Question about creating surface panels on a frame.

redfinger · Post by **redfinger** » Tue Feb 19, 2013 12:36 pm

I am working on a scratch build project located in this thread;

http://www.starshipmodeler.net/talk/vie ... p?t=104936

This is more or less the inspiration picture I am using for the build;

https://picasaweb.google.com/lh/photo/h ... directlink

I was planning on chopping up the front end of a '49 merc to create the front fairing. However I do not think it is going to work now, so I am looking at building it from scratch. I was planning on using plastic card beams to build a frame and then "skin" the frame with thin pasticard. I was wondering if anyone has done something similar to this and if anyone has any advice to offer on how to go about doing this?

Ashton

Tankmodeler · Post by **Tankmodeler** » Wed Feb 20, 2013 3:00 pm

I have done similar work on tank models. To make a model of a convoluted curvy casting shape like a turret I have used this sort of process several times. The difference is that once the thin styrene shell is in place, I make the smooth exterior surface out of epoxy putty, like Aves, Milliput, Tamiya Epoxy Putty or good old A+B.

Think of it like plaster & lath in a home. The frame you mention is the studs in a house. The skin of plastic strip is the thin lath boards and then, ontop to make the final surface, you "plaster" it with epoxy putty. Once it's cured, wet sand to shape. You will absolutely NOT get it perfect first time, so expect to lay down 3-5 (or more) layers of putty in most areas to get the shape exacly as you want it to be. Do the basic shape first and then build up from there.

The putty won't stick well to the plastic, so rough up the sirface of the plastic with really coarse sandpaper and leave small spaces between the sticks so that the putty makes a mechanical lock as well as a chemical bond. With patience you can get a reall nice finish and, because teh putty cures so hard, yuo can eventually polish it up really smooth for a great paint finish in the end.

Don't forget to make teh plastic shell a bit undersize to allow for the thickness of the putty! That cost me a mulligan one time, so learn from my mistake!

Paul

modelnutz · Post by **modelnutz** » Wed Feb 20, 2013 5:26 pm

That design looks like a great candidate for vac-forming !

Tankmodeler · Post by **Tankmodeler** » Wed Feb 20, 2013 7:24 pm

Oh, and if using the plaster & lath method, the frame and skin should be made of at least .030" (.75mm) sheet to help prevent the putty from flexing & cracking while you sand it. The putty should be about a mm (.040") thick, as well or more.

Paul

redfinger · Post by **redfinger** » Thu Feb 21, 2013 6:23 am

modelnutz wrote:That design looks like a great candidate for vac-forming !

yup, but I dont have access to that equipment. I am strongly considering it, and I might end up putting the project on hold until I can get access to one.

@tankmodeler - thanks for the tip but I think vac-forming is going to have to be the route I go.

Ashton

Tankmodeler · Post by **Tankmodeler** » Thu Feb 21, 2013 7:21 am

redfinger wrote:@tankmodeler - thanks for the tip but I think vac-forming is going to have to be the route I go.

Ashton

What will you use as a pattern?

redfinger · Post by **redfinger** » Thu Feb 21, 2013 8:19 am

Tankmodeler wrote:
redfinger wrote:@tankmodeler - thanks for the tip but I think vac-forming is going to have to be the route I go.

Ashton
What will you use as a pattern?

I will just make a solid form out of styrene and pink foam, then skin it with bondo. I wont detail it, just getting the shape.

modelnutz · Post by **modelnutz** » Fri Feb 22, 2013 4:59 pm

How big will it be ?
Length/Width ???

redfinger · Post by **redfinger** » Fri Feb 22, 2013 8:07 pm

modelnutz wrote:How big will it be ?
Length/Width ???

A little longer than a 1/24 scale car, and about half as wide

ajmadison · Post by **ajmadison** » Fri Feb 22, 2013 10:25 pm

I have built many subjects that involve compound curves. Of a variety of dimensions. The poster who recommends carving a 'buck' and vacuforming a shell. But the shell itself has issues, since it does not have structural strength. Great for a car body, not so good for any subject with details hanging off of it.

So here are the choices.

Carving a buck and vacforming a shell. The shell will still need some structure inside it. But if you can sculpt the buck, this is the quickest way to getting the final exterior surface of your subject. One important point, the buck can be sculpted out of a very cooperative medium, like floral foam, styrofoam, bass wood, pine, or even a high tech medium. Before you poo-poo this, try carving some styrofoam, you'll be amazed how quickly you can attain the desired shape. DOWNSIDE, how does one smooth over the nasty voids in the styrofoam surface.

Creating a sheet styrene frame and attempting to coax sheet styrene to adapt to the compound curves. This will not work with anything under a 1" radius. Trust me, I've tried. You can still skin the frame, but it will require a variety of fairly ugly compromises. One is a fairly tight frame (meaning no span between frames of greater than 5mm) with lots of little panels glued to it. And once the skin is on, lots of sanding and filler. This will require a stunningly tedious number of frames, and a frustrating large number of skin parts. BUT, this may be the solution, depending upon your confidence and ability.

Creating a sheet styrene frame, and filling the spans between frames with A+B epoxy. Paint the framework with black paint before smushing the epoxy into the framework. The epoxy will be lumpy when you apply it. You will have to sand (nay sculpt) the epoxy back to the framework. When you see black paint, stop, or at least switch to a higher grit sandpaper until the desired shape appears. Continue to use higher grit sandpaper until the final surface is as smooth as desired.

There are other variations. But also can be tedious. You can laminate sheet styrene to approximate the exterior shape and use filler and sandpaper to sculpt the final shape. I have done hybrids between this technique and the skin on frame, and the skin with epoxy techniques, so that only the compound curve portion is laminated.

