Last time, we learned about composite sandwich structures and we built a custom bulkhead for the BugE’s baggage compartment using Burt Rutan’s Moldless Composite Construction techniques. Today, we’re going to finish the bulkhead by building a support tray for a Grizzly retracting cable reel and by adding a small project box for the countdown timer (described in the last post).
Foam Structures for the Cable Reel Tray
The first step in building the support tray is to construct a set of walls around the cable reel using a couple of different types of structural foam. The blue foam in the photo above is the same 3/8-inch-thick PVC foam that was used to make the bulkhead. This foam, which comes in sheets of varying thickness, is good for making flat panels. The yellow foam is urethane foam. Urethane foam is preferred when the application calls for making complex shapes because it is very easy to carve and sand. In fact, the best sanding block for urethane foam is another piece of urethane foam. All of the foam pieces were cut on a band saw (although a hand-held hacksaw blade would work just as well) and glued to the the bulkhead (and each other) with 5-minute epoxy. I decided to leave about 1/8″ clearance on all sides of the cable reel to leave room for the fiberglass facings and to make installing the cable reel easier.
Once the foam was shaped to my satisfaction, the next step was to glass the interior of the foam. I did this in three separate lay-ups — the bottom of the traywas done first, followed by the left side and the right side. This was done so that gravity would assist me in keeping the lay-up flat during cure.
Installing the Inner Lay-Up on the Left Side of the Cable Reel Tray
For each lay-up, micro-slurry was applied to the foam and dry micro was used to form fillets on the inside corners. I used three plies of bidirectional fiberglass for each of the three interior lay-ups. Fiber orientation for each ply was on the bias (at a 45-degree angle to the edges of the foam). The bottom lay-up overlapped onto the bare foam of the sides by at least 2 inches and the side lay-ups overlapped onto the bottom lay-up by the same amount. All three lay-ups lapped onto the bulkhead by at least one inch. After each lay-up was performed, peel-ply was added and the lay-up, the fiberglass and peel-ply were trimmed to within 1/4-inch of the foam and the lay-up was allowed to cure. After cure, the peel-ply was stripped and excess fiberglass was trimmed off with a hand-held hacksaw blade and a 60-grit sanding block.
After all of the interior lay-ups had been completed, the foam was carved in preparation for the exterior lay-ups. Foam was removed from all of the edges so that a glass-to-glass bond could be achieved around the perimeter of the tray. The one exception to this was is the area where the cable exited the cable reel. Here, the foam was left uncarved (see the picture above). I did this so that I could show you how to deal with exposed foam edges and we’ll look at that shortly.
Hardpoint for Cable Reel Retaining Strap
I also made a pair of hardpoints out of 1/8-inch-thick aluminum so that I would have some way of attaching a retaining strap for the cable reel. You can see one of these in the picture above. The 5 lower holes (away from the camera) allow wet flox to bond the straps into the fiberglass structure and the uppermost hole (closest to the camera) is where the retaining strap will attach. All foam and micro were removed in the area under the hardpoint to promote a solid bond with the fiberglass.
Adding the Exterior Lay-UpsChargers and Electrical Sub-Panel
As with the interior lay-ups, the three exterior lay-ups were performed one-at-a-time (bottom, left side, and right side). The foam was covered with micro-slurry and the interior corners were filleted with dry micro. On the left and right sides, the hardpoints were installed with generous amounts of wet flox prior to adding the fiberglass facings. Three piles of bidirectional fiberglass were applied on the bias on each side, wrapping around adjacent corners by at least two inches and lapping onto the bulkhead by at least one inch. Peel-ply was applied over each lay-up and the epoxy was allowed to cure overnight. After cure, excess fiberglass was trimmed off and the glass edges were trimmed flush with a 60-grit sanding block.
Treating Raw Foam Edges
To finish the exposed foam around the area where the power cable emerges from the reel, I used a Dremel to remove about 1/4-inch of foam between the two fiberglass facings, all the way around the perimeter of the cut-out. Then, using a mixing stick, I troweled in dry micro to fill the “trench’, leaving the micro proud of the edges of the fiberglass. After cure, I sanded the excess dry miro flush with the edges of the fiberglass. This leaves a nice hard surface that can be primed and painted along with the rest of the bulkhead.
