Master Models - Making injection molds
The mold making process usually involved making a wooden model (Master Model) using blueprints from which the mold would be manufactured. Some master models were all wood while prototypes were wood and metal, or in the case of the mini Gulstream II, all metal cast. The size of the blueprints would vary, depending upon the scale drawing.
The Precise Models C-2A and a few other Master models are shown below. The rolled up blueprint drawing in the C-2A case is dated October 5, 1966 and 1/16th scale.
Grumman C-2A Master Model
The master model below was shipped from Grumman to Topping with a request to quote on tooling and price to produce 10 models of the Grumman Hydrofoil Gunboat. The master model mounts on the walnut presentation base and was held securely in the box for shipping. The accompanying blueprints are for the outboard profile & front view and the main deck. The blueprints and quote request are dated November 10, 1964.
Grumman Hydrofoil Gunboat - 1964
Topping Navajo F-5 Quail Roadrunner F-111B EF-111
Grumman 1/240th scale Mini Gulfstream II
Gulfstream Mini II Engineering Blueprint & Brass Master Model Signed by Ken Lango 5/19/72
Mini Gulfstream II - Master model - Blank on Sprue - Finished Model on engineering blueprint
Injection Molds
The cost of the cast molds could run upwards of well over $100,000 and were returned to the manufacturer after production ended. As Precise did not own the molds, they were prohibited selling contractor models directly to the public. However the F-105 mold was purchased from Republic and Precise could sell those models directly to the public.
The costs of other injection molds included the General Dynamics 1/40th scale F-16 at $112,000 and the F-16XL at $140,000. The McDonnell Douglas YF-17 mold was $70K-$80K of which approximately 50 samples were made by Precise. The Northrop YF-17 Cobra lost in competition to General Dynamics F-16 Falcon.
Northrop YF-17 Cobra - 1/60th Scale
A large number of original Topping and Precise molds were stored in the warehouse while in use. A roof leak in the early 1990s rusted many of the molds beyond use and damaged a portion of the model inventory. Some of the injection molds previously at the warehouse are pictured below.
Per Gary Schneider, the plane most difficult to produce was the metal Republic F-105 Thunderchief by Topping. The plane was poured as a solid zinc die cast metal and the mold would become superheated making it unusable in a short period. Also the sharp metal wingtip edges frequently caused injuries to the employees. This model was produced at a loss to Topping. The mold would become super-heated in use and become unuseable in a short time. Based upon the short mold life, a new injection mold was designed for making a plastic injected F-105. The larger scale F-105 was given to Vietnam pilots for completing 100 missions along with a 3 day trip to Las Vegas.
1/48th scale F-105's lined up for presentation to Thud pilots
The Topping F4U-4 Corsair injection mold has been refurbished and a limited number are available. A short run of 50 were completed in blue gloss ABS in 2009 using oversized stars n bars, similar to Topping. Also included with these models will be a Numbered Certificate of Authentication signed by myself and Gary Schneider, President of Precise Models, Inc.
F4U-4 Mold at the warehouse F4U-4 in reburbished mold
First F4U-4 Production Run Chance Vought F4U-4 Corsair
Injection Molding Process
The process cycle for injection molding consists of the following four stages:
Clamping - Prior to the injection of the material into the mold, the two halves of the mold must first be securely closed by large press. Each half of the mold is attached to the injection molding machine and one half is allowed to slide. The hydraulic powered press pushes the mold halves together and exerts force to keep the mold securely closed while the molten plastic material is injected.
Injection - The raw plastic material, usually in the form of pellets, is fed into the injection molding machine and advanced towards the mold by the injection unit. The plastic pellets or granules are heated until melted. The melting point depends on the type of plastic used, but typically ranges from 350-550 degrees F. The molten plastic is then injected into the mold very quickly to fill the mold with the molten plastic. The amount of plastic resin required to fill the sprue, runner and cavities of a mold is called a shot. The injection time can be estimated by the shot volume, injection pressure and injection power. Water is injected through cooling ports to maintain a constant temperature.
Cooling - The molten plastic inside the mold begins to cool as soon as it makes contact with the interior mold surfaces. As the plastic cools, it will solidify into the shape of the desired part. However, during cooling some shrinkage of the part may occur. The packing of material in the injection stage allows additional material to flow into the mold and reduce the amount of visible shrinkage. The mold cannot be opened until the required cooling time has elapsed.
Ejection - After sufficient time has passed, the cooled part is ejected from the mold. When the mold is opened, a mechanism (ejector pin) is used to push the part out of the mold. To assist in the ejection of the part, a mold release agent can be sprayed onto the surfaces of the mold cavity prior to injecting the material. Once the part is ejected, the mold can be clamped shut for the next shot to be injected. The larger Precise models such as the A-10 were cooled in water immediately after ejecting to prevent the wings from drooping as it cooled.
Plastic Material Types
Topping and Precise models were made using three types of material, Butyrate, ABS and styrene.
Butyrate cellulose acetate butyrate was used for all of the early Topping models. This material would shrink slightly as the model cooled, releasing the oils thru the plastic and have a slight odor.
ABS (Acrylonitrile butadiene styrene) is derived from acrylonitrile, butadiene, and styrene and results in a lightweight, rigid molded product. ABS is a middle-of-the-road type of material with no shrinkage and is preferred for models. Per Gary Schneider, the first Precise model made with ABS was the Lunar Module in the early 1980s. The F-15, F-16 and F-18 were also molded with ABS.
Styrene, also known as vinyl benzene is a very lightweight thin plastic that is used today for the plastic model kits. The cost of styrene is very low and molded parts can be very detailed with this material. Models made with styrene include the F-101 Voodoo and the Polaris base.
ABS Butyrate Styrene
Small Parts Molding
Most of the small parts were included in the larger injection molds. For larger volume small parts needs, Precise molded the smaller parts in shop using a small Arburg mini-molder and molds. Most of the mini molds were steel, the 4 blade C-130 Prop mold was made of Beryllium at a cost of $2,500. A 6 blade prop mold was made for the C-130J at a cost of $2,800 but was not accepted by Lockheed.
Arburg Mini Molder | Currently available are the F-4 narrow Sparrow missiles, F-15 & F-4 Sparrow missiles, F-18 wingtip Sidewinders, C-130 props (4 & 6 bladed), YF-17 Sidewinder, and F-18 tailhook.  
C-130 Prop F-18 Sidewinder & Tailhook These are available on the Model Parts For Sale tab of this site. The mini molder and two of the small molds are shown above. |
Stand Production
Both Topping and Precise made some of the model stands, cutting the acrylic sheets with a bandsaw, filing, sanding and buffing for a polished finish. Stands were also injection molded for both companies by a Plastics Company located in Cleveland. The dies pictured are part of the collection of Topping and Precise imprints.
A limited number of original stands are available on the Models & Stands For Sale tab. Other stands will be listed as they are cleaned and inventoried.
Brasss Topping and Precise stand dies
Two of the larger brass dies are the Agena T The Lockheed Agena Space Vehicle
and Gemini-Agena pictured above measuring brass die measures 8" x 5" x 3/8" 4 1/2" D x 2" Ht. and at 9.5 lbs. ea.
Reproduction Topping and Precise model stands can be custom made based upon the number of requests and economics.