Using this wood in a marine environment where the boats are constantly exposed to water is dangerous because of the ability for the balsa wood to rot.  Once water enters the cored areas of boats using balsa wood, it is a complicated repair job.  The balsa wood is between two layers of fiberglass, and to remove and replace it requires removing a layer of fiberglass.  This usually involves grinding and sawing as seen here:

As you can see, there is a lot of dust created from removing the fiberglass to get to the rotten balsa. The balsa must then be replaced before the removed fiberglass layer is restored. Care must be taken to ensure that this is completed correctly in order to maintain structural integrity of the area that is being repaired.

To prevent balsa rot in the first place, care must be taken when doing activities that have the potential to expose it to water. Adding fittings and features to structures that contain balsa wood require careful craftsmanship to prevent water infiltration.

Installing fixtures and fittings through balsa wood is possible, but careful work upfront will be very valuable in the long run. There are several ways to do this, one of them is here:

This method of making holes through your balsa wood-cored structure will provide a wall of epoxy resin around the hole and keep the balsa wood back away from any water that may pass through the hole. Good marine-grade sealants applied to the hardware will add another layer of protection.

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To accomplish this, it is important to begin with a solid foundation material.  Very often this is wood, which allows for screwing and stapling.  Next, the speaker mounts need to be properly attached.  Orientation of the mounting surface is established for the speaker that will be used in the finished installation.

Fleece fabric material is one method that is used to span the surfaces and transition across the different areas.  This material allows for smooth transition, holds staples, is easy to work with, and is inexpensive.  Once it is in place it can be covered with resin and fiberglass to establish a solid surface.  This can be sanded smooth and painted for full effect.

WestCoastCustomsTV demonstrates how the fleece is applied in the video below:

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Placing reinforcements (usually fibered glass) and resin in a heated metal mold before compressing it under high temperatures will result in a finished piece with very unique properties.  The parts made in these matched metal molds have very repeatable properties, high strength to weight ratios, and are corrosion and chemically resistant.  The parts can be painted, and have many positive design attributes.

Ashley Industrial Molding is a company that manufactures such parts.  These large parts are made with compression and RIM molding for customer such as John Deere and Case tractors.  They have a good video demonstrating their equipment, processes, and finished parts.

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I found a video from Eastbay Composites that demonstrates a method for making small molds in a very quick an inexpensive fashion.

As you see from watching this, the basic construction materials are tooling gelcoat and inexpensive bondo for the support structure.

This mold construction technique certainly has drawbacks, but also has several advantages.  None of the materials required spray equipment, which is messy.  Brushes are inexpensive and easily disposed.  A disadvantage of this method is that surface finish might suffer from a lack of consistency on the coating thicknesses for the gelcoat and the release agents.

Using bondo as the support structure is quick and easy compared to glass and resin, but can cause problems as well.  It is more likely to crack, and can warpage issues as it cures and may be hotter in some areas than others.  Bondo may have some difficulty maintaining dimensional tolerance as it shrinks during cure.  Industrial resins used to create molds have minimal shrinkage in their chemistry and are placed on slower to minimize heat from the chemical reaction.

For quick, inexpensive and easy parts, this method from Eastbay Composites may work well for you.  What has not been discussed yet is that the mold model can be the most difficult part.  Off the shelf items are easy, but custom ones may be difficult.  Creating a shape or surface is time consuming and tenuous.  After that is complete, you can make your mold and final production parts!

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There are many advantages to vacuum bag molding, a few of which include:

• Improved resin/glass ratio
• More consistency across the laminate and part -to -part as compared to open layup
• Containment of air emissions from the resins

As compared to hand layup and chop layup, there are a few disadvantages, including

• Higher consumable material cost
• Higher capital equipment cost
• Difficulty with superior surface finish

Some parts are more suitable for vacuum bag molding than others.  It also depends upon which process it is being compared with.

Vacuum bag molding requires an extremely tight seal between the mold and the bag.  Molds with multiple pieces or holes for inserts can be difficult to complete a seal.

Parts that are overly large and complex can present challenges with placing resin and reinforcement before the cure cycle starts.  The bag must be completely sealed and under full vacuum before the curing cycle of the resin begins.

The basic premise of vacuum bag molding is that the air is removed from the bag, allowing the atmosphere (air on the outside of the bag) to push the bag onto the part on the mold, compressing the layers of resin and reinforcement.  Many misinterpret the process as “sucking the extra resin out.”  We are merely allowing the laminate to be compressed by the weight of the air above us in the atmosphere to consolidate it before cure.  The excess resin is usually absorbed by extra layers of sacrificial material inside the bag.

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There of course are several ways to go about building a basic structure to use for the basic shape.  This video gave lots of good ideas and examples of materials that are relatively inexpensive.