Glassing In the Timer Box
The final job consisted of mounting a small ABS-plastic project box that will be used to hold the countdown timer. The exterior of the box was roughed up with 60-grit sandpaper. Then, wet flox was used to adhere the box to the bulkhead. After cure, two plies of bidirectional fiberglass were applied to the outside of the box, lapping 1 inch onto the surrounding bulkhead. The glass was covered with peel-ply and allowed to cure. Red electrical tape was used as a temporary clamp to keep the fiberglass from pulling away from the edges of the box. After cure, the edges of the fiberglass were trimmed and sanded flush with the lip of the box.
Finished Bulkhead -- Ready for Installation in the BugE
Before installing the bulkhead in the BugE’s fairing, I decided to wire up the 110 VAC circuitry to make sure that everything was working properly. The photo above shows the countdown timer, to the left of the cable reel. The fuse, above and to the right of the timer, protects the 48-volt charger. I’m not thrilled about having exposed line current in this area and I am going to see if I can find a better fuse holder to do this job. The retaining strap for the cable reel is made out of 1″-square aluminum tubing, cut at a 45-degree angle and with some angle brackets bolted to each end.
The next photo shows the two chargers and the electrical sub-panel, mounted and wired…
Chargers and Electrical Sub-Panel
- Close-Up of Electrical Sub-Panel
… and the last photo shows the wiring on the electrical sub-panel.
I’m happy to say that everything worked as expected. When I plugged in the cable reel, the charger interlock relay energized. When the count-down timer was activated, the chargers came on line. Best of all, none of the precious blue smoke stored within the electronics escaped.
Next time, we’ll install the bulkhead in the BugE’s fairing.
Trial Fitting the Foam for the Forward Bulkhead
In the last post, I promised to show you how to make fiberglass sandwich structures and that’s what we’re going to do today. A peanutbutter and jelly sandwich meets the definition of a composite sandwich structure because it has (1) two facings — the bread; (2) a core — the peanut butter and jelly; and (3) the whole is better than the sum of the parts. In a composite sandwich structure, fiberglass and epoxy comprises the facings, the core is made from a structural foam, and the completed structure is better than the sum of the parts because it is strong (which the foam alone isn’t), light-weight (because the fiberglass and epoxy alone aren’t), and rigid (a property which none of the materials alone possess). It is the spatial relation of the two facings that gives the structure its rigidity. It works sort of like an I-beam, wherein the flanges accomodate the tensional and compressional bending loads and the web accomodates the shear and torque loads. In a composite sandwich structure, the facings accomodate the tensional and compressive loads and the distance between the facings — provided by the foam core — allows the facings to accomodate the shear and torque loads.
In the stock BugE, the rear of the fairing’s luggage compartment is left open and is contiguous with the passenger area. I wanted to install a rear wall into the luggage compartment, reasoning that I could probably stuff more groceries into it if the bags weren’t trying to fall backwards, all over my feet. As I continued work on the battery area of the vehicle, a change in charger specification by Mark suggested that the installation of an horizontal panel above the baggage compartment might be a good place to hold the new charger. All of this led to the design of a fiberglass bulkhead, the construction of which will be described below.
- Foam for the Forward Bulkhead
The photo above shows the configuration of the foam for the bulkhead. In the photo, the structure is inverted from the way it will be intalled in the BugE, so that I can apply the fiberglass facing to the underside of the structure. The curved portion tucks into the front of the fairing above the baggage door. The large flat sheet is the vertical wall at the aft end of the baggage compartment and the small panel, mounted at 45-degrees to the aft one, blends into the curved part of the fairing’s fiberglass over the chassis’ fairing pivot tube. The panels were made from 3/8-inch-thick PVC foam (available at Aircraft Spruce and Specialty) and were glued together with 5-minute epoxy. The shape of the curved portion was determined by trial and error, with the aid of a cardboard template. The underside of the structure has been prepared for fiberglassing. All of the foam has been covered with micro-slurry, the external corner has been rounded and the internal corner has had a dry-micro fillet applied.
