Foam to Composite Scale Model Mold - RC Groups
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Nov 09, 2012, 08:42 AM
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Build Log

Foam to Composite Scale Model Mold

The following is my attempt to provide information on how I build my molds and turn a foam kit plane into a scale composite that I could be proud of.
Last edited by acesimmer; Nov 09, 2012 at 09:06 AM.
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Nov 09, 2012, 09:04 AM
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The Beginning

A year ago I decided to try out the FOAM scale warbirds that you see all over these days. After flying one of the larger models being this T-28.... I was impressed enough to go all electric. So I rapidly built up a fleet of several types including EDF's.

Then I purchased an estate sale that had twelve balsa models that I converted to electric. WOW! What a difference. The balsa ones fly so much better on electric without the mess of fuel residue and noise.

So being a Magyver type, I started to mess with sound systems, telemetry and other stuff. I reached my limit of experimentation and still found myself getting bored. So I sat back and made a decision. I wanted to build versions of these models in composite and reduce my fleet to just several of the best flying birds in my fleet that I enjoyed the most.

I decided to sacrifice my T-28 to make a set of molds from. Many guys build a balsa kit or a scratch built plug of either balsa and or foam. Then detail them and make the plug. I approached this a little differently. I wanted to test fly my model and see if it was worth the time and expense prior to making the molds. With the low cost of these foam kits and the fact that they are quite close to scale in many cases it was a no brainer.

So this build begins half way through the process due to many asking for me to make a build thread. So here we go..........
Last edited by acesimmer; Nov 09, 2012 at 09:29 PM.
Nov 09, 2012, 09:29 AM
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I began by stripping down the entire model of servos, plastic brackets. In fact, anything that was not foam. After doing this to my red version and finding a bowed fuselage from a prior crash. My friend gave me a brand new one that I had sold him several months ago. So now you see a grey T-28 being abused. After the strip I wet sanded the entire model to level and clean off any residue that decals and sloppy manufacturing had left.

You may notice that I have chopped an inch or two off the nose. This is to allow me to install a solid ply firewall in the final model that will accommodate just about any motor unlike the foam one which mounts are engineered for the factory 500KV version. This would also allow for a nitro motor if desired.

The rear stab was also removed. I was going to use a two part stab with a spar tube then decided to mold the stab in one unit and have hidden internal control surfaces. I also have to be very concerned with weight on this conversion.

I also made the decision to have the option of a scale working cockpit. So I used the front portion of the canopy and attached to the fuse permanently. This was then filled with two part expanding foam to make it rigid. The biggest part of all this conversion is to imagineer the finished fuse while deciding what goes here and their so you can place equipment or scale working bits like sliding canopies and such.
Nov 09, 2012, 09:47 AM
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At this stage it is time to start filling and shaping any area's that need to be filled. On this build I had used spackling type compound to fill the indented panel lines in prior to glassing. On future builds I will just glass first then fill with auto body fillers of whatever type is needed. So far I have only used two part scratch putty that seems to be the best medium and easy to shape and sand. When using these fillers it is important to note that they will eat foam so you must cover with Epoxy resin and glass cloth first or say good bye to your plugs.

For filling and adding shapes I use either the pink or blue insulation sheet foam that can be purchased from any of the big box hardware stores. These foams are easy to machine, sand and shape and leave quite a smooth surface to glass over. I learned this one from both Andy and Brent who built and flew two super nice 12 ft T38 twin EDF Talons at Vegas last month.

One item of note is that I cut off the hinge blocks from the vertical stab. I then made silicone molds of them and cast in a urethane resin so that I could have the ability to shape them for a more crisper finish. I then re-attached them to the stab after the epoxy resin was applied. This makes for a much easier mold to be made with a finer finish.
Last edited by acesimmer; Nov 09, 2012 at 09:57 AM.
Nov 09, 2012, 10:08 AM
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Time to experiment.

One of the hardest parts on this model is the detailed engine cowl. I decided to make this in three parts. Two halves for the cowl itself and a silicone casting of the radial engine. I would then layup the cowl halves and seem with tape or just lay it up in one piece. Then I would pour a casting of the radial engine and then attaché the two units together.

So I filled in the top engine to make a parting plane then formed up the the two mold halves. The first set of molds did not work out due to the cowl nose being very sharp and causing a release problem from the molds. So I changed my plan of attack and made a silicone cast of both the engine and front cowl nose in one part. Then I attach the cowl halves together and lay them on the silicone mold in the correct position. I then pour the resin mixed with fillers to reduce weight directly in to the silicone mold and when dry they are welded together forming a one piece unit. The weight came out a few grams lighter than the original which is plus one for me. yeah baby!
Nov 09, 2012, 10:16 AM
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I made several prototype cowls to test different methods. The mold picks up the rivet and panel detail really nice. However, I need to improve my techniques as this is a difficult part to make with all that detail.

