Surfing Vancouver Island  

Fibreglass repair FAQ  


===== Fibreglass repair FAQ  0.1 26 Aug 94 =====
 Part 1
 This FAQ looks at (a) fixing dings in "conventional" surfboards and 
 (b) some other materials and uses
 
 Thanks to (at least) for comments, advice and comments that I've 
 ruthlessly plagerised without permission.
 tele1@eternity.corp.sgi.com (Eric N. Valor - Ding Repair Suggestions)
 ttweed@ucsd.edu (Tom Tweed - setting fins)
 flynn@cats.ucsc.edu (Eric Flynn - building a board)  
 dmp@bmesun1.MCG.EDU (David M Parrish - aircraft epoxies)
 Charles.K.Scott@dartmouth.edu (Charles K. Scott - more aircraft stuff)
 
 1. Fibreglass for Surfboards
 ------------------------------
    Dings
    Ding Repair Suggestions
    Setting Fins
    Building a Board
    GRP - Fibreglass and resin sources
 2. Other Stuff
 --------------
    Epoxy and Other Materials
    Some Books
    Composite Workshop Review
    Fibreglass Update
       **
 1. Fibreglass for Surfboards
 ------------------------------
 Dings
 -----

For big holes - clean out the hole, cut a chunk of foam to fit and stick it in with resin. Shape (180 grit) and re-glass.

For small holes - pre-mix glass beads with resin. Add catalyst as normal: ie 7-8 drops MEK per 20ml of resin (more if cold, less if hot weather).

Reglassing - (torn or missing glass). Clean all torn bits. Fill any hole or depression to taste. Feather the edges of the glass (sand @ < 30 degree angle) with 80 to 180 grit. Wipe with acetone soaked rag. Cut glass cloth to slightly over cover hole+ feathered bits. Mix resin. (if anything go under on the MEK). Use a bit of sponge/squegee to apply resin to totally wet the glass. Then use the sponge to remove all excess. Do this by dabbing/wiping with the sponge, periodically squeezing out the sponge. The finished surface will have the texture of the cloth.

Once this has set, sand (w' #180) any rough bits or high spots. This also keys the resin for the hot coat.

Mix another batch of resin, this time hot (extra MEK-1 extra drop per 20ml) This will gell really quickly (5-10 minutes). Brush on just enough to provide a smooth finish. When set, sand smooth with progressively finer paper (180, 280, 400, 600 then cutting compound) until either bored or satisfied. [Mals tend to be finished with an additional hot gell coat, and highly polished- competition boards are often not even sanded at all.]

Resin, MEK and microballons can be bought from most shapers. Offcuts of foam and cloth can usually be scrounged from the same sources.

The process I've described is time consuming and most shops don't do that when they "fix" a ding. They mix up a hot batch of resin with lots of microballons, fill the hole & sand. It's quick (only one setting time vs 3 or 4). It's also weak. Some at least mix some chopped mat in to give it some structural strengh, but you've still got a future source of leaks.

Ding Repair Suggestions (Eric N. Valor)
---------------------------------------

First off, fill the holes with foam. Most surf shops that do ding repair may have some around that they'll flow you. Either that or find a shaper in the area. But do NOT fill in a hole with just resin; it makes for bad weight and an ugly repair. Cut out the hole until it is nice and even, then cut a piece of foam to shape and insert. Make sure it matches up evenly or you'll get ugly lines.

btw: that powder is most probably microballoons; small glass bubbles with air. They space out the resin and make it a bit lighter.

Ok, next: Use 10-12 drops of catalyst per ounce of resin. I don't know how big your dings are, so I don't know how much resin to use. Just eye it. Stir the catalyst in for about 60 seconds to get a good mix. Then coat the bottom of the "filler foam" with a bit of resin and insert into the hole. Then cover with a sheet of fiberglass (cut to shape of the hole) and pour a little bit of resin on top and smooth it out over the hole and the existing glass (you'll sand off the excess later). Put a piece of Saran Wrap over the top and let set overnight.

You can use 80 grit sandpaper to start the process, then once you start to get down to the existing glassjob, switch to 100 or 120. To finish off, use 400 wet/dry (and use a bit of water). That should do you.