- Bottom Fiberglass Facing Applied
Two plies of bidirectional fiberglass, with a 45-degree orientation, were applied to the bottom of the bulkhead, as shown above, and peel-ply was applied over the lay-up. The fiberglass and peel-ply were trimmed to within 1/4-inch of the edges of the foam to prevent the fiberglass from lifting along the edges and the lay-up was allowed to cure overnight. After cure, the peel-ply was removed, excess fiberglass was trimmed from the edges of the lay-up with a hand-held hacksaw blade and a 60-grit sanding block, and any remaining roughness on the face of the lay-up was sanded smooth with 60-grit sandpaper.
Positioning the Electronics
With the bulkhead oriented properly (top side up) on the edge of my workbench, I determined the locations for the charger electronics. The large charger in the center of the photo is the new 48-volt unit specified by Mark. The small box to the right of the 48-volt charger is a 12-volt charger, used to top off the accessory battery. The small aluminum panel to the left of the 48-volt charger holds a charger interlock relay, the turn-signal flasher and two barrier strips for the 110 VAC wiring.
110 VAC Electrical Sub-Panel
The charger was modified in two ways. First, the fuse holder on the 110 VAC line was removed because it wound up in an awkward position — on the forward face of the charger and tucked under the nose of the fairing. If the fuse were to blow, it would not be possible to replace it without removing the charger from the vehicle. Instead, I decided to mount the fuse in an external location (on the aft face of the vertical panel — see the next post) that was more easily accessible. The second modification involved changing the manner in which the charger’s rubber feet were installed. As supplied by the factory, the feet were installed with small sheet-metal screws. I changed these out for longer pan-head screws, with the screw heads located inside the charger. The ends of the screws protrude about half an inch below the bottoms of the feet. By doing this, it is possible to bolt the charger to the bulkhead with the feet acting as shock absorbers.
The 12 VDC charger was disassembled and modified in a similar manner for mounting. Also, the 110 VAC supply line for this charger was removed and a pair of 14-ga. wires were installed to facilitate wiring in the unit.
The aluminum panel is used primarily to mount the charger interlock relay. This relay has a 110 VAC coil that energizes the relay any time the BugE is plugged into a wall socket for charging. Once energized, the relay’s switch interrupts current flow to the motor solenoid, preventing the vehicle from being started when it is plugged in. The two barrier strips are used for the 110 VAC wiring. The forward strip takes power from the mains and distributes it to a digital count-down timer, to a 110 VAC panel lamp that indicates that the vehicle is plugged in, and to the coil of the relay. The purpose of the timer is to set a limit on how long the chargers are allowed to operate (usually 8 hours). This keeps the batteries from being over-charged in the event that the protective circuitry in the chargers should fail to operate properly. The second strip distributes 110 VAC from the output of the timer to the two chargers.
Once the locations of the electronic components had been determined, the foam on the upper side of the bulkhead was prepared for fiberglassing.
- Carving the Foam
The foam under the electronics was removed down to bare fiberglass, and the edges of the foam were radiused for a smooth transition between the upper fiberglass facing (to be applied next) and the lower one. The bare fiberglass was roughed up with 40-grit sandpaper for a good mechanical bond. If you choose to do this, it is imperative that all foam and micro slurry be removed from the lower fiberglass facing in the areas that will bond to the upper facing. If you fail to do this, your glass-to-glass bond will be very weak. A cut-out was made in the bulkhead’s vertical face to accomodate the shape of a Grizzly cable reel, the installation of which will be discussed in the next post. The foam and micro slurry along the edges of this cutout were removed for a good glass-to-glass bond.
- Glassing the Upper Surface
The foam was slurried and dry micro was used to fillet the internal corner. No slurry is applied to the bare fiberglass — glass-to-glass lay-ups are done with pure epoxy only. Four plies of bidirectional fiberglass, with random orientations, were installed into the each of the three foam depressions where the electronics will sit. This was done to provide extra thickness (strength) at the mounting-bolt locations for the chargers and aluminum panel. Then, while the epoxy was still wet, two plies of bidirectional fiberglass were applied over the entire top surface of the structure. Peel-ply was applied over everything and the lay-up was allowed to cure. After cure, excess fiberglass was trimmed from the edges with a hacksaw blade and the edges were squared up with a 60-grit sanding block.
