Carbonfiberboy 

I always epoxy bond hardware. However in your case, the weak point might be the skin/core bond. You'd have to test. I wet sand the hardware part with epoxy mix before bonding.

chojn1

Thanks for the tips on fasteners. I was going to save time and use rivets, but that sounds like a big mistake. I think I will probably combine the nuts and screws with epoxy for insurance.

The foam is from Home Depot, but you can also get it from Lowes here. Why? I have not started the layup as I am still experimenting with the schedule. I am pretty happy with the 5 layers of glass in alternating 0-45 degree fiber direction. It is strong enough even without any additional support. The glass also adhere very well to the foam; so much so, that I think it is going to be very difficult to remove selective parts of the foams for the hardware mounts and internal support.

I thought of another approach this morning: Conceptualize a solid block of hard foam, covered with fiberglass. The foam is cut in multiple sections with cavities precisely formed for the bike parts. What do you think?

Here are the wheel mounts:



CJ

Carbonfiberboy 

One assumes that you've tested the plastic for epoxy adhesion. One also assumes that you've calculated the completed weight of your finished panels. For comparison, 1/8" plywood weighs about 5.5 oz. per sq. ft.

chojn1

CFB,

I did test and found that there is very minimal adhesion. My solution is to completely encase these mounts in fiberglass with extra screws for insurance. Support structures to be added to the skin to keep these mounts rigidly in place as these wheels will have to take the entire weight of the case. Each set (wheel, mount, and hardware) weighs 12 oz. I need two per case. My 5 ply fiberglass with epoxy weighs 3.2 oz per sq ft. Foam weight to be determined - the pourable stuff is much heavier than the insulation. The hardware, handles, hinges, and pulls will take up the majority of the weight. Not much I can control there.

I am hoping for less than 15 lb per case, but will be happy regardless.

CJ

PMK

To increase the foam to laminate bondline strength. You should at a minimum prickle punch the foam on the face side. A large diameter wooden dowel with nails oriented radially to make small holes allowing the epoxy to penetrate deeper into the core.

To remove foam where needed, it will grind / sand out with minimal effort.

If you take the time to rough fab the box, then place internal webs to support the bike and glass them in place, it will offer a hug amount of support with less weight. Once complete cover the internal glass structure with felt or other material to protect the bike.

There are many options and ideas that will all work. Sometimes this gets difficult not seeing the project and desired goal in person.

PK

PMK

Wanted to add, bond foam to foam with microballons, or cab o sil, but micro would be my first choice.

PK

chojn1

PK,
I drew up the case this morning trying to figure out where I want to mount the hard wares.
Hope the pictures will help you see what I am planning.



Layup is delayed until my next shipment of fiberglass. I had less than I thought and I want to do all the layers at the same time.

CJ

PMK

Sorry for the delay in replying, the design looks god and should work well.

If I had not mentioned it before, rather than burn out the foam, you can always grind it and get better mechanical bond.

PK

chojn1

PK,
Not a bad idea! How would you grind it?
CJ

PMK

Easiest way is to purchase a small diameter Roloc mandrel and a low cost 90 degree grinder, air powered. If you can, get the really small mandrel, if not, most times a 2" mandrel on the wire wheel will remove the rubber backing, making it small. Common are 2" discs, trim these with old scissors and true on the belt sander while spinning in the grinder. In the end, you should have a disc about the size of the plastic roloc or smaller. If the plastic mount is a good diameter, you can scissor them only.

Harder to explain by writing.

FWIW, this small disc grinding is how I remove the remaining honeycomb core and abrade the interior side of the face sheet for good bond. With foam construction, I just grind and vacuum out the foam until the face sheet is abraded.

Also, with the small grinder, edges you prefer to bevel for strength and ease of ply layup can be set to 45 by a looks about right technique. If you want a crazy strong wheel pocket. After beveling, undercut the soft foam about 1/2 ", densify with microballon / epoxy mix, with a consistency where it won't slump during cure (peanut butter), fill the undercut, final shape by hand since it sands easy, then add the facesheet all the way across the pocket. Step the plies about 3/4 larger for each added ply.

PK

vrooom3440

Sounds like PK has done a fair amount of composite work...

Really just about any medium to coarse grit sanding device can make quick work of the foam. The best tip I can offer there is not try and take too much or too much pressure. To much pressure may tear out larger (relatively) chunks of foam which then roll across the surface leaving divot trails. You are trying to make sand granules of foam. It is a messy process and the bits like to stick to everything. Air tools not really required but will make lots of foam sand in a hurry. I was envisioning something like a rotary drum working the sides to create wheel matching arcs in the foam before laying up the insides. The process goes fast enough to be satisfying but slow enough to control and get good results.

