Boatbuilding/Materials Question

[Slowboat510]

Stock Outboard recommends reinforced cockpits (Safety Rule 24B). I plan to use a composite with wood outer skins and a core material (foam, honeycomb or balsa end grain). Based on the recomendation I will add a layer of 5 to 6 oz. Kevlar. Here's my question. Will I experience problems cutting out a lightening hole or access hole in this panel after it's been layed up? What's a good tool or method to use when cutting the holes in the panel? Mainly I'm concerned about the Kevlar. If I used a router, will the Kevlar grab? Is there a preferred blade type to use if I use a saw?

I should clarify that I would prefer to make the panel first and then cut out the lightening or access holes.

[Tom Cronk]

Material

Slowboat
You need to get in touch with BOB WARTINGER
on reinforced coamings.
Tom

[Smiley]

I built a composite fiber glass airplane and did a fair amount of glass work. I also made some parts with Kevlar.

Composites are fun to work with. You lay up the parts with epoxy, let it cure and when the materials are set you can cut these materials with a grinding wheel, skillsaw but I prefer a finer saw like a bandsaw and cutting tools like circle cutting saws etc. The edges of the holes or edges of laminates with nomex core or foam core are hollowed out about 1/8th inch and then filled up with an epoxy micro mix to create a smooth edge. sand the edge smooth and go forward to the next step.

When building a boat from these materials you can use fewer frames because these materials are very rigid and the seam can be very structural. A couple gussets at the appropriate places is all that is necessary. Perhaps around the steering wheel location and forward a couple feet to provide structural integrity for the deck. When gluing the edges use about a 4 inch wide bid tape about two plies with the full length bids cut on a 45 degree bias thus each thread will cross the seam at a 45 degree angle providing for a very strong joint. A small amount of micro rounded with a popcicle stick before applying the two bid bonding tape will allow for full contact and a very strong transition for the bid tape.

A one bid tape on the exterior seam completes the joint.

have fun.

Smiley

[Smiley]

OOps..


I forgot. You need to use a good mask before cutting away on glass. This stuff is sharp and painful when you stick a piece into your hand. It is also invisible. Imagine what fine glass particles can do inside your lungs?? Yes, use a good quality filter mask. Also protect your hands with some creme and cotton gloves and latex gloves over the cotton gloves. Available from Aircraft Spruce. Even so. A glass boat like a glass airplane is unbelievably strong, rigid and light. No flexure in the airframe also boat frame provides instantaneous input control responses, repeated predicitable equipment behavior every time and optimum performance.

The glass airplane I built had only three frames in the fuselage as opposed to about 7 frames in an aluminum skin plane. A boat should have at least two, Transom around the steering wheel and perhaps some gussets forward. The bottom aft planing surface may have two ply of laminated core structure and you will not have any warping or flexure.

Smiley

[Slowboat510]

Thanks for the response. I've used several composite materials before (usually carbon fiber or regular glass and core materials) and as you said, cut them with an abrasive grinding disc or grit edge blade. It's Kevlar that I'm worried about. I know it doesn't wet out very well and will have to be bagged. It's just that I haven't cut it after it's cured. Will it cut just fine with a grit edge blade or will I experience problems?

[Smiley]

I never did any vacum bagging with my work so I cannot speak from experience in that area. What I did do was cover the wetted part with wetted dacron cloth. This material was cured in place. When cured you peel the dacron cloth away from the finished part taking away that waxy substance that surfaces on cured epoxy leaving a dacron weave texture on the finished part. There is no need for sanding or cleaning the part for the next gluing step or finish step. Keep the dacron on the part until you are ready for the next step, peel it off and the wax comes with it. Fiberglass and carbon veil wets out just fine. Kevlar wets out ok from my experience. What is difficult is that kevlar is stiffer and does not bend around or lay down on compound curves easily. It has a tendency to rise so you must cotinuously push the fibers back into the desired position. Bagging would be helpful here. Cutting will take some extra care but it can be done. Kevlar is tough material. In all cases, fiberglass, carbon fiber and kevlar will dull your tools quickly. I used a dremel tool, hobby size and wore out two motors and many tips building the plane. In retrospect I could have used a 1/4 inch drive tool for faster work but I was able to get very intricate on detail work.

Light strong joints and glued sections require a 50/50 cloth to epoxy weight ratio. I accomplished this by:

laying 2 mil plastic sheet on the hard plastic layout table,
laying two bid (two plies) of cloth,
wetted the cloth with epoxy with a squeegy or bondo plastic squeege,
applied 2 mil plastic on top,
used a 4 inch paint roller with a piece of pvc pipe covering the rollerand rolled out the excess epoxy from the center of the material out to the edges being careful not to create dry spots as evidenced by white spots on the glass,
cut out the bid tapes on a 45 degree bias with a straight edge and a cloth roller cutter(pizza cutter style) obtained from Joanns or Michaels stores.

take your piece to the work area,
peel off one side of the 2 mil plastic being careful not to deform or stretch the fiber layout,
lay it down onto the seam and roll it out and stipple out the air bubbles with a cheap 1 inch paint brush that has the brush hairs cut down to about 3/4 inch.
Remove the two mil plastic,
take a twice folded paper towel and blot out the surface of the epoxy so that there is no epoxy shine, no white dry spots and you see the cloth weave texture. Epoxy above the weave adds weight and does not add strength.



I have used a jig saw in some instances but it is not my preferred tool as it makes a rough edge.

Good luck
carpe diem

Smiley

[modhydro]

Working with Kevlar

I'm not quite sure where all the mystery of working with Kevlar has come from. It simply isn't nearly as bad as everyone seems to make it out to be. Here are some hints and observations that I have learned by using it for quite a while now.

