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Old Feb 15, 2015, 08:41 AM
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Southport Merseyside UK
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Mini-HowTo
Easy Depron Forming

Although there are a few threads explaining how to form depron and the method that our group of indoor fliers use has been gleaned from other sources, people have asked me how I do it so thought I a short tutorial might be useful.
The method I am going to describe works for us and is a fairly simple way but does not give highly detailed surfaces, if you want that then suggest you look for posts by Harpye.
Using our technique we have constructed a number of scale indoor models ranging from WW1 biplanes, WW2 fighters and bombers (single and multi-engined) to the model I am using as an example which is a 16" span twin edf of the S3 Viking.
The Viking weighs 40gm ready to fly including a 220maH single cell lipo and a steering nosewheel, it is painted using sprayed Copic poster pen and stick on vinyl markings, originally I did not have the flaps or slats but for the slight addition in weight it slowed down the flight speed and the flaps also gave an increase in wing area, the wing features a simple Jedeslky section which seems to work ok. I know it should be a drooped leading edge and not slats but it looks ok and if they did't work I could have easily removed them.
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Old Feb 15, 2015, 09:06 AM
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To produce the moulded fuselage we will require the following items.

1. A sheet of 3mm Depron or AeroDepron.
2. Some 12mm (or thicker) MDF or Ply.
3. Parcel tape (cheapest you can get as you will use a lot)
4. Pink or blue insulation foam sheet (I used 50mm thick from the local DIY store)
5. Sharp scalpel blades which must be used sharp ( as soon as they start to lose their edge replace as anyone who has tried to cut depron with a blunt blade will know it tears the edge rather than produce a nice clean edge).
6. Sandpaper in various grades.
7. A bandsaw, jigsaw, fretsaw or coping saw.
8. Small hot wire cutter is useful but not essential as the foam can be cut using any of the above saws just very messy.
9. Finally a domestic oven big enough to take the mould that has a reasonably accurate thermostat. (Mine is not very accurate so I took a number of measurements using a digital thermometer and then marked required temperature next to the settings indicated on the oven, as you can see in the photo quite a difference but it is an old oven and has probably lost its accuracy over the years.) If you do not have a multimeter then it might be worth paying a little extra and getting one that has a temperature probe. (as an electric flier a multimeter is essential)
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Old Feb 15, 2015, 09:33 AM
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Right lets get started.

