MAKING THE MOLD
The first part of making the mold, is selecting the part to be replicated. The angles (positive and negative) will dictate how the mold is made, and whether it is going to be a simple mold (one piece) or complex mold (multiple pieces that bolt together).
If there are negative angles involved, it will require a complex mold so the piece made in the mold can easily be removed without “locking” into the mold.
Simple hand tools, and a few air tools are all that is needed to successfully make a mold. Pictured here is a small air powered chop gun, a small air powered gel coat gun with paper cups, varnish or paint rollers, a small plastic roller with ridges to help disperse bubbles, a disposable paint brush, and one gallon cans of resin and gel coat. Temperature, ventilation and sufficient work space are serious considerations. The entire Mako Shark body, and 1970 L88 hood molds shown in this article were all made in my small back yard and one car garage. Drop cloths help with cleanup as well.
Small packages of resin, gel coat, fiberglass, can be purchased at relatively low cost at any local hardware or boat repair dealer. Larger amounts are cheaper purchased via mail order, however keep in mind that most of this stuff carries Hazardous Materials Shipping Charges. I learned the hard way when a can of Gel Coat cost me $24.00 (US), and the shipping charge was $32.00 (US) due to HAZMAT! Buyer beware! ASK FIRST!
If you plan on making a full size boat hull, or a one piece car body, I highly recommend you get a professional sized chop gun that uses industrial sized fiberglass rolls, and fifty gallon drums of resin. This will allow you to make the complete mold in one run, preventing premature cure and weak spots by using smaller sized tools.
Step 1: Make sure the piece you are molding is cleaned well with soap and warm water. Any residual dirt or imperfections on the surface will be duplicated in the mold. If the surface is smooth and clean, every piece you make out of the mold will be the same. Otherwise, every piece you make from the mold will need the exact same sanding or body work, every single time you make one. So the object here is to keep the workload down to a minimum by taking the extra precautions before you make the mold.
Step 2: Green Wax, called parting wax, is applied to the part. There are different manufacturers of parting wax, some with silicon bases and others without. PARTALL is used in this series because it is cheap, readily available, and does a great job allowing the mold to be removed from the part. A minimum of six coats of wax are used, being sure to get good coverage over the entire surface and buffing it off in between coats. The last coat is left on until it hazes over. Be sure not to leave any swirl marks, or wax ridges, as this will be replicated in the mold. (Note: Be sure to use a quality wax remover on the part after the mold has been removed. Any residual wax will severely hamper any paint or finishing material that may be used on the part later).
Step 3: Poly Vinyl Alcohol (PVA) is then sprayed over the entire surface. It dries to a strong, thick film much like household Cling Wrap, or Wax Paper. This is a weird substance. It is impervious to paint thinner, gas, oil and cannot be sanded off the part. However, warm water will dissolve it in seconds. It is very harmful to breathe the mist of this product so be sure to use a respirator mask for your protection. After each coat of PVA is sprayed on, allow ample time for it to dry, and again make sure it has no runs, sags, or ripples in the surface. A damp paper towel can be used carefully to smooth out any imperfections. Usually two to three coats of PVA is sufficient. It will leave the part coated with a fine green film. This provides a strong coating that can easily dissolve between the mold and the part, making it very easy to separate the two. The green wax is the insurance policy, and helps to separate the PVA and the part from the mold.
Step 4: After all three coats of PVA have dried, GEL COAT is then mixed with the appropriate amount of catalyst, and sprayed onto the part over the PVA. Different grades of Gel Coat can be purchased, depending on the intended amount of use the mold will have. If you are only replicating one or two parts, standard Gel Coat is sufficient. However, if you are making hundreds of parts out of the same mold, Tooling Gel Coat will help extend the life of the mold. It is very hard, smooth, and usually requires elevated temperatures to cure it properly. (i.e. oven baking)
Step 5: Fiber Glass reinforcement is then laid out and cut to size. The type and amount is called a “schedule” as described earlier in this article. Reinforcement glass comes in a multitude of weaves, weights, lengths, widths and thickness. It even comes in multiple strand continuous length boxes weighing up to 100 pounds in a roll, which is fed into an air chopper gun. The gun has slots for razor blades, and a rubber wheel that feeds the strand through the gun. More blades installed, makes for shorter strands. Less blades, means longer strands. Shorter strands are used for quicker fill in of corners, or small pieces. Longer strands are used for larger pieces, and bigger surface areas.
