Model Maker’s How-To: Molding and Casting Model Hands

Model Maker Joe recently shared the process by which he created a total of 300 model hands for a client in the medical field:

We had a customer contact us with the need of a class room training aid to use in a practical exercise, measuring gout build-up on a hand. I was initially tasked the job to produce 100 realistic hands with gout build-up at designated locations, using particular dimensions for the bumps.

First we set out choosing a hand model. Then I brushed on a platinum-cure silicone rubber (hardness: 10A, tear strength 102 ply, 1000% elongation at break to guarantee a stretchy, nearly untearable glove) over the model’s hand in thin (this rubber is very thick and traps bubbles) layers.

After achieving a desirable thickness, I shelled the mold with plaster cloth while still on the model’s hand. I made this exo-shell in two halves (palm and back) so that I could pull the mold out.

After the plaster cloth was dry it was time to separate the two halves of the shell and release the model’s hand from the silicone glove.

The next thing for me to do was pour a master by putting the glove original in its shell and banding the two halves together. After putting the unit in a standing base (resting on its finger tips, wrist up), I poured a polyurethane casting plastic (hardness: 70D, tear strength 3000 ply, 7.5% elongation at break) with some black tint and put it under pressure.

When the plastic was cured, I peeled the mold back to reveal the master. It revealed many small nodules around the finger tips and palm (most likely do to sweat) that I cleaned off. After the master was cleaned up a bit, another member of the team built up specific (height, width, length) gout swells out of Bondo, per the customer’s request, at particular locations on the hand.

After the art work was done I repeated the same steps above to make three working molds, but this time the polyurethane plastic was tinted with a flesh color.

We shipped the client an initial quantity of 20, and upon their review, found the hands too hard and life-like for their studies. We needed to re-tool and come up with a new game plan – a softer plastic or a fast curing rubber.

I came up with the idea of a two part silicone mold. A hand cast out of a softer material might not hold up to being pulled out of a glove mold and the cast piece would have to be fully cured (no short cuts).

Meanwhile another team member was preparing a new master cast by brushing some blackened polyurethane plastic over one of the previous working casts, to smooth out the skin texture. After that cured, he fine-tuned the gout buildup back to customer specifications and tolerances.

When he was done, I built three two-part molds (fingertips down, wrist up) and begin production casting of my next 80 pieces. This time I used a polyurethane casting plastic (hardness: 80A/30D, tear strength 2264 ply, 233% elongation at break) with the same flesh tint.

This plastic had a 90 minute demold time, but with the two-part design I was able to turn the mold (pull the product and pour the next piece)  in 60 minutes. These pieces came out of the mold with no flash and very little seam line.

The customer was very impressed and the molded hands did what they needed to do. The client ordered 200 more castings.

Pinewood Derby!

 

Those of you who have spent any time with the Boy Scouts of America will be familiar with the Pinewood Derby race. This much-anticipated event takes place annually within the Cub Scouts community and is usually hosted by individual packs.

A child and his parent are given a block of wood, wheels and nails and asked to design and build their own car for the race. The car has weight and length restrictions and must be able to run on the track used by that particular scout pack.

An employee’s son belongs to Pack 9 Of Penfield, NY, and KiwiMill was asked to create an award for this year’s race. We were happy to supply the winning trophy for this community event.

Congrats to Max - the winner of this year’s Pack 9 Pinewood Derby race.

Shipping Containers Find New Uses Worldwide

 

Shipping containers are one of those items you take for granted in life. The intermodal container or “sea can” is a reusable steel box with standard measurements that transports all types of goods around the world. Their universal appeal comes from the ability to transfer from sea to rail to road without having to take the contents out along the way.

There are tens of millions of these containers world-wide. Most of the containers are 8 ft wide by 8 ft high. Lengths vary from 20 footers to 56 feet long, with corrugated steel walls and a door at one end. They can be stacked on top of each other – all 8 corners have fasteners – and can carry over 20 tons of product each. Each container is marked with a BIC code to identify ownership.

Because of their relative ubiqiutousness, and the fact that it takes so much energy to melt down 8,000 pounds of steel, these containers are being given second lives. An entire industry has sprung up with creative ways to reuse these containers that would otherwise be languishing in shipyards at the end of their useful shipping lives. Twenty footers in particular are in plentiful supply, as shippers have moved on to larger sizes over the years.