For some parts like your wheel mounts you can also use a knife to slice pieces out. Depending on foam type (polyurethane ok, urethane not) a soldering gun or iron can make pretty quick work of things too. I used to take solid copper house wire and make special cutting heads for my soldering gun. You can then use wood guide strips to provide better control. Regulate the temperature of the cutting head by turning the soldering gun on/off or they can get too hot and melt too much. This process can go very fast and mistakes are easy to make.

One comment about the saran wrap: do not wait for a full cure before taking it off. It will come off better if things are still a bit green or hard gelled.

Ever work or watch someone work concrete? We think of concrete as being either soft and pourable or hard but in reality it goes through a whole range between those two end conditions. If you think about it we use different tools/processes throughout that process: forms for initial gross shaping, screeding for rough moving, tamping, floating, edging, brushing. As it hardens we work smaller and smaller amounts of the mix doing finer and finer finish work.

Composites are similar in many ways and we can do some work between the end points, like removing saran and trimming off extra bits.

PMK

Vroom, just to clarify, you mention it is acceptable to hot wire polyurethane foam, but not urethane foam.

I may be wrong, but wouldn't polyurethane foam be soft like a pillow and urethane foam be rigid. Neither should be good to hot wire. Just wondering if you were meaning polystyrene foam that hot wires very nice.

Have you ever worked with Divinycell or similar PVC foams?

PK

chojn1

While waiting for the fiberglass, I've started working on the edge trim.
This is what I have so far:



These are 3d printed parts. The top ABS piece will be epoxied on the base, and the bottom piece is rubber and will be epoxied on the lid. These parts are designed to 1) align the two halves, 2) stiffen the edges, and 3) provide a water resistant seal.

Let me know if I am boring you guys with too much details. I know this is a tandem forum.

In reviewing the fiberglass layup procedure on the net, I am now completely confused. Which is the best method?

a) Hand lay up one layer at a time with sanding in between.
b) Hand lay up all layers at one time.
c) Vacuum bagging.

Also should I lay the carbon fiber on fiberglass while the epoxy is still wet, or wait for the epoxy to cure.

Thanks,
CJ

vrooom3440

Yeah poly*something* ;-)

Yes Polystyrene would be ok to hotwire. The urethane foams give of toxic gaseous fumes, cyanide or some such, when melted. Very not good. Fortunately the urethane foams sand ok.

My work has emphasized commonly available (read: Home Depot) materials on smaller projects. I like the blue (and sometimes pink) extruded foam insulation sheets. I avoid the yellow foil covered sheets. I have read a fair bit about composite aircraft construction as well. I have a dream kicking around about building a composite delta recumbent trike.

As to layup procedure for something like this... I will first talk principles...

The strength comes from the fibers, be they glass or carbon or kevlar. The weight comes from the resin binder. Therefore the ultimate strength and minimum weight results from minimizing resin content while fully binding the fibers. This is the domain of vacuum bagging and pressure molding. The aircraft guys love vacuum bagging for this reason.

However there are many applications where you do not need the ultimate. Think touring bicycle. You only need good enough and reliable. Cheap and easy do not hurt either. I think these cases ball into this bucket too.

The strength comes from the fibers being locked together which takes a good bond. Best strength will be achieved with the strongest bond. Adhesion between cure layers is not as good as within the layer.

So what this all means is the more layers you can layup at the same time the stronger. But there is a limit or tradeoff that you need to complete the layups before the resin sets off. For the home shop this drives us towards fewer layers. For the commercial folks this drives them to prepreg that is oven cured.

Polyester resins are cured by a thermal process using a catalyzed chemical reaction. The resin is not a good heat conductor thus large masses will generate a lot of heat and thus higher temperatures. This can melt the mixing container and accelerate the resin cure. So these resins are fairly critical to get on the part and spread quickly where surface area is increased preventing the temperature rise and providing some working time. You can expect shorter "pot life" in warm temperatures and vice versa.

Epoxy resins are cured by a chemical reaction between resin and hardener which is more like a zipper of the two compounds combining. Therefore it is critical to mix the proper amounts of resin and hardener lest you have extra of either trapped in the cured resin. Heat is still a factor in pot life and some epoxy systems have hardeners with different cure times to accommodate environmental conditions. Further heat can be used as part of the curing process in some cases.