The fuselage is going to be made in 2 halves with the split being vertical as most fuselages are symmetrical about this line.
First thing we do is to get a drawing of the side elevation of the subject and scale it to the size of the model then reduce all round by the thickness of the depron being used, in my case 3mm.
I then print out 2 copies of this and stick to 12mm mdf or ply, I then roughly cut around the outline leaving about 2 or 3mm (about 1/8").
These 2 spine elevations are then aligned and stuck together using double sided tape, we now sand the outline down to the printed outline being careful to ensure that the sanded edge is at right angles to each outside surface so that we have 2 identical spines. (If these are not identical then the 2 fuselage halves will not have a good joint.)
The next thing we have to do is produce the 3d plug onto which we will mould the depron.
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Old Feb 15, 2015, 10:02 AM
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Once the spines have been sanded to the correct outline and before separating mark each outside face.
Cut 2 rectangular blocks of your styrofoam about 12mm (1/2") larger than the spines and 12mm (1/2") thicker than half the width of your fuselarge.
Separate the 2 spines and onto the unmarked face affix a block of whatever styrofoam (pink or blue)you are using. This way the edges of the finished fuselage halves will be as identical as you can get them for when they are joined together.
Onto the top and bottom faces of these blocks mark out the plan view of the fuselage, the centre line of the fuselage drawings must coincide with the join between the foam block and the wooden spine, again don't forget to reduce the width of each half of the fuselage by the thickness of the depron.
Cut with a fretsaw etc vertically following the lines showing the plan view (I used a simple hand held hot wire bow to do this, next cut elevation using the spine as a guide being careful not to damage your nicely finished spine (tip here before starting to cut this put some masking tape along the edge of the spine as protection.
Once the rough 3d shape is done now you put on your dust mask and take the 2 fuselage halves and sandpaper and go outside to sand to shape. (otherwise you workshop will be full of styrofoam dust and bits for years)
Don't worry about slight imperfections as the plugs will be on the inside of the moulded fuselage.
Attached photos of my plugs showing the spine and the finished shape ready for moulding.
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Old Feb 15, 2015, 10:35 AM
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[ATTACH][/ATTACH]Next we prepare our depron and attach it to our plug.
Take a piece of depron a few cm large than the plug and cover with one layer of parcel tape, overlap the tape edges by 6mm (1/4") as shown on one side only of the depron.
Now we have to attach the depron to the plug, starting at one of the long edges of the depron sheet stick a piece of tape onto the taped surface about 20mm (3/4") with another 50mm (2") loose try and position this tape at the top and widest position of the plug, align the edge of the depron with the edge of the plug and tape to the exposed side of the spine such that once the depron is wrapped over the plug the taped surface is outside and the untaped surface of the depron is against the plug.
pull the depron over the plug at the widest point and tape to the other edge.
If necessary cut the depron so that it does not protrude beyond the bottom edge.
We then proceed to work our way around attaching tape and pulling down onto the plug.
I find it best to tape the top edge and then the bottom edge working alternatively and away from the center although if there is a particularly awkward area such as round a cockpit it is sometimes best to try and get that area neat and let any creases that might develop be on the bottom (out of site), it is impossible to get rid of all crease but try to minimise. (It is surprising just how much you can pull and push the depron.
Where I have tight double curvature parts I cut the tape into narrow strips and pull down a small section at a time.
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Old Feb 15, 2015, 10:48 AM
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Once the depron has been taped completely to the plug (ensure there are no gaps in the tape covering anywhere for hot air to get directly to the depron), we are now ready to bake.
Pre-heat the oven to 80C (176F) and once the temperature is reached we put in the plugs covered in depron, leave in for about 10-12 minutes tehn take out wearing oven gloves and allow to cool for about an hour.
These timings are not exact and you might have to experiment a bit until you find what works best for you but they are a good starting point.
I have even on occasions turned off the heating element and left the plug with the mould in for a bit longer and still produced a good moulding.
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Old Feb 15, 2015, 10:52 AM
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Have you ever tried dipping in boiling water instead of using the oven? Not sure if the tape will hold.
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Old Feb 15, 2015, 10:52 AM
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Whilst the moulding is taking place we can now make our mould release tool.
This tool is to ensure that we get a nice neat join between the 2 halves of the fuselage.
We take an offcut of the MDF or Ply or whatever you used for the spine and smooth the edge to the top face we glue or tape a new scalpel blade or sharp modelling knife blade as shown in the photo.
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Old Feb 15, 2015, 11:01 AM
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Quote:
Originally Posted by epilot View Post
Have you ever tried dipping in boiling water instead of using the oven? Not sure if the tape will hold.
The various members of our indoor flying group have produced at least 50 components over the last few years using this method and not had the tape come undone. Another advantage is that we have less chance of injury due to hot water.
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Old Feb 15, 2015, 11:04 AM
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I meant: Not sure if the tape will hold in boiling water.
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Old Feb 15, 2015, 11:51 AM
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Time to remove the moulded fuselage half from the plug.
Using the cutting tool we carefully cut along the edge as shown in the following video and then carefully remove the moulding from the plug.
Note that the video shows a number of layers of tape over the depron but after producing a number of fuselages I now find that the moulding is better if only one layer of tape is used on most of the moulding except where extra is required for particularly difficult areas.
Once the moulding is removed carefully remove the tape from the moulding.

Link to video
Depron Moulded Fuselage (3 min 42 sec)


Once removed carefully remove the tape from the moulding.
If all has gone well the edges should fit together with the minimum of fuss if necessary sand very gently for fit.

If you find you have some creases what I did was to put some UHU POR on the inside of the crease before joining the fuselage halves together.
Join the halves together using your favourite glue for depron preferably using it as a contact adhesive (i.e. coat each edge with UHU POR allow to dry for ten minutes then put together carefully aligning edges as you join).
Leave aside for 24 hrs then sand the join also sand any creases using about 600-1000 grit sandpaper but be careful not to go to far although one of are members who has made the most mouldings managed to get an engine cowl down to about 1.5mm (1/16") from 3mm depron. You can also fill any small blemishes with the litest ready mixed filler that you can find,
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Old Feb 15, 2015, 11:53 AM
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Quote:
Originally Posted by epilot View Post
I meant: Not sure if the tape will hold in boiling water.
Sorry if I misunderstood what you were getting at but I was busy with my train of thoughts trying to get this done.
As only parcel tape I do not think it would hold in water, if you used some waterproof tape you might find difficulty removing the tape from the depron.
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Old Feb 15, 2015, 12:01 PM
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Thanks for taking the time to put together the tutorial. Easy to follow with all the pictures.

To answer my own question, the tape will hold up in boiling water. I did a quick and dirty test using a drinking glass with compound shapes as the mold. It came out really well. It only has to be dipped in the boiling water for app. 30 seconds. Removes the need for experimenting with oven settings. Downside is the plug needs to be waterproof. MDF is like a sponge. Painted plywood would last longer. As you mentioned there is also he risk of being scalded but I use tongs when dipping the mold.
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Old Feb 15, 2015, 12:05 PM
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Apart from fuselages we also mould wings and other components using the same method.
The mould shown here that I used for a wing was made from wood using light ply ribs filled with balsa then skinned in 1/64" ply, I had trouble releasing the wing a couple of times but then was given some release agent that a friend was using when moulding composite glider wing and this seems to work ok, I am afraid I cannot say what it is as he just gave me a small amount.
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Old Feb 15, 2015, 12:09 PM
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A bit of talc sprinkled on the Depron and wiped off with your hand will also prevent the Depron sticking to the mold.
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