Next time, I’ll show you how I made a fiberglass mount for the Grizzly cable reel and we’ll finish the bulkhead up to a point just prior to installing it in the BugE’s fairing.
At this point, there are a lot of bumps and ridges where the new fiberglass onlaps the old. To smooth everything out, we need some sort of a non-structural filler. The airplane folks would use dry micro (see the post on 03/22/09) because it is extremely light weight and they have to smooth out the weave on hundreds of square feet of fiberglass (wings, fuselage, rudders, etc.). While Bondo is a LOT heavier than dry micro, it has several advantages. First, it cures in about half an hour (dry micro takes overnight) so we can do multiple layers in a single day, if we need to. Also, it doesn’t develop nearly as many pinholes as dry micro (pinholes develop when air bubbles get trapped in the material while you’re mixing it), so we won’t need to fill nearly as many pinholes.
Mix the bondo according to the instructions and just slather it on all of the new fiberglass with a mixing stick, overlapping at least an inch onto the old work. Then, exercise your creative genius as a sculptor with some 60-grit sandpaper. You’ll probbly sand down to raw fiberglass in several areas and that’s fine. Blend the bondo into the old fiberglass as smoothly as you can. When you’re satisfied with the contour, go back over the Bondo with 120-grit and then 220-grit. Don’t be surprised if you have to go thru a bunch of Bondo cycles (I needed four) to get the contour exactly where you want it — with all of the pinholes filled.
Motor Cover in Primer
When you think that you have the Bondo exactly right, shoot the entire outside of the motor cover with a coat of a sandable primer. I use Krylon gray, right from the rattle can. Let it dry overnight and they check the smoothness of your work. I usually find a myriad of sins at this point — bumps, ridges, unfilled pinholes, etc. That’s OK. You’re using the primer as a marker coat — nothing else — so have at it again with the 120- and 220- grit sandpaper (even the 60-grit is OK if you have a particularly bad area). At this point, your motor cover will probably display quite a spectrum of colors: black (the original gel-coat), red (the old fiberglass), green (the new fiberglass), pink (Bondo), and gray (primer). If it does, you’re doing just fine. Once you’re happy, try the sandable primer again. I usually wind up having to go thru this prime-sand-contour routine 3-4 times before I’m happy with it. Once you are, it’s time for the color coat.
Finished Motor Cover
I shot my motor cover with two coats of flat black. Once the paint had cured for a couple of days, I masked the outside and shot the inside with Eastwood Rubberized Undercoating. This was the first time that I had used this Eastwood product and it worked like a charm. The finished undercoating looks as good as anything that would come out of Detroit. Hopefully, it will add a bit of sound dampening to the motor area. The undercoating comes in a standard rattle-can. However, because you’re shooting a very thick product, the nozzle in the can is very large and it produces a very wide, blobby spray pattern. Protect the area around the motor cover from overspray.
So, that’s how I did it — a motor cover with a one-of-a-kind shape. Next up, it’s time to tackle the fairing. There’s a bit of custom fiberglass work that I want to do there, too. Follow along and you’ll learn how to make composite sandwich structures.
Adding a Motor Stud
In the BugE plans, the motor cover is mounted to the rear of the chassis with Velcro tape. For many climates, this probably works just fine. But, here in the Las Vegas summer heat, the adhesive on the Velcro would probably soften. Not wanting my motor cover to depart my vehicle, I decided to mount the cover with standard hardware.
I began by removing the brush-end of the motor case. As it comes from the factory, there’s a small hole drilled thru the center of the casting. I enlarged this hole to pass a #10-32 bolt and then countersunk the hole on the inside of the casting. The countersink is necessary because there is very little clearance between the inside of the casting and the face of the motor shaft bearing (less than 1/16″). By countersinking the hole, I was able to install a flat-head bolt into the hole and have the head of the bolt be flush with the inside surface of the casting — no worries about the bolt contacting the bearing. The bolt is held in place with a nut and some red Loctite on the outside of the case. On top of the nut goes a wide-area washer and a neoprene washer (left over from a toilet rebuild kit — never throw away anything!) I driled a hole in the center of the motor cover to slip over the bolt, followed by another neoprene washer (there were two in the toilet kit), another wide-area washer and a locknut.