The second part of the video shows some of the actual fiberglass work.  This video of less than eight minutes does not nearly do justice to the amount of work and effort that went into finishing this project!  It was great that the author documented his work and shared with all.  This was a major project that is not for the faint of heart.

He does a very good job explaining the process and materials used in this construction. Every project is unique, however. When discussing the thickness of the fiberglass skin, there are many variables that determine the finished strength. The number of layers to use is dependent on the amount of underlying support structures, part geometry, and required load bearing capacity of the structure. Some areas may need to be stronger for impact resistance and structural loads.

The video author discusses only using epoxy resin with Styrofoam as opposed to polyester resin which will react with the Styrofoam.  Polyester resin can be used if separated from the Styrofoam with an additional layer.  While I have only seen it advertised, there are new spray on primer materials available to cover the Styrofoam and allow polyester resins to be utilized afterward.

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Composites will reduce the number of parts for the airplane, and Boeing predicts that the front section alone would normally require using 1,500 sheets of aluminum, which also means drilling between 40,000 and 50,000 holes for the nuts and bolts to attach these sheets together and to the underlying framework.  Carbon Fiber composites will allow for the skin and underlying supports to be molded as one large piece.  Boeing predicts that assembly line time will be reduced from about three weeks to attach all of this aluminum together to about 3 days to attach the large composites sections together for the entire plane fuselage.

Switching materials has its’ own set of problems to overcome.  The customers’ mechanics will need to be trained to repair damage on these composite planes.  Damage detection will be important as well.  Some will be visible to the naked eye, and other damage will not.  Several forms of Non Destructive Testing will be employed to test for damage and wear on the composites body to ensure a safe aircraft.

Composites have been used in aircraft before, but not as extensively in commercial airplane bodies.  Existing commercial airplanes have made use of composites in other areas to help make the planes stronger and lighter.  Military jets have used carbon fiber composites for many years in their technologies for strength and weight advantages.  Private business jets have utilized fiberglass composites for many years in their construction.  Homemade kit planes have also made extensive use of fiberglass to make inexpensive craft in personal shops.

The profile of carbon fiber composites will definitely be elevated if Boeing’s 787 becomes as successful as promised.

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Material Fatigue in the corner

The loose panel flexed so much and for so long that it fatigued the material and failed in the corner of the inner fender next to the attachment to the rest of the hood.  To repair this, I removed the area with the rivets, ground down the surfaces of both pieces on both sides, and reattached them with fiberglass and epoxy resin.

Prepared glass and resin

I wanted to place epoxy and fiberglass on both sides of the repair area to ensure a good, solid bond that would hold very well.

Epoxy Resin and Fiberglass applied

After the area was prepared, I applied epoxy resin to the surface to ensure good adhesion.  I had a low spot that was a gap, so I mixed some microfiber and epoxy to make a paste and fill this gap.  A stronger bond is produced when the fiberglass is not spanning an open gap between the two pieces.  I placed two layers of 3oz Chopped Strand Mat over the paste and worked the air out to make a nice consistent repair.  I then ground down the surface to make a nice-looking, consistent repair.

The rear of the inner fender had similar problems.  A hole had emerged in the black SMC piece.  I ground down both surfaces and placed some fiberglass across the area to bond it together.

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The main goal of this substitution is to reduce weight, which improves fuel efficiency.  Other positive side effects include fewer assembly operations, additional design freedom, dent and impact resistance, and the elimination of corrosion.  Several “green” resin formulations have been introduced that make use of bio resins, which use much more renewable resources such as soy products.  The fillers and reinforcements in this material can also be made from recycled and renewable materials.

SMC has overcome several hurdles in order to get to its present use and application.  General acceptance and education had to be proven to the OEM manufacturers and consumers.  Paint application and adhesion was one large consideration that had to be proven out.  There were issues with popping and blistering from the SMC surface.  Making sure the SMC parts held dimensions and aesthetics was also an important milestone.

SMC has become widely used today for many applications, and will find its way into many more.  The weight saving aspects are paramount for reducing fuel consumption.  The anti-corrosion and dent resistance are loved by consumers.

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Outside of the chemistry, the control of the time and temperature is important to the curing of the resin. If the actual temperature is outside the range of the intended formulated temperature, it will affect the curing reaction. If the part is demolded too early, the resin will continue to cure, but the final shape of the part may not match the mold. The manufacturer of the resin is the very best source for information on the recommended cure time and temperature.

As these resins change from liquid to solid states, there is a certain amount of shrinkage involved. A part made on a female mold will shrink towards the center, and a part made on a male mold will tighten around that mold. This shrinkage factor depends upon the resin chemistry and its additives, but is generally less than 3% by volume. This is why male molds more difficult to demold, and the design of the mold needs to account for part shrinkage and part removal.

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