DIY custom frames, home carbon-fiber method simplified

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spinningmagnets   100 GW

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DIY custom frames, home carbon-fiber method simplified

Post by spinningmagnets » Jun 11 2009 12:24pm

I stumbled across this recently. This frame isn't my style, but the construction method is intriguing. You take a stiff foam urethane blank, then cut and shape it (easy) and insert metal hard-points for the BB, head-tube, etc...apply layers of CF cloth, sealing each with a vinyl-ester goop that doesn't require vacuum bagging. Foam core is left in-place rather than chemically dissolved.

http://www.rqriley.com/xr2.htm

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$125 Carbon Fiber Cloth 3.5 yrd
$35 Vinylester Resin 1 gal
$65 Urethane Foam 4 x 8 ft x 2.5"
$25 Steering Housing 25" of 1.5 OD x 0.035 T6 alum.
$16 Bottom Bracket Shell
$25 Tandem BB Shell
$290 Total

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Last edited by spinningmagnets on Jan 27 2010 9:43pm, edited 2 times in total.

jag   10 kW

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Re: Custom frames, home carbon-fiber method simplified

Post by jag » Jun 11 2009 12:59pm

Building on foam is pretty popular in the airplane and boating community.
Farrier trimarans are built this way.
http://www.f-boat.com/pages/construction/index.html
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and Burt Rutan's revolutionary aircraft designs of the 70 and 80's and their current derivatives (e.g. Cozy Mk IV)
The Long EZ is constructed primarily with foam (blue styrofoam, Divinycell, and polyurethane foam) covered in two types of fiberglass (RA7715 and RA7725) laminated with an epoxy resin system such as MGS L285, MGSL335, or West System (only certain types), or EZ-Poxy.
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http://www.pimaair.org/collection-detail.php?cid=236

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Re: Custom frames, home carbon-fiber method simplified

Post by gogo » Jun 11 2009 1:34pm

That process combined with CNC shaping seems a killer combo. And think of how easy it would be to route the wiring and make integrated lighting.

Enclosed 3-wheeler anyone?

Cupholders!!
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Re: Custom frames, home carbon-fiber method simplified

Post by 12p3phPMDC » Jun 11 2009 4:35pm

that is a beautiful bike!

I'll dig for a thread on a build that used woven carbon fiber socks/tubes that shrink
like a chinese finger trap when you pull on it.

This guy built a nice recumbent bike over a maple hollow core....
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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 11 2009 4:37pm

jag wrote:
The Long EZ is constructed primarily with foam (blue styrofoam, Divinycell, and polyurethane foam)...
I'm surprised they used blue polystyrene foam - that stuff offgasses for some time and ends up forming a very poor bond with the resin/epoxy. I know a lot of boat builders who won't touch the stuff. Divinycell is specifically made as a core material and so are various polyurethane foams.

An expert can do layups without vacuum bagging that are lighter and stronger than vacuum bagged parts. However, that is quite a skill - you have to squeegee out the excess resin without messing up the layup. If you've ever worked with composites, you will know how tricky that is.

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Re: Custom frames, home carbon-fiber method simplified

Post by jag » Jun 11 2009 5:16pm

JS Tyro wrote:
jag wrote:
The Long EZ is constructed primarily with foam (blue styrofoam, Divinycell, and polyurethane foam)...
I'm surprised they used blue polystyrene foam - that stuff offgasses for some time and ends up forming a very poor bond with the resin/epoxy. I know a lot of boat builders who won't touch the stuff. Divinycell is specifically made as a core material and so are various polyurethane foams.
Remember, this is from the beginnings in the 70's and 80's VariEz and Long Ez, not current home airplane building.
JS Tyro wrote: An expert can do layups without vacuum bagging that are lighter and stronger than vacuum bagged parts. However, that is quite a skill - you have to squeegee out the excess resin without messing up the layup. If you've ever worked with composites, you will know how tricky that is.
Any links to tutorials or pictures for how to get good results w/o vacuum bagging?

