Fiberglass Mold Making and Fabrication How To – Project Blog

In order to mount this plug to a parting plane, I am going to need a flexible piece of material, something that will easily follow the curve of my fender plug without causing distortion. What I ended up with is a six-inch wide piece of mahogany door skin that will act as the parting plane that will be mounted to a one inch thick, six inch wide by 36 inch long piece of MDF.

To mount the fender plug to the door skin, I used some bondo to stick wooden blocks to the inside of the fender plug and then I screwed the mahogany to the blocks. I then used my hot glue gun to attach the ends of my newly mounted plug and parting plane to the MDF. Just for visual reference, what I ended up with was similar looking to the Dunlop walk-over bridges that you see crossing over the track at automotive races.

With the plug mounted, I am ready to start the molding process. As with all plug molds, I begin by filling any and all gaps that exist between the plug and the parting plane with clay. In this case, I had no gaps so I went straight for the mold release wax. Since my parting plane is a very porous mahogany, I used 5 full coats of wax to ensure that the chances of my plug sticking to the final mold would be minimal. I allow the wax to completely dry and then apply two coats of PVA mold release and allow it to dry.

This plug is now ready for molding. Anyone who has read any of my prior blog projects knows the process that I am about to explain. I begin by mixing enough black tooling gelcoat to brush a nice thick coat over the surface of my plug and parting plane. Once this cures to a tack, I apply three layers of 1 ½ ounce fiberglass matt and fiberglass resin.

When applying the fiberglass mat and resin, I am always careful to make sure that the material has no air bubbles trapped inside. This is especially important with the corners. In this case the critical area is where the plug meets the parting plane. Remember, hurrying through this portion of the mold build will result in defects in your final product. The more defects that you have – the more repairs you will have to make to your parts.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

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I have received many questions from those who purchased my manual set regarding mold releases. Especially when preparing the plug. The bulk of the questions seem to come from the use of PVA as a mold release.

Let me start by saying that I like and prefer to use PVA (polyvinyl alcohol) mold release at all stages of my projects – both to release the plug and my parts. I like the security it provides. I have never had a part or a plug get stuck in mold when I have used PVA.

The problem that some people have with PVA is the orange peel appearance that is left on the inner surface of the mold after you have separated the plug from the mold. More often than not this orange peel is visible but can’t be detected by touch. Unfortunately, sometimes the orange peel appearance can transfer to the parts that you will make with your mold.

For me, this orange peel appearance has never been a problem because of the type of projects that I like to build. If you are planning on painting your finished pieces, as I do, the orange peel look of the gelcoat is of no concern. You will be at the least priming and painting the parts so you will never see the gelcoat. Even with R/C boat hulls that I have made I always plan on painting them for the final finish.

If you want to produce finished parts that have that glowing perfect gelcoat surface you will need to take a different approach with the plug. You will have to rely on mold release wax alone to allow for the separation of the plug from the mold. With this approach, you will want to follow the waxing procedures outlined in my manual. Use great care with applying and polishing the plug.

Another consideration with an approach that doesn’t involve the use of PVA is that more than likely you will damage (if not destroy) your plug when you de-mold. This is another reason why I like using PVA – I work hard on the plugs that I build and I like to save them.

I hope that this helps with your PVA questions

1/10 Scale Radio Controlled Fiberglass Mach 5

Happy Glassing

Steve

www.fiberglassmoldmanual.com

Continuing with the helicopter build …

At this point, I can begin to produce profile drawings of the copter.  I definitely need to start with a view from the top and a view from the side.

Some of this is accomplished through artistic ability and some of it is what I consider cheating.  The model that I bought had these views in the painting instructions.  Based on the diameter of the fan blades, I figured that the fuselage should be about 40 inches from nose to tail.  I simply used my copier to blow these views up to the size that I need.  Then I drew in some details that were lost in the enlarging process.                            

