A guide to making a 3D paper model using a 3D scale model as the primary mold

2006 Dodge Charger R/T

(2) http://cs.finescale.com/fsm/modeling_subjects/f/4/t/186944.aspx

Introduction------------

“A guide to the experiences of casting and building up 3D paper models by using 3D scale plastic or diecast models as the primary molds OR how to make paper models from other models”

This long-winded title is a response to two postings of two models that were "cast" and constructed using paper products.

My rationale for doing this tutorial is to explain in detail what I have encountered in the processes of these first two builds and what I am encountering so far in my third build. I want to share what mistakes, procedures and techniques that so far have happened in hopes that others, who either have had better successes or who are inclined to begin to attempt to build such vehicles, will inform us of their results and we can all benefit from this shared information.

THE PROCESS::::::::::

Terms----

Mold = original scale plastic or diecast model you want to copy

Cast = the piece formed when applying paper,etc., to the mold, resulting in your new “model”

A two-step process with a number of accompanying steps along the way. Have patience, use common sense and think through each and every action. Don't try to hurry and get quick results, this is not your typical or average build.

It is said that the process that sculptures and painters use to achieve their works involve either “taking away from” OR “adding to” a specific medium, such as a marble slab or a blank canvas. We are, in effect, attempting to “sculpt and paint” a model vehicle (the cast) from another model (the mold, the medium) by “adding to” the mold a layer of paper and casting material. We are then “taking away from” the cast, by scraping, sanding and forming, casting material in the same way a sculptor would “takes away from” marble chunks with a chisel.

The huge difference between the sculptors and the painters and us is, we have to “create” our own medium from scratch each and every time we want to make a cast. This is a very significant fact : Our molds do not become an actual part of the cast! We do not “add to” or “take away” anything from the mold that alters or changes their physical characteristics, in other words, they remain as untouched, unmarred original model vehicles. They are separate and distinct from our cast. What this means is, we have a huge labor and time investment in the mere medium itself . If painters and sculptors make mistakes and opt to start over on a project, they do not have to make their own medium from scratch. They simply obtain a blank canvas or another marble slab.

STEP 1) compose the cast

STEP 2) finish the cast

Step 1 Composing the Cast

This step consists of selecting a suitable scale model for the mold, covering and securing to the mold a suitable paper product, and then applying layers of cast material.

Selecting a Suitable Scale Model for the Mold:

Initially, one must decide on a body style, either a plastic or diecast model, they want to replicate. There are two key decisions that need to be made here.

First, selecting a model that is either important to you or not important to you whether the exterior finish COULD get damaged. You want to choose a model that COULD be damaged in these processes as opposed to a model that has a good paint job, nice decals, graphics, etc.. You don't want to risk damaging or ruining a perfectly good model as a mold. However, if that is not important to you, then you need to seriously consider the shape of the body style.

Second, the shape of the body style you select is fairly critical, the reason being that it will determine the magnitude of difficulty in removing the cast from the mold. If the model (mold) has some undercuts to it, the cast will be difficult if not impossible to remove without either damaging the cast, the mold, or both. You want to think of a larger can fitting over a smaller can and how easy they separate and come apart. The smooth sides of the smaller can has no undercuts , so the larger can slips on and off it easily enough. But if the smaller can was larger at its top than its bottom, and the larger can conformed to this shape, the larger can could not be removed from the smaller can without altering the shape of one or the other or both.

A fundamental and difficult problem that is encountered after a suitable mold has been selected is deciding on whether to use and then to choose a relevant release agent. A release agent is a substance put on the mold that allows the cast to be removed easily from the mold. Various release agents possible include cooking sprays, Vaseline, mineral oils, baby oils, or substances which would not harm the mold or interfere with the absorption of cast hardening material by the paper. Without some reasonable way that the cast can be easily removed, the cast and the mold will remain attached together as one piece. So before paper products (either tissue, toilet, kitchen roll towel, blue shop wipes, brown paper, newsprint, etc.) are applied to the mold to begin the very start of the cast, a solution to the release agent problems need to be thought out and decided. You don't want to build up your cast with layers of paper and hardening material only to realize later that it is impossible to separate it from the mold. Here is what I encountered.

