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8178 gave me the task of copying Ron Ellis's Blue Angel canopy for his build and he suggested I do a thread on it. Bearing in mind that how I plan to copy it has not yet produced a plug from which I can vacuum form useable canopy's I'll document the process as I proceed.
Ron sent me his MK kit canopy which just might be the last one in existence. And that carries a responsibility to use a process that will minimize the risk to it.
Here's the plan:
1. make a silicone female mold of the MK canopy (two reasons for using silicone are that the cure process creates very little heat which is less likely to warp the original – the second reason is that the mold silicone doesn't adhere well to much other than itself and Vaseline works well as a release for it).
2. make a male vacuum form plug using the silicone mold and urethane resin (plaster could be used but I have urethane casting resin on hand and I'm familiar with using it with silicone molds)
3. prepare the urethane plug and start pulling canopy's.
To be continued.
< Message edited by tony-howard -- 3/31/2006 8:49:50 PM >
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I think this is really great! There's a thread in the Kit forum pleading with Great Planes to bring back the Ultra Sport 60. Well, here's a group of people taking it on themselves to make it possible for other modelers to scratch build a classic design. For me, this is what it's all about. Modelers working together with various resources and areas of expertise. SAM works this way, in a sense. One guy makes the shut-off and DT timers, another guy sells the ignition components, and another guy has points assemblies, etc. I think the resources are around to build anything you want. It's great to see this.
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I saw that too. Once you have friends with the plans, foam wing design and manufacturing ability, a gold canopy and canopy manufacturing ability you are good to go! Shoot, that’s why X-acto is in business. Plus you get to cut the parts so they fit perfectly!
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8178 and Tony, This is great stuff!! I have recently procured a new and original Top Flite Kwik Fli III canopy by a very kind RC friend. I have been pondering which of the several methods to use to make copies for the upcoming reproduction release. This thread will help a bunch. Thanks for posting the topic.
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I hope the thread will be of use. The process I'm going to use is by no means unique - it's just a collection of ideas I've gathered and used over the years. So there are other ways that will work too!
I started by cutting out the parts for the box that will contain the silicone mold material. The basic dimensions are determined by the canopy dimensions with some extra around the sides for the material itself. In this case the canopy measures roughly 13" L X 2-1/2"W X 2-1/2"H. So the box interior dimensions are 15"L X 3-1/4"W X 3"H.
The box parts were cut from scrap out of my lumber pile. The sides are 1/4" utility plywood and the bottom and ends are 1/2". There's no magic in these sizes, but the sides do need to be stiff enough to resist bowing when filled with silicone. The bow itself would not be a problem but it might throw off my calculations for how much silicone I need to mix.
Before I assemble the box I'll fit some pieces of blue foam to fill in some around the canopy so I can reduce the amount of silicone I'll need. The stuff is fairly expensive and there's no need to waste it.
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I need to explain the piece that will hold the canopy in place on top of the box (which will be mounted inverted over the box when I'm ready to cast a mold).
I cut a hole under the canopy that will allow me to see the level of the silicone as I pour it. During the molding process I'll add water to the inside of the canopy as I pour the silicone around the outside which will equalize the pressure on the canopy to help keep it from deforming.
The OEM canopy is open at the rear and needed to be plugged. For this I cut and formed a piece of 3/4" hemlock to fit the opening. This plug will be glued to the canopy mount before the canopy is mounted. The portion beyond the canopy was rounded to help the plastic transition over the end without forming webs.
< Message edited by tony-howard -- 4/4/2006 5:10:09 PM >
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Now that I'm over the flu I'm back on the project.
The forced 'vacation' time allowed me to reconsider the mold process. What was nagging me was that each time I estimated the volume of silicone needed even after packing the mold box, the amount needed seemed excessive. We just need a thin layer around the canopy and I kept thinking there must be a better way.
What I decided to do was to hollow out a chunk of blue foam to fit around the canopy with a gap of about 1/4" all around. Then the canopy on its frame could be laid on top of the foam block to support it over the cavity while silicone was poured into the gap.