For a layup such as this... vacuum bagging perse is overkill and just adds a lot of complexity and fabrication cost. You would have to support the inside of the box for vacuum bagging. However using a plastic wrap and squeegee process over the layup will give you most of the benefits of vacuum bagging and reduce your finish work. It would best if you can layup all the layers at one time including the carbon. But if you cannot get them all layered on within one resin cure cycle you may need to backoff. For most cases sanding between cured layups is a good idea to improve adhesion between layers.

Planning your layups and having everything cut and laid out for access will be a big help.

What I might do is plan on a single layer layup with plastic wrap and see how it goes. Then when the resin has set about 2/3 remove the plastic wrap and start the next layup. The green resin should not need sanding and you should still get some chemical bonding between layers this way. But if it gets ahead of you you can always let it cure fully and sand lightly (with the plastic there should not be much resin, especially over the fibers, so you do not want to sand too much and cut fibers).

Steve

PMK

Sorry for the short less detailed reply, all methods of lay up have their place.

Much comes down to how many layers, what weave or style of fabric, working conditions and acceptable number of defects allowed.

For what you are building and the quality you desire, at a minimum the carbon will be placed on well smoothed and prepped substrate of glass. Working with foam, you will want to smooth away blemishes and fill spots with a micro / epoxy mix. Honestly, it would not hurt to skim and sand the entire foam surface.

On account of the shape, you may find it easier to apply this a ply at a time, especially if there are few plies in the sandwich areas. The monolithic laminate areas will have more fabric and can also be smoothed later if bubbles present themselves.

Plan to use a form of peel ply, not plastic to work the glass down onto the foam, this will release entrapped air easier. A groove roller will make easy work and are inexpensive. Once cured the peel ply is discarded. A course textured peel ply will offer a surface ready for bonding without sanding. The smooth plastic will not.

If you consider going multiple plies at a time, and you may, there is more likelihood of entrapped air. This is where the efforts of bagging come into play.

For best control of resin and uniform wetting, with most importantly less fiber distortion, use clear plastic sheets like Visqueen, CLEANED OF MOLD RELEASE, and wet out your fabric between two sheets, peel the backside and place the entire sheet like a decal, slowly remove the remaining plastic as you work the glass smooth.

What fabric style, plain woven, satin, twill or ???? This can make a difference in how it drapes.

I have an idea on the quality of the final product you expect, that's why I lean toward ply by ply rather than a multi ply stack in one shot.

As vroom stated, prepregs...once you use them you become spoiled, not always practical, but they are nice to make parts from. More involved, but nice.

Use the wet preg technique of wetting between plastic, it will be a nice case, carbon will go on last and solo being equal parts appearance and strength.

PK

vrooom3440

The devil is always in the details...

When working the glass/resin start in the middle and work outwards. I have read and seen the plastic sandwich method of making a home prepreg and it looks quite slick. I have done this work draping glass over the part, pouring resin in the middle, and working it around with a squeege (BTW: old credit cards can make pretty decent squeeges). For a flat surface this will actually work quite well and you will not have bubbles unless you ask the glass to bend unnaturally (this is why I earlier recommended rounded inside and outside corners). My thoughts on the plastic is that working from the middle you can work the air bubbles out as you spread the epoxy. Keeping the air from entering prevents bubbles from forming giving an effect similar to vacuum bagging.

PK does make a good point about the peel ply leaving a surface ready for the next layer though
Also about having the surface perfect prior to applying the final carbon fiber layer. I usually think of carbon fiber from a structural perspective and PK picked up that here is it probably more cosmetic and thus the good advice to get it perfect prior to that final money shot layup.

The plastic idea is inspired by these folks working on a composite aircraft:
chapters

You may also find value here:
EAA Video Player - Hints for Homebuilders: Composite

Steve

PMK

You will want to wet out the carbon between the plastic to minimize / prevent ply distortion. The carbon will look better aligned.

Once wet, remove the backside plastic film, drape it carefully and place, rub it down to prevent movement as you remove the upper plastic film, get it layed how you like then peel ply, you might need to tile or shingle the peel ply in small strips and work it smooth. The peel ply finish should offer a slight texture but allow entrapped air to be worked through it. As the resins gas off, the peel ply will allow some flow, where the plastic will not.

Consider also, epoxy does not polish well, so plan on adding some clear to get a deep finish.

As for credit cards, to work resins. Yes they can be used, however the suggestion comes in an effort to save money. A quality non ribbed Bondo Spreader, with no nicks in the contact edge is a lot more controled, offering wider range of pressure and has far less chance of ply distortion.

Snagged fibers shout out Schoolboy Mistake and hard plastic spreaders are a source.

