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Making a Custom Hood
Want to make a custom part out of fiberglass for your ride?
Maybe make a custom console, custom door panels or trunk lid?
Below is the process I used to make molds of my hood then ultimately a custom hood for my car.
|The first thing you need to do is make a plug:
An actual part that represents exactly how you want the final part to
be. This plug can be made from anything: clay, bondo, wood, etc and it
can be just a temporary part but it does need to be as perfect as you
can get it and this plug just needs to last long enough to make the
molds then it can be thrown away if desired
For my project I customized my hood and used it as my plug. My hood started out as a factory Mach1 hood that originally had a hole in the middle of it for a factory hood scoop. To make it more unique the factory hole has been filled in with a fiberglass patch panel then a lot of bondo to countour the top. Along with patching the hole other modifications were done on the underside of the hood to clear the turbo piping. Again, this plug is to represent EXACTLY what I want the final product to be so it needs to have all the details that I want.
The above modifications were done before I chose to use it to make a mold and with these modifications the hood looked great but after six months the bondo started shrinking and minor cracks where showing around the edge of the panel that was glassed in on the underside. So while the hood still looked decent I decided to make a mold of it then use the molds to make the new hood pieces.
The first thing was to sand the top of the hood to get the desired contour back and smooth out any issues on the underside and lucky for me there happen to be enough primer filler on it that block sanding it got it back to where it needed to be. Starting with a perfect part is critical because if there is any flaws in the hood then these flaws WILL show up in the molds.
Below is the hood after we block sanded it smooth again.
Now that the top surface is smooth it was time to work on the underside. The goal for prepping the underside is to fill all seams and cover all the holes. When the 'glass is laid and resin brushed on you don't want the resin to seep into any cracks preventing the mold from popping off. ALL the smaller cracks will be filled with soft modeling clay but large gaps or deep holes will have a pattern made from 1/8" nylon sheet to cover them.
The first nylon pattern I made was for the one side of the hood. I started with a paper pattern then transferred it to the 1/8" thick nylon sheet and cut it out. I fine tuned the shape with the jig saw and the bench grinder. Although I'm not ready yet I will lay masking tape along the surface of the hood then apply hot glue on top of the tape and press the pattern into the glue. The tape allows the hot glue to be removed from the hood easier. Once the pattern is stuck onto the hood I will use modeling clay around the edges of the pattern to fill and smooth the corners.
Once all these nylon panels are made they need to be glued into place with hot glue. To prevent the glue from sticking to the paint I ran tape on the hood and on the panels then ran a lot of hot glue all along the tape and held the panels in position. At one point I had issues with one of the large panels and had to remove the panel and this dual tape method made removal easy. I'll leave the bottom side like this until I'm ready to fill the gaps with modeling clay which is still a ways off.
The next step is to create a 6" wide flange all around the outer edges of the hood for the fiberglass to rest on when it's laid on the hood.
I first lay masking tape all around the hood so the glue doesn't stick to the paint.
Then I make 6" wide templates that go all around the perimeter of the hood. Since the front and rear pieces have a lot of contouring these were done in two pieces while the side flanges were done as one piece.
Once they are made I hot glue the flanges onto the bottom of the hood and hot glued the seams on the nylon flangers.
This side of these flanges do not need to be pretty or smooth but they NEED to hold. The flanges will need to support the pressure of all the layers of fiberglass as I lay it on the top of the hood and if a flange comes loose then I have to start all over.
These NEED to be secure so I used the hot glue liberally along all seams and where ever the flanges have a drastic twist due to the curvature of the hood.
At this stage the flanges are done and I can flip the hood over so I can work on the top surface of the hood which is the first surface that gets glassed.
Once the flanges are glued to the hood the seams between the nylon flnages need to be taped so I taped all the seems with green PET tape which prevents the 'glass from seeping through the seams.
Next step requires adding modeling clay to the edge of the hood. This is needed to create a draft angle along the edges so the mold doesn't get hooked under the edge of the hood so the mold comes off easily.
The clay is not smoothed out at this time but will be contoured after the wax is applied.