The next step for me was to trace these profiles onto a base that I can use to build a plug.  I like to use 1/8 inch mahogany door skin for this.  I like mahogany because I can buy it at home depot for cheap and one sheet is more than enough material for a project like this. 

Next, I want to decide along which line to epoxy the primary horizontal shape to the vertical shape.  Having access to my plastic model makes this decision easy.  Angle aluminum stock helps me align the mahogany pieces with each other.  I use the angle aluminum to clamp the pieces to each other which assures reasonably accurate alignment of the parts.

In addition to angle aluminum making alignment of not so straight pieces easier, it also gives a pretty good 90 degree alignment of one piece to the other. 

I begin by applying black tooling gelcoat with a dump gun at about 80 psi. I make sure to keep the gun close to my work because gelcoat makes a huge mess if it gets on something other than your project. I lay down a nice thick layer of gelcoat making sure to get good coverage around the base where the plug meets the board.

Once the plug is covered with gelcoat, I let it cure to a tack. I did this project on a nice hot San Diego day so it cured to a tack in about 45 minutes.

At this step I used a different approach than I am used to. I came into possession of a large roll of veil that I decided to use in the corners and angles of the mold. In the past I have always used a combination of cabosil and resin. I found the veil easy to work with, especially when pushing it into corners with a chip brush. With the veil in place, I proceed to build the mold with three layers of 1 ½ ounce chopped mat.

I begin applying the chopped mat by brushing a nice thick layer of catalyzed resin over the area of the plug that I am working on. Then I place a piece of mat that has been pulled off of my roll and lay it on the plug. I like to keep the pieces fairly small on a project like this, no larger than 6 inches square. Pulling the mat apart will leave many loose fibers that will help the strength of my final product once it has cured. When applying the mat, I like to overlap my pieces by about 20% and build a nice flange around the base of the plug.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

For my friends purpose, this is going to be a display only model. I will definitely make mine radio controlled. The differences in the two models should be minimal with the RC version simply allowing for easier access to the underside of the deck.

The full scale 11 meter RHIB is approximately 36 feet long. The first this that needs to happen is we need to decide on a size. My buddies wife would be happy if it were no longer than a foot from stem to stern. I think that making it 1/6 scale to fit GI Joe would be the way to go. Obviously we are pretty far apart on this so we decided on 1/10 scale making it about 43 inches long. This sized boat will allow me to buy some off the shelf detail pieces such as guns, ammo boxes and maybe even the 50 caliber machine guns (hopefully, I would hate to have to make these!)

Scale is important with a project like this. To make sure that I get as close as possible, I scour the internet looking for photographs and drawings of the 11 meter. I was able to get my hands on a digital owners manual which was of great help as well. The first thing that I did with my photographs and drawings was to use my copier to blow up a drawing of the 11 meter from the top and from the side. My copier has a function that lets me resize a picture up to 200% with each pass through the machine. I did the math and ended up with side and top perspective drawings that give a length of exactly 43 inches long and 16.5 inches wide.

This series of blog posts will be done in real time and will follow my project as I make progress. Stay tuned!! I will post pictures as I progress.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

At this point, I will start to fiberglass over the foam. I have decided to hold off on forming in the turbine housing and the top of the tail section. My thoughts are that I would like to have something to place clamps on so I can check the alignment of the body halves during this next phase of the plug build.

I begin the fiberglassing process by using a brush (a cheap disposable brush is best) to cover the foam with catalyzed resin. I have decided that initially I will only do the main part of the fuselage and I will do the tail later. Once the foam has been soaked with a coat of resin, I can start applying chopped mat over the foam.

Work the mat onto the surface of the fuselage. It must lay as flat as you can get it. I have spent a bit of time forming this fuselage. I don’t want to get sloppy at this point. Laying fiberglass mat over the foam will provide a nice hard surface for the next step of this build which will be the bondo application. Once the fiberglass has been laid, the only thing to do is let it cure. It is time to put the chemicals away and clean up.

After the resin cures, the surface can be rough sanded to knock down any loose fibers.

