Scratchbuilding complex shapes

Got a question about techniques, materials or other aspects of physically building a model? This is the place to ask.

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bmagee
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Scratchbuilding complex shapes

Post by bmagee »

Hello All,
I am inspired by all of the truly talented people here at SSM and have learned a great deal by reading and posting in the forums. To this point, I have never scratchbuilt any models. But now I feel like I want to try. I have chosen for a subject, the USS Excelsior. I want to build her in 1/350th scale= 52.5 inches long/ saucer dia. 20.25 inches; if I have worked the math right. I have a plan for an internal armature to keep the model from sagging, made from sheet aluminum and acrylic and bolted/screwed together.
My question here is how can one go about making complex shapes like the saucer halves, upper and lower; and the secondary hull? I need a few ideas here. What do you do when faced with making these types of parts. I have seen everything from plank on ribs const. to carving with blue or pink foam. This phase of the construction is the intimidating point to me. Building up parts from styrene is no problem; when the part is basically a box as I've done it before. The beautiful curved lines I have seen on some of the scratch built models here is fantastic and my hat is off to those of you brave enough to take on a project like that. What kind of options do I have? If any of you have pics of any process you use feel free to email them to me! Thanks in advance! :?
Shinnentai
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Post by Shinnentai »

For unilateral shapes like a saucer, I like the lamination method. All you need is a circle cutter and, a cross section drawing of the shape along its axis.

See lasse Henning's excelent site for a description of the method. Though for a saucer, I'd make the layers perpendicular to the part's axis rather than parallel/circumferential (hence the circle cutter).

Much faster, more accurate, and less fussy than plank-on-frame or foam, IMHO.

The forcastle decks could then be built as a simple box construction on top of that. The neck joint recess could be traced and cut out, and a drop-in plug to fit the top of the neck can then incorporated into forcastle decks assembly.

That's my thoughts on the saucer at any rate.
"Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized."
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bmagee
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Post by bmagee »

thanks for the ideas! I will look into the circle cutter, I don't have one yet. As far as the bridge/impulse deck, I had the same idea as you gave. I know the project will be time consuming because I am just starting out but I am looking forward to it.
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Mr. Badwrench
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Post by Mr. Badwrench »

I have never scratchbuilt anything that large. But I think if I did, I would use fiberglass. Still use the aluminum and plexi framework you have plans for, but build the hulls out of fiberglass.
I speak of the pompatous of plastic.
octagon
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Post by octagon »

If I am building a rounded shape with 4cm diameter at the base and 1.8cm diameter at the top, and the distance between the two is 0.8cm, does that mean I cut round sheets of styrene from (4cm to 1.8cm) till its 0.8cm thick and then glue them all together and start sanding?

Any advise would be great. Thanks guys.
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Chacal
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Post by Chacal »

octagon wrote:If I am building a rounded shape with 4cm diameter at the base and 1.8cm diameter at the top, and the distance between the two is 0.8cm, does that mean I cut round sheets of styrene from (4cm to 1.8cm) till its 0.8cm thick and then glue them all together and start sanding?

Any advise would be great. Thanks guys.
Pretty much it, but not quite. You have to take into account that the last (topmost) disk has to be bigger than the 1.8 cm needed. The best way to figure out how big is to draw the half profile (cross section) of the part you need to make, then divide it into horizntal slices, each one the height equal to the thickness of the styrene you'll be using. Then you measure the radius of each disc by taking the distance from the centerline on your drawing to the bottom of each horizontal "section". I'll draw up a sample and post it in a few minutes. Hang on.
Sheer elegance in its simplicity.

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Chacal
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Post by Chacal »

Chacal wrote: I'll draw up a sample and post it in a few minutes. Hang on.

Here it is.

In this example you can see that the topmost sheet will have to have at least 12.2mm of radius, instead of the 9mm that the 18mm diameter of the top would suggest.

The grayish blue "stairstepping" is the profile the sandwich would have before the sanding. Got that?
Sheer elegance in its simplicity.

Political unrest in dictatorships is rather like a round of rock-paper-scissors: The oposition goes on denouncing the regime on the papers, the regime censors the papers, rock-throwing ensues.
octagon
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Post by octagon »

Thanks chacal. That really helps, especially when the styrene I am using is also 1mm thick.

I went away to try it this morning right after posting the question. And then wondered why it didnt work out. Now I have the answer. The 12.2mm was exactly what went wrong. :evil:

Let me get back to the bench and rework it a little more. :twisted:
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