***NOTE: It is important to have all the reinforcement material cut out, wadded up or broken from the starch, and ready to laminate with the resin, BEFORE the catalyst is added to the resin. Once the catalyst is mixed into the resin, you have a limited working time before it starts to harden. You need to spend this time wisely, rolling out bubbles and adding the correct amount of layers, instead of wasting time trying to cut out fabric and lay it on the mold.
Step 6: To ensure the fiber reinforcement and the resin stays where you want it when making small molds, or thin width molds, cardboard and a hot glue gun are the ticket to success. Strips of cardboard are hot glued to the part making a boundary for the resin and glass. The cardboard can then be waxed and PVA coated along with the rest of the part, limiting the need for excess resin. Partial molds are also beneficial when you want to keep the mold light weight. External bracing is then more important, to keep warpage to a minimum. (see next step).
Step 7: Resin is then either sprayed, rolled, or painted onto the part with a brush. The method is not important, but uniform thickness throughout the part is very important. The fiberglass reinforcement is then laid up, rolled into the resin and allowed to cure. Plastic sheeting can be used to cover the resin lay up. This will accelerate the curing process by keeping air off the surface (oxygen retards the curing process) and keeping the heat in which really speeds things up. Heat is a natural by product of the catalyst working with the resin. It can become VERY hot depending on the type of resin, so be careful. Gloves and long sleeves are a very good idea. Also, make sure no catalyzed resin gets between your watch, rings or other jewelry and your skin, as this can cause serious chemical burns.
Special Note: Vacuum bagging techniques can also be used. This eliminates all the oxygen near the part, collapses all the bubbles, and puts pressure on the resin and glass pushing it into the mold for a much stronger part. Excess resin is squeezed out, leaving the maximum resin to glass ratio. Vacuum bagging can achieve up to a15-25 percent greater strength in the part. There is much more to vacuum bagging than space here allows. Suffice it to say, it takes more time in preparation, more equipment, and a more precise lay-up schedule and resin mix. Well worth the effort if the part is going to be used for high performance structural parts.
Step 8: External bracing is used on the back of the mold. This can be constructed of cardboard, or wood and is used to prevent warping of the mold. It also gives you something to handle the mold with, attachment points for storage, and a place to clamp the mold down when you are filling it with resin and glass. Warpage can ruin a good mold and render any parts made from it worthless. So be careful how you store the molds. Keep them out of the sun as the heat and UV rays will degrade the resin and cause it to fail early. Shown here is the inside support structure of a Corvette hood. The mold has a hollow center to keep the weight down, less resin and materials were needed, and wooden support pieces were glued across the piece to prevent warpage and provide something to hold on to. Once I make a piece out of this mold, all I need to do is bond it to the inside of the hood I make, and it will be as the original, hood latches and all.
Step 9: Removing the mold is easy (( if you followed the procedure correctly for applying the mold release wax and PVA)). Using small wooden wedges and a garden hose, water is sprayed between the mold and the hood. Wedges are gently tapped in to split the parts from each other. DON’T FORCE IT! The water will dissolve the PVA, and the mold will literally POP off the hood. Now wash out the inside of the mold to remove the remaining PVA, and you are done!
Depending on temperature and humidity, I will normally allow a minimum of 24 hours for the mold to completely cure before removing it from the piece, and at least TEN DAYS before I attempt to make a piece out of the new mold. Newly cured molds have a tendency to warp or bend if they are not completely cured. I would rather wait a few days to use the mold, than take a chance of bending a mold and have every part I make from it be warped. I also have seen the heat from the new resin and catalyst warp a mold that was not cured long enough before it was used to make a part. Make sure you use enough reinforcement to keep this from happening, or you will be back to brick one.