Three-Point Mounting System for the Motor Cover
Two additional bolts make up a three-point mounting system for the motor cover, as shown in the photo above.
Forward Mounting Bolt
The forward mounting bolt is threaded into a tapped hole in the shock tower. There is a stack of four neoprene washers between the motor cover and the shock tower (I rebuild a lot of toilets).
Aft Mounting Bolt
The aft mounting bolt is threaded into a tapped hole in the upper surface of the left trailing arm. There’s also a neoprene washer between the motor cover and the trailing arm.
Ta-da! The motor cover not only fits, it mounts solidly. All that’s left is to make it look pretty. That we’ll do next time.
With the exterior lay-up complete, the next job is to perform the interior lay-up. To do this, we need to remove all of the foam and some of the old fiberglass from the inside of the motor cover.
Inside of Motor Cover -- Before Trimming
The photo above shows the interior of the motor cover as it currently appears. The outside lay-up has cured at this point and the next job is to dig out all of the foam and remove some of the old fiberglass so that the new work blends into the old work.
Motor Cover Jigged for Inside Lay-Up
In the photo above, you can see how the foam and old fiberglass were trimmed away. Removing the foam was fairly easy. Most of it was just dug out with screwdriver tips and an X-Acto knife. Removing the old fiberglass involved a lot of work with a Dremel and a dust mask. Once the old and new work were blended together (use 36- or 40-grit sandpaper), all of the interior of the motor cover was sanded with 36-grit sandpaper so that the inside lay-up would bond well with the existing (new and old) fiberglass. The cover has been jigged onto the workbench with Bondo, so that the inside lay-up will drape well.
Only pure epoxy is needed to perform the inside lay-up because all of the bonds are glass-to-glass — there’s no foam involved at this point. Four plies of bidirectional fiberglass were wet out with a random fiber orientation, lapping at least 1″ onto the old work. Again, the edges of the four plies were staggered where they lapped on to the old work. The edges of the fiberglass were scissor-trimmed to within 1/4-inch of the edges of the pre-existing work and small pieces of peel ply were added prior to cure.
By the way, you can use MEK to clean off any epoxy on your scissors before it cures. Never use any solvent to clean epoxy off your hands. The solvent will carry certain chemicals in the epoxy into your blood stream! Of course, you don’t need to clean epoxy off your hands because you’re always wearing butyl rubber gloves when working with epoxy, right?!
Inside Lay-Up Complete
After the lay-up has cured, remove the peel-ply and trim the edges with a hacksaw blade and sanding block. Also, blend the new work into the old work with 36-grit sandpaper for a pleasing appearance. This completes the stuctural work. Next, we’ll figure out how we’re going to mount the cover and then we’ll do the cosmetic work, including filling, priming and painting.
Back on October 12, 2008, I started making some modifications to the motor cover so that it would fit properly over the custom motor retaining strap that I had fabricated. Back then, I promised to show you how the shape of the motor cover was modified (with fiberglass) and how the fiberglass work was accomplished. We’re going to start looking at that today.
- Motor Cover Jigged for Outside Lay-Up
Above is a photo of the motor cover as it was back on October 10th. Blocks of urethan foam were epoxied in place with 5-minute epoxy to define the new shape for the cover. I’ve jigged the cover to my workbench using some scrap wood and Bondo — positioning it so that the exterior fiberglass lay-up will drape nicely over the foam. Bondo is the best material for jigging fiberglass because it is strong enough to hold the parts in place but not so strong that it can’t be broken free with a few judicious whacks of your fine adjusting tool (hammer). You can’t use 5-minute (or any other) epoxy to do the jigging because it grabs the fiberglass too well. If you try to whack off the jigging blocks after having used 5-minute epoxy, you’ll destroy (delaminate) the fiberglass.
Adding Micro Slurry to the Foam and Using Dry Micro to Form the Fillets
To make the outside lay-up, we begin by mixing up some pure epoxy in a paper cup and then add microballoons to form micro slurry — a material with a consistency similar to pancake syrup. The slurry is spread all over the foam but not on the surrounding fiberglass. The slurry fills the voids in the foam so that the foam won’t wick epoxy out of the fiberglass layup. You don’t want to get slurry on the raw fiberglass because it will weaken the bond between the old and new glass-work.
