Fiberglass Mold Making and Fabrication How To – Project Blog

At this stage of the build, the project gets a little tedious. Sand, prime and fill – sand, prime and fill. This process is repeated over and over until the surface is smooth and the two halves join in the center with a nice smooth border.

Spending time at this stage pays off in the end. Like I always say, every flaw that you are too lazy to work out of the plug at this point will become a flaw that will have to be worked out on every piece you ever make with the final mold. In other words, you can fix a flaw once here, or you can fix it on every piece you ever make, maybe 100 times! Do yourself a favor and fix these problems on the plug.

Once I am happy with this plug, it is time to apply a nice heavy coat of automotive heavy fill primer from my air gun. This primer will fill all of the remaining imperfections. After the primer dries the plug can be fine sanded, polished and prepared for the actual molding of the plug.

At this point, I believe that I am done with the helicopter. Now it is time to stare at it. As you can see in the picture above, the two halves of the plug are clamped together. I have already painstakingly aligned the two halves but now I am reaching the point of no return. I spend a good bit of time looking at the alignment of the two halves and at the plug itself to make sure that it meets my expectations. I notice obvious departures from my reference model and need to decide if I can live with the variations.

Remember what I said about my expectations of model building at the beginning of this manual – I like my projects to look like what they are supposed to look like but I don’t expect them to be completely scale. Keeping that concept in mind, I can easily identify this as a Huey UH-1 so I am good with what I have in this plug.

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

With all of the buck stations in place, I can examine the two halves of this project for symmetry. The best way to do this is by clamping the two halves together and carefully examining the big picture. I also use a ruler and check the basic measurements of buck stations that I consider critical to the final outcome. These don’t have to be perfect, but it should be pretty close, more symmetry at this point will insure a greater ease of building this model in the later stages. Once I am comfortable with the symmetry, I can move on and start filling the two halves with dry floral foam.

Filling the voids with dry floral foam is easy. I simply push the foam into the forms in away that provides the best use for each foam block. When necessary, I use an adhesive to secure the foam to the developing plug. I find that using regular automotive bondo as an adhesive is an excellent way to attach this foam to anything. It holds strong, cures fast and is cheap compared to epoxy adhesives.

After I have a few blocks of foam in place, I like to rough trim the foam with a blade to make it easier to work with. Trimming can be done with a sawing motion using any type of serrated blade. Usually I use a hacksaw blade but a serrated steak knife works well too. I continue adding foam until all the stations are full.

After the foam is installed, I can sand the foam down to the level of the buck stations. This is a simple and fast procedure. I usually use a sixty grit paper to do this job. Once the bulk of the foam is removed, I will use a medium grit paper to do any fine shaping.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

Now, I move forward with creating buck stations.  A buck station is a guide that ensures that your plug is going to resemble what you want it to in the end.  For this project I use the same 1/8 inch mahogany that I used for the initial profile pieces.  My strategy for placement of buck stations is simple, I put one anywhere that I am concerned about maintaining the correct lines of my project.  Usually I am of the opinion that more stations are better. 

Another rule that I like when deciding how many stations to use is to make sure that my sanding block is longer than the span between the stations.  I am going to fill the spaces between the stations with floral foam blocks and then sand the foam down to the level of the buck stations.  The sandpaper will easily cut the foam down.  If the sanding block is shorter than the distance between the stations it will create a depression in the foam.  Not that a depression in the foam is enough to ruin your project, but it is enough to cause you more work in finishing your project. 

Make sure to measure all of these out when building a mirror image project.  Another way to ensure symmetry of your project is to cut the buck stations for each side at the same time, if necessary, clamp the mirror image pieces together and smooth them with a sander to ensure identical shapes and epoxy the stations in place at the same time.  These procedures keep you in focus and your project symmetrical.

More Soon

Steve

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 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. 

To begin laying up a fender, I mix about a half a cup of gelcoat with the recommended amount of hardener.  Once this is thoroughly mixed, I use a disposable chip brush to paint the gelcoat into the mold.  I try to get a heavy layer of consistent thickness.  This gelcoat needs to cure to a tackiness before I apply the fiberglass mat and resin.  Usually this takes about 45 minutes. 

While I am waiting for the gelcoat to cure a bit, I begin to prepare for the next steps of this process by tearing 1 ½ ounce mat into small pieces that will be easy to lay into my mold.  Since this is a fender, it has compound curves – one that goes side to side and one that goes front to back.  In my experience, smaller pieces of mat are easier to work with in a mold like this.  Just FYI, my pieces of mat are approximately 4” X 4”.

Now that the gelcoat has cured to a tack, I mix an 8 ounce cup of resin and catalyst (as directed by the manufacturer) and begin to work my way around the inside of the mold with resin and mat.  I soak a chip brush with resin and use it to blot the resin onto the mat over my freshly applied gelcoat.  Since the gelcoat is still tacky to the touch, it holds the mat in place while I soak it with resin.  I work my way from one end of the fender to the other and then back again (two layers of mat and resin) being careful to make sure that the mat has no air trapped underneath and that the mat overhangs the mold by an inch or so.

Once this mat and resin cure to a gel-like state (this takes about ½ hour of 45 minutes) you can safely trim the overhanging extra mat with a razor knife.  If the resin pulls or is too sticky to cut, check back in another 15 minutes and try it again.  This is the best way to clean up your parts of excess fiberglass.

After trimming, I allow the part to sit in the mold for a day or so to let it fully cure.  Once fully cured, I pop the part from the mold using a couple of plastic putty spreaders.  I simply use my fingers to pick at the part until I get slight separation from the mold then I push the plastic spreader between the part and the mold and work my way around until the part pops out.  Since I used adequate release wax and two coats of PVA, this part easily separated from the mold.  One fender down, one to go!  

My New Beach Cruiser With Fiberglass Fenders Installed