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Old 02-21-2009, 01:46 AM
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Leif Ohlsson Leif Ohlsson is offline
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Laminated props in paper

I think I have found a reliable method for making good scale models of two-tone laminated propellers in paper. The search for such a method started with the on-going Sopwith Camel build, and has kept me occupied for well over a month now.

The basic idea is to use two tones or shades of wood-coloured paper. For a 1/16 scale prop this requires 36 layers to build up into scale thickness. Original vintage props of this kind were laminated from 9 layers, judging from photos and drawings. The scale prop therefore is built up of four layers of one shade of wood-coloured paper, alternating with four layers of the other shade.

This is what the finished 1/16 scale prop looks like, against a background of previous generations of test-builds, more or less unsatisfactory:



The method

Each of the 36 layer parts consists of a prop part and a rectangular jig. The jig is just what's left when the prop is cut out from the rectangular layer part. Jigs and prop parts are glued in order to form a stack, and at the end of the build the jig parts are peeled away in halves.

This method accomplishes some important ends:

1) The jig ensures precise and automatic alignment for each prop part in spite of the very small dislocation called for at each layer.

2) As presure is applied to the stack during the build, each jig section will press down evenly on the trailing edge of the prop part beneath it.

3) Concurrently, each jig part will support the leading edge of the prop part above it.

The result is that all angles and profiles are properly maintained throughout the build. Sanding will still be necessary, but is kept to a minimum.

The kit

With the help of Jason I have uploaded the 1/16 scale kit to the aviation part of the downloads section of the site. It consists of four pages. Here are illustrations of the first and last pages (the two others are just more parts, similar to those shown; quality is much superior in the download):





I wish to thank Gil Russell for reviewing the instructions of the kit, as well as the method in general. His comments and thorough scrutiny of a first version (which I optimistically thought might be alright...) led to a much clearer description of the method, and made me rethink & simplify some elements of it to great advantage.

Gil should also take credit for the idea of using petroleum jelly (Vaseline) on the edges of jig parts. This is absolutely crucial to enable a smooth peeling off of the jig parts at the end, and I learned it from one of his many experimental threads, pushing the envelope of paper modeling.

Without it, layers and parts will only get glued to each other into a hopeless lump of paper and glue. I know, since I've tried the method without the petroleum jelly.

Leif

Last edited by Leif Ohlsson; 02-21-2009 at 01:54 AM.
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Old 02-21-2009, 01:49 AM
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Leif Ohlsson Leif Ohlsson is offline
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Building the prop

I'll describe the general procedure for adding a layer to the stack of jig & prop parts, step by step.



Here, the prop part has been cut out from what the rest of the layer part. The rectangular remnant forms the jig. The inner edges of this is carefully brushed with petroleum jelly (Vaseline), on both sides of the paper. Next, glue is applied to the end parts only of the already started stack:



Glue is always applied to the stack, not the part to be glued. This is to avoid making the slender prop parts even more flimsy from wet glue. (The two bottom layers of the stack are treated somewhat differently, as described in the instructions of the kit; here we are only concerned with the general idea.)



To keep the glued jig part from bulging ("lifting") from the stack, a thin line of glue is applied to the long edges of the stack.

After a while I discovered a better way, namely to sort of "edgecolour" the top of the stack with glue before pressing down the jig part. The "edgecolouring" is done so that a very thin line of glue is left on the top surface of the stack. The effect when a layer jig part is pressed on to this is somewhat like the binding of a paperback book or a simple tear-off notepad.



The stack with the glued jig part is placed between two glass panes (from cheap picture-postcard, clips-type frames). A hefty weight is then placed on the glass panes (with the frame backside as protection). I used between 2,5-5 kg (5-10 lbs) for this build.



Glue for the prop part is spread through the cut-out in the jig. Avoid smearing too much glue on the very edges of the jig. In spite of the petroleum jelly, some might adhere.



Stick a needle through the centre of the prop part and place it in the cut-out of the jig part. Alignment is almost automatic. And press down again:



After a while I learned to make these two operations in one go, which saves time. But making this prop is still a time-consuming process. Be prepared to do something else while each layer, or at least every second or third, is left alone to dry out for a while.