NOTE: Be sure you use a good cleaner to remove the wax and PVA from the original piece you made the mold from.
Step 10: If the wood supports become too heavy, (defeating the purpose of trying to use less resin to make a lightweight mold) I often use polyurethane foam. Although used in boat manufacturing for floatation, it is also used for insulation, sound deadening, and torsional rigidity. Balsa wood can also be used, but foam is more readily available and easier to work with. I use the EXPANDING FOAM INSULATION in a can that is used for household insulation. I spray it into patterns on the back of the mold to make the part rigid. It is much lighter than wood, and can be cut with a razor blade.
If I am going to keep the mold for very long, or multiple uses, I will cover the foam with resin and glass, thus protecting the foam from environmental breakdown. It is waterproof, lightweight, and provides excellent strength to prevent it from warping. If I am going to cover the foam with resin anyway, I also use an even cheaper method, which is old carpet padding (see initial story) which can be glued to the mold easily.
Step 11: Once the mold is cured and removed from the part, allow up to ten days before you use the mold. Then follow “Steps 1-9” to make a high quality hood from your new mold. Or whatever part you are making. This is what the final hood looked like when it came out of the mold. After painting and putting it on a customer’s car, you cannot tell the difference. Except for the price!
THE BOTTOM LINE: IS IT WORTH ALL THAT TIME AND EFFORT?To many of you readers and SHARK owners with deep pockets, the answer is probably NO! For the purist, if it was not made by General Motors, it is no good either. But then again, the subcontractor to GM made the parts this EXACT SAME WAY!
To those of us on a budget with a deep need for know how, the answer is an unqualified YES!
But lets look at what the numbers say. You can find an L88 hood in after-market fiberglass catalogs for anywhere between $600 and $800 U.S. Considering I spent just shy of $100 to make the mold, I think I am already ahead. The amount of resin, gel coat and fiberglass to make a new hood out if the mold should put me back approximately $150 U.S. So I saved between $350 and $550 U.S. But then again, I now have a mold from the original parts!!! Even if I only sell them to a few friends for COST, I think I am way ahead of the game. Favors always come in handy! Then there are the guys that just want a hood scoop, so I only have to use part of the mold, and make a partial piece with less resin and glass, which costs much less than an entire hood. These can be put on all sorts of cars and trucks. The possibilities are endless.
Speaking of endless possibilities, polyurethane foam is the ticket. Stay tuned for another run down on making custom wings, air intakes, scoops, and ground effects using foam as the medium. Following the same techniques as described here, you can make permanent fiberglass body parts. Paint to match!
FIBERGLASS BASICS
Definitions
1. Glass mat is layered according to a “schedule”. This Schedule is dictated by what the piece being fabricated will be used for. (hoods and air scoops will have a different lay up than structural components such as floor boards or fenders. ) The intention is to ensure uniform thickness over the entire piece as well as structural performance commensurate with the intended use of the part.
2. The Basics: Resin, when fully cured is very brittle. Strength of the resin differs based on the chemical composition such as polyester, vinylester, epoxy. Resin alone cannot provide enough strength to make a durable panel. Thus “glass reinforcement” is used. Carbon, graphite and Kevlar can be used to reinforce different resins in differing amounts to provide maximum strength to weight ratios. Like wise, the reinforcements are worthless without the resin.
3. The Basics: Plain strand fiber glass is strong when added to resin. This strength is multiplied enormously when the strands are woven. Different weave patterns and strand counts as well as the thickness of each strand provides endless options for strength, flexion, shear and torsional stiffness when added to resin. The engineer is the one that sets the requirement and the “glass man” follows the prescribed lay-up schedule to produce the part to specification. Some weave patterns are more suitable to curves, others for flexibility. And some are used to provide intentional failure points for break away panels and chassis parts in case of extreme contact or high speed impact. These safety points are engineered into the fiberglass panels as intended features to protect the drivers of race cars and speed boats.