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Re: Custom frames, home carbon-fiber method simplified

Post by wanders » Jun 11 2009 5:28pm

gogo wrote:That process combined with CNC shaping seems a killer combo. And think of how easy it would be to route the wiring and make integrated lighting.

Enclosed 3-wheeler anyone?
This is from the (in)famous R.Q.Riley website, which has been selling DIY vehicle plans for years. In fact, they DO have an enclosed 3-wheeler kit or plans.
Willie

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Re: Custom frames, home carbon-fiber method simplified

Post by StudEbiker » Jun 11 2009 5:45pm

I think he meant a human powered three wheeler...which was my first thought when I saw this post as well. Too many projects, not enough time.....not to mention how am I going to explain to my wife the new Tidalforce frame and parts showing up that I have no use for right now. Just to good a deal to pass up:!:

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Re: Custom frames, home carbon-fiber method simplified

Post by northernmike » Jun 11 2009 6:37pm

JS Tyro wrote: An expert can do layups without vacuum bagging that are lighter and stronger than vacuum bagged parts.

Sorry but I have to disagree.

A PROPERLY bagged part will, by design, have less porosity, higher glass/resin ratio, and most importantly, much better wet-out and consistency than a roller and brush can possibly obtain.

If you have an expert that can work at the molecular level and compete with 25 inches of mercury, please show me!

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Re: Custom frames, home carbon-fiber method simplified

Post by jag » Jun 11 2009 9:36pm

One issue with resin on foam that comes up in lightweight boat construction is that the foam soaks up some of the resin, resulting in a heavier laminate than desired. Is there a way to minimize unwanted soaking into the foam?

How is commercial foam core done? Glass and resin on top of the foam, or is the foam simply glued into the premade plastic part? I had a Hobiecat years ago, and noticed those were foam core hulls, but I doubt they made 100,000's by hand.

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Re: Custom frames, home carbon-fiber method simplified

Post by gerhardt » Jun 11 2009 11:37pm

I plan to build a "nose cone" fairing for the front of my delta E-triken using carbon fiber. I appreciate this topic and any recommendations that members can give me. I plan to eventually build a complete carbon fiber body. The nose cone will be approximately 25 inches in diameter and enclose a 20 inch front wheel. The length will be approximately 24 inches. I purchased some sample carbon fiber from Aircraft Spruce. Any recommendations on additional sourecs of carbon fiber and supplies will also be appreciated.
I thought about vacuum forming a Lexan nose cone and then applying a carbon fiber layer to the insided surface for strength and appearance. Has anyone done this?
Don Gerhardt

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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 12 2009 12:13am

northernmike wrote:A PROPERLY bagged part will, by design, have less porosity, higher glass/resin ratio, and most importantly, much better wet-out and consistency than a roller and brush can possibly obtain.
Roller and brush? That's for amateurs. :) Once the fabric is on and smoothed out, they go over the whole thing with a squeegee - relatively stiff plastic, not cheap window cleaning rubber stuff. They press the layers down and squeeze out the excess resin. The fabric is not oversaturated to begin with, so the squeegee forces the resin into all pores before it can remove any excess. If the fibers are no saturated, they tend to suck up the resin quite well. I've seen it done (on video) and explained to me by a (now retired) designer of racing kayaks and canoes. I've also seen the results on finished kayaks and you couldn't tell the difference visually from vacuum bagging. However, the results are superb. The most noticeable difference is on the inside - not the mold side. That surface tends to be quite smooth with vacuum bagging. With hand working, the surface is rougher. Sanding can clean it up. No gel coat on these hulls either - they are finished with epoxy paint.

