Foam building ABC - RC Groups
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May 01, 2011, 04:16 AM
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frank40's Avatar

Foam building ABC


I have been getting a lot of PMís regarding how I build in foam. So I have decided that I will do this thread to show my approach on building with foam. I learned from some of my good friends, and I think it works very well.

First find a suitable building material.
To make sure the material is uniform I cut my 100 mm foam down to 90 mm

In the design processes you need to divided the model in sections, that match the building material.

I use a hotwire to cut the foam this can have many forms, but itís just at wire extended between tow points. The wire I use is a 0.35 mm constantan wire. You also need a power supply to feed the wire, you need 2-3 amps. Depending on how hot you like your wire. If you have a charger with current limiter, you should bee able to use that. The wire for cutting the wings are a bit different, comes at a later time.

Some picís of my hotwire cutter: More to come.
Last edited by frank40; May 01, 2011 at 04:26 AM.
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May 01, 2011, 06:40 AM
it wasn't me flying that plane
Hover or die's Avatar
Thanks for taking the time to do this Frank..Many of us will bebefit from a thread of this nature..A big thank you!
(Chris raises hand as 1 of those sending PM questions)

Thanks Frank!
May 02, 2011, 12:30 AM
Registered User
LuvEvolution7's Avatar
deffinitely watching with eagerness to learn.
May 02, 2011, 03:31 AM
Alpha Whisky

Foam Building ABC

I`ll be watching for sure.

Can you please include use of Depron in this if usage differs from your wirecut foam....

Is there such a thing as a portable hand-held wire-cutter for shaving foam - sorta like an electric paring or whittling knife....?

Alan W
May 02, 2011, 12:55 PM
miniture aircraft pilot
rcshirt's Avatar
i'm subscribed
May 02, 2011, 01:26 PM
Registered User
frank40's Avatar
Hi there, Pleas bear with me, English is not my first language.

AlphaWhisky, Sorry but I have never build in depron.

Now for cutting the sections:

You have to cut each section out, so you need some jigs to make the cutting easer. Before cutting you need to decide on how thick you want the walls, I use 7-10 mm this give you some material to sand and it your end up with 5-8 mm. I use something called a “passer” in Danish, don’t know the word for it, to draw the inside line.

I make my jigs by gluing my print (with ref. lines) on a 2 mm cardboard using stencil glue, and then cut it. I sand the edges of the jigs to get a nice smooth edge so my wire don’t get stuck while cutting a section.

When I cut a section I start buy cutting a piece of foam to size I need, make sure all
edges is 90 degrees otherwise you will get a bad result. I draw some reference line on the foam so I can align my jigs just right. To fix the jigs on the foam I use stencil glue and needles. The section is now ready to bee cut, much like cutting cheese.

Ones all section are cut inside and out it’s time to glue them together, for that I use a mix of light weight sparttel (not sure if it is the right word) and some expanding glue.
You will have to play around with the ratio on the mix, it may chance depending on the type of glue you are using.

When all the section are glued together and the glue is dry, I split the fuselage in two half for sanding inside the fuselage. Then you got all the bump and unevenness sanded away it is time to glass the inside of the fuselage.

Hope this make seens.

Here is some pic's, I will try to get back soon.

Take care
Last edited by frank40; May 02, 2011 at 02:15 PM.
May 02, 2011, 08:26 PM
Addicted to building...
Freddie B's Avatar

I thank you for this great thread idea. I am subscribed and will follow closely.

I build in foam a lot, but need to know more about, and do more wire cutting.

A good source for power to the cutting wire is a Brushed ESC, and a servo tester. A TX and RX can be used with the throttle channel, but Servo testers are cheap enough. I am using an old 40 amp ESC and 2 or 3 cell lipos. I heard a 1o amp ESC is more than enough power, I just hapened to have the 40A sitting around.

I use standard .022" music wire (from hobby store), but I heard SS stranded fishing leader works well too.

Thanks again

May 03, 2011, 12:30 AM
Registered User
Thank you for sharing your techniques. When you split the glued up fuse in half ,are you using the hot wire to cut throught the center or are you using a cutting edge ( like a knife). Thanks
May 03, 2011, 08:51 AM
Registered User
Pity that when some of these "How To" threads start, there isn't a parallel sycophant and bu*****t thread to keep instructions all in one place.

2 build threads and 7 (including mine) of clag

Regards Ian.
May 03, 2011, 10:59 AM
An itch?. Scratch build.
eflightray's Avatar
Originally Posted by AlphaWhisky
I`ll be watching for sure.

Can you please include use of Depron in this if usage differs from your wirecut foam....

Is there such a thing as a portable hand-held wire-cutter for shaving foam - sorta like an electric paring or whittling knife....?

Alan W
There is a lot of info on using Depron in the Foamies (Scratchbuilt) forum
May 03, 2011, 02:31 PM
Registered User
frank40's Avatar
Hi Claus

That looks abselut AWSOME, is the drawing complet, sure I am going to build the WF33.

Claus is one of my friends that taught me to use this technique, in fact I think he is the one that came up with this technique.

Claus if you want to chip in on this thread you are more than velcome.
Last edited by frank40; May 03, 2011 at 02:41 PM.
May 04, 2011, 01:47 PM
Registered User
frank40's Avatar
Carl. I use a sharp knife, it not very critically.

I am happy to say that Claus has decied to join this thread, he is the man when it come to this building technique. We are at the monent talking about doing a bit different, we might star all over. We will get back to you, see you.
May 04, 2011, 05:19 PM
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Osprey Engineer's Avatar
Can you post some pictures of the jigs you use to cut the foam blocks evenly with 90 deg angles? This was my biggest issue when I attempted this method. Not all my left and right sections were the same thickness and this caused alignment issues as I assembled the pieces. I also did not have a side view template to align the section on. That would have saved a lot of head aches.

May 05, 2011, 01:16 PM
Registered User
frank40's Avatar
Hi Osprey Engineer

That a nice build you are doing. I have posted a pic. of my jigs. Maby it would be better if you did't cut your jigs i half, this will give you a better sability.

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