glued the 'window' to it. Using tape, I positioned the whole thing and then secured it so it wouldn't move.





The surface of the bezel is a section of an eliptical cone. And as we all know, all conical surfaces (circular or eliptical) are flat planes rolled up. This means we can make the surface out of flat plastic sheet stock. Here, I've slipped a sheet of .020 styrene into place. If I had really been paying attention in High School geometry, I could probably lay this out on a single sheet and cut it out. But, what can I say-- the guy was boring and I was rotten at math. So, I'm stuck doing this by trial and error, but I know its going to work.



Here you can see how the bottom piece is glued in, with another piece going in at the top. You might also notice the notch I cut into the brace. This is so I can lay a ruler across the whole thing to check the angle of the window-- we don't want it getting out of place! I guess I should explain this better... The depth of the window is controlled by the spacer and the position of the brace on the outside edge of the window opening. Once the eliptical plate that represents the surface of the window is in its proper 'north/south/center' position, the brace is taped into place, so we don't lose that orientation. The surface of the window itself is at a specific angle to the window opening (the big hole). It is almost parallel to the 'north/south' surface of the opening, with the top tilted slightly forward. Once the window piece is glued to the bottom piece of the bezel surface, that angle is fixed and the rest of the bezel can be built. Yeah, I know-- that's a lot to chew on, but someone would have asked!



See-- Told ya! The finished bezel surface. Of course, someone will wonder why I don't just scribe the grooves into this piece and be done with it. Well, first, its only .020 thick. If I'd used thicker plastic, it would have been a b-- a lot more trouble since it wouldn't curve as easily. Second, most scribers aren't wide enough to do these grooves. I could make one, but then we come to the third point-- If I screw up, I have to start all over again. Oh, yeah- Forthly, putting in all those scribe lines would weaken the part and it may take on a new shape due to the plastic being under tension.

Okay, I can see all of you scratching your heads-- how do we get from this to the negative part that I need? We're going to pour plaster into this to get a negative. But, I can't use the plaster part as my master because it won't hold the strips of plastic I'm going to use as the 'grooves', so we have to generate a hard-tool (mold) of the plaster part, so we wind up with another postive that we can vacuform plastic into, to get our final styrene negative part. Watch--



Using tape as a 'dam' to keep the plaster from running all over the place, we make a plaster negative. A little Vaseline was used for a release agent.



Here we have the plaster negative. Its a little rough around the edges, so--



I cleaned up the edges on the bandsaw. I left them beveled on the outside because the angle will help the part come away from the tool after it is poured. This angle, used to keep a part from locking, is called 'draft'.



I've mounted the part, used green plasticine clay to do some patching and built a mold-box. Before pouring the goo in, the whole thing is painted with Vaseline so nothing sticks and--



The vacuform tool! I will use this to make a vacuform part that is the negative shape of the window bezel. That will be in the coming week, though. Stay tuned!

Now we get to heat up some plastic! This is the part of the job that really sucks, too! (Yeah, I know. Sorry about that...)



Here's the pattern in place. I designed it so that it would act like the cavity was actually inside the plenum (airspace) so the plastic doesn't have to stretch over the outside, as well as the inside. This way it will just lay flat, except where the part is formed. The only thing I need to do before making the part is to use some duct tape to seal the bottom of the pattern to the plenum. I've drilled small holes in the pattern to allow the air to be sucked out once the plastic is lowered into place.



This is the plastic after the machine sucked it into the pattern. Now you can see what I mean about the plastic laying flat over the top.



Here you can see how the plastic part is just like the original.



The surface of the plastic is dimpled. This is the result of using a plaster pattern and not letting it dry before making vacuform tool from it. The curing urethane generates heat, which causes the water in the plaster to react and form the inward dimples that the plastic was sucked over. These dimples are the reverse of those, so all I have to do is sand them down and use a bit of filler to correct some other minor flaws.



Scraped, sanded and filled. And I've put the lines on for the strips that will eventually become the gaps between the slats. Remember-- we're building the negative version of the bezel! I'd go into how long it took me to lay out those lines, but I don' t want to start shaking again...