View Full Version : Carbon Composite?

03-18-2005, 02:51 PM
Has anyone here ever dabbled with laying up carbon composites? I'm looking for information and first hand advice for wet lay-up and vacuum bagging in particular. Also, any ideas or sources for an inexpensive vacuum pump would be most helpful.



03-18-2005, 03:03 PM
Glen, how big a part, and how much shape does it have? What is the tightest radius on the part, and where are you at? Have a plastics guru sitting in my cube, would be willing to give you some pointers. Shawn

03-18-2005, 03:07 PM
The intake side of your air compressor.

American Science and Surplus had some used vacuum pumps.

03-18-2005, 03:17 PM
Take a look at the CAD pictures here to see what I'm up to.


I want to assemble custom bicycle frames from existing carbon tubes and join them by laying up carbon from one side (with some plates down the center) then when it's set lay up from the opposite side and trim off the excess. I'd be using a high drapable cloth and vacuum bagging each side.

Dave Opincarne
03-18-2005, 03:41 PM
Glen, I've worked as a composite toolmaker for an aerospace manufacturer and have experience with carbon, aramid, and glass both wet and pre-preg both vacum and traditional layups.

As a starting point how much experience do you have with this type of layup?

If I understand you corectly you're making the lugs for a bike frame using off the shelf tubing for the frame correct? And you want to make each lug in two halves layed up in place correct? If I am correct in my understanding I wouyld stongly advise against this course of action. If not then please clarify.

As for a vacum source you can use a vacume genarator run off an air compressor or if your willing use your car engine at idle and pull vacum off of the intake manifold. At idle you should get more than 22"Hg. Obviously you need to make sure there is no danger of CO accumulation and be willing to run your car at idle for an extended period of time. Renting a vacum pump from a composite supplier might be an option as well since neither of the alternatives mentioned will produce as much vacum as a dedicated pump.

You didn't mention it, but be sure to incorperate peal ply and a bleeder cloth into your layup for best results.

I'll be around for a while but I've got my daughter this weekend as well so I might not be responding too quickly for the next couple days.


03-18-2005, 03:52 PM
Hi Glenn,
These parts look like a good candidate for two piece compression tools. Use clearance wax and lay up the backside. The radii as seen on your photo page make bagging iffy at best. Go to your local tooling supply shop and they can set you up with all the stuff. If you have a buissiness or a school project, ask for free samples from the manufacturers, don't be shy. They can give you tons of free advice and free stuff. Try Tool Chemical or Ren Plastics.

03-18-2005, 04:02 PM

Thanks for the information. I am aware of the need for perforated release film and bleed cloth etc. My experience however lies more in cutting and welding thin wall steel tubing for frame building. Your advice would be more than welcome. One of the reasons I posted to this board is the vast variety of experience here.

You are correct, I was thinking of laying up one side of the lug in place and then the other when the first was cured. I am concerned about shrinkage of the layup affecting alignment but not sure how much of an issue that would be.

Could, when you have time, elaborate on why you advise against this method. There is another company building frames using a similar method (www.calfeedesign.com) but they squeeze the joints between aluminum tools. I was hoping to have more freedom with joint design and avoid the dedicated tooling expense.

Any suggestions or alternative methods of creating joints oriented like I have in the photos


would be much appreciated. Thanks for any help you can provide.


03-18-2005, 04:08 PM
I had considered using low melting temp alloy (Woods metal etc) to make compression tooling for each joint. I imagine clearance wax would melt below the 158F that the alloy goes liquid.

I was worried about the radii of the bends using a vacuum process. Thanks for the heads up.

Dave Opincarne
03-18-2005, 04:42 PM
Clamshell tooling would certainly give you a better finish, a necesity if you're thinking of selling these frames. It also gives better results than bagging. I disagree that this could not be bagged with a little forthought but it would take a little practice.

Simply stated my objection to the design is that it is prone to failure and negates any advantage provided by the use of composite material. Keep a couple things in mind: 1) Composite material is just that, a composite of fiber and a matrix in which to encapsulate it. 2) The fiber's streangth is not omni-directional, depending on its construction it only exhibits streangth in one or two axis. Stated planely the lamination itself can be easily broken. 3) The matrix (epoxy resin) achives its streangth through polimerizing, forming long chains though chemichal reaction. When applied to an already cured surface it can only bind via mechanichal bonds. It will never become integral with the surface it is applied to but is limited to atachment via small surface imperfections it has worked itself into.

By forming the lugs in two halves you not only do not have the streangth of the carbon fibers working for you but you do not even have the full streangth of the epoxy. If you have any experience as a woodworker think of this joint being made out of a block of wood. Functionaly you have run the tubing in the same plane as the wood grain. Any loading will work the grain apart until it fails.

