Seamless Paper Model construction

[rmks2000]

Looking forward to this. I'll have to see if instructables.com has a how-to for making a foam cutting wand.

[Leif Ohlsson]

Foam-cutting wand - if you find that how-to, please share the link... - L.

[cdavenport]

Give me a bit of time and I'll draw a plan for a foam cutting wand. It's a really simple thing. For now, go to Ebay and purchase some 20 gauge nichrome or stainless steel wire. You'll also need a 12 volt DC power supply; a car battery charger will work as well.

[cdavenport]

Basic Construction: sanding the foam

I have a number of different commercial sanding blocks because I wrote for a several hobby magazines, and I was sent this stuff all the time. For my full size '55 Chevy project, I made a sanding block out of wood and foam. You can do the same thing with some heavy cardboard and the foam from an old mouse pad. You can make any shape you desire.

I believe I forgot to mention an important construction point. BEFORE I glue in the foam blocks, I seal the edges of the bulkheads and longerons with CA (superglue); you'll learn why in a moment.

Once I work the foam down with the previously mentioned wand, I carefully sand the foam with 220 grit sandpaper. The foam goes easily and quickly; you might want to turn on a vacuum cleaner because the foam dust flies in the air currents.

Once you hit the bulkhead/longeron, the foam is sized correctly. By adding the superglue, you ensure a rigid edge that will not fall apart as you sand to it.

Here's another VERY important point if you want to achieve the best possible look to your model. Since our airplane and ship paper models are designed as a series of truncated cones, the longerons/keel sections between bulkheads tend to be represented by straight sections.

Quite often, airplanes and ships feature gentle curvatures, especially aircraft designed after the biplane era. When I sand the foam, I also sand the contours back into the profile, using pictures and drawings of the real aircraft as a guide.

You will see how I handle the fuselage skins to account for the curvature in the next couple of installments.

[cdavenport]

Basic construction: putty

It never fails! To get a precision looking model, you need putty. Invariably, I will get a little rambunctious with my foam wand or pull some foam away while sanding. In addition, when replacing contours, you will notice that the foam surface is above the longeron/keel. Those spaces need to be filled in order for the paper skin to lie correctly.

You can make your own putty with paper mache, but it takes forever to dry and often shrinks. I prefer using artist's acrylic Gesso available for a few dollars at any art supply outlet. A bottle of this stuff should last you through hundreds of models.

DO NOT USE any acid based putty such as Squadron's Green Stuff or Bondo. It will eat right through the foam.

BTW, I artificially colored the putty in this photo so you could see it. In actually, it's dead white when dry.

[calinous]

Originally Posted by cdavenport

Give me a bit of time and I'll draw a plan for a foam cutting wand. It's a really simple thing. For now, go to Ebay and purchase some 20 gauge nichrome or stainless steel wire. You'll also need a 12 volt DC power supply; a car battery charger will work as well.

I've seen an old AT power supply used for this purpose too

[Jan Hascher]

Hi Charles,
nice work so far. But don't make her too round. She is planked with simple sheets of plywood without heat-forming. So the straight sections are quite ok.

Cheers
Jan

[cdavenport]

Originally Posted by Jan Hascher

Hi Charles,
nice work so far. But don't make her too round. She is planked with simple sheets of plywood without heat-forming. So the straight sections are quite ok.

Cheers
Jan

Quite so. The sides were dead flat. However, the profile was nicely contoured. The model does not have that gentle contour; it's merely a series of straight lines between bulkheads.

[Zathros]

Originally Posted by cdavenport

Give me a bit of time and I'll draw a plan for a foam cutting wand. It's a really simple thing. For now, go to Ebay and purchase some 20 gauge nichrome or stainless steel wire. You'll also need a 12 volt DC power supply; a car battery charger will work as well.

A Rheostat will really help you control the current and keep things under control.

[Golden Bear]

Whoa! CD, you just turned this into a different tute... using that foam stuff.

I wish that your posts could be extracted and highlighted somehow because they explain a lot... and folks will never find it under this thread!


C.