Spend the couple dollars for a few quality spreaders. Wipe them off after use and they last a long time. Prior to use, ensure there are no nicks in the working edge to snag items with use.

By using peel ply there is no contact of the spreader on the actual fibers, much of the air is bled through and done right there is a uniform epoxy layer after curing.

When under plastic, whether in a vacuum bag, a wet lay up or even careless wet out between plastic films, can see the fibers float with moving resin. It can also happen with peel ply, but requires a greater effort to cause damage to the ply orientation.

PK

Wanted to add, I don't recall your resin system, but thought it was Hysol. If you use a low viscosity system and more important I have experienced this when using West System 105, you often get resins shrinkage or similar that tends to cause ripples in both peel ply and plastic. The best 105 products tend to be done with vacuum or in thin layups. Even thin is not assurance.

Carbonfiberboy 

I've had good results fixing most of that by post-curing the 105 at 140° with heat lamps for an hour, scrubbing the surface with 3M 7447 pads, then overcoating with 1 or 2 more coats and sanding smooth.

OTOH if the part is to be clear-coated, you can get away with a lot more than if it were to be painted.

Oh, and I always use 207 for clear finish.

PMK

100% agree, it can be dealt with. Personally I just prefer to pull peel ply and be done.

To this day, I don't know the exact reason why West 105 curdles at the end of gel or during full cure, but it has many times when I use it.

FWIW, I will be utilizing 105 for an upcoming event away from home...hope we get good results.

PK

Carbonfiberboy 

I'm talking the glass and other density variations printing through, regardless of how the layup was done.

PMK

Sorry, I misunderstood and thought you were meaning the small ripple lines 105 sometimes leaves.

207 would make a pretty naked topcoat.

Don't get me wrong, I like and use 105 series many times for non aircraft stuff. Only Aviation Partners has 105 as an approved system to repair winglets and those are just cosmetic repairs typically.

Most of the repairs or fab for me deals with a little bit more viscosity, with elevated cures. Not everything is bagged but a lot is. Resin content before beauty, but done right, little more than removing the bagging expendables and peel ply, no sanding and off to the paint shop. Wire mesh for lightning and static protection is a second repair over the structure, but again, done right, no sanding involved.

Paint is the real key since we don;t see a lot of naked carbon in what I do. Naked carbon is normally not difficult, but can be, just takes patience and time, plus a bit of luck to get it right the first time.

PK

chojn1

Just a quick progress report.


The fiberglass finally arrived this week. But, my wife's foot felt good enough to ride, so we have been out riding rather than building. I did manage to get the lid started:





This is after 4 layers of fiberglass (2x 6oz and 2x 10oz). I did the all layers at once with the credit card technique as per your recommendations. The corners, edges, and hardware mounting sites got a few more layers of reinforcement. The lid felt thick and strong enough for me to skip the 5th layer. Even then, I think it is a little bit over built.


I am using the Fibreglast 2000 epoxy system with a 2hr pot life. I am not sure if that is the best one to use, it is the one I had left over from the bike build.


The fiberglass for rest of the cases should be finished this week. Looking forward, any recommendation for surface treatment of the fiberglass in preparation for the carbon fiber?


Thanks,
CJ

vrooom3440

Looking good. That 2 hour pot life really helps out. I think I will leave the surface prep to PK, it sounds like he has more experience with that. I have always used paint on my projects.

PMK

At this point, it gets easy...one money ply. I am not sure of the finish texture based on the photo. If you worked it with plastic film, let it cure exposed to free air, or peel ply covered and cured.

Essentially, you need no blemishes, either proud or shallow. You will need a respectable uniform abraded surface unless peel ply cured with the smooth finish. Uniform sanding with 80>120 grit will expose cured laminate for a good mechanical bonding.

I am not sure either of the underside, is that solid foam?

Two options, finish the case in glass, all the cuts, core removal, pockets etc, both inside and out, then apply the carbon vale. Or if the pockets and such are already there but not shown, do the carbon now but understand the risk of damage during upcoming steps.

In simple terms, smooth textured surface is needed for the carbon layer, it needs to be blemish free. If applied now, be extremely careful on upcoming steps.

PK

chojn1

Monday Morning Progress Report:

I finished the exterior fiberglass on the base and started the carbon fiber layer of the lids:



Notice the base in the background. The foam core is 3/4in sheets of insulation glued together, not solid. The next step is to selectively grind out that foam for the reinforcement fiberglass layers around the wheel and the hardware mounts. Then I'll layer on the carbon fiber on the base.

What is a reasonably priced top coat I can get from Lowe's or Home Depot? I am running a little short on free time.

CJ