If parts of layers start to bulge, you have been trying to speed things up too much. Leave under pressure for some additional time.

When all layers have been glued, let the finished stack dry out completely overnight.

Leif
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Old 02-21-2009, 01:52 AM
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Leif Ohlsson Leif Ohlsson is offline
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Finishing the prop

This is what the stack looks like when it has dried out under pressure:



It is very compact, and satisfyingly straight and aligned. Now cut off the very ends of the stack (where glue has been applied more liberally). This frees the jig parts to be peeled off:



Here the peeling has been done, one layer at a time, down to about half the height of the stack. Peeling is very easily accomplished, thanks to the petroleum jelly. No layer has glued itself to another (except where intended along the edges), and jig parts dissassemble very easily from the prop core, even where they are inserted between layers of prop parts, like at the leading edge.



The last two layers are cut loose at the trailing edge. This procedure is described more closely in the instructions. The bottom two layers are glued together for the whole section behind the trailing edge. The reason is that you want to stabilize the very slender prop parts at the beginning, and also to get a stable start for the build of the stack.



It is advisable to varnish the whole prop once before sanding. This is to seal all loose ends and possible gaps.



This is what the prop looks like when it emerges from the stack, after peeling away all jig layers, and after having received the precautionary coat of varnish. It is ready to be sanded, and - if I may say so myself - exceptionally clean. No further trimmings or shavings have been done yet.



Sanding is necessary, but the amount of it is comparatively small, since each prop section is carefully drawn to correct profile. Continue sanding & varnishing until you are well pleased with the outcome.



The final task is the hub parts. I printed these on the backside of silver paper and embossed the nut & bolt markings.



This is what the back side of the finished prop looks like. (I have already shown the front at the beginning of the thread.)

On the front I tested cut-off pins for bolts. It worked beautifully well, but they were too shiny (bolts were hardly nickel- or chromium-plated at the time), so I painted them with silver gouache before varnishing.

Only water soluble glue, varnish and paint were used when building this prop.

I'd like to think that the general method of making laminated parts from coloured paper might be used by some designer for other purposes.

Leif

Last edited by Leif Ohlsson; 02-21-2009 at 02:46 AM.
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Old 02-21-2009, 02:46 AM
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Amazing , looks so real.
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Old 02-21-2009, 03:10 AM
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A well done tutorial, well explained and well illustrated; overtime work by master model maker.
Thanks Leif.

Orazio
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Old 02-21-2009, 07:46 AM
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Holy prop blur. I don't have enough adjectives to adequately express
my disbelief. Simply astounding Leif. Truly a masters work.

Ray
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Old 02-21-2009, 07:46 AM
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Thank you Leif - I will refer to this when I start building some of the planes in my collection where a wood-grain prop would be appropriate.
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Old 02-21-2009, 08:15 AM
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ct ertz ct ertz is offline
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That is so cool. I have to try one, even if I currently have no plane to put it on!
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Old 02-21-2009, 09:09 AM
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Outstanding technique!

I just love the idea that the rectangular cut-outs -- normally scrap to be discarded -- can serve as a jigs to guide the part placement! Elegant and ingenious!

Using the cut-outs as guides - this idea could be applied to other similar assembly situations where part alignment is critical, but tricky to perform accurately. It could also be used for situations in which it is not possible to mark the place where a part is to be attached. It's easy to very accurately align identically-shaped pieces with straight edges ... then let the "holes" do the precision work!

This is another great example of ground-breaking techniques that are going to carry this hobby forward. Digital card modeling is so new, techniques like this are creating standards for the future. If designers continue to innovate techniques that make assembly challenges easier to perform accurately, models can become increasingly complex without becoming increasing difficult to assemble.

Bravo Leif & Gil!
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Old 02-21-2009, 10:20 AM
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willygoat willygoat is offline
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Nice work Leif! That is just an amazing prop. Now, If only I had something to put it on.
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