Shown below is the modeling clay I used BUT IT CAUSED ISSUES. This clay has oil in it that bled into the gelcoat and caused it to blister. Do NOT use this clay. Somewhere out there I think there is a sort of wax/clay that doesn't have oil in it but I don't know what it is. That will be up to you to find...sorry.
Initial research I did indicated that TR Mold Release paste wax is the desired wax but after having the material supplier review my materials list they informed me that this was is not compatible with the resins I will be using and instead recommended Partall Paste Wax #2 so this is what I waxed the hood surface with.
Warning: When using Partall Paste Wax shown below DO NOT do a large area! ONLY do an area about 18" inches sq. This wax goes on nice and easy but dries in 30 seconds. I initially did the top of the scoop only to find out it dries so hard that it doesn't want to buff off and it took me an hour to simply buff/rub out the wax. The best way is to put on coats in very small areas then rub it out until dry. Don't try to get the wax smudges and streaks off you'll never get them out w/o a chemical. As you can see in the pic there are a lot of smudges but the surface is smooth and VERY SLIPPERY. Three coats of wax are needed and the streaks shown below are perfectly fine to leave alone.
Once the hood is waxed it's time to contour the clay around the outer edge. I used the rounded corner of a bondo spatula to scrape off the excess clay and produce the desired draft angle I wanted.
Once the claying was done I wiped off any residue from the hood and the flanges then called it done and ready for the next step: Spraying PVA mold release on the top surface then laying glass.
Note: Spraying the mold release, spraying the gel coat and laying the first layer of fiberglass needs to be done the same day so plan these steps accordingly. One reason is because the Partall Film #10 mold release can absorb moister out of the air if it's humid outside and it won't set up properly which may affect the gel coat. In addition you want the gel coat to remain tacky while applying the fiberglass.
At this point the hood is prepped with the nylon flanges, the outer edges are clayed and the hood is waxed so now it's time to start making the mold.
The first thing is to spray the mold release onto the hood. This mold release (Film #10) is basically solvent with melted plastic in it and creates a thin plastic film (like saran wrap) that prevents everything from sticking to the actual hood.
This mold release is VERY runny and it's sprayed as-is with no reducer.
To start you want to mist 3 to 5 coats on first otherwise the liquid will run. Once these mist layers are dry (about 15 minutes) then apply 2-3 wetter coats to get a smooth shine on the surface. This finish will be what the surface of the mold will be so if there is any runs these will show up in the mold. Runs can be acceptable because they can be sanded out later if needed but it's best to not have any.
Time to Spray Tooling Gel Coat:
Materials for Mold:
Tooling Gel Coat (I chose Orange)
Next step was to spray the Tooling Gel Coat. There are two different types of gel coat that is used. One type is a tad softer/flexible which is used for the actual part the other is a Tooling Gel Coat which dries a bit harder. This is what you want for the mold. I chose orange so I can see the different color contrasts when spraying.
In addition to the gel coat I use Styrene to thin the gel coat to make it easier to spray.
A note on gel coats: Once sprayed gel coats will remain tacky in air so in order to completely cure the gel coat a wax additive is used on the final coat. The wax will float to the top of the last paint layer and protect the gel from air so it can harden fully. However, with this process the fiberglass will be laid on top of the gel coat preventing air getting to the gel coat so it will fully cure. In fact if I did use wax it may prevent the fiberglass from sticking to the gel coat so I'm not using any wax additive.. In other words: Do NOT use a wax additive mixed with the gelcoat.
To spray gel coat you will use what they call a dump gun which basically just starts dumping paint out into the air stream as soon as you tip it over, there is no shut off needle. As soon as the gun is tipped horizontal paint will spewed all over the place so make sure you pull the trigger while the gun is still pointing up in the air.
Spray one coat of gel coat then wait about 30 minutes or until tacky then spray another coat and wait 30 minutes then spray the third coat. Let this third coat dry until hard but still a little tacky. This could take an hour or two depending on the amount of catalyst you used, temperature and humidity.
Three coats gives a thickness of about .035 thk and used about 3/4 gal of gel coat.
Pics below show only the first coat, it goes on REALLY THICK like mashed potatoes.