Fins are a bitch to set properly, as placement of the fins absolutely determines how the board will respond. Make sure you get right and left fins for the twins (yes, there are sides) and a normal single for the rear (this is a tri-fin, right?). Angle them out a few degrees from straight up-and-down, and toe the front edges of them in just a bit. This is the hardest part, as they have to be braced while the resin dries.. it's a bitch and I've only done it (badly) once.

Eric N. Valor

Setting Fins -(Tom Tweed)
-------------------------

A trick that some of my glasser friends use is to set the fins with a bead of hot-melt glue right on the bottom- have the front and back toe-in marks penciled on the board, and a little cardboard template cut for the camber angle (usually about 5 degrees outside of perpendicular to the bottom). Slam the fin down while the glue is hot right on your marks, slap the camber template up against the side and hold it steady for 15-30 seconds while the hot glue solidifies. Voila! You're ready to rope and glass them in without the obstruction of tape braces, etc., holding them in place. Don't bump them too hard, though, it's not that strong before glassing....

Tom Tweed- La Jolla, CA e-mail: ttweed@ucsd.edu

Building a Board
----------------

From: flynn@cats.ucsc.edu (Eric Flynn)
Subject: Re: Building a board...
Date: 24 Jul 93 05:40:52 GMT

In article pa_warren@Merrimack.edu (Warren Crossfield) writes:
>
>Anyone here build their own board(s). If so, any tips (materials) for a
>novice builder?

Well it looks like this is a good time to give you all the update on how my board-building project went. First, a little review.

I have been surfing an old 60's style Team Becker. It's 7'4", kind of half-way between a longboard and a bonzer. It has a round tail, and a very wide, round nose, with a large concave. These characteristics give it nice watch-catching ability, even in small surf, good handling, and it nose-rides like a champ.

The board I just got finished building is based on this design, and has almost all the desirable characteristics of its predecessor. I chose to copy this board because I like it a lot, and the guy who owns it wants it back!

I went to Monterey Bay Fiberglass and purchased all the materials necessary which ended up costing about $150. I then had a shaper here in town shape the blank, which cost $70. I was fortunate enough to run across one of the guys who used to glass for the Haut,and he basically taught me how to laminate. I paid him for his time, bought him lots of beer, and ran him around town for a couple weeks ( he doesn't have a vehicle ) in retrun for his help. In the meantime, we have become good friends, and this worked out so well we plan to build another board.

The next board will be a 9'3" shaped by Doug Haut, and glassed by me and Jeff Thompson.

One other stroke of good fortune: Jeff happens to be a personal friend of Jimmy Phillips ( of Pack-Your-Trash fame ), he talked Jimmy into designing a custom logo to put on my board. I paid Jimmy for the work, but I can tell you that I got it at a very handsome discount.

I took some pictures of the new stick before I waxed it, and plan to use the scanner at work to digitize a few and will post them to the surfing GIF mailing list. The board came out really nice, and it surfs like a dream.:-))))))) Yaahhooo!!

So I guess I ought to address the questions asked at the beginning of the article.

First, it helps _worlds_ if you can find someone experienced to help you. My board woulda been a giant resin barge if I hadn't had Jeff there to bail me out of some really sticky ( literally! ) situations. Failing this, at least get someone to let you watch them glass a side or two so you can see how laminating is done.

Second, you will need a place to work. A spacious garage is what I used. You will need an enclosure of some sort for the hot coat and gloss coat, otherwise the resin may do nasty things like split or get bugs in it.

Next, you will need the following equipment and supplies:

Glassing stands

 
Grinder or Sander/Polisher - I use a Makita 9207SPC
 Paint brushes 2,3,4"
 Wide wall-papering brush
 Rubber Squeegee
 Sanding discs
    60 grit, 100 grit Aluminum Oxide
    400 grit, 600 grit Wet or Dry
 Jars or #10 cans
 Canister-style organic vapor rated respirator - IMPORTANT
 
 X# gallons of resin - I prefer Cargill, its stronger than some others
 1 gallon of acetone
 masking tape - don't get the cheap kind, 
        get 3M paint masking from a paint store
 Single-edged razor blades
 X# yards of fiberglass cloth
 

I'm not going to try to explain the whole process, but here are some helpful hints in general:

A plastic trash bag masking taped around your waist make a cheap disposable apron. And speaking of disposable, go down to the thrift store when buying clothes you plan to wear while glassing.