1. Scissors: You don't need to buy the expensive special Kevlar shears that are out there. I've used the same pairs of cheapo scissors to cut glass, carbon and kevlar. I used to build inboard safety cells. Between those and regular outboard stuff I've probably gone through close to 100yd of Kevlar and it will still cut just fine. A neat trick that really helps is to give them a light sharpening on a grinding wheel. Run the blades perpendicular to the wheel and leave the slight burr that is created. They should feel "gritty" when you work them now. This will help hold the fibers and keep them from "squirting" forward away from the cut. The other thing I do is to pull them back as I'm doing each cut. It is like using 4" of blade to cut 2" of material. Sort of hard to explain, but I think you will figure it out.

2. Surface prep: I have seen many times where people talk about pouring epoxy over the bare wood and then laying on whatever fiber they are using. Next time you epoxy coat something pay attention to how some spots wind up glossy and others look dry when it is cured. This same thing will happen when there is fiber over it. The dry looking spots are now resin starved layups where the part will have far less strength. It is better to coat the part, let it cure and then clean it, and scuff sand it. This primer coat ensures that your fiber will maintain the resin content you want and not be too lean in some spots and too rich in others.

3. Bagging: Kevlar doesn't need to be bagged. While I say this, also bear in mind that it is lighter than you resin and will actually float. If you keep putting on resin, it will just keep floating up. I simply put on the pre-cut kevlar on my prepped panel and pour resin down the middle of the part. Gently work the resin through the fiber with a body filler squeege. The more of it you get wet out, the more aggresively you can work the resin through. You don't want to squeege fast or you will induce a lot of tiny air bubbles to the resin. Just work with gradually harder pressure and you will see the color change slightly. You will also be able to see any spots that need more resin by the way they have a flat look rather than glossy. Let is set for 10 minutes or so and then add resin where necessary and squeege one more time for uniformity. Remember to only put enough resin to wet it out completely and then quit. Any more is just extra weight and wasted money.

4. Peel ply: Dave hit this one in another post. My test at the fabric store is to try to blow through the cloth. If you get one that is very hard to blow through, it will peel off easily. I just get 100% polyester cloth with a very fine weave. There is alway something on sale in the bargain corner. Usually the only problem is getting the cashier to believe that the small stain or whatever put it in the sale rack won't affect my use of it. Don't even try to get into that discussion at the store! Once my layup is wet out evenly, I put a piece of the peel ply over it and squeege again. I use a good bit of pressure here. If you have the right amount of resin, you will see the pattern on the peel ply change from just the dots at each high point of contact with the weave to one solid color. any excess resin will work up through the tiny holes in the peel ply and come off when it is removed. The peel ply can even be used to hold things in corners much like bagging. What happens is that between the surface tension and the difficulty with which air passes through it, it will hold the fibers in some fairly complex shapes with no vaccuum. A hint when peeling it is to pull it off 45 degrees to the weave direction. This way, just like gaining strength by laying up gusset strips on the bias, you are pulling on tiny strings in two directions rather than one. It should pull up without too much effort if you work slowly and work from side to side.

5. Green trimming: I alway time the lay up the Kevlar so that I will be able to come back later and trim the parts when it is say 80% cured. I don't mean to full cure, but rather when it is no longer tacky, but still pliable. At this point the peel ply will come off very easily. Don't try this too soon, or it can actually lift the fibers you are keeping down. After you have the peel ply removed and you are done admiring your very flat surface, trim the edges with a new utility knife blade, You will quickly find the ideal angle to hold it by experimentation. I always have all the cuts made in the wood first so that this becomes a simple tracing step of following the lines.

6. Dry trimming: If you need to make any cuts after the stuff is cured, make the cuts however you normally would. Use carbide tools or you may as well throw them away. It is very hard on cutting edges. You will see the edges fuzz up like crazy. Don't sand them or they will only get worse. A lot of this can be cut off with a brand new utility knife blade. It won't get it all though. You will need to wet out the fuzz, and trim it in the green state or let it cure and sand and repeat a time or two. With patience it will all come out with no ragged edges.

7. Flat straight cuts: If you have an edge that you want straight across a panel that extends beyond the fiber, here is a neat trick. Put down a piece of 2" wide tape that butts up to the desired edge. Lay the fiber so that it extends on to the tape. When it is in the trimming state of part 5 above, simply come back 2" from the exposed edge of the tape, and cut it. Peel up the bottom layer of tape and all the wierd little stuff that happens at the raw edge of cloth is gone and you are left with a perfect crisp edge that looks great.

8. Not quite a vaccuum bag: A neat trick for holding any fiber into complex shapes is to use a garbage bag with water in it. Put down the peel ply and then use a garbage bag with some water in it. As long as there is slack in the bag and it isn't bridging over any shape detail you will get modest pressure in all directions to hold the cloth to the more complex shapes. You will be amazed at just how little water it can take to accomplish this. To make this method one better use warm water and accelerate the cure!

That is about all that I can think of right now. I probably have photos somewhere that show some of this if anyone needs more to go on.

Steve Roskowski

[ZUL8TR]

Working with Kevlar

Steve that is a great detailed response for all especially those that have never worked with kevlar.

[Smiley]

Steve,

You have presented some very good hints I never heard before. With your permission I would like to post it on the Lancair website for those builders. Great stuff.

Smiley

[modhydro]

Kevlar hints

That is fine by me. Cut, paste and post away!

Steve

[proprider]

Gotta like

a guy that knows what he's doing......cause he's done it already!! Thanks Steve, for sharing the info.

[Slowboat510]

I'll second that. Thanks Steve. #6 was exactly what I was looking for.