Hope this helps.

Mr. Badwrench · Post by **Mr. Badwrench** » Tue Feb 26, 2013 10:40 pm

From what I see in the picture, there is no need for the model to be hollow. If you can build a buck for vacuforming, then you can build the basic shape and to heck with vacuforming.

Scotaidh · Post by **Scotaidh** » Wed Feb 27, 2013 5:44 am

Tankmodeler wrote:Oh, and if using the plaster & lath method, the frame and skin should be made of at least .030" (.75mm) sheet to help prevent the putty from flexing & cracking while you sand it. The putty should be about a mm (.040") thick, as well or more.

Paul

What Tankmodeler said. I made this mistake on the Travelling Model build, and it cost me no end of time - and PSR - to correct. Had I used sufficiently thick plastic card for the panels, I'd have only had to do it once.

redfinger · Post by **redfinger** » Wed Feb 27, 2013 10:03 am

Mr. Badwrench wrote:From what I see in the picture, there is no need for the model to be hollow. If you can build a buck for vacuforming, then you can build the basic shape and to heck with vacuforming.

If you read through my build thread my intent in vacuum forming the front fairing/body is that I would like it to be hollow so I can build and detail the engine below.

Unless I misunderstand what you are saying...

ajmadison · Post by **ajmadison** » Wed Feb 27, 2013 9:54 pm

Scotaidh wrote:
Tankmodeler wrote:Oh, and if using the plaster & lath method, the frame and skin should be made of at least .030" (.75mm) sheet to help prevent the putty from flexing & cracking while you sand it. The putty should be about a mm (.040") thick, as well or more.

Paul
What Tankmodeler said. I made this mistake on the Travelling Model build, and it cost me no end of time - and PSR - to correct. Had I used sufficiently thick plastic card for the panels, I'd have only had to do it once.

I'm one of those modelers that use superglue and accelerant, (brand) namely Zip-kicker. So I don't have issues with the joints cracking. However, superglue as a filler has its issues. As much as I love Pacer's glues for assembly, it is not that great for filling gaps and feathering out between panels. So in fact, I use 15 thou sheet for tight curves, 20 thou for not so tight curves, and when I need a tube like shape that is also structural, I'll use 30 thou.

Mr. Badwrench · Post by **Mr. Badwrench** » Thu Feb 28, 2013 9:55 pm

double post

Mr. Badwrench · Post by **Mr. Badwrench** » Thu Feb 28, 2013 9:55 pm

Sorry Redfinger, I missed that. You're right, a solid model won't work for that.

redfinger · Post by **redfinger** » Fri Mar 01, 2013 9:15 am

Mr. Badwrench wrote:Sorry Redfinger, I missed that. You're right, a solid model won't work for that.

No worries....though I am thinking now about just making it a solid piece and forgoing to engine detail all together. I have limited funds and the casting/mold making supplies I have I need to make last, and there is another project that I am working on that might use up most of what I have, so I think the sled will be solid.

Ashton

redfinger · Post by **redfinger** » Fri Mar 01, 2013 9:15 am

double post..

naoto · Post by **naoto** » Fri Mar 01, 2013 11:05 am

As for forming the shell...

I wonder if aluminium can material (e.g. soda or beer can) would work out... (probably would work better on larger size rather than smaller)
http://www.youtube.com/watch?v=LVNewuTkWkE

or soda bottle?
http://www.foamflyer.info/canopy.pdf

http://paperinside.com/wp-content/tutor ... orming.pdf

...and making the body shell in sections might help to make fabrication easier.

Tankmodeler · Post by **Tankmodeler** » Fri Mar 01, 2013 3:15 pm

PET (pop bottle plastic) is a completely crap material for model building. It is terribly heat sensitive, so using it as a buck or master for further thermoforming is unwise and very few adhesive stick propely to it making it a poor material to use as that actual model (nothing will stick to it, really).

Aluminum is a better material, but is much harder to form than styrene or ABS. For subjects with a single radius of curvature, it's OK and is good for straight wings and prismatic fuselage sections, however, getting it to form over compound curves actually requires you to push the metal around with hammers & anvils. Waaaaay more work than laying down epoxy putty & sanding to shape.

You can use the aluminum and then add some small details to it, but if the shape has a double curvature, metal shold be avoided,. Unless you want to develop metal working skills of course. In which case, you're into a new hobby and feel free to enjoy yourself.

Paul

raser13 · Post by **raser13** » Sun Mar 10, 2013 6:48 am

i had to do some pretty intense curves on the engineering hull on my ambassador class ship. what i did was build up a "keel" by making a center spine in the side view shape of the hull in a fairly thick styreene.

http://s1015.beta.photobucket.com/user/ ... ort=3&o=37

http://s1015.beta.photobucket.com/user/ ... ort=3&o=75

i then mad up ribs out of the same thick styreen in the shape of the left to right curvature of body. next i simply took some much thinner styreen and using a pot of boiling water and a set of tongs i submerged the styreene and let it get hot and soft. once plyable i would quickly pull it out of the water and put it up to the skeleton and bend it to shape.(you might want gloves to handle the plastic during this step) this took several submergences and bendings to get the right shape. once i got my shape i glued it down smoothed out with sandpaper and putty,primmered, and detailed.

http://s1015.beta.photobucket.com/user/ ... ort=3&o=76

http://s1015.beta.photobucket.com/user/ ... ort=3&o=78

http://s1015.beta.photobucket.com/user/ ... ort=3&o=65

http://s1015.beta.photobucket.com/user/ ... ort=3&o=55