Once the foam has been slurried, we add additional microballons to any of the remaining slurry until the consistency of the mixture resembles bread dough. At this point, the material is known as dry micro. Dry micro is used to form a fillet around the edges of the foam. This is done to help the fiberglass lay smoothly into the inside corners. If we didn’t do this, we’d probably wind up with air bubbles trapped under the fiberglass along all of the inside corners.
Applying the Fiberglass
Next, lay up four plies of bidirectional fiberglass over the slurried foam, lapping at least 1″ onto the old fiberglass. Stagger the edges of the overlapping fiberglass so as to minimize the bump between the new and the old work. The weave orientation of the fiberglass is not critical in this application. Use a heat gun to help decrease the viscosity of the epoxy and allow it to wet out each ply of fiberglass thoroughly, but don’t get the heat gun so close to the foam that you risk melting it. After all four plies have been wet out, use a pair of scissors to trim the layup to within 1/4-inch of the edges of the foam. If you don’t do this, any excess fiberglass that hangs over an edge will lift the fiberglass over the foam along the edge, causing a bubble.
Adding Peel Ply to the Lay-Up
Once the fiberglass has been trimmed, add peel-ply over all of the new work, lapping onto the old fiberglass by half an inch or so. Peel ply doesn’t do well around compound curves, so you’ll have to use a lot of short pieces to get all of the new fiberglass covered.
Exterior Lay-Up Completed
Allow the lay-up to cure overnight. Then, remove the peel-ply and trim off any excess fiberglass. Be careful — those edges are SHARP! Use a hand-held hacksaw blade and a sanding block with 60-grit aluminum oxide paper to true up the edges. Also, blend in the new work into the old work as best you can. This doesn’t have to be perfect, but a little extra effort now will save you from having to do the job with Bondo later. Enough for now. Next time, we’ll do the interior lay-up.
It’s been a while since my last post, mainly because I’ve spent the last six weeks studying for a certification exam that comes due every two years. Accordingly, progress on the BugE has slowed a bit.
In the last entry, I promised to show you how to install a set of EZ-Point EZ Studs. I’m going to use the studs to secure some cushioned cable clamps to the underside of the fender pan. The cable clamps will hold a wiring harness that will bring the rear lighting circuitry (directional indicators, brake light, tail light and license-plate light) forward to the door contacts that were installed earlier.
Drilling the Studs
EZ-Point EZ Studs — available from Aircraft Spruce and Specialty and other vendors of aircraft hardware — consist of a small round aluminum plate with a threaded stud mechanically pressed in place. The studs come in various sizes. For this application, I chose to use the 1/4-20 variety.
As supplied from the manufacturer, the plate-portion of the stud has no holes in it. However, I like to drill a set of six holes in the plate to help flox anchor it to the fiberglass structure. To locate the holes, I mark three lines on the bottom of the stud plate using a small template which I make out of out of MDF or some similar material. The template has a hole drilled into it so that I can position the stud upside-down on the template. Then, using a set of 60-degree lines that I have draw on the template, I extend the lines across the bottom of the stud plate. I use a circle template to draw a circle on the bottom of the plate and then center-punch the intersections between the lines and the circle to get my hole locations. None of the dimensions here are critical — I just do what looks right. Once all of the EZ-Studs have been marked, I take the template over to my drill press and drill out the holes.
Once the holes are drilled, I deburr them and sand off the alodine on the mounting plate with 60-grit aluminum oxide paper. I also install a short piece of plastic tubing over the threaded portion of the stud to keep epoxy from gumming up the threads. You can also do this with a small piece of electrical tape.
To mount the studs to the bottom of the fender pan, decide on the location for each stud. Then, sand each stud location with 36-grit sandpaper in a 4-inch radius around the stud’s center-point. Mix up some flox — a bit on the wet side this time – and use a mixing stick to apply a generous blob to the bottom of the stud plate. Then, press the plate in place on the fender pan. Using your mixing stick, evenly spread the flox that has oozed up through the holes and also build up a small flox fillet around the perimeter of the plate so that the fiberglass (that you will install next) will have a smooth transition from the stud plate to the fiberglass fender pan.