Soak your squeegee and paintbrushes in acetone overnight before glassing. They will be much more pliable and easy to work with.

Tape down a couple layers of tar paper (roofing cloth) on the floor so you will not leave any post-Columbian artifacts thereon.

Have two pairs of scissors: one exclusively for cutting fiberglass cloth, and the other for cutting sandpaper and other such things.

When you cut the cloth around the edge of the blank, leave a 2-3" lap, begin careful not to leave any dangling strings. These will be a real pain later if you don't eliminate them now.

Use the wall-papering brush to smooth out the fiberglass on the blank. This helps to avoid the cloth "floating" off the blank.

Laminating has three basic steps: 1) saturate the cloth 2) squeegee out the excess and 3) work out the cloth to a burlap texture. Start your pour near the middle and work toward the ends of the board. This is where it gets hard to explain without someone holding your hand and showing you what to do. The basic idea is to keep the squeegee vertical and apply just enough pressure to spread the resin and saturate the cloth. Then, using a bucket to catch the excess, take firm even strokes the entire length of the board, squeezing the excess resin out of the cloth. No doubt there will be some dry spots, so use the resin you catch to thoroughly soak them, and squeegee out the excess again. Once this is done, take medium firm strokes the length of the board, starting at the middle. The key here is to leave the squeegee in contact with the surface as much as possible. If you pick it up, you will create a puddle.

The hot coat and gloss coat follow in much the same way, only you use a brush to apply them.

After the hot coat, use the grinder to sand the board smooth. The fins and rails should be done by hand. Then wash the board with a soft rag soaking wet with acetone, much as you would wipe down a table, catching the debris by folding the rag. Do the same with your bare hand while the acetone is still evaporating. You will be able to feel when the surface is clean.

After the gloss coat, you have the option of polishing it. I personally think boards surf just fine unpolished, but a mirror finish on a showroom board will sell faster to be certain.

NOTE: ALL of the organic chemicals used in surf-board building are KNOWN carcinogens. Although many people have had long and happy board-building careers and never gotten cancer, please use all due caution when dealing with these volatile, corrosive and highly toxic chemicals! Buy a respirator like the one mentioned above and WEAR it!s

Well, if you all want more gory details, feel free to mail me at flynn@cats.ucsc.edu, or post a question in reply. I'm pretty new at this, and as I mentioned above this is far from a complete description of the process, but it should at least give some idea of what you need to know.

Happy board-building!

ERic

GRP - Fibreglass and resin sources
----------------------------------

Fibreglass is more properly known as Glass Reenforced Plastic (GRP). Most surfboards are built using 1950's materials - plain woven glass cloth and polyester resin with Methyl Ethyl Ketone peroxide catalyst on a polyurethane foam blank, reenforced with a single wooden stringer.

You'll have to pay for your resin, hardener and micro-balloon filler. If you know a local shaper you should be able to scrounge some off-cuts of foam and glass cloth. Rovings (basically fibreglass 'rope') are usually bought, but if you're cheap, pull apart some cloth.

Boat manufacters usually use either chopped strand mat - which is much weaker than cloth or a sort of spray gun which pulls in fibreglass rope, chopping it up and sucks up resin, mixes it with catalyst and the chopped strands before spraying the lot out. Usually into a mold.

Speaking of molds, watered down PVA (White wood working) glue apparently works well. YMMV.

*
2. Other Stuff
--------------

Epoxy and Other Materials
--------------------------

Not suprisingly, materials have come a long way since 1950. Almost everyone knows about Carbon fiber and Kevlar. Not so well known are the changes in the foam and resin. Most high-tech fibreglass jobs (ie commercial and homebuilt aircraft, and some sailing boats) are constructed using a two-part epoxy, with a stronger glass fibre.

Some surfboards have been made, using a special closed cell (to stop waterlogging) polystyrene or polyvinylxloride (PVC) foam, both in the West Coast of the USoA and on the east coast of Oz. The few reviews (Aust.Surfing life had one recently) seem impressed by the weight and strength of the boards - down to 2.5kg for a 6' board you can jump on. One other advantage is that they can be repaired with 2-part expoy glues (such as Araldyte).