As you are aware the lugs are the area of a bike frame prone to the greatest concentration of stress. I'm sure you're also aware that just because someone makes and markets a product does not mean it's safe. Given that thes are doubtless intended as high preformance frames and prone to severe duity I would strongly caution you to reconsider the design. I'm guessing that you are trying to take advantage of the additional rigidity the flange would provide. Remember that an increase in ridgity will also serve to concetrate load rather than distribute it, making the need for a sound joint all the more desirable. It is possible to incorperate this feature into a one piece lug.

You will also need to incorperate larger radius into the flange, carbon fiber does not like to form itself into small radiusus. There are a couple of solutions to this problem.


Dave Opincarne
03-18-2005, 04:48 PM
Do you have any close up photos of the other frame lugs? Their web site doesn't seem to show anything in detail.

03-18-2005, 04:49 PM
Here's a guy who vacuum bags using a Tilia foodsaver:


Haven't tried it yet, but I bought a Tilia, and will give it a try when I get the time.


Dave Opincarne
03-18-2005, 04:55 PM
Just a quick scan of the page doesn't state how much vacuum the food saver would pull, anybody know?

03-18-2005, 05:13 PM

The existing frames constructed this way (Calfee Design) are well regarded and come with a lifetime warrantee so they must be doing something right. I don't have any close up shots of their joints.

I do know that the bond between the lug and tube will not be taking advantage of the carbon but will be a simple glue joint. Trek makes all their carbon frames from carbon tubes glued to internal carbon lugs.

I'd like to figure out a simple method for forming the joints without the webs if it could be done with inexpensive tooling and have an acceptable finish. The plan would be to clear coat the whole frame so joint finish is not super critical.

Whatever method I went with I plan to test joints to failure prior to building an entire frame.

I guess I have a bit more investigation to do.

Thanks again for all the info.


03-18-2005, 05:26 PM

If you do decide to make tooling, Devon has a line of industrial putties that work well.

Aluminum Putty is designed to work at 250F continuous: http://www.devcon.com/devconfamilyproduct.cfm?familyid=107.0&catid=15

Titanium Putty is designed for 350F continuous: http://www.devcon.com/devconcatsolution.cfm?catid=34

I haven't tried the Titanium Putty, but the Aluminum Putty is really nice. It's about as thick as peanut butter (like Jif without nuts). Once in place it does not move, sag or flow out of position. Turns, bores, faces & finishes much like solid aluminum. Pretty handy for prototype work where you may want to change features and dimensions.

Barry Milton

[This message has been edited by precisionworks (edited 03-18-2005).]

Dave Opincarne
03-19-2005, 12:36 AM
It's not the lug to tube joint that concerns me, it's failure of the lug itself. Are you CERTAIN that Calfee is making the lugs in two pieces? I don't mean to sound like a wet blanket, but I honestly can't think of a weaker way to produce this part with the exception of excluding the flange and butting the cloth ends together at the parting line.

I'd like to get a little better understanding of your reasons for going this route. Are you thinking of building custom frames and want to be able to change frame geometry without having to re-tool? There are some ways around that. If the flanges are not critical then why not make a single layup around the tubes? Even if the flanges are key they can be incorporated with a little planning. Would you consider making the lugs as seperate pieces and then potting the tubes in place?

03-19-2005, 04:17 AM
straight from the calfee site: "By making the lugs separate from the tubes, we are able to use more power tools in the finishing process, saving a tremendous amount of labor."

03-19-2005, 04:35 AM
Pretty much any vacuum cleaner will pull more vacuum than a food saver. At least the one's I've had anything to do with. A basic shop vac is probably a better choice for vacuum bagging.
Also, that does look like too tight of radii for vacuum bagging. I think I would be inclined to use pressure instead, and a two part clamshell mold. Just an opinion.

[This message has been edited by darryl (edited 03-19-2005).]

Dave Opincarne
03-19-2005, 06:03 AM
Sorry, but there's no conection between bagging and tight bends. Yes a bridge can occure but just add a pleat and the problem's solved. Also don't confuse volume with absolute vacuum. I don't know what the food saver pulls but I'm sure it's more than the shop vac. My greatest concern with the food saver would be duty cycle. I doubt it would hold up to extended use and I'm dead certain it was never intended to run for hours on end.

If you're going to make the lug seperate from the mold you'll want to consider a three piece mold, two outside halves and a bladder or other expanding mandrel to form the inside. This could also incorperate pre-preg material and the use of an oven. By using a material for the mandrel with a greater CTE (coeficiant of thermal expansion) than the outside the mandrel will expand at a greater rate and exert preasure against the mold. The result is a controled surface on both the IML and OML. The IML is critical if you're going to fit tubing. I have built tooling that acomplishes this using aluminum for the outside and RTV-J silicon rubber for the mandrel. FWIW the part that was produced was the control surface spars for the then Mcdonnell Douglas MD 500N, MD 520N and MD 600N helicopters based on the Kiowa Little Bird. These needed to maintain a controled mold line on both surfaces.


[This message has been edited by Dave Opincarne (edited 03-19-2005).]

03-19-2005, 02:13 PM

I believe that Calfee is making the lugs in two halves but at the same time using clamshell tooling. Here is a photo.