As you can see in the below pics the gel coat poured out of the gun before I pulled the trigger. Don't worry too much if this happens as you have two ways to fix this:
1. While it's still wet take a putty knife and try to smooth the run out. It doesn't have to be perfect because the next several coats will cover it.
2. Wait about 20-30 minutes for it to cure then sand it smooth. I've used both methods successfully.
The reason why this isn't real critical is b/c the important surface is the smoothness of the hoods surface and it is smooth even under all this gel coat. However, fiberglass will be laid on this surface and if there is a huge flaw as shown below then getting the 'glass mat to lie flat could be difficult.
Time to lay Fiberglass:
Materials for Mold:
1.5oz Chopped Strand Mat
Polyester Tooling Resin (anything cheap since it's only a mold)
Rollers to roll out air bubbles
Acetone (5 gal for cleaning)
3" Wide Brushes
The top of the hood is fairly flat but it is still best to lay the mat in pieces. Makea sure you cut pieces that will overlap a few inches and that extend out over the nylon flanges.
Before I lay the mat I start by brushing on a layer of resin onto the gel coat in the area where I will lay the first piece of mat then lay the mat on top and brush more resin on top of the mat.
Roll out the air bubbles using the rollers. You MUST get all the air bubbles out otherwise there will be an air pocket directly under the gel coat which will crack...bubbles are bad!
To make sure I have enough working time with the resin I only mix up 1qt at a time. I tried mixing more but it started setting up before I used it all.
Get the first layer of mat rolled on and try to make it as smooth and even as possible then wait about 40 minutes before laying the second layer of matt on. You want the first layer of mat to be hard but still tacky before laying on the second layer of mat. Again roll out the matting to get rid of all the air bubbles.
Let these two layers set up over night then put on two more layers of mat to make sure the mold is strong. To add more rigidity add some framing to it and cover the frame with a few more layers of mat.
The top of the mold is now all done but the top mold and the hood stay together while the bottom mold is made. I'm leaving the nylon flanges on for now just to prevent me from damaging the mold flanges but they will be removed before I start laying 'glass.
The bottom of the hood has a lot of holes that matting will not fill so I used the PET green tape and taped all the holes closed and also put a dab of clay over all the rivets. The tape marks will show up in the mold and thus in the final part but these will be sanded smooth in the final part.
I also made some bushings to fit over the factory hinge studs so the fiberglass doesn't stick to the threads. These bushings will also act like a drill bushing for drilling out the hood for locating the factory hinge brackets. They are sealed in place with clay. I have some factory hinge plates and a hood latch from a factory hood that I will be gluing into position when the time comes.
Also got started adding clay to the edges of the plastic panels on the bottom of the hood. Again I used the radius edge from the putty spatula and on the tighter corners I just used a flat washer to scrape away the clay to make a nice radius in the clay.
There is a large hole at the back of the hood and I just filled it full of clay. The hole must be there to clear something on a Mach 1 motor but I don't have anything there so I filled it in.
Now I remove the nylon flanges and once they are off I filled in the gap around the hood with more clay making sure to create a draft angle. Also, since the factory hood is in two pieces there is a gap along the edge that I also filled with clay. Remember, all seams need to be filled in.
I've seen a few vids where people separate the two mold halves by taking a hammer then wedge a chisel between the pieces then pry the halves apart. This seems risky to me so I made some nylon wedges that I placed around the edges and that are held in place with some clay. Once the 'glass is laid on top of this side of the hood and it cures good I can pull the nylon wedges out leaving a pocket that I can squirt water into and also use a pry bar to help separate the halves as the water dissolves the mold release.
At this point I apply three coats of the past wax just like above and because I wanted to make sure that the parts separated easily I sprayed about six coats of the Film #10 mold release on making sure to just mist the first several coats on.
After the Film #10 mold release dried I applied three coats of gel coat. In the areas where I knew I was going to need to do some sanding I added it a bit thicker especially around that large hole that I had to fill with clay. I never could get that smoothed out nice so the mold will be sanded and probably the hood too.