There are rumoured to be people making kevlar (reef-proof) boards in South West Oz.

Many of the newer resins come preimpregnated in carbon/glass/kevlar cloth (to order) and require autoclaving (cooking) to set.

I'm not going to go into detail on my own, but rather I'll include a few articles from regular rec.aviation.homebuilt contributors. Tune in there for more info (unfortunatley they don't seem to have an all singing/all dancing composites FAQ). Also try rec.autos.racing.* and rec.models.rc (or whatever)

Strengths of materials
----------------------

 Tm Tensile Modulus 
         (Giga Pascals 1gpa = 10^9 Newtons/m^2 ~= 140,000 psi, i think)
 Ts Tensile Strength 
         (Giga Pascals)
 D  Density      (grammes per cubic centimeters)
 Material        Tm      Ts      D
 E-glass         77      2.5     2.54
 S-Glass         85      3.5     2.48
 Graphite AS4    190     2.8     1.80
 Kevlar 49       130     2.8     1.45    - note kevlar is shitty 
 Aluminum        70      .14-.6  2.7             in compression.
 
 Note these are unidirectoinal free fibre, with no expoxy.  
 Reality is only 1/4 as good.
 There are lots of different grades of each material.
 

 Some books - various people
 ----------
 (I haven't been able to find these at my local library - 
   I haven't tried the Uni yet.)

 "Graphite Fibers and Filaments" by M. S. Dresselhaus et al, 
 Springer Series in Materials Science 5, (Springer-Verlag, Berlin, 1988), 
 chapters 1, 2, and 12.
 
 ASM Engineered Materials Handbook
 Volume 1: Composites
 ISBN 0-87170-279-7 (v. 1)
 (c) 1987 ASM International
 
 
 'Composite Construction for Homebuilt Aircraft' Jack Lambie's 
 
 "Composite Basics". Andrew "Bud" Marshall 
 
 "Composites Design", by Steve Tsai   
 
 "The Behavior of Structures Composed of Composite Materials"
         J.R. Vinson and R.L. Sierakowski        
 
 
 Composite workshop review (by Daid Parrish)
 
-------------------------

This weekend, I attended the composite basics workshop put on by Alexander Aeroplane in Griffin, Georgia and I thought that others on the net would like to hear my impressions on the workshop and what I think are some very useful techniques presented.

First off, a little about the workshops and in particular, the instructor for the composite workshop, Stan Montgomery. Currently, Alexander is running three - two day workshops on basic composite construction, welding and fabric covering that are held in Griffin, Syracuse, Oshkosh, Trenton, Bloomington, Houston, and Lakeland and will soon be adding workshops on other topics like wood and metalworking. Stan also mentioned the possibility of three and five day advanced composite workshops and another workshop on finishing.

Stan Montgomery is a very good speaker, has a masters in chemistry, so he knows his resins, and was a military pilot and has built numerous homebuilt aircraft, so he knows airplanes and composite construction. He's also VERY passionate about composites. This has caused some - er - disagreement with illuminaries such as Dick Rutan, but anyone that can make a spar shear web out of heavy, finely woven bid glass and achieve 40% resin, BY HAND, and still use peel ply should be listened to seriously.

For those that don't have the foggiest what I just said, some extra information. The spar carries the weight of the plane through the wings, and the spar web carries the load between the upper and lower spar caps, forming a strong and very stiff I-beam inside the wing. In fiber/resin composites, the fibers carry the load while the resin keeps the fibers together. If there is too little resin, the fibers don't stick together as well, and the part is weakened. If there is too much resin, which is much weaker than fiberglass, then the resin starts taking some of the load, and produces a weaker product.

The problem is, most homebuilders think that if resin is good, more is gooder. But anything above 60% resin, 40% glass, is actually weaker than 50-50 or 40-60 and is both heavier than it should be and more expensive, since any resin, from $20 a gallon polyester to $100 plus a gallon epoxies are expensive to buy.

Bid glass is a fiberglass cloth that has nearly equal number of fibers both along and across the bolt of cloth. Peel ply is a light weight and finely woven nylon or polyester cloth that is used as the last layer in a layup. When peeled off, it fractures the resin surface for a stronger bond with subsequent layups without using sandpaper, which damages the glass fibers on the surface.