Case Experiences

On my first cast, the 1951 Chevrolet Fleetline, I used a non-stick cooking spray as a release agent. This turned out to be a huge mistake as the sticky "goo" got on both my hands, making for the application of tissue and toilet paper to the mold a real mess. The paper ended up quite wrinkled on the mold, and sticking to my fingers when trying to position it on the mold. One must also realize that oil and water do not mix, so applying water-based casting material and glue onto paper might not allow for it to adhere to the paper. The multiple dillemas here are that you want the paper to conform to the mold without a lot of shifting around; but you also don't want the cast to stick to the mold when all the casting layers have been applied and the cast is to be finally removed from the mold. In addition, you want the casting material to stick strongly to the paper which, ideally, would be oil-free. The cast did come off the mold fairly easily; however, the initial layer of paper had saturated the cooking spray and did not accept any casting material, thus remaining dry, weak and flimsy. Also, since a few layers of tissue paper were used in the cast, moisture was permanently trapped between the inner and outer layers of paper, thus not allowing the cast to harden properly.

On my second cast, the 2006 Dodge Charger R/T, I used a section of roll kitchen towel. It was perforated some. I did not use any liquid release agent on this mold. After applying the paper to the mold and brushing the paper with a mixture of white glue and Elmer's Wood Filler and letting this harden, I applied a second coat of the filler/glue mixture. After hardening, I sought to remove the cast from the mold. This required a careful peeling-type process, getting in between the mold and the cast by using a thin, flat, narrow piece of metal and using my fingers to gently pry and separate the cast. What I found was that the perforations had allowed casting material to seep through onto the mold, but the spaces in between the perforations did not, so the adhesion to the mold was rather weak and the cast came off fairly easily. This was aided by the fact that there were no undercuts on this particular body style.

On my current cast, a 2012 Ford Mustang Boss, I did not use a liquid release agent either. I used a blue shop towel which also has perforations. This paper allowed much more penetration of casting material onto the mold and caused some real problems in removing the cast, so much so, that some tears occurred because there was a slight undercut of the rear of the mold. The cast came off as a thin "skin" and needed to be put back onto the cast after the mold had been washed off and cleaned up of casting material. The technique here in returning the cast to the mold was to first use masking or a similar tape to cover and protect the mold, thereby not allowing for the cast to adhere to the mold again. If it does, it should separate easily enough from the masking tape.

Covering and Securing to the Mold a Suitable Paper Product:

Choosing a suitable paper product as the starting point or the basis for the cast is important because we are looking for strength, porosity for accepting the cast material, ease of positioning on the mold, as well as thickness. Perforated paper towels and wipes seems to have most of these desirable traits.

We want to be able to drape the entire paper over the mold, and secure it to the underside of the mold, trimming excess paper from the wheel wells and the areas where it is not needed. The idea here is to get as close a fit as possible so that the paper conforms to the mold's details as much as possible. Note any areas that might cause a problem upon releasing the cast from the mold; that is, undercuts in particular. Secure the paper to the mold with some masking or similar tape. Just some short, small pieces enough to hold in place the paper while adjustments to the fit continue to be made. This can be a frustrating task, but it is crucial that the best application of the paper be done so as to ensure a well-formed cast. Spend the necessary time here to get a good fit. Since a flat piece of paper has difficulty bending and conforming to curves, angles and irregular surfaces, wrinkles will inevitably occur. Try to minimize these wrinkles as much as humanly possible. And try to position these wrinkles in an area on the mold that would strengthen that particular spot or would be relatively unnoticeable. This area, when casting material is layered on the paper, will stick up higher than the rest of the surface and will require more finish work, sanding, etc. later in the build.