Once the gel coat is applied I wait two hours then lay one layer of mat on. After the first layer of glass went on it looked really good but I stopped at the parting line b/c this was going to take some extra thinking. The parting line is a deep groove and no matter what I tried I could not get any mat to feed down into the groove so I just poured resin into the groove until it was level then simply laid mat on top.
I applied two layers of mat on then let it sit overnight then applied two more layers. I also added extra matting for strength over the nylon tabs because I will be prying on the holes to get the halves to come apart.
With four layers of mat I'm calling it done. I'll let it dry for the day then cut around the edges to remove the rough edges of the flange then wait a day or so before trying to separate it all.
To get the molds apart I pulled out the nylon tabs then use a garden hose and squirted water into the grooves. I also use a few screwdrivers in the slots to apply pressure along with letting the water wash away the mold release. Because the bottom mold has a lot of contours I let the water flow between the mold halves for about 40 minutes then applied more pressure with the screwdrivers and it separated very easy.
Optional: Fixing/Perfecting the molds
If there's any imperfections in the mold you can use bondo or clay to make any corrections. I made some areas flatter using bondo and filled in some grooves with clay. There was a few areas that I knew I was gloing to block sand so when applying the gel coat I added extra coats in those areas. Now that the molds are apart I can block sand all I want until those areas are smooth.
Making the Actual Parts:
Materials for Parts:
1.5oz Chopped Strand Mat
Vinyl Ester Resin (This is a High Temp Resin)
Rollers to roll out air bubbles
Acetone (5 gal for cleaning)
3" Wide Brushes
Part Gel Coat (White)
I put the usual three coats of mold release paste wax on the top mold then sprayed about 7 coats of Film #10 mold release and let it set over night. The humidity was down compared to the previous days so I was confident that spraying the mold release the night before would not cause any issues and it didn't. The next morning I sprayed three heavy coats of regular white gel coat (Not Tooling Gel Coat) then laid two very dry coats of mat/resin on. For the actual hood parts I'm using a different resin than what I used for the molds. Due to the heat the hood will see (black car and engine compartment) I'm using a Vinyl Ester Resin. Compared to making the mold which is a temporary part, when applying resin to the actual part you don't want a lot of resin on the actual part. Instead of brushing resin onto the mold I first put the mat pieces on then brushed on as little resin as possible on top of the mat then immediately laid the second layer of mat on top and worked it into the the resin that was already laid for the first layer. In some really dry areas I had to add more resin with a brush but with continuous working it eventually soaked up the resin but you do have to work fast otherwise the resin will start setting up.
I did not lay the mat down in one large piece instead the mat was cut into several long pieces and laid down with the seams located approximately where the contours were on the hood and the pieces were overlapped about 3" to 4".
I let these two layers cure over night then added one more layer of matting over the hood and several extra layers of mat over the nylon wedges then called it good. With three layers of mat the part should be about .10" thick which is what my buddies aftermarket hood measured and the factory hood also measured.
After letting the part cure for two days I again used the garden hose and some small pry bars then separated the part from the mold. The part has zero flaws and once the flanges are trimmed it only needs some light block sanding before it is ready to paint.
The same process and materials are used for the underside of the hood but this part takes a lot longer due to all the smaller pieces that are needed due to the complex geometry of the part.
For the bottom of the hood I sprayed the mold with 5 good coats of gel coat because I wanted to block sand several areas of the hood before priming.
After letting the gel coat cure for about two hours I applied two layers of mat then let it set over night. Again I laid the first layer of mat down then brushed resin on top then laid the second layer of mat down with no resin so it would soak up any resin that was applied to the first layer. You want to use as little resin as possible for the actual parts.
The next day I added two more layers of matting for a total of four layers and again all these layers are applied with as little resin as possible just like what is described for the top of the hood. Let the part cure for at least 24 hours.
Before removing the part from the mold I drilled the holes for the hood brackets using the bushings that are glassed into the mold.
Now it's time to separate the part from the mold using the garden hose again and after about 15 minutes the part pops loose.