Two EZ-Studs Glassed in Place
Once the stud has been positioned properly, glass it in place with three plys of bidirectional fiberglass. Use squares measuring about 4″ x 4″. The orientation of the weave is not critical. Wet out the fiberglass using a small brush and a hot air gun to assist you. Remember the rule — not wet, not white. Once the three plies of fiberglass have been wet out, cover the entire lay-up with a piece of peel ply and allow the lay-up to cure. After cure, strip off the peel ply and sand the lay-ups with 60-grit sandpaper for a smooth transition onto the surrounding surface.
Fender Pan with All Fiberglass Work Completed
I installed a total of five studs to support the wiring harness from the luggage box to the contacts under the fender pan. As a final step, I sanded all of the underside of the fender pan with 36-grit sandpaper to remove any roughness in the part’s original fiberglass work. This job took several hours but the resulting surface is very smooth. Any remaining roughness should easily be hidden by the Zolatone paint.
Painting the underside of the fender pan is the next step for this part, but that will have to wait until I am ready to paint the underside of the fairing, so that I can do all of the Zolatone work at the same time. In the meantime, the next job is to finish up the fiberglass work on the motor cover. I’ll show you how that’s done next time.
The last job consists of mounting the hardpoints for the front mounting knobs and for the trunk mounting bracket. We’ll have to do this over two days. On the first day, we’ll clamp the fender pan on the workbench with one side down and install the three left hardpoints. On the second day, we’ll do the three right ones. If you attempt to do all of them at once with the fender pan lying upside-down, the epoxy will run and you’ll have a mess on your hands.
Hardpoints for the Front Mounting Knobs
The techniques that we’ll use here are exactly the same as we’ve already done. Prep-sand the bonding areas on the fender pan with 36-grit sandpaper and on the metal parts with 60-grit. Mix up some wet flox and bond the hardpoints in place, using dowels to register the hardpoints with the holes in the fender pan. Then, add flox fillets around the hardpoints for a smooth transition onto the surrounding glasswork. Add three plies of bidirectional fiberglass over each hardpoint, lapping onto the fender pan at least 2 inches in all directions. Wet out the fiberglass with just enough epoxy to do the job and stipple out any air bubbles. Then, peel-ply the layups for a smooth transition. After cure, strip off the peel ply and sand the cured layups for a smooth transition onto the fender pan.
The hardpoints for the forward mounting knobs were made from 1/4-inch aluminum plate and that turned out to be the correct thickness. After cure, I reinstalled the fender pan onto the chassis and there was no side-to-side slop in the front of the fender pan. I used wide area washers for the trunk bracket hardpoints. You might wonder why I used hardpoints here at all. The reason has to do with the curvature of the rear fender. By installing hardpoints at these locations, the flox under the hardpoints takes up the curvature of the fender, allowing the mounting nuts for the trunk bracket to sit tight against the hardpoints. Without the hardpoints, the nuts and washers would cock with the curvature of the fender.
Hardpoints for the Trunk Mounting Bracket
The last job that we have to do on the underside of the fender pan is to add some mounting studs to hold the wire run from the trunk to the door contacts. We’ll hold the wire bundle in place with cushioned clamps and we’ll mount the clamps on some EZ-Point EZ-Studs. The studs will need to be glassed in place, but you already know the procedures. We’ll show you how it’s done next time.
The next step is to glass the other side of the mounting brackets. Because of their locations, we’ll also be adding the five hardpoints that mount to the underside of the fender pan. Four of these hardpoints are for the seat sliders and the fifth one reinforces the area around the rear monunting point.
Floxing the Hardpoints In Place
As usual, we begin by roughing up the existing fiberglass with 36-grit sandpaper and we rough up the bonding surfaces of the metal parts with 60-grit. After suiting up, mix up some wet flox and bond the five hardpoints in place. Use wooden dowels to keep the hardpoints registered with their respective holes. Then, form flox fillets around each hardpoint to allow for a smooth transition of the fiberglass. Also, fill in any remaining gaps under the mounting brackets and add flox around the bases of the brackets between the brackets and the adjacent hardpoints.