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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 12 2009 12:25am

jag wrote:How is commercial foam core done? Glass and resin on top of the foam, or is the foam simply glued into the premade plastic part?
You couldn't get a better bond with an adhesive applied to the foam and hardened composite panel than you could with laying the wet composite fiber directly on the foam. Just getting the pre-made surfaces to match would be a problem - the wet layup takes care of that by filling any voids and surface undulations when it's made.
I had a Hobiecat years ago, and noticed those were foam core hulls, but I doubt they made 100,000's by hand.
I can't say exactly what Hobie does, but very many composite boats of all shapes and sizes are basically handmade. Military aircraft manufacturers have highly automated CFRP making systems and Airbus and Boeing probably use similar on their commercial jets. however, most boat makers are much smaller and less well funded. Labour is cheap compared to fully computerized composite layup technology. At best, some small boat makers can use computerized fabric cutting (borrowed from clothing industry) to cut the glass, CF, Kevlar etc. The places I've visited have been all hand work.

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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 12 2009 12:33am

gerhardt wrote: thought about vacuum forming a Lexan nose cone and then applying a carbon fiber layer to the insided surface for strength and appearance. Has anyone done this?
My only comment is that polycarbonate is relatively heavy compared to an all-CFRP solution. If you're using it for mostly-transparent window and using the CF for reinforcing some parts for strength and/or stiffness, then that's OK. I wouldn't recommend using fully carbon-reinforced polycarbonate for an opaque skin. If you've got a mold for vacuum forming the polycarbonate, you can use it as a form for making the CF version. Ideally you'd want a female mold so that the smooth surface is on the outside. You might want to make up some ribs on the inside for stiffness. Put a clear coat on the CFRP when finished for UV protection - polyurethane clear coats as used for automobile paint protection would do fine.

Resins - polyester is cheap and, well it's cheap. Vinylester is more expensive and better quality. Epoxy is best (strong, tough) and most expensive. All three need UV protection - that's what gel coat is for in boats and such. Clear coat painted on is lighter and just as effective, though less able to absorb abrasion than gel coat.

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Re: Custom frames, home carbon-fiber method simplified

Post by Jeremy Harris » Jun 12 2009 2:02am

JS Tyro wrote:I'm surprised they used blue polystyrene foam - that stuff offgasses for some time and ends up forming a very poor bond with the resin/epoxy. I know a lot of boat builders who won't touch the stuff. Divinycell is specifically made as a core material and so are various polyurethane foams.

An expert can do layups without vacuum bagging that are lighter and stronger than vacuum bagged parts. However, that is quite a skill - you have to squeegee out the excess resin without messing up the layup. If you've ever worked with composites, you will know how tricky that is.
It's an extremely well-proven home-built aircraft construction method that works extremely well and lasts for years. Lots of people are still building using this method; I've used it for a few years and have had no problems at all.

I've never heard of, or experienced, the outgassing problem with the pink or blue extruded polystyrene insulation foam (the stuff specified for Rutan designs and the stuff I use in the main). The adhesion to epoxy is extremely good, too. The best technique is still the one that Burt Rutan came up with years ago, butter the foam with a very thin layer of microballoon thickened epoxy, then lay the first layer of cloth up in the normal way. This keeps the weight down, by preventing too much heavy epoxy getting into the top surface of the foam and increases the bond strength slightly.

I can get glass:resin ratios of around 40:60 or so with a hand-layup and a fair bit of squeegee work. I can better this with peel ply and a thin polythene sheet over the top, as I can then squeegee out more resin without letting air back in, I can get maybe 50:50 with a bit of patience but it's hard to do curved parts like this. The best technique I've seen is the low vacuum technique that the CozyGirlz developed for their build (see here: http://www.cozygirrrl.com/ and click "LoVac" on the left menu). They get really good glass resin ratios using this cheap method.

Jeremy
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Re: Custom frames, home carbon-fiber method simplified

Post by spinningmagnets » Jun 12 2009 2:33pm

Thanks for all the great responses ! I am constantly AMAZED at the breadth and depth of experience of the members here !

