A "sticky" course in Depron?

[Foxfan]

Dave,

I could talk you through every stage of making a master pattern for a model car, say, out of brass or Ureol, but it would only be what works for me. The fact that I've made over 500 brass masters since I was 18 (I'm now nearly 63) must mean I do a useful job, but it won't necessarily be the best way and certainly not the only way, but it'll work and it'll be the quickest way I've found, which is important, too, when you're trying to feed a family and pay a mortgage on it, but as I always say to people, "If you know a better and/or quicker way, please let me know!"

I greatly appreciate your time and trouble on the subject of foam which is completely new to me. I recall being shown round Lola Cars when they were doing carbon fibre monocoques, using a huge autoclave. I was clueless, but fascinated. I can't understand people who cast aside new materials without at least a questioning attempt to appreciate the benefits and problems attached.

Cheers,

MrTin

[Dave Hopkin]

They best way forwards is for you to get some depron and have a play, get a feel for the material and what it can do and what it cant, one thing though is you are cold forming curves let the depron warm up to room temp before attempting (if like me the sheets live pinned to the ceiling of the shed held up there by bungee cord!) or the likelyhood of it splitting is increased

[Foxfan]

This time of year, Dave, my shed inner roof is baking hot! I think that's why my new Super 60 twisted on it's aft end.

But you're right. I'll get some Depron and just have a bash at it.

I'll report on my progress, one way or another<G>

Thanks again,

MrTin

[McG 6969]

Hey Foxfan, hello to all,

I've already been posting this before but I thought this could be of help regarding finishing techniques for foam or Depron. This method is not really intended to add some structural strength though, but still very applicable where no lamination is required.

Freddie B's Secret Sauce...

Not such a big secret, as Freddie B - an American foamie guru - himself talked about it in an RCgroup’s earlier thread. Here are some photos to help 'show and tell' in case some of you'd want to try this.

Basically, it’s a filler & primer coat (all-in-one) that doesn't weigh much but works really well. He does this on his foam builds often when there is no covering, lamination or other coating involved.

While many have been amazed by Fred’s finished airframes, this was the process he used. Let’s have it in sequence.

1). Take some light weight spackle (Polyfilla or cellulose based filler) and put a nice size plug in a little mixing bowl. This time the plug of filler is about the size of a nut.

2). Next add some Polycrylic clear varnish (water based of course), about the same volume as the plug of light weight spackle.

3). Get some Talc Powder. Baby Powder or Foot Powder, but the Baby kind smells best… Watch out because many powders are Corn Starch, which we don't want! Talc is the magic that made balsa filler work in the old days of tissue and dope finishes. It is very fine and does a great job of getting those tiny imperfections filled, but sands away nice. Note the 'pile' of powder about equals the volume of the light weight plug we used too.

4). Add two or three drops of acrylic paint (craft paint, water based), and it can be white paint, but often you can use a colour to see the work in process and the finished results shows up better. Anyway, use a colour that works for your intended top coat. Light for light topcoats, gray for everything else. You can use Yellow in the primer if you are painting Yellow top coats, because Yellow (and Reds) don't always cover well.

5). Now mix it well. It is very thick, but get it creamy and all one colour and texture, working out any chunks. Now add water until it is like very thin whipping cream, thin shaving cream, or even thinner like a very thick paint. Brush this on your pre-sanded foam, making sure to completely wet everything and force mixture into any hollows, dings, scratches, etc.

Let this dry. Then sand it all with some 180 grit, and 220 grit papers, mounted to some sheets of beaded white foam. The foam sanding blocks are flat, but 'give enough' to not cause grooves and scaring. Just make sure to remove sanding dust often and use a reasonable pressure while sanding.

When you have sanded most of this formula away, you will see some original foam, but also many areas of filled and flush mixture and the surface will be very smooth. Little weight gain, yet ready for top coating with paint. You can sand with even finer papers, depending on what top coat paint you will be using. This is good enough using craft paints, but if you intend to spray with Model Master or Tamya paints, you could go to 320 or 400 grit paper. All three kinds of paint work well with this process.

I’m truly convinced by Fred’s method and really worth trying this out on a piece of scrap foam or Depron.

Last photo is a sample on a scratch build FFF (Folding Fan Foam) Russian Mig that Freddie B built with his filler/primer method.

Happy filling

Chris

Brussels / Belgium