Next, wet out the exposed metal surfaces of the mounting brackets and hardpoints with pure epoxy and add three plies of bidirectional fiberglass as we did last time. The fiberglass for the mounting brackets will also cover the adjacent hardpoints. Use a heat gun to help wet out the fiberglass and stipple out any air bubbles with your brush. Then, peel-ply the layups for a smooth transition onto the surrounding fiberglass.
Adding Peel Ply to the Hardpoints
Peel ply doesn’t take compound curves very well, so you’ll need to add the peel-ply in sections instead of just applying one large piece over each hardpoint.
Hardpoints Blended Into the Seat Pan After Cure
Once the layups have cured, strip off the peel ply and sand the layups with 60-grit sandpaper for a smooth transition onto the surrounding fiberglass. You’ll need to drill out the holes in the monting brackets and hardpoints carefully. With the hardpoints, do this from the underside of the fender pan. I didn’t, and you can see the results. If you attempt to drill out the holes from the gel-coat side, you’ll cause some delamination of the layups over the hardpoints. In this application, a small amount of delamination isn’t a big deal but it’s better to develop the proper technique now. Who knows? Someday, you may want to build a fiberglass airplane.
With the mounting brackets securely attached to the fender pan with flox, the next step is to fiberglass the brackets in place. This will have to be done in two stages. The first stage will involve placing 3 piles of bidirectional fiberglass over the horizontal and vertical surfaces of one side of each tab. The fiberglass will overlap onto the bottom of the fender pan for at least two inches in all directions. The second stage will involve glassing the other side of the vertical portion of each bracket. We will need to add the four hardpoints for the seat sliders at this point, because two of the hardpoints are located very close to the brackets for the door contacts. While we’re working on the bottom of the fender pan, we may as well add the 5th hardpoint for the mounting knob at the rear of the fender pan.
Preparing for the First Lay-Up
To prepare for the glasswork, the first step is to sand off the excess flox with 36-grit sandpaper. You need to consider how the fiberglass is going to lay while doing this. Fiberglass doesn’t like to take sharp corners, so sand off the flox leaving fillets between the mounting brackets and the fender pan whereever possible. Next, prep-sand the bottom of the fender pan with 36-grit sandpaper for an area at least 3 inches around all sides of each bracket and rough up the brackets with 60-grit sandpaper. Vacuum off any dust around the layup area with your shop vac and suit up with your protective gear. Mix up some wet flox and fill in any gaps under the mounting brackets. Also, make flox fillets around the base of the brackets so that the fiberglass will lay up nicely. Wet out the horizontal and vertical faces of the brackets with pure epoxy and wet out the areas around the brackets for 3 inches in all directions. Then, add the first ply of fiberglass over each bracket, lapping onto the fender pan. Use a hot air gun to help the epoxy wet out the fiberglass and stipple out any air bubbles with your brush. Remember the rule — “Not wet, not white.” Add the two dditional plies of bidirectional fiberglass in the same manner, using enough epoxy to thoroughly wet out the glass but keeping any excess to a mimimum.
Glassing the First Side of the Mounting Tabs
Once you have all three plies in place, add a layer of peel-ply over your layups and allow the layups to cure. Peel-ply, if you’re not familiar with it, is a very tightly-woven form of Dacron cloth. It comes in rolls ranging from 1″ to 6″ wide and is also available in 6-foot-wide rolls for larger layups. What makes peel-ply special is that it doesn’t stick to the epoxy very well. After the lay-up is cured, you can pick up a corner of the peel-ply with your X-Acto knife and pull the piece off like a zipper. Peel-ply produces a surface that is rough enough to apply additional layers of fiberglass without having to prep-sand the area. Also, it eliminates the step transition at the edges of the layups by trapping a wedge of pure epoxy along the edges of the of the fiberglass. This produces a smooth transition between the new layups and the underlying fiberglass of the fender pan.
Layup with Peel Ply Added
After the epoxy has cured, strip off the peel ply and sand the layups with 60-grit sandpaper for a smooth transition onto the fender pan. In the photo below, the fiberglass has been sanded and trimmed around the left mounting tab. The peel ply has been stripped from the right one and it awaits sanding.
Cleaning Up the Layups After Cure
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