Back to the workshop.

The syllabus had an ambitious schedule that we were unfortunately unable to keep up with because of time constraints. Even saying that, the most important points and procedures were hit upon. The first part of Saturday was a lecture that covered what composites are, safety with composite materials, and various techniques used in composite construction. Most of the rest of the two days was hands on building of a short section of a canard with interspersed discussions on other composite techniques, including a hands on vacuum bagging.

The construction of the canard started with a block of blue polystyrene foam and a pair of templates, so we had to hot wire out our own canard cores. Hot wire cutting the foam is a very intense few of minutes where you have to be aware of wire temperature, cutting speed, wire drag, tension against the template and exactly where your partner on the other side of the wire cutting frame is at on the templates. This is done by numbers around each template that one calls off and the other gives faster or slower cues as the pair cuts around the templates.

Once cut out, the leading edge just in front of the spar cap recess is hot wired off and the front edges of the trailing edge part were rounded so there are no sharp edges for the spar web to go over. Once rounded, the spar web area is filled with epoxy filled with microscopic glass balloons or Alexander's superlite filler. Both are very light in weight and prevent raw epoxy from soaking into the foam.

A quick, unsolicited ad for the superlite epoxy filler. This stuff is a very light weight epoxy filler that can be used in place of either Bondo or microballooned epoxy and was developed by Stan. It has a density at least half that of Bondo, doesn't shrink, is very sandable, and contains a built in chromate conversion for use on aluminum. It also contains an agent that helps tiny entrapped bubbles rise to the surface and burst so pinholes are greatly reduced. The only thing I've tried it on so far is to fill an aluminum nose gear fork, and it has very nice working properties. I'm definitely going to try it when I start finishing the wings on my Velocity.

Anyway, next Stan showed us how to a layup with 40% resin, yet still be fully wetted out. First he cut out two ply of glass cloth to approximately the right size, weighed them, and then placed them on a piece of plastic and poured on a weighed amount of epoxy to an exact 40% resin, 60% glass by weight ratio. He then put another piece of plastic over the layups and worked the epoxy into the glass. To evenly distribute the epoxy, he would occasionally fold the glass and work it some more, making sure not to crimp any folded glass and carefully applied heat from a hair drier to thin the epoxy out. When he was done, the layup was totally saturated with no white streaks indicating dry spots. Once this was done, it was applied to the canard core and a sheet of peel ply was squeegeed onto the surface, further reducing the epoxy content of the layup.

According to Boeing, this is impossible. They can achieve a 37-63 ratio, but only by using multi-million dollar autoclaves. While a 40-60 ratio takes quite a bit of experience, I was able to do a 50-50 layup with no problems on my first try. Wake up guys. Homebuilders are at least ten years ahead of anything that comes out of the big iron plants. The only thing that may come close would be the formerly Beech Starship, and it was designed by the homebuilder's homebuilder: Burt Rutan.

I do have one nit to pick with Stan on epoxy though. Being a chemist, he wants exact molecular ratios of resin to hardener, therefore the only way to do this is by weighing both the resin and hardener before mixing instead of using an epoxy pump, which does do ratios by volume. For me, working alone, all that extra weighing of resin and hardener just takes to much effort and time. Assuming the pump is working correctly, the volume ratio is based on the weight ratio of the two components and the only weight ratio change would be from the DIFFERENCE in the expansion rates of the components with temperature. Since most epoxy systems has a 5% margin of error, I'm not overly concerned about this difference, but I am going to retest my pumper at various stroke lengths. Also, if you have a scale that can only register to 2 grams and you're doing a batch of ten or twenty grams for a small layup, you may end up with an error greater than 5% anyway. Knowing the weight of the glass and the epoxy used in most layups I totally agree with.

Another neat technique he showed us was with unidirectional spar cap tapes. The tapes are only a few inches in width and produce a thick layup. The rovings are held together with a sparse cross thread, but any weaving in a glass cloth reduces the strength. What he did was find the single fine thread on the edge that held the cross thread in place and removed it after the tape was placed on the canard. Once it was removed, the cross thread was carefully removed, leaving straight, flat fibers in the spar cap. That one even surprised the epoxy manufacturer that sat in on our workshop on Sunday.

