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Using resin to create a new wing?


obdl3945

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Hi, guys...

 

I have a model kit that requires a completely new wing for the version I want to make.  I'm hoping perhaps some of you would be able to help keep me right.

 

I wondered if I could perhaps use a similarly-shaped injection moulded wing from another kit as a master, create the mould using a vacuform machine, and thereafter, filling the mould with casting resin.  Once the new casting resin piece has been removed from the mould, I would hopefully be able to adjust it using wet and dry paper, to the exact form required.  Casting resin seems to be a worthwhile option, according to what I've read up on so far, but one article described the end result as having 'slight flexibility'... I'm not sure if that means if I tap it with my hand, the resin piece move up and down, or do you think the resin would have sufficient strength/rigidity?

 

Just for clarity, if it was possible to do this, I would be intending to sit the 'master' wing vertically on the vacuform platform, so the styrene sheet would be drawn over both surfaces of the mould.  Should I expect the possibility of the heated plastic sheet puncturing, given it being drawn down over a realtively tall-standing piece (about 12cm) ?  I don't really want to do separate upper and lower surface moulds and then try to align them prior to pouring in the resin.  Can anyone suggest a good casting resin brand to use? 

 

And finally, I use enamel paints for my colour schemes - would such paints be suitable for use on casting resin?

 

Thanks for any help you can provide.

 

Regards,

 

Paul

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I don't think a vacform mold will work, for two reasons: 1. Many casting resins are not compatible with styrene and will in fact dissolve it. 2. All casting resins generate heat as they cure and are likely to warp or even melt a styrene mold. Your best bet is to use a silicon RTV rubber to make the mold. You can make a one-piece mold from rubber, then, after it cures, cut carefully around enough of the rubber to remove the master while leaving the mold in one piece. 

 

Enamels should work fine on resin, but it's better to use a primer first.

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If you can make a vac wing, why replace it with resin? Even experienced manufacturers regularly turn out resin wings that warp in either the short or long term, and thin WW1 wings are particularly prone. Some of the better ones have metal wire embedded during casting to provide strength, but I have two sets of Al;batros wings from the eighties that prove it doesn't always work - they've warped from the horizontal down 2cm at the tips, and also adopyed sweepback of about 1cm per side, in 1/48th scale. The wires have been bent by the resin, and in some places pulled through the surface. Total mess.

 

As to flexibility, I have many resin kits, and the wings vary from brittle to like the average plastic. So long as you uise rigid strut material the resulting wing cellule once constructed is okay. Won't prevent future warping though (although rigging with monofilament line may prevent it depending on the severity - nothing could have prevented what happened to the Albatros wings).

 

You won't be able to draw a two surface vac wing, the sheet will thin out too much, and anyway the resin will be trapped inside even if you could. If the model you're making is 1/72nd scale, a single surace (the upper one) is all oyou need anyway. Looks fine. Just either add lower wing rib detail afterwards by whatever method best natches that on the kit piece you're replicating. If in 1/48th, well, it depends on the subject as to whether or not a single surface will surfice.

 

Paul.

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21 hours ago, obdl3945 said:

I have a model kit that requires a completely new wing for the version I want to make.  I'm hoping perhaps some of you would be able to help keep me right.

I think you are overthinking this.  Too complex,  try this way of making WW1 wings

 

The pioneer of scratchbuilding in plastic was Harry Woodman, he wrote the book, literally

book.jpg

 

see  

http://web.archive.org/web/20080122044909/www.wwimodeler.com/harry/woodman.html

note "by kind permission of Harry Woodman"

for wings

http://web.archive.org/web/20080327095940/http://www.wwimodeler.com/harry/chapter3/09-wings.htm

 

Note this note at the end of the description

"The process as described may seem very long and complicated but it is not so. It has taken the author almost as long to describe it in print as it does to do the job once the wing pattern has been scored. A s always, it is most strongly recommended that a 'dummy run' be carried out first to learn the hazards; one of the commonest faults is to provide over-generous helpings of cement, resulting in the softening of the thin plastic card. When the knack is leamed it will be seen that it is the most effective method of reproducing fabric covered wings and is ideally suited for 1:48 scale and larger scales. The adventurous can use the system for 1:72 using 5 thou card, but great care is needed, especially when applying cement."

 

I posted up a link to the whole book,  as a download, the above is as web pages.

https://rclibrary.co.uk/files_titles/1216/ScaleModelAircraft_Woodman.pdf

 

I have some old Scale Models magazine from the early 70's and his work was outstanding, I was gobsmacked to get a 1976 issue where he describes making his own photo etch, and provides templates.  A true pioneer.

 

Note, if this seems daunting, the materials are fairly cheap,  so you can experiment, and when you succeed in work like this it is very satisfying, and then you can add new skills to those. 

Having grown up reading old model magazines,  there is now a tendency to go direct to aftermarket, or in the case of the methods you proposed,   aim to make your own aftermarket, when for a one off wing, a simpler solution exists using some modelling skill. 

 

HTH

T

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      It is impractical to cast resin for one or two parts. You need tin cured silicone rubber and catalyst, sulphur free bedding clay, urethane resin that has both strength and sufficient pot life before it begins to thicken, vacuum pump for degassing, and sometimes a compressor if pressurizing the poured resin is necessary to force it into small cavities (example: cooling fins on rotary engine cylinders).

       If you decide to make multiple castings, a very good book is Secrets of Expert Mold Making and Resin Casting by Karl Juelch. Available through Amazon. An important factor to prevent warping in parts with thin cross sections is heat curing the castings. The book shows the use of a group of incandescent light bulbs for the heat source but I would suggest using a pail or drum heat band with a built-in thermostat. 

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