The process was started by tracing an outline 1/4" larger than the canopy base on a piece of paper. The outline was then cut out and centered on top of a block of foam measuring 4" X 4" X 15".
Then the fun began hollowing out the foam. Messy, messy, messy. Fortunately the job goes quickly, the cavity doesn't have to be neatly finished and progress is easy to gage by putting the canopy into the hole. The primary routing was done using a Moto-Tool set on very low speed, followed by coarse sandpaper.
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Before attaching the canopy to the plate I first glued the stopper for the rear of the canopy in place. Then the canopy could be set on the plate and – once centered – a pencil line was traced around the outside.
A rather large gap on one side of the canopy precluded using canopy glue (the gap was the result of the factory being a bit careless trimming the canopy). So a mix of slow set epoxy, fumed silica and micro balloons was used, mixed to a moderately thick consistency. In the area of the gap the thickened mixture was stiff enough to fill easily. A couple of pieces of tape held the canopy down lightly. (Ron will be happy I managed not to leave any epoxy prints on the canopy!)
After the epoxy had set, I noticed a small gap at the rear that had not been filled, so a second small batch of epoxy solved that problem.
To recap, the epoxy's function is:
* to hold the canopy in position (very little strength needed for that)
* to seal and fair the edges of the canopy so the silicone won't get trapped in an undercut
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To the ends of the foam 'box' I epoxy'd on scrap pieces of wood that will be used to support the ends of the canopy holder. Two slanted troughs were added along one side to allow topping off the silicone since the canopy holder covers most of the cavity.
The canopy was then coated with Vasoline which was buffed smooth with a soft towel. Vasoline was also wiped over the filler block at the back of the canopy – as thick as the silicone is, it will key into the wood pores and I didn't want that to happen on a part that has to slip out of the mold vertically!
Finally a couple of pieces of double sided 1/32" foam tape were attached, one at each end of the canopy frame, to hold it in place on the wood strips while the silicone set. (Since the canopy will be filled with water there is no tendency for it to float and so the tape just needs to hold the canopy centered in the cavity.)
Finally it was time to mix and pour the silicone. Two batches were used, each with about 6 oz of material. The first batch was poured into the cavity and most of the second. Then the canopy was lowered into it and water added to the inside of the canopy until it was full to with 1/16" of the top. Silicone was added via the troughs until the cavity was filled to top.
Then all one can do is sit around and wait.
If you haven't used this stuff, it's thick, slimy and very messy to handle. On the other hand it forms around almost anything and will replicate #600 sanding marks perfectly. And it releases mixing bubbles very well in all but areas where they can't rise to the top.
It's a curative silicone – as opposed to the hardware stuff which is a condensate silicone – and uses a curative additive. It's pure white and the curative is deep blue, which turns it a baby blue color when it's well mixed. Pot life is about an hour and it takes at least 24 hours before de-molding.
There are a lot of formulations on the market for mold making silicone, some with widely varying characteristics. I use a Silpak product I get from Fiberlay which is a local fiberglass retailer. It's farily stiff cured, yet has a lot of give without breaking. This makes it easy to get molded parts out of it that wouldn't be even close to possible with rigid molds.
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Me too! No matter how often I make molds there's always that burning desire to pull the parts and see what it looks like.
3-4 hours to go (added 4 hours to be safe).
Actually on a form like this even if the surface of the mold isn't perfect it's no big deal. One advantage of female mold forms is that surface bubbles make a molded part that has 'pimples'. And that makes it easy to sand them flush easily without losing the overall shape. On male molds bubbles mean lot's of filling before you can sand.
I like instant gratification (in this case anyway).
< Message edited by tony-howard -- 4/21/2006 4:57:13 PM >
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Success!
I parted the canopy from the mold with my usual anticipation. As with any molding job like this with deep, steep sides, getting an initial movement of the plug (in the case the original canopy) is the hardest due to suction. A steady prying from both ends and the canopy came out quite easily. (The best process for parting rigid plugs that are having trouble coming out is air pressure by the way – but that was not an option here.)
The canopy is in perfect shape and the mold is just fine.
Next step is to cast a canopy plug for vacuum forming
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Reproducing a canopy for the Blue Angel - 
