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Skinning models in metal - tutorial on compound curves..


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Hi gang :)

 

Having done a tutorial on how to cover models in sheet litho plate here, it is now time to show how to address compound curves.

 

Litho plate even when annealed does not take too kindly to full compound and convex curves, for this we need to use pewter or very thin aluminium

 

So, first a little about the materials – on the left is very thin aluminium 0.03mm thick, almost like very heavy tin foil. I wish I could say more about what it is and where it comes from, but it was sent to me by someone on Hyperscale after they saw what I was doing with my F7F (for free – very generous and the only reason I don't put who they are is I wouldn't want them to be contacted off board without telling me its ok first - sorry)

 

On the right is a sheet of pewter – 0.08mm thick and one A4 sheet cost me £22 GBP! So to be used sparingly

 

005_zpsluajbdl7.jpg

 

So today we need to cover this wingtip – you can see it curves in many directions and is not flat or linear anywhere apart from the edge the abuts the wing panel...

 

..the area you are going to put a panel on needs to be as smooth as if you were going to paint it, otherwise any distortion will come through the new panel as the material is so soft..

 

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..first step is take a piece of household masking tape and cover the area, the soft balsa block is to burnish the tape down over the shape...

 

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..you can see here it is burnished down and has a few wrinkles where the tape won't take a compound curve either, next step is to run a cocktail stick around all the perimeter where the tape meets other panels or where we need close definition to see what is going on underneath..

 

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..then we run a pencil (proper one with a 0.3mm lead, not one you sharpen) around the outline of the panel we want to make – also mark any access panels or any rivet lines that need to meet other rivet lines, like the ones here on the top wing..

 

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..carefully peel the tape off and lay it down on the foil / pewter and roughly cut it out...

 

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..add any rivet lines or scribe any access panels etc...

 

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..carefully cut out the part – a sharp blade and steel rule for straight lines, a pair of scissors for curves – make sure you cut to the outside of your pencil lines as this is the actual defined edge where the pencil rubbed up against the adjacent panels etc

 

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..now we need to burnish the panel flat again as it will have deformed under the rivet wheel or scriber – you can see here it is just a round handle being slid along on a clean cutting mat - (must be free of bumps/glue/cuts etc or these will end up on your part)...

 

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..then we tape the part where we can burnish away from a fixed point, so here I can tape it to the wing panel straight edge, and use the balsa block to work away from that fixed point over the edge of the wing tip..

 

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..more..

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..as we work over the edge of the wingtip you can see the material starting to kink at the front of the tip as it responds to trying to go over compound curves...

 

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..you can see the rear of the wingtip is fine – nice and straight with no kinks, so we want to tape this bit down and chase down the kinks at the front..

 

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..with the rear taped down it now can't kink while we work on the kinks at the front – this is all about localising where the metal distorts to the smallest area and using the balsa block to smooth our way through it...

 

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..now we have pretty much gone as far as we can with balsa and have a few persistent kinks to deal with, we can also tape down the front to localise the kinks even further...

 

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..then we need to work these ones out with a harder tool – a cocktail stick is ideal, work from the back of the kink, always moving towards the edge where you want to run them off completely...

 

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..eventually they are all chased out ..

 

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..now if we peel off the supporting tape, (but not the attaching tape) we can pull the part down and check how it fits with the adjacent panel..

 

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..any adjustments are easy with a sanding stick – always go slowly as you can always take more away by sanding, but never add it back..

 

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..then we take the panel off and any persistent kinks can be worked out with a curved hard tool onto a hard surface – here I use scissor handle and a Perspex cutting board...

 

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..it's now time to remove the template tape and have our first look at the complete panel – this needs to be done pretty gingerly as we can easily distort the panel or bend it if we are not careful. If we do just put it back in place and burnish out the damage..

 

084_zps9zqfwlyv.jpg

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..time to mask up for glueing – I do this with every panel as it means no mess and no waste glue affecting the surface where we attach other panels – anything on the surface will come through..

 

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..this is the glue I use – any good contact adhesive will do, but it must be diluted to the consistency of syrup – use the cleaner to dilute it and keep a supply in an airtight jar..

 

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..paint the glue on both surfaces and IMMEDIATELY peel away the masking tape – if you don't the glue will start to go off and when you peel the tape you will take big gobs of glue surface with it...

 

..the panel is held on a little tape roll so I can paint the glue without getting it all over my fingers..

 

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..the most critical part – the alignment needs to be spot on first time – there is NO adjustment, so use a good point of reference to work from – I sometimes put pencil ticks on the surfaces to line them up – here I used the straight edge of the adjacent panel and the lens of the light for alignment...

 

..use the balsa block again to work the part down onto the glue surface..

 

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..final burnishing of edges with a cocktail stick...

 

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..and 20 minutes after starting the panel is done..

 

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.. I see the other tutorial has helped some to take the plunge and try it so I am very pleased – I hope this one does the same

 

I am always here for any questions...

 

TTFN

Peter

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hi all..

 

a little appendix to add as I found something vital out in the last few days..

 

..where really tough curves mean the material kinks in a way that just cannot be burnished out, like on these cowling nose panels..

 

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just burnish them down with some hard wood like a cocktail stick as far as they will go...

 

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..and then get a good but fine needle file and carefully file out the kinks - as you do it you will see the material sort of feathers itself into itself (I never was much of an author...)

 

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..then get some fine wet'n'dry and use it dry, or micro mesh or whatever you have that will give a few stages of abrasion...

 

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..then get some 0000 wire wool and polish it up - I was pleased with the result...

 

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good luck & try it..

 

TTFN
Peter

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Great stuff Peter - good fix on the cowl lip. That is exactly what I did on my 1/72 Matchbox P-51D Mustang wing tanks and around the nose cowl area (this was actually a basket case model as I rescued it from the scrap bin as my first attempt at experimenting with foil covering 11 years ago).

 

Finishedmodels012small.jpg

 

Finishedmodels015small.jpg

 

Derek

Edited by Derek B
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Thanks again, Peter, for this tutorial.

 

One question: You said elsewhere that you are using 0.05 mm aluminum. I have some of that myself, but personally found it a bit thin and have mostly used 0.1 mm aluminum so far. Would you suggest, that thinner is better for these tough curves?

 

Cheers

Rainer

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