4. The Basics: Fiberglass comes in varied packages, weaves etc. Chopped matte comes in different weights, usually described by the ounce (i.e. 12 oz matte, 15oz matte, 36 oz matte etc.) which is the weight of the glass matte in a 12 inch by 12 inch piece. Most of this chopped matte is “starched” to hold the strands together into sheets or rolls for easier handling and packaging. This starch must be “broken” by wadding the piece up to make it fluffy, thus allowing resin to fully penetrate the reinforcing glass, called “wet out”. NOTE: Be careful when choosing chopped matte as some resins can react adversely to the starch that binds the matte, thus rendering the part useless when cured.
5. Straight cut edges leave weak seams in the laminate. Whenever possible, tear the edges and make them jagged so they will wet out better and overlap without a seam. This will ensure a strong part. Conversely, when intentional failure points are required for safety features, seams are intentionally introduced, and layers are thinned out or intentionally perforated. Engineered failure points are key to breakaway parts.
6. The Basics: BUBBLES ARE BAD! Always use a roller to press out and break up any bubbles in the resin. Air bubbles cause weak spots in the laminate. Vacuum bagging methods can also be used in the case of large or complex parts with a propensity for air bubbles. Pay particular attention to the parts that have 90 degree angles in them, have multiple angles, and use tightly woven materials. The weave can cause air to be trapped under the resin and reinforcement, causing unseen weak spots in the part.
7. The Basics: RESIN IS NOT PAINT! Therefore don’t try to spread it like paint. Instead, flow it onto the fabric or reinforcement with a roller or dab it into the matte with a brush. This will help eliminate bubbles, tears in the matte, and undesired movement in the weave making inconsistent strength in the panels. For best penetration and absorption, use as much resin as possible. However to provide maximum strength to weight ratios, (see next para) materials like perforated peel ply can be used with vacuum techniques to squeeze the excess resin out of the part, leaving substantially lighter and stronger parts behind. The excess resin beads, when cured, can be used to make your own bondo!
8. The Basics: Resin to reinforcement ratios are important in the manufacturing of parts. Too much resin in a part can make it very heavy, and brittle in some cases. Not enough resin, or too much reinforcement, can leave dry spots which causes weakness in the part. The correct ratio of resin to reinforcement matte is critical to a lightweight, strong, useable and dependable part. Selection of resin type and reinforcement also has a lot to do with the final product. For example, a polyester resin part with normal fiberglass may weigh 10 pounds. The same part constructed of epoxy resin and carbon fiber or graphite could weigh up to 50 percent less, and have a shear and puncture resistance up to ten thousand times stronger than polyester and fiberglass. Selection of materials and curing temperatures and techniques play a great part in the final quality of the part.
9 The Basics: Temperature and humidity wreaks havoc with resin and catalysts during the curing process. Heated or cooled molds can advance or retard the curing time. When controlled, larger parts can be successfully laid up without danger of part of it setting up prior to achieving full lamination. This can be very helpful when making full car bodies. Conversely, heating the mold can speed up the curing process increasing the production run of a part in the same amount of time, as a mold left unheated. Heating and cooling also helps control atmospheric temperature and humidity which advances and retards the curing times of specific resins and reinforcements.
10. The Basics: Ventilation is critical to the survival of the worker! Vapors can be toxic and COMBUSTIBLE! Always read and follow the directions and safety precautions from the manufacturer of the materials you are using. Some resins cause severe neurological damage, cancer and other severe medical problems in humans. Inhaling catalyzed resin will not only burn your lungs, it will also harden very quickly with internal body heat and humidity. USE ADEQUATE SAFETY EQUIPMENT or suffer permanent consequences. Keep an eye on children and pets as well that may drift into the vicinity of your work area.
Steve Kuryla
