Fiberglass Mold Making

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

After the resin cures, I like to let the new mold sit untouched on the plug for a few days.  Letting the mold sit for a few days prior to de-molding helps prevent warping of the mold.  In this case, my plug is of a long, thin fender and has a much greater chance of undergoing a noticeable warp then some of my other projects so I am more careful at this stage then usual. 

De-molding the fender becomes an easy task.  The PVA and wax layers were not breached and as soon as I began to pull one corner of the fender plug loose the entire mold separated from the plug.  Just as planned – so far.

The next step in a project like this is to clean up the new mold of any defects or sharp edges around the flange areas.  I begin by using a rag and water to remove the PVA from the inside of the mold.  The result of my cleaning reveals a perfect molding surface.  Had I found any defects, I would have filled them with bondo, sanded them smooth and then thoroughly waxed over them before molding any parts.

In order to make my first parts with this mold I begin by applying several (four) coats of mold release wax to my mold’s surface.  When the wax has dried and has been polished to a smooth shiny finish, I apply two coats of PVA with a foam brush.  On larger projects I will use my air gun but this project didn’t warrant that much hassle.  In this case, I applied a light PVA coat, allowed it to fully dry, then applied a second coat for extra protection.  With both the PVA and the wax applications I made sure to cover any areas of my mold, including the flanges that were formed over the parting plane.  This will insure that my parts don’t get stuck on the mold.

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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Fiberglass Mat Fiberglass Cloth

With the recent application of bondo leveled and cured, I can now smooth out the surface of my fender - again. As it turned out, the two outer thirds of the circumference of my fender were about the same height. The middle section was about ¼ to 1/3 inch on the shallow side. It is in this center section that I need to reshape the fender around my newly formed ridge of bondo. I accomplish this with more bondo and a credit card that I use as a spreader. I like using credit cards or other thin pieces of plastic as spreaders because they can be used to produce a flat smooth surface or a nice smooth curved surface.

After the surface of the plug has been re-shaped with bondo I go through a short series of filling and sanding until the surface is smooth and ready for a quick coat of primer. The primer helps me spot any defects in the surface. I like using primer because it dries quick and I can bondo right over it to fill defects if necessary. As it turns out, my new plug surface is nice - nearly perfect.

The next step in this project is to apply 2 or 3 more coats of primer. After the primer dries completely, I sand the surface smooth with 400 grit wet sand paper. This really smoothes out the surface of my plug and gets me closer to molding.

With the plug at this stage, I have to trim it and then remove it from the foam and rim. To trim this plug, I have decided to use my Dremel tool and the piece of stock aluminum that I used to smooth the surface of the plug. The first thing that I do is attach the aluminum piece to the hub with the retaining nut. I run the nut tight but not so tight as to hamper smooth movement of the aluminum. I then decide how far I want the fender to wrap around the tire on my finished product. I mark that line around the length of the fender plug with a pencil being sure to mark that spot on my aluminum guide so that I get the same depth on the other side of the fender plug.

With my lines marked, I attach my carbon - fiber cutting wheel to my Dremel tool and then attach my Dremel tool to the aluminum guide with masking tape. Before I begin cutting, I sweep the tool around the length of the fender to make sure that the aluminum guide is going to keep the cutting tool on course. Since it does just that, I start the tool and begin trimming the edges of the plug.

The tool and the guide work perfect. When finished with the one side I flip everything to the other side and trim there as well. Now I remove the foam from the inside of the plug and begin to think about how I will mount this plug to a board for the molding process.

So far - so good!

Happy Glassing

Steve

www.fiberglassmoldmanual.com

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Fiberglass Mat Fiberglass Cloth

Now that the foundation for my plug is laid, I can start building a fender. At this point I will just take a moment to regress.

When I was younger, I am sure that this plug would have been built from a much more difficult process than what I have outlined. I am not sure how I would have done this but it wouldn’t have been easy - I probably would have used a template of the rim, done complicated measurements of the total tire diameter and so forth. Building plugs for projects like this are much easier and more likely to provide a nice product if you can use the base object as the foundation for your plug. In this case, I used the actual rim itself. In one of my manuals, I actually used the hood of my jeep as the foundation for building a plug for the hood scoop. This method of plug building takes much of the guess work out of the building process.