I have now several more parts and a couple of molds later and am 95% happy with the results. The engine looks simply amazing. I can also pre-paint the silicone engine mold in black or aluminum so that it pops out pre-painted and the cowl is pre-primed ready to touchup and final paint finish.
Nov 09, 2012, 10:28 AM
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I had thought my plugs ready until I took a trip to Ace in the hole in Vegas last month. Then I saw many models of fine finish and scale looks. Particularly John Morgan out of Tennessee. John is a super nice and skilled model builder with quite the lineup of models at the show. So with that said I had to step up my skill level so that next years event I could have something decent to show. I researched all kinds of methods of how to make panel lines look real and so forth. Then I came across this method of masking then spraying with high build 2K primer and feathering the panel back into itself. So I used electrical tape that is 0.010" thick that I got from the Lowes electrical section. It cost about $5 and you get a package of several colors that are about 3/8" wide. This is absolutely perfect for making tight curves and leaves a crisp finished line at just about the correct height to look nice and scale.
Nov 09, 2012, 10:34 AM
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So two weeks of eight hour days and I'm installing the parting planes. I have pre-waxed the plug with several thin coats of parting wax. This will allow me to be able to add masking tape to the parting plane back for hot gluing the planes to the plug and to stop drips if any from damaging the back face when applying resin. I used 1/2" melamine shelving that has a smooth finish. Once installed ready for resin I will add the bumper stops to the PPlane face for alignment and then several coats of parting wax and a couple of mist coats of PVA parting agent.

I'm doing the fuse mold in four quadrants due to some very deep cavities and the wing saddle. I will add a few tire air valve stems in strategic places so that I can use air pressure to help release the mold and for final laid up parts. I used this method thirty years ago when I built my first mold of a BA Hawk that was 6ft long and it worked really well. The wing saddle on this bird will also end up being a natural battery box that could take very large packs that will be centered right on the CG for both Yaw and roll axis.
Last edited by acesimmer; Nov 09, 2012 at 10:40 AM.
Nov 09, 2012, 10:57 AM
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And here we are now caught up and almost ready to layup the mold. Sorry that My pics and write ups are so out of sequence but I'm trying to do this update all in one go. So today is the day that I assemble it all together and begin the long molding process starting tomorrow morning.

Now here is the rub..... How much detail do you add to your models?. Well a couple of months ago I was at the Reno air races and came across a newly restored T-28. The owner pilot was gracious enough to allow me to crawl all over his nice new bird and take lots of pics. My intent was to be reasonably scale. Then seeing J Morgans models I had to go a few steps further. So I began laying out the panels to be raised and over lapping and just go full out. Then I was online and saw a model that was detailed exact to scale and was also a very large 1/4 or larger scale model. In truth it would look like crap on a smaller model of my size. Just to many rivets and panels would be distracting and look like my model had the pox.

This is because it is extremely difficult to make rivets that small that would look good yet still show up after a coat of paint. So a balance must be found. I made my own Rosy Riveter tool so I could get the size that I wanted. I mixed up a blend of Tight bond yellow carpenter glue with about 10% Elmers white glue then added water to get the right drip consistency. I then spent a few hours applying rivets or well Rosy did at least. She was a bit wobbly to begin with but soon got the hang of it. So the final result is that I used the main panels with rivets but decided not to do the rivets within the panels that would be holding down the panels to the ribs and stations. The test piece that I did was so crowded with little dots that you really could not make the actual detail out. So I'm glad that I resisted to much detail. Once painted and decals attached I think this will look very nice.
Nov 09, 2012, 11:43 AM
Should've, Would've, Could've
v8truckin's Avatar
Great work!!!
Nov 09, 2012, 11:55 AM
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raipe's Avatar
So cool, really nice detailing. Subbed in to see the outcome

Nov 09, 2012, 12:52 PM
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DamonH's Avatar
Wow...very nice!
Nov 09, 2012, 01:45 PM
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Prof100's Avatar
Double WOW!
Nov 09, 2012, 02:29 PM
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J Morgan's Avatar
Wow! Great work Ace!
Looking forward to watching the rest of your work and learning some new things. Thanks for starting it and sharing with us.

Nov 09, 2012, 03:06 PM
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Willsonman's Avatar
Looking forward to this.

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