Applying Layers of Casting Material to the Mold

Having the paper in place, it is time to apply casting material to the mold. Casting material consists of water-based products such as clays, fillers, and glues. We want to use products that will harden fairly quickly, that are easily sandable, that are easy to apply and that are fairly durable. Sheet rock mud mixed with yellow glue seems like it might work okay, but I've not tested it. I have used primarily Elmer's Wood Filler diluted with yellow Elmer's carpenter's glue*. This mixture is applied to the paper using a foam brush or a synthetic bristle brush. It works best if it is the consistency of a thick cream. After drying, apply a second coat. Use your judgment here as to additional coats. We want to build strength but not create a really thick shell per se. After deciding that the applied levels of cast material has made the cast fairly strong and stiff, I have followed up with a final coat of a mixture of Durham's Rock Hard Water Putty** and yellow carpenter's glue. Use your judgment in your various application of layers regarding bristle or foam brush.. A foam brush produces the smoothest finish but lays down less material. A bristle brush will put down more material but creates burrows and ridges which certainly impairs getting to a smooth surface right away by requiring additional fillings and sandings.

* White glue can be used, but yellow glue is better providing more strength since it is designed for use with wood and it sets up and dries faster than the white glue. Of the two white glues shown below, the tack glue sets up faster and is the stronger white glue.

** Note that the Durham's Rock Hard Water Putty mix will set up and cure hard if excess is stored in a covered container whereas the Elmer's Wood Filler mixture will not. Excess wood filler mix can be reused if stored in a closed container. Excess Durham's will be hard and non-reusable.

Casting materials:

STEP 2) Finishing the Cast

This step consists of removing the cast from the mold, forming and detailing the cast, and decorating the completed cast .

Removing the Cast from the Mold:

Removing the cast from the mold can end up being be a tough job depending on whether a mold release agent is used or not and what type of paper is used to make the cast. It is imperative that the cast be removed at this point in time. With the cast continuing to remain on the mold, further advanced work necessary to shape and form the cast's final appearance would be fruitless indeed. Also, if the cast were to come off eventually with exceptional effort, all that previous finish work could be seriously at risk of major damage or ruined entirely.

So remove the cast before any future work is done to it. See above Case 1, 1951 Chevrolet Fleetline and Case 2, 2006 Dodge Charger R/T and Case 3, 2012 Ford Mustang Boss.

Forming and Detailing the Cast

After having successfully removed the cast from the mold, it is time to begin the final operations to complete the cast. Clean and wash off the mold as needed and return the cast to the mold.

Positioning the cast again on the mold serves as a solid underlying base for the cast.

Additional layers of casting material are applied , sanded and formed to obtain a final smooth surface to the cast. Having the cast on the mold lends good support for filling, smoothing, inspecting, sanding and ease of handling when performing these various tasks. Corrections to imperfections in and on the surface and problems with body areas are also corrected here as well.

See how the surface needs to be filled and sanded smooth:

Decorating the Completed Cast :

Now that the cast is fully formed and sanded smoothly, it is time to apply a finish to the surface of the cast. Begin by applying a primer paint to the entire cast, both outside and underside. This serves as an initial sealing of the cast material and assures a much better bonding with a top coat of paint. If need be, a finish top coat can be applied to the inside of the cast; one or more top coats definitely should be applied to the outside of the cast. Once the top coat or coats of paint have cured thoroughly, decals, paper windows, and any other types of decorations can be applied.

Final Thoughts:

The finished paper model will be slightly larger than the mold model, so its scale is not completely accurate, of course. And the precise details and other parts of the mold will not necessarily be clear or authentic on the cast. However, the essential form captured in the cast is easily recognizable as the “real thing” and does serve as a legitimate platform for future upgrades and improvements if desired. My foremost intention in making these paper bodies was to put a body on a bare Monster Jam chassis as my logical conclusion was, “some thing is better than no thing”.

Thanks for your interest and feedback.