Recommended tools were scales, layup rollers and a hair dryer. The scales are used for weighing the glass and epoxy to calculate their weight ratios. The rollers are for working out air bubbles and to distribute the epoxy. He was against using a paint brush to remove air (a process known stippling) because it tended to break up bubbles instead of removing them. Layup rollers are shaped something like a small paint roller, except the roller is plastic or aluminum and has a grooved surface that allows entrapped air to escape. The hair dryer is probably his favorite tool. With it he can drastically thin the epoxy to improve wetting of the glass and speed up the setting time.

Another point he made was that all epoxy layups should be post cured at an elevated temperature. All epoxies have what's called the glass transition temperature, where it looses it's strength. They all have a maximum transition temperature, such as 190 degrees Fahrenheit, but the actual temperature that it weakens is only thirty or forty degrees above the temperature the resin was cured at. If it's 60 degrees when you make a wing, the wing will sag when the skin reaches only 90 or 100 degrees. Not good if you fly down to Sun 'N Fun!

To fix that, after the initial cure is done, Stan post cures the part by heating it to 130-150 degrees for a few hours with the part supported so it doesn't bear any weight. This can be done by painting the part with black tempera and leaving it out in the sun or by putting it in an 'oven' made out of cardboard boxes and a small forced air heater.

All in all, I really enjoyed the workshop. There were some problems that I think were due to the newness of the workshop and limited time, but over all, it was well worth the $150.

I finally got to try the techniques from the workshop, and the short answer is: It's harder than it looks.

That's not really a fair statement, as I didn't really allow for the differences in my application. My first trial was the installation of my canard bulkhead into the fuselage. To do that, the bulkhead is aligned plumb and square with the proper station in the fuselage and then taped in place with 2 ply of bid cloth cut at a 45 degree angle. The tape goes about an inch and a half up on the bulkhead and down on the fuselage, both fore and aft, along the full joining line.

So I used a string to find approximately what length of bid tape to use for the four sections. (Fore and aft and left and right of the nose gear door cutout.) I cut the tapes to length, weighed them, and poured an equal weight of epoxy over them on plastic film. With the layup roller, I spread the epoxy out. With narrow bid tapes, this can be a bit difficult without the tapes distorting, but the roller did a good job as long as I didn't move the epoxy ahead of the roller too quickly. They're rather expensive, but I think they do a better job than stippling with a paint brush.

Once wetted out, I cut the film to rough size and carried the whole thing over to the plane and put it in place. One thing though. The bid tape conforms to the surface much better than the plastic film that keeps it from stretching, so you have to carefully peel the cloth from the film as you put it in place. Once in position, I used the corner and layup rollers to press the cloth in place and covered that with peel ply squeegeed in place.

When I peeled the peel ply off the next day, there were streaks were there was no epoxy between the bulkhead and the bid tape, mostly on the vertical surfaces of the bulkhead. The problem has to do with the surface of cured triax cloth that was used on the bulkhead. In triax cloth, there are three layers of fiber bundles, stitched together like a quilt instead of woven, giving it greater strength. But it also makes the surface more uneven, with valleys between the bundles of glass fibers. The streaks I saw were the valleys that had not filled with resin.

My mistake was not heating the layup with a hair dryer to thin the resin out. I had even prewetted the triax with resin on one side as a test before taping and it didn't seem to make much difference. As a second test, I cut out a 3 by 3 inch piece of bid and laid it over the original streaked tape and out onto the bulkhead, this time using heat. When I peel the peel ply off this time, the dry streaks were OVER the bundles of glass, indicating I'd used too much heat and pressure and had worked too much resin out of the cloth. The valleys were filled nicely though. Ah well. Live and learn.

One thing I feel fairly certain about is the actual best resin to glass ratio will depend heavily on the weight and weave of the cloth and how much work you want to put into thoroughly wetting it out.

The next time I try layups like this, I'll try the other technique he showed us. In it, he marked off the size and shape of the layup on the plastic film with a Sharpie pen and cut the cloth to approximately the correct size and shape. After weighing the cloth, he poured an equal weight of epoxy directly on the film and spread it evenly with a plastic bondo squeegee. He then laid the cloth on the spread epoxy and worked the epoxy into the cloth. When the glass was completely wetted out, he used a razor blade to cut both the cloth and plastic film to the marked line, leaving a layup ready to be used.