The baby-boom bulge in the population demographic (born 1946-64) means there is a significant portion of the population that forms the "pig-inside-the-python" bell-curve of old folks. They are bored and have some money, and are walking/biking for boredom and health. As soon as many of them try a recumbent, they want one, but the price is daunting (Wal-Mart recently began selling a cheap Chinese copy of a popular 'Bent http://endless-sphere.com/forums/viewto ... 78&start=0)

Most recumbents use fairly off-the-shelf (OTS) hard parts, and the only custom part is the odd-shaped frame. I myself bought a WM MTB because it was the cheapest way to get full-suspension, fat-tires, and a front disc brake. I immediately converted it to a semi-recumbent ("beach cruiser" style of seating) and I find myself drawn to custom-framed bikes to study alternative (affordable garage-made) building methods. No need for me to "re-invent the wheel".

I posted this thread and the "wooden bikes" thread as a result of alternative frame-building research I felt would be amusing to the E-bike community.

That being said, I feel compelled to emphasize the need for engineering. By that I mean, if you take your common aluminum soda/beer can, it can be easily collapsed by a thumb and forefinger closing in on its sides. But place 4 of them together on the floor and place a wooden square plank on their tops...such a configuration can support a 200-lb man if the weight is applied slowly and carefully.

So, I encourage any experimenters to make a project "too strong" and use each element to emphasize its strengths and avoid its weaknesses. Heliarc-ing thin-wall aluminum tubing would be expensive and time-consuming to learn, but I am now certain that I could make a custom recumbent E-frame based on the collected information you have all supplied me. For that, I am grateful ! and I hope this thread will prove useful to others...

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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 12 2009 3:37pm

Jeremy Harris wrote:I've never heard of, or experienced, the outgassing problem with the pink or blue extruded polystyrene insulation foam (the stuff specified for Rutan designs and the stuff I use in the main).
That's fair. It could be the local boat building community that I know is basing their bias against the polystyrene on some bad examples rather than a wider sample (or the aircraft building community). I just know that they are very vocal in their opposition to the stuff. I was going to use it once but was persuaded not to - I still have the thin blue foam in the garage. Maybe I should experiment. I'm making a trailer for my e-bike; I could make the trailer deck with glass/blue foam and see what happens. Of course, some might argue that after having that foam in the garage for a decade, all offgassing is finished. :)

It's also possible that the shear forces in the different applications are in different ranges. Are the aircraft using polystyrene for both high-load and low-load components? Microballoons weaken epoxy so that suggests a lower-load environment if it's being used for the highest shear point between the foam and glass.

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Re: Custom frames, home carbon-fiber method simplified

Post by northernmike » Jun 12 2009 4:03pm

JS Tyro wrote: Once the fabric is on and smoothed out, they go over the whole thing with a squeegee - relatively stiff plastic, not cheap window cleaning rubber stuff. They press the layers down and squeeze out the excess resin.
How can a squeegee compete with atmospheric pressure? There's physically no possible way it can conform to the shape of the part the way a flexible membrane can.

JS Tyro wrote: I've also seen the results on finished kayaks and you couldn't tell the difference visually from vacuum bagging.
Visually, sure.

Let's see some destructive stress test comparisons and then we can apple-to-apple the issue.

:wink:

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Re: Custom frames, home carbon-fiber method simplified

Post by Jeremy Harris » Jun 12 2009 4:21pm

True, the microballoons do reduce the epoxy shear strength, but it's still much higher than the shear strength of the foam, so it works well. What happens is that the microballoons key into the interstitial spaces in the sanded foam, so keying the resin/foam joint and adding strength. They also act to reduce the sharp transition in modulus between the relatively stiff resin and the relatively flexible foam, I think, as the thin layer of foam/microballoon/resin mix is less stiff than the resin, but stiffer than the foam.

This method is used for high load bearing structures is virtually all the Rutan designs. The key to producing good wing spars is to ensure that there is a decent shear web incorporated into the foam, so that the spar caps are properly supported and not wholly reliant on the strength of the foam core. The easy way to do this is split the foam, lay-up a glass web on the split faces, overlapping on to the spar cap surfaces, bond the two foam halves back together with the glass sandwiched and then lay up the spar caps. The result is a glass I beam set inside a foam core, which is both stiff and strong.

