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Old 03-11-2004   #1 (permalink)
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Working with Blue foam.

Blue foam can be the solution to many problems,if you need a quick plug from which to prepare a glass fibre or other shape then this could be your answer,there are many different ways to tackle the problems of making difficult shapes for our models which we will discuss in detail some other time,but for the present here are a few tips gleaned from using this versatile material-
Main suppliers are builders yards or those dealing with insulation,I have found it in both blue and pink colours but the density looks the same,biggest problem is is the sheer size of the panels,so dont forget to take a bread knife (the best tool for rough cutting large areas) with you to make it more manageable and fit into your car.
Say we are intending to make a fuselage then best way is to prepare card templates for the side view and top view,mark out the side first with a marker pen and if you are lucky enough to own a bandsaw rip out the shape leaving a margin all round,next take a large sanding block and sand up to the line,now mark the top shape of the fuselage and all you need here is a Surform with a new blade fitted which will rip through nicely,having done this start shaping to the cross sections from the plan,if there are any undercuts such as a flying boat hull use a curved Pirmagrit tool which you will find invaluable in your tool kit,keep going until you have the rough shape and then start to finish off with coarse glasspaper moving along to fine,you will be surprised at how good a finish that can be obtained despite the porous nature of the material,now mix up some PVA adhesive 50-50 and apply all over,leave overnight and sand down all over,to get a really noice finish cover with lightweight tissue using the thinnede PVA,apply as many coats as desired depending on the models weight factor.
Now for the interesting bit,with your bandsaw ( or an hacksaw blade) cut either down the middle from the top of the fuselage or consider cutting horizontally along a set datum line,either way this prepares the blue foam 'log' for internal removal of material,aim for a sensible wall thickness depending on your skill level or the models application,a good tool for this is an ordinary domestic spoon with the end cut off,sharpen the end like a chisel and ram this into a file handle,scoop out the foam until you are happy with the result,just feel the weight going down along the way ! some soldering irons have hot wire cutter fittings but beware of noxious fumes as it produces that ever dangerous cyanide when heated,best to work outside as this is messy material and it sticks statically to everything it lands on,convince the wife that your lawn really does need to be a different colour and blue is in this year.
Once the sides have been thinned you can join them with PVA if you think a few formers will not come amiss then press a carpet fitters corner tool into the fuselage at the point you want,then transfer this shape to some balsa and glue into place using T-Pins to hold while the glue dries,another tip is to press a glue gun into use to tack glue these while the main glue dries.
Once the joint is dry,run a strip of bandage along the joint and impregnate with thinned down PVA adhesive,the surface takes enamel,acrylic or even emulsion paint nicely.
If you have not tried using blue foam then why not give it a try ? it can be the answer to many difficult to reproduce shapes.
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Old 03-11-2004   #2 (permalink)
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I was warned to wear a respirator when cutting blue foam as, when cutting with a hot wire or soldering iron, small particles are given off which, if they get into the lungs, can cause allsorts of very unpleasant and fatal illnesses. As it’s better to be safe than sorry I use a respirator when cutting white foam as well.
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Old 03-11-2004   #3 (permalink)
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Sound advice Dave,we cannot be too careful here,a lot of early foam wing core people ignored this advice and have suffered the consequences from those fumes,inert when cold but dangerous when heated,also applies by the way to PTFE tubing etc.
Thanks for reminding us all.
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Old 04-11-2004   #4 (permalink)
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Almost forgot to mention the finest tool for removing large portions of foam,the humble wire brush works really well,give this one a try you will see what I mean ? by stroking the foam it cleanly removes a layer in one sweep,experiment with the wire brush and see a pile of surplus foam emerge.
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