The most obvious second use for a shipping container is housing. Many architects have created eye catching, unique urban designs  with the 20 foot container as their building block of choice. Other companies are focusing on 3 bedroom, 2.5 bath designs for USA consumers who find the reusable aspect appealing & want lots of square footage. Even more practical is the use of one or two containers to make reasonably sized homes for places and people around the world who need or prefer a smaller footprint.

The use of shipping containers as modular units in the building process is seen as an upcycling of materials. Not only does it cost less to adapt these units than it does to melt them down for materials, but leaving the units in their original state provides a stronger structure than conventional housing frames. Not just limited to housing, containers are being used for office space, retail buildings, museums and even works of art.

An off shoot of the intermodal shipping container is the expandable shelter concept. These modular units are used for deployment to situations world-wide that can benefit from ready-made, pop open, adaptable shelters. Shipped just like an intermodal container, these spaces then open up, or expand, to offer support services in the event of natural disasters or other types of emergencies. An excellent example of this are the ESS units offered by SAIC.

Intermodal containers are increasingly the focus of businesses looking to create a unique shelter out of a familiar design. Their modular shape, inherent portability, structural soundness and availability make these containers an intruiging concept to design from and build with.

Click Here for an interesting pictorial of shipping containers that are lost at sea.

Patriot MIM-104 (PAC-3) Missile Launcher

Reblogged from KiwiMill Blog:

  Description  The Patriot MIM-104 is a surface-to-air missile (SAM) system used by the United States Army and many other nations. The prime contractor for this system is Raytheon. You can read more about this system here. This scale model was built mostly from scratch with one exception. The cab and chassis are a die-cast model that we used as a starting point for the truck in the pictures. When a high-quality mass-produced model is available in the proper size, we will often use it as a starting point …

Gate Valve Model for Training

Our client, FMC Technologies, requested a working model of a gate valve that would assist with maintenance training. Talking with model maker Scott, it was determined that the best way to serve this purpose would be with a 1/2 scale cutaway model that would pull apart and reveal interior components that could be manipulated. Once the general concept was agreed upon, our team discussed the build in general, and the associated costs and time frame, and a detailed quote was written up.

Once the job was awarded, model makers Mike, Chris and Scott came up with a plan of action including a list of materials, fabrication techniques and assemblies, along with a break down of each task and its associated steps. The over all design of the model would include an exterior shell opening and closing with the use of magnets, a working wheel that would move the gate up and down, and numerous interior pieces that could be assembled and reassembled.

FMC provided 3D geometry which was used to create the various parts of the model. Some parts were 3D printed.

Others were formed from  machined  tooling board. An aluminum rod with threads was created on the CNC lathe. Metal gate sleeves were formed on a press brake, and some off-the-shelf hardware was added as well. As parts were formed, they were attached to each other as required. Magnets were imbedded in the outer shell.

Most of the parts were then primed and painted. Various bright colors were used for the individual parts to enhance the training process.

The whole model was assembled and disassembled multiple times to assure its functionality and durability. The wheel was tested to make sure it moved the gate up and down on the rod correctly. The model was taken for professional photography, then carefully packed and shipped to Canada to our esteemed client.

Click Here for a slideshow of the model build on YouTube.

Giveaway Truck Models

Recently KiwiMill was asked to make reasonably priced multiples of a truck to be used as giveaway premiums for special clients. The trucks are used to spray weed control substance on railway beds. The trucks actually ride on the rails in order to do so.

In order to keep costs down, our model makers used two different types of off-the-shelf die-cast truck models that were then “kit bashed” or disassembled for parts. The chassis was taken off one truck and the cab off another.

Custom parts were  3D printed, laser cut and machined out of resin. Each truck was then hand-built and painted to resemble the Rumble Spray Truck.

Casting a Hand in Pictures

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An Engineer’s Approach To Mechanization In Models

Recently I took a few minutes to ask one of our model makers about his approach to building scale models. I was particularly interested in models that require mechanics – movement or lighting. Our resident engineer, Chris, seemed like a good candidate for my questions.

Like many of his fellow model makers, Chris starts with an image in his head of the finished model, focusing particularly on placement of seams. He then visually breaks apart the model at these seam lines, and begins concentrating on each individual part that makes up the model. How will he construct each part? What materials will he use to build the part, and with what equipment?

After Chris breaks down the model into parts, he will make a list of materials and fixtures needed for fabrication.  He might even draw up a specific part in 3D using Solid Works, and  have it printed out full-scale so he can assemble it over top the drawing.