If I were making a composite electric bike, then I'd forget about trying to simulate tubes and go for a stressed skin monocoque, with space for all the components inside the "frame". This is easy to do with the glass on foam method, because you just carve the foam to shape, layup glass on the outside (using epoxy, not polyester or vinylester resin) and when it's cured pour some petrol (gasoline) in to melt out the foam core, leaving a hollow shell. The only thing to watch is to make sure that the access holes are cut into non-load bearing areas. Should make a nice light "frame" though, with no hassle about where to fit parts around awkward tubes. If you want extra stiffness in some areas, then a variation on the wing spar method above would allow internal webs to be added, or some foam can be left in, if it's sealed up from the petrol.

Jeremy
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Re: Custom frames, home carbon-fiber method simplified

Post by 12p3phPMDC » Jun 12 2009 6:19pm

Really cool homebuilt carbon wood composite recumbent as promised.

Uses the carbon sock tubes that skrink when you pull em..



http://carbonbent.bravehost.com/index.html
homebuilt_carbon_recumbent.jpg
homebuilt_carbon_recumbent.jpg (136.96 KiB) Viewed 14034 times
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Re: Custom frames, home carbon-fiber method simplified

Post by John in CR » Jun 12 2009 8:56pm

My plan is to go to the local plywood factory and get some of the thin wood sheets before it becomes plywood...maybe even get large enough scraps for free. Then create a sandwich of 2 layers wood, 1 fiberglass, and 1 carbon/kevlar weave, making my curves first and using epoxy as the adhesive. Squeegee on wood results in a very lightweight but strong structure only surpassed by resin infusion, but is very simple. I used this method except starting with 4mm ply to build a 5 meter beach catamaran that weighs only 73kg, far less than half the weight of comparable Hobie.

I don't want to start with foam, because this is far easier to finish, and I want interior room for all cabling and batteries. If it works well as an open bike, I'll proceed to something with rain protection as a tilting delta trike.

John

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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 13 2009 11:32am

northernmike wrote:How can a squeegee compete with atmospheric pressure? There's physically no possible way it can conform to the shape of the part the way a flexible membrane can.
The contact stresses under a squeegee can be much higher than 15psi (nominal max possible vacuum). You are creating a "wave" of stress pushing the layup down and pulling the excess resin out. Conforming is not an issue. Resins are sufficiently viscose and the fabrics are sufficiently sticky that the whole thing holds together without requiring vacuum bagging.
Let's see some destructive stress test comparisons and then we can apple-to-apple the issue.


The guys that design and build Olympic class racing kayaks and canoes are not stupid. They have decent budgets for R&D and do test these techniques repeatedly. We're talking not only stress tests but tank tests as well. Given the cost of the most experienced layup technicians, if vacuum bagging was both cheaper and superior, they'd use it.

Vacuum bagging is an excellent mass production technique. It is widely used and can produce very good results with minimally trained and experienced staff. It is highly recommended for anyone building good one-off designs when they don't have lots of experience with composites.

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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 13 2009 11:34am

Jeremy Harris wrote:True, the microballoons do reduce the epoxy shear strength, [...], if it's sealed up from the petrol.

Lots of good information here. Thanks for this!

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Re: Custom frames, home carbon-fiber method simplified

Post by chet » Jun 13 2009 11:53am

When they first made fiberglass hulls (before carbon fiber) the woven glass fabric was laid up by hand forming layers. Now the Glass mat is sprayed using a chop gun. Building up glass fibers with a polymer.

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Re: Custom frames, home carbon-fiber method simplified

Post by JS Tyro » Jun 13 2009 11:55am

<jealousmode>I hate it when people post stuff like that</jealousmode> :)

Very sweet design and construction.

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