Once the surface of the plug has been cleaned up with coarse sandpaper, I can examine the pieces and decide where to go with this plug from this point. I began this plug imagining depressions with well defined edges where the windows should be. At this point, it seems that following this course will make this plug much more difficult to complete. This being the case, I have decided that the next phase of this plug build will see the side windows smoothed flush. Flush windows will make building the mold and pulling parts from the mold much easier.

After the rough sanding is complete, I can apply bondo to smooth out the surface of the helicopter. I only mix enough bondo that I can use in a few minutes. By mixing a little less bondo than I can comfortably work with, I am able to be much more efficient from a number of perspectives. First of all, I have time to work the bondo on the surface since I am not rushed by the thought of unused bondo curing on my mixing surface. Secondly, when I mix too much bondo, I end up just piling it on only to have to remove most of it later on because of sloppy application.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

Its funny how we do things that we think are not only the right way but the only way only to find out later that there are better ways. Years ago, when I first discovered the use of dry foam as a medium for plug construction, I thought that I had found the perfect plug building material. I easily carved out complex structures in a fraction of the time that it used to take when I used plaster and wood.

Then my bubble burst. I finished carving the foam for my new plug, covered it with resin and sea glass from the hobby store and let it cure. To my surprise, when I was applying bondo and glazing putty to level the surface of my plug, the plastic putty knife that I used easily went through the surface of my plug. It was then that I realized that the outer skin of this plug was too weak and needed re-enforcement. I fixed this problem by removing the thin layer of glass that I used to cover the foam and applying a 1/8 inch layer of bondo over the entire surface of my now less than pretty plug. Since this episode, I have always used foam in my plug construction but I always took that extra step with shaving down the foam and covering it with a layer of bondo before I start the final finish.

Recently, I began to evaluate my plug building procedures. While my tried and true method described above never failed me, I wanted to try something new. I recently was building a plug that I wanted to move quickly with. After carving the foam, I went ahead and decided to cover it as it was with 1 ½ ounce chopped mat and resin. I remembered when I had my bad experience with this method I had used very light material from my hobby shop. The 1 ½ ounce mat worked perfectly. It provided a very solid surface to work with without adding excessive size to the plug that I had carved from the foam.

I basically did two things differently with the foam. The first thing that I did was thoroughly saturate the surface with resin. The second thing that I did was use a much heavier chopped mat to cover the plug.

I always read and research fiberglassing techniques. I had not really researched or evaluated my plug construction techniques for years. This “new to me method” saved me a TON of time and materials (bondo). I don’t believe that this way of plug building affected the quality of my final product at all.

I would recommend trying this method for your next project.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

When I first started working with fiberglass, I found it a fascinating yet frustrating material. While I enjoyed the fact that it was water proof and could be formed into any shape, I was often frustrated by my attempts to finish it in a way that would make my final product look presentable. Over the years I have come to the realization that a nice fiberglass finish requires a little preparation and a little improvising.

Obtaining a nice smooth finish can be obtained on a consistent basis when using a mold to produce your parts. Even so, thought and preparation are still necessary. A nice thick gelcoat layer that is covered with a layer of veil that is then covered with a layer of chopped mat will create an end product with a nice finish and no pattern transfer to the final product. The gelcoat layer should be thick enough to allow light sanding without getting into the mat.

When repairing a broken piece of fiberglass, getting a smooth finish takes a little more work. On painted surfaces, I like to remove the paint around the damaged area with sandpaper. Depending on the size of the damaged area, I like to remove enough paint around the damaged area to give me a couple inches of working room. I will then tape over the finished side of the damaged area and apply my repair to the backside of the repair.

Once the resin has cured, I remove the tape and access the exterior of my repair. If the repair is flush or depressed, I will smooth over the surface with either bondo, finishing putty or a thick mixture of resin and cabosil. Once this has cured, I will sand it smooth, primer it, inspect it and go from there. If there are defects in the surface, I will refill them with the medium that I find appropriate and repeat the sanding, inspecting and primering that I had done before. This process continues until the finish is right.

