“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

For reference, here are the two links to the two finished 3D paper models:

1951 Chevrolet Fleetline

(1) http://www.diecastaway.com/index.php?topic=69785.msg686105#msg686105

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 302, 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. It did.

The cast came off the mold fairly easily and went back on just as easily. A few more layers of casting material were applied so as the give the cast sufficient strength and integrity for it to be worked on separated from the mold. A small piece of wood was attached underneath the hood to give it some needed strength and reinforcement. Obviously work such as this is impossible to do while the cast is still on the mold. That is why it is so important to have an overall solid cast formed and ready for exterior painting before removing it from the mold for the very last time.

Elmer's Carpenter's Glue (yellow)

Durhan's Rock Hard Water Putty

White Glues

Covering the mold with a protective tape such as masking tape might be a good idea, too.

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A major and extremely important consideration is how to treat the windows on the cast. Obviously the windshield should be cut out from the cast. It is debatable whether the other windows should be cut out also. What determines this is whether or not doing so would jeopardize the integrity of the cast as a whole. If the cast were to be jeopardized as such, a workable alternative to cutting out those spaces for the windows is using black decals or black paper pieces applied to those appropriate window areas. I spray painted a sealer on the back of black colored paper and applied these facsimiles using a Glue Stick as an adhesive to the cast.

What I found, in Case 1 -1951 Chevrolet Fleetline, was that by cutting out all the windows, this seriously weaken the support pillars of the roof as well as the roof itself. Consequently a substantial amount of reinforcement material went into beefing up the underside of the roof and scabbing on wood and metal pieces to the roof pillars. These structural problems could have stemmed directly from using tissue paper as the starting point of the cast as opposed to perforated paper which appears to make a much stronger shell. The point here is to carefully access how cut outs for windows will impact the structural integrity of the overall cast. You don't want to get to this advanced stage of completion and fatally remove sections of the cast that would essentially “destroy” the cast. The window cut out situation is a point of no return. Give this extra attention and thought. There is no easy turning back after the cuts are made.

Another aspect that needs special consideration is replacing a part or parts that have to be removed from the mold to expedite the initial application of paper to the mold. These parts cannot be formed from paper and need to be made separately. In Case 3- 2012 Ford Mustang Boss, I had to remove and duplicate the front grille of the model mold. I made an impression of the actual piece in Play Dough and filled the impression with Durham's Rock Hard Water Putty. When the cast is completely finished, this grille section will be attached to it.

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