When it comes to models with moving parts, Chris prefers to design the housing that goes around the mechanics first. Creating the structure which frames the mechanical parts helps Chris understand how he will lay out the inner workings.

Motion in a model can take on many forms. Chris determines whether the movement needs to be circular,  linear or lever-like, at what speed and whether it needs to be continuous or intermittent. He then chooses the mechanics that will most accurately produce that movement. Will it be pulleys, actuators, motors or gears?

Sometimes the mechanics can closely mimic the original object that is being modelled. This means that the model will be run the same way, albeit in a miniaturized fashion. Most times the motion needs to be represented in a unique way that the model maker must figure out, design and implement.

Off-the-shelf mechanical parts will be ordered in the size and design required for the model project, though usually modifications are necessary. Adaptations need to be fabricated and added on to the stock mechanical parts. Safety is always an issue when working with mechanics, particularly when they are altered in some way. Knowledge of the properties of the mechanical devices and careful placement of the power supply is necessary.

Electrical engineering may come into play with particular special effects in scale models. Lighting or movement can be controlled by switch or circuit board. Chris might be tasked with programming  lights or motion to occur at specific times and in a specific order. In these instances he uses a 2D wiring diagram to program the circuit board, which then guides the micro controllers to perform specific actions.

When it comes time to test the motion or lighting of a scale model, Chris is 95% sure it will do what it is supposed to do.  Still, there may be some trouble shooting involved at this stage, or minor tweaking. The model’s mechanics will be run for several hours continuously to confirm the integrity of the design. Only then is Chris satisfied that the model is going to perform as expected for his clients.

Casting Cars

KiwiMill recently designed a car model to be used for a sales display. The models will be used to showcase automotive paints for Hyundai. We chose to cast these from a carved resin master made from our original computer drawings.

A generic car body was created in Rhino 3D by one of our designers.

A  CNC milled resin master was created from this drawing.

A negative mold  of the core was made from the master.

 

 

 

 

 

This core was inserted in the mold to create a hollow space in the cars when cast.

 

 

 

 

 

 

Three molds were made to cast the cars.

 

 

 

 

 

 

                                                   

 

                                                   The molds were put in a pressure pot for a smooth cast.

 

 

 

 

 

 

 

 

130 castings were created.

 

 

 

 

 

 

 

The bottoms of the casts were sanded smooth.

 

 

 

 

 

 

 

 

The resulting cars will be painted various colors by our client, but here is one we painted.

 

Not Sure of What You Are Looking For?

There are plenty of clients that are entertaining the idea of a scale model for their sales office, trade show display or company training, but are unsure of exactly what they are looking for. While there are companies and individuals who come to us with exactly what they desire – right down to the scale, level of detail and finish - it is  not unusual to have lots of questions about scale models in general, and our capabilities specifically.

Our KiwiMill team can help guide you in the process of choosing a model; determining what your goals are and how best to achieve them through a scale model presentation. There can be seemingly endless options for portraying a product, place or concept via modeling. Narrowing your options down to the choices that will work best for your particular situation, is something we can talk through with you. With model makers on staff that have 20+ years in the profession, we feel confident in our ability to present you with ideas that fit your particular situation.

You may have a product that would be best displayed in a particular scale, as a cut away, or with lighting and movement to highlight particular attributes or abilities. It might make sense to have multiple models to show various design options, or just one model that transforms into different configurations.

Size or scale is a consideration that often requires additional clarification or guidance. Some features will not display correctly in a scale that is too small, for example. Larger scales have their own considerations, such as the need for very realistic detail in order to have the impact necessary for a quality display.

The amount of detail to put on a model is another area we can offer guidance with. While it might make sense in many instances to have as much realistic detail as your budget allows, there are circumstances where it might be unnecessary and even visually distracting to go that route. This is where our model maker’s artistic eye and vast experience might help steer the direction of the project towards a mutually satisfying outcome that otherwise would not have happened if our input wasn’t offered.

There may be questions about a model that do not involve artistic interpretation,  but are more practical in nature. A client may be interested in learning about how a model can help train personnel on procedures, logistics or safety issues. We can come up with a model design that helps simplify or clarify a process, cutting down training costs and increasing efficiency.

If you have entertained the idea of a model but aren’t sure what it can do for you, or you aren’t sure what your options are in terms of types of models and their uses, give us a call. Our model makers like to talk about models, and your project or concept, matters to us. Finding the right fit between a client and a scale model that communicates its message correctly, is part of the service we offer. You don’t need to know exactly what you want in order to start the conversation.