Getting back to the plug, I begin building the plug by laying a layer of 1 ½ ounce mat and resin over the foam. Once this cures, I follow with a plastic spreader and bondo to smooth out the surface of the fender. Once the bondo is cured, I smooth out the surface with my electric sander with a course (100 grit) sandpaper to smooth it out. Like with any plug build, I go through many bondo applications followed by sanding to smooth out the surface.

As with many plugs, just about the time that I get this thing smoothed out I see a problem with it. From a side view, it appears as though the center section of the fender, when viewed from the side, isn’t as thick as the ends of the fender. In order to check this, I drilled a hole in the end of a 1/8 inch, inch wide by 36 inch long piece of aluminum stock. The hole is just large enough to slip onto the hub of my rim. I then clamp an L bracket onto the stock aluminum and slid it down until it makes contact with the fender at what I perceive to be the highest point. As I sweep the L bracket around the top of the fender from one end to the other it becomes obvious that not only is my center section low, but I have many uneven points along the surface of the plug.

Fixing these uneven points is pretty easy. I now have a way to measure the outer diameter of the fender and I can use this tool to obtain consistency in the outer diameter.

To smooth out the surface of my fender, I lay a bead of bondo in the center along the length of the plug. While the bondo is still able to be spread, I drag the L bracket which is still attached to the hub through the aluminum stock along the surface of the plug at a level that represents the highest point of the plug. The L bracket levels the surface of the plug creating consistent thickness of the plug.

After this application of bondo cures, I can begin spreading bondo over the surface again to smooth it out. This time I am careful to use the newly laid central ridge of bondo as a guide.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

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Fiberglass Mat Fiberglass Cloth

My most recent fiberglass project is a set of fenders for my beach cruiser. I know that there are already fenders available on the market, but I really didn’t care for them. In addition, I do enjoy building my own things when I can and it just so happened that this would be one of those projects.

To start with a project like this, I first needed to decide how I would get the shape and size of a fender that I was looking for. I want to have a fender with a round contour that would provide better coverage of the tire than what store bought fenders provide.

Initially I considered obtaining the right shape for the fenders by covering an inflated tire on the rim with foam weather stripping and then using that as the foundation on which to build a fender. The more I thought about this the more problems I was imagining.

Then one day I was walking by the 99 cent store and I saw those round foam pool toys that the kids use, I think they are called noodles. I knew right away that I was 99 cents away from the perfect base on which to build a plug for my fenders.

Once I got that foam roll home I pulled a wheel off my bike, removed the tire and proceeded to tape that foam roll to my rim. It fit the channel perfectly, and was the right height and width. I wanted my fender to cover about one half of the diameter of my tires so I used enough of the foam to accomplish this.

With the foam roll secured to the rim, I decided to cover the foam with a layer of masking tape. I did this to protect the rim and because I wasn’t entirely sure what the fiberglass resin would do to the foam, or if it would release cleanly from the foam.

At this point it is time to think about applying the fiberglass resin and mat. I began by building a simple cardboard stand to hold the rim steady while the materials are applied. Once I was happy with the stand I covered the entire rim and tape covered foam with PVA release agent.

Now I am ready to build a fender plug.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

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Fiberglass Mat Fiberglass Cloth

Hello fiberglassers,

I maintain Steve Jone’s web sites and blogs.  Well, I sort of maintain them. I had to move this blog to a new server due to a couple of issues.

1. I did not stay up with WordPress Security Updates which resulted in the site getting hacked. (You would think hackers could find something constructive to do with their time.)
2. The older version was a pain for Steve to manage.

I am sincerely sorry and apologize to you for the time this blog was down.  Know that Steve will be posting his no fluff straight talk posts on Fiberglass Mold Making and Fiberglass Fabrication.

Thank you for your patience and understanding,

Mike Claggett