Within the next couple of weeks, I'll be ready to skin my left wing, so I'll be reporting again on how well the layup rollers do when working on (very!) large areas of glass.

David Parrish

"You have to be crazy to build an airplane and not yet be a pilot."

Fiberglass update (corky Scott)

------------------

As promised, I put in a call to Alexander Airplane Co. to ask their epoxy expert about some of the concerns aired on the network.

1.David Doshay asked: how accurate must the mix be? Stan (Alexanders epoxy exptert) stated that the mixture must be within 5% of the ideal mix ratio by volume or weight in order to be a properly bonded reaction.

2. Venky asked: Even though the mixture I've been talking about is odorless, does this mean it's safer, or must a mask still be worn. Stan said that this particular resin, and all the resin's they are now struggling to formulate are safe to be used WITHOUT A MASK. He further stated that as long as the room was properly ventalated, use of mask was not necessary. He said that basically he and Hexcel decided that the old MEK type blends were too dangerous to use, that most old timers distained the use of masks and were therefore putting themselves at risk. So the latest batch of resins are formulated without the two most potent carcinogins, and also, without the smell.

We spoke for some time, he had lots and lots of interesting things to say, among them was this; the bonding of the resin and hardener can be enhanced by as much as 30% by placing the part in an area of sustained heat of about 120 to 130 degrees until cured. Normal room cured fiberglass achieves about a 50% bond, he said but if you can figure out some way to heat the area evenly, you can get a bond of closer to 80%. During experimentation, while he was attempting to figure out ways of heating his wing for the first time, he actually melted the core right out of the wing. But, as he stated, that's how you learn, by trying things.

He further stated that he was designing and building a composite *6 PLACE AIRPLANE* with a gross weight of 4000 lbs and capable of carrying a ton of load. He's planning to break the around the world record for a single engine airplane with an engine bumped from 600 to 900 horsepower. "Uh", I said trying to sound casual, "what type of engine would this be?" He said it was a Titanium block Ford Nascar engine. The block alone was worth $35,000. This guy is serious about the record.

Finally, I spoke about using fiberglass for my landing gear and he said that was not a problem. When I was ready to do that, all I had to do was give him the gross weight of the airplane and he'd calculate the width, thickness and dimensions for me and explain how to make the mold. He also recommended that when the time came to build this, that I buy one of their weight scales to make sure the ratio was not just close but perfect since the weight can vary depending on temperature and humidity. He also stated that they'd work out a "veil" to coat the gear with to act as a UV barrier and fuel barrier so that nothing could penetrate the gear and cause a delamination or failure.

He signed off with these words. "Corky, our advice is free, but we want to be your supplier".

I thanked him profusely and hung up very impressed. Stan has worked directly with Hexcel for several years to work up new resins that are safer and more effective. The guy knows his resins and fiberglass.

What do you think Venky? Worth giving this stuff a try? It's Hexcel 2427.

Corky Scott

--

Sue Ralph Nader, too, he was supposed to have prevented this kind of thing by now. Oh, and my fee is 40%

Ed "gettabike" Green, rec.motorcycles

"Email: conrad@pico.qpsx.oz.auSnail: QPSX Communications, Private Bag 24, West Perth 6005, Australia.

Numbers:(ph) +61 9 262 2000, (fx) +61 9 321 2984 (dod) 0604

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Speed on a Backside Wave
Backside Bottom Turn
Backside Air

Layback Snap
Backside Floaters
Backside Re-entry
Pumping on a Frontside Wave
Frontside Bottom Turn
Frontside Air
Frontside Roundhouse
Frontside Cutback
Frontside Floaters


♠ more surf stuff

» Ding repair FAQ
» wave / board / surf terminology
» Surfboard Design Guide
» surfboards we love
» Rip Currents & Undertows - Ray McAllister - Steve Baum - Neil Savage
» about waves & sets - John Sidles - Timothy B. Maddux
» foam in the surf? - James G. Acker
» Lud's Wave Prediction - Ludwig Omachen
» cold water & rubber
» local surfing Q & A
» surf travel tales and pics
» bc/pnw surf comps archive
 
 
 
 

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