The use of tooling limits the geometry or gets very expensive per frame.

Another builder creates external lugs in one piece without the webs show in the photo above.


I'm just trying to determine the best and most straightforward (and low $) way to produce joints between carbon tubes. The flanges are not key to any design, they would be a result of either sandwiching the joint or doing one half then the other. If I could wrap each joint and compress them or bag them to achieve the right resin/carbon ratio and end up with a good finish and no flanges then I'd be all set. Any suggestions?

Barry: Thanks for the info on the aluminum putty, it looks interesting.

Thanks for all the information everyone.


[This message has been edited by glenj (edited 03-19-2005).]

Dave Opincarne
03-19-2005, 03:56 PM
The Calfee looks like it's done as a single lug. To my eye the photo was taken during demilding and the fram is sitting in the fixed half of the mold. The open mold in the forground is for the top half. Note how the composite is tightly formed to the frame at this point. I still think having the layers running parallel is a bad idea, but at least their not laying up onto a dry joint.

The Parlee frame looks like a much better design to my eye. It would not be difficult to make a jig out of easily worked material such as MDF to hold the tubes in alignment during such a layup. Bagging for this is certainly feasible. This type of araingment would be quite flexible in terms of changing frame geomitry and negating the need to make aditional tooling for each joint.

On the other hand clamshell tooling could be made with nothing more than a decent drill press, a good vice, and a boaring head. Nylon block could be a good candidate for material. A salvage yard might have inexpensive drops available.

Sorry if this sounds like conflicting advice but I'm uncertain as to your macining capabilities.

All things being equal I'd opt for machining the clamshell molds. It's not necicary to build up with wax. A close estimate of the ply thickness can be made and added to the tubing OD. Bore a hole at this thickness along the parting line of the mold blank which has already been cross pinned. Repeat for each tube. Radius all junctions and you're good to go.


03-19-2005, 11:06 PM

Just to clear things up, I do agree that the Calfee "lugs" had both sides created at once and that the two halves of the tooling are clearly shown in the photo.

I do have a fairly capable shop in a 500ft^2 building I constructed last year in my back yard. In it I have a First brand Bridgeport clone mill, Standard Modern 11" lathe, assorted tooling and a Miller Syncrowave 250 pulse TIG welder. I've made all my own jigs and fixtures so far for building thin wall steel alloy frames. I build and sell frame as a hobby business.

The bike industry is really going all carbon these days but there is still a niche for custom frames. I am trying to expand and offer custom geometry carbon frames using main tubes tubes from MacLean Composites http://www.macqc.com/orderForm.php and carbon rear ends from Dedacciai http://www.dedacciai.com/products.asp?type=2&tid=7

I'd like to avoid having to make hard tools for each joint so I may look into bagging them while everything is held in alignment in my current frame jig, at least to start.

Thanks again for all the help, you've no doubt saved my lots of time and frustration.


03-19-2005, 11:23 PM
i'm not a carbon fiber expert, or bike frame expert, but the PARLEE method looks to me like it has two advantages. one, you hand-lay-up the lugs, so you can make any geometry you want. two, you hand-lay-up the lugs and can charge more because each frame is custom handcrafted. i am being serious about #2. my bike is an older aluminum-framed model. when i bought it there were still some bugs with the composite frames, specifically lugs cracking. if i was to buy a new bike, it would probably be composite.

i also have to agree with Dave regarding making the lugs in two separate pieces. the only thing holding the lug together would be glue or resin/matrix. i don't see how the lug would hold unless the fiber was wrapped around the tubes in several orientations to provide strength.

andy b.

Dave Opincarne
03-19-2005, 11:50 PM
Glen, let me know if I can be of assistance in bagging. Are you familiar with making pleats to avoid bridging?

Given a source for materials I think it would be cost/time efficient to make the clamshell mold. It's nothing more than a fancy drilling operation.

03-20-2005, 02:22 AM
man, i dont know anything about carbon-composite`s BUT, i can say that the parlee frame is made exactly in the same fashion as my 54 triumph frame is! `course, the triumph frame is cast steel lugs and steel tubing brased together, but the technology remains the same....heard a lot about how weak and dangerous this style of frame construction is, just cant seem to find any evidence of that....have identified a certain style triumph frame that seems to crack the downtube right above the rear motor mount, but i would believe thats more due to not having the top mount tight...NEVER seen a cast lug/tube joint fail! again, i realize your doing composite`s and NOT steel, but i think the physics will remain the same.....very interesting thread....

it never hurts to look
unless i`m welding!!!!

My Webshots Page (http://community.webshots.com/album/51872821KYjlSY)

Dave Opincarne
03-20-2005, 05:13 AM
Brazed lugs is old school stuff. Been around forever and almost as stong as TIG frames, atleast less prone to error. Failure is more likly due to overheating or inferior metulurgy or tubing. A well made steel lug frame is a thing of beauty. Personaly, I prefer a steel frame, aluminum is just to harsh. I wish I'd gone with the Bontraiger over the Canondale Super V 700