You should not be afraid to sand fiberglass. If you happen to sand it to the point that you expose glass fibers, clip the long ones off and brush more catalyzed resin on. Let the resin cure and re-sand. You may have to repeat this process several times to get your repair right. If your sanding continues to expose fibers, you may want to cut the surface down an 1/8 of an inch or so and fill over the surface with either gelcoat, resin mixed with cabosil or even bondo. Once this has cured you will have plenty of room to shape and sand without exposing fibers.

The bottom line is that many people feel as though the final outer surface of a fiberglass repair must be fiberglass. This is nice if possible, but there is nothing wrong with smoothing over the outer skin of a fiberglass repair with gelcoat, bondo, resin mixed with cabosil or body putty.

Fiberglass Shooting Star Body (Speed Racer) For RC Car

Happy Glassing

Steve

www.fiberglassmoldmanual.com

I have received many questions from those who purchased my manual set regarding mold releases. Especially when preparing the plug. The bulk of the questions seem to come from the use of PVA as a mold release.

Let me start by saying that I like and prefer to use PVA (polyvinyl alcohol) mold release at all stages of my projects – both to release the plug and my parts. I like the security it provides. I have never had a part or a plug get stuck in mold when I have used PVA.

The problem that some people have with PVA is the orange peel appearance that is left on the inner surface of the mold after you have separated the plug from the mold. More often than not this orange peel is visible but can’t be detected by touch. Unfortunately, sometimes the orange peel appearance can transfer to the parts that you will make with your mold.

For me, this orange peel appearance has never been a problem because of the type of projects that I like to build. If you are planning on painting your finished pieces, as I do, the orange peel look of the gelcoat is of no concern. You will be at the least priming and painting the parts so you will never see the gelcoat. Even with R/C boat hulls that I have made I always plan on painting them for the final finish.

If you want to produce finished parts that have that glowing perfect gelcoat surface you will need to take a different approach with the plug. You will have to rely on mold release wax alone to allow for the separation of the plug from the mold. With this approach, you will want to follow the waxing procedures outlined in my manual. Use great care with applying and polishing the plug.

Another consideration with an approach that doesn’t involve the use of PVA is that more than likely you will damage (if not destroy) your plug when you de-mold. This is another reason why I like using PVA – I work hard on the plugs that I build and I like to save them.

I hope that this helps with your PVA questions

Happy Glassing

Steve

www.fiberglassmoldmanual.com

I have made many things out of fiberglass over the years.  Typically, my projects involve building a plug, making a mold from that plug and finally using that mold to make pieces. 

One project that I have wanted to do for a while was inspired by a ceiling fan that I first saw years ago.  I am sure that you have seen the fans that look like the nose of a WW II fighter plane.  From the moment that I saw that fan, I thought that it would be cool to have a helicopter body that would hang from the underside of the ceiling fan making the fan blades look like rotor blades.  Of course the helicopter would have to be a classic – I chose the UH-1 from the Vietnam era.

Thus the project begins.  The first thing I like to do when I am building something like this is to go to the hobby store and pick up a model of the helicopter that I want to build.  I use this model as a three dimensional reference.  While 3D references are not always available, I do like to use them when possible.  For this project, I selected a 1/35 scale UH-1.  Using this model, I can get a good idea of the size that the fuselage has to be relative to the diameter of the fan blades in order to maintain a scale appearance. 

I begin to build the fuselage of the model and to analyze the proportions, angles and curves of the copter.  

At this point, I can begin to produce profile drawings of the copter.  I definitely need to start with a view from the top and a view from the side. 

Some of this is accomplished through artistic ability and some of it is cheating.  The model that I bought had these views in the painting instructions.  Based on the diameter of the fan blades, I figured that the fuselage should be about 40 inches from nose to tail.  I simply used my copier to blow these views up to the size that I need.  Then I drew in some details that were lost in the enlarging process.