Now that both parts are out of the molds the flanges can be trimmed with a carbide toothed jig saw blade. I trim them to within 1/4" to 1/8" of where the actual edges will be and will fine tune the edges with a belt sander or file to make sure the edges are straight.
For this project I got ahold of some factory hinge plates and a factory latch plate. The holes for the hinge plates were drilled out in an above step and the hinge plates dropped in nice and snug. Then I used them as a template to drill the two attaching screws holes. The plates will be glued but the screws need to be there to squeeze it all together. I'll be using stainless button head screws b/c when the hood gets washed and water gets between the two pieces I don't want the hardware to rust and eventually show through.
Below are the holes for the prop rod and the latch plate which were cut out with the jig saw. The top edges will be rounded when I prep the parts for paint.
Once I bolted the plates on I test fitted it on the car. I was hoping to see how the edges line up with the fenders but there was too much tension to really get it to push down properly. It looks real close is about all I can say.
Before I glue the halves together I marked where the edges of the parts need to be sanded down to and also sanded the glue surfaces flatter and thinner.
A quick test fit by bolting the lower have to the car then simply laying the top portion on top. Looking good so far.
I glued the hinge plates in with a special epoxy that is made for bonding metal to 'glass. After applying the adhesive I screwed the plates on with two #10 screws then immediately bolted the hood onto the car so I can use the actual hinges to really tighten the plates down good. This adhesive was HARD in 5 minutes so I had to work efficiently. When applying the epoxy I made a bead around each bolt hole to keep water from seeping into the hood.
Since the hinge plates and the latch plate will be bolted and bonded I block sanded the gel coat where the screw heads are so I don't need to worry about trying to prep those tight areas before painting.
Before gluing the latch plate in I had to make some support plates to help keep the surface of the hood flat while the screws were tightened down. The last pic is with the stainless steel screws that will be used on the final product. I also decided to glue the crap out of the nuts on the back side and this allows me to remove the screws before I paint the hood then reinstall them.
Time to glue the panels together! To bond the two fiberglas halves together I used a 3M fiberglass panel adhesive that is made for bonding f'glass to itself. I squeezed the adhesive all around the hood then used a putty knife to smooth it out to a 1/8" thick x 1.5" wide bead all around the outer edge of the hood then laid the two halves together, clamped it and waited 24hrs.
Note: When clamping the pieces together try to avoid creating bends/waviness at the seams. I spent several hours trying different clamps and positions and concluded by using a flat aluminum bar across the nose of the hood then just a few clamps around the edges.
The factory hoods outer edge/flange is 1/4" thick and my part is a lot thicker than this so in order to make sure the top edge of the hood matches the top of the fender the next step is to grind the outer flange where the adhesive oozed out to eliminate all the shiny areas and to thin the flange up. I will make it thinner than needed but build it back up with more panel adhesive. Any place where panel adhesive is to stick the gel coat and fiberglass must be roughed up good. I used 34 grit and a die gridning bit to shape the surface down to about .080"-.125" thick.
I want the flange to be a consistent thickness around 1/4" so I used hot glue and attached several nylon strips together and stuck them to the hood. I'll dump a lot of adhesive along the flange then use a spatula to spread it flat. I'll have to do one side at a time to make sure the contour is good.
Spreading the adhesive just needs to be fairly close b/c once it dries I will scuff that up real good then I will use Evercoat as the top finishing coat before sealing/priming it.
Once the adhesive dries I block sanded it with 180 grit. Looks great! I'll fill in the low areas with more adhesive as needed making sure that I scuff those low areas good so the adhesive will stick.
Glazecoat is applied to fill in pin holes and low areas then sanded smoooooth. Just about ready for paint!
To prep for paint I blocked sanded the gel coat with 180grit and when it was nice and flat I sanded with 240grit.
After three good coats of primer I sanded with more 240grit making sure everything was smooth. Then I waited 24 hours for it to cure.
Bottom side was painted in single stage Black and looks great!
Not bad for a rookie!
Top of the hood was block sanded with 600grit then sealed and primed.
The primer was blocked with 1000grit then then painted with base/clear.
The clear was block sanded with 1000 grit then 2500grit
After polishing and installed below!
Not a single flaw!!