Head tube cluster:
You have been busy! Looks brilliant.
The only observation I would make is about the couplings. Are they sleeved compression couplings?
Sorry I have not updated in a while. Now that the holiday break is over, my day job is getting in the way of ride time and build time.
Here is the bike so far:
Rear bottom bracket cluster:
Front triangle and mid section:
Weight so far is 4 pound.
The sleeved compression joints would have been a more elegant solution. I kept mine simple, however. It is just a simple compression over a double butted top tube or a triple butted boom tube. I am hoping that would be sufficient. I do have plans for additional attachment point using titanium rods if needed later.
If I don't use vacuum bagging, should I go with heat shrink tape? Which do you use?
Also, automotive clear coat better than gel coat for the top layer?
The AC 130 prep is on its way. Skygeek found me another solution for the primer.
I would definately do automotive clear instead of gelcoat.
What did Skygeek find to substitute for BR127 primer. I ask so that if I am familiar with it, I'll send pointers / tips.
I am using Bostik L1007M for the primer.
Works pretty well. Here it is on the drop out:
I put my entire body weight (140 lb) on that bond and it held.
I got busy with other stuff and ran out of time this weekend. Could not finish the rear triangle as I had planned. But I did manage to do a dry run with the parts I have to check for clearances. The rear wheel with 40 mm tires fit with about 6 mm clearance on both sides. The BB7 barely fit on the chainstay but only after I switched out for the Shimano adapter.
Current frame weight is 6lb 8oz.
Looks very nice. Never used the Bostic product. Glad the AC130 and adhesion primer is working well. Sounds like a very strong joint.
As for brake disc clearance, you might consider something similar to the recent solutions posted on the same topic in regards to some Calfees. Ritterveiw stuffed a huge disc in his frame after some mods. I believe in a nutshell, they removed a section of the tubes rounded portion and replaced it with a flat portion. This is very easy to do, especially at this point.
Also, and this is part of the day job coming to you...Don't get lax or lazy about ALL safety concerns with dust and chemicals plus splinters.
The frame is looking great. I am impressed with the rear tire clearance for 40mm tires.
Are these 700C wheels?
Also reading the thread it looks like you have used manufactured tubes. I don't know which tubing you are using but I looked at the ICE tubing web site they state all their tubes are custom designed for stiffness. How did you decide which tubes to use? Is there a stiffness rating system that allows the user to define the stiffness desired?
How are the chainstay tubes rated for stiffness?
How is the top tube rated for stiffness?
Thanks for your time,
One thing with Calfee style construction is the tube laminate schedule, while important is less important.
On a metal bicycle there is a lot of emphasis placed into butted tubes. With a wrapped lug construction, the tubes can be thinner walled, and with minimal data, a safe design can be sorted out. The OP may not have the most optimum strength to weight ratio, but I would be confident in that it favors strength over less weight, but is pretty close.
back to Calfee style construction, the bulbed joints produce a huge tapering in stress / strength through the joint. In effect providing external butting of the tubes.
If the op had elected to build a smooth profile frame, the exterior would not be bulbed at the joints, but a huge investment in molds and more exotic construction methods and materials would need to be utilized.
Honestly, my opinion is the op is doing a very good job. Lot of thinking and planning, then detailed execution of the plan.
I am also curious and will await the op reply on tube selections.
I was not clear in my previous post. I am assuming the frame is strong enough to avoid failure and was asking about tubing flex as it relates to ride quality. I am interested in understanding the flex that might be anticipated on the OP's frame under hard pedaling. I am trying to understand if the chainstays and top tube will flex more or less than another frame.
I am not an engineer and so do not understand how tubing flex can be compared across materials. The relative flexibility of metals is known but since carbon fiber tubes are custom designed how can a given carbon tube be compared to a reference metal tube? Is there a stiffness rating similar to the tensile strength rating seen in tubing specs?
After writing the above I found the attached on Reynolds web site rating various metal tubing stiffness. Is such a rating applicable to carbon tubing?
Research Balance, Symmetry, and Quasi-isotropic in regards to composite structures. There are almost an infinite number of ways to build or lay the fibers (tows) in regards to endpoints and angles. Many off the shelf tubes are fairly neutral in regards to strength. Most likely these are what he chose.
We really need to wait on the OP to answer. This should be a good reply from him.
Wayne#1; "Please, before you make statements like the one above..."
Well first, a closer reading will show that I catagorized my thought as "in my humble opinion." Not then or now was it offered as a law of physics or what not. I don't think your response has changed my opinion per say, but I respect your right to have yours. As I will explain in a moment, I don't necessarily disagree with your view either.
Wayne#2; "...ride a cf tandem, itis obvious that you have not, because if you had you would not make that statement.
Well actually I have ridden a CF tandem. Actually I have ridden two Calfee CF tandem's and had a short unimpressive ride on one resprayed no-name CF one. From my view the two Calfee's, were both very comfortable and very nice bikes. I viewed the fit and finish as to a very high standard. As least as good as any other branded tandem in my experience, regardless of material. Ride wise I would also give them high marks but not such a huge deal breaker difference compared to the other top quality bikes (independent of material). If I were shopping today for a new tandem in that price range, I would certainly consider one of them. However I and many other owners of other top quality brands, whether CF or AL or steel or Ti, also feel all or most of those postive attribtutes about their bike of choice or destiny. Although I have never felt positive about any of the aluminum ones, I respect the view of the many others who simply can't see how anyone could possibly be happy to ride a steel or a CF or Ti bike or Bamboo for that matter. I know of no repeatable method to predict how a team will react to the material a frame is made from. It seems highly individualistic at least and substantially subjective. My goals remain those of getting more folks on tandems vice fussing too much on the material ingredients.
Wayne#3; "...He has ridden over 21,000 miles this year alone and most of those mile on the Giant. So please do not keep preaching about the long term life of carbon fiber bicycle frames."
It makes me happy that a tandem team you know is getting good long team service from his Giant Alum/CF hybrid (I think several of the CF brands are establishing good reliability records also, so the Giant isn't just a single data point that some might malign it). But it makes me happier that he did it at all, as 21k in a year is a major metric. I wish I could do that many miles a year. Wondering thouh if you would notice it as being as significant if they had achieved the same miles on a Ti or AL framed bike or a old Schwinn? I would hope so...
Hope this helps you better understand where my thoughts come from, but making no attempt to sway your views on the topics which are generally ok with me.
Mileage on our Zona carbon fiber tandem (ICE tubing) is currently 34,000+.
All our previous tandems (4) were steel.
All, except our very first tandem, logged 50,000+ miles on the odometers.
Have ridden steel, alu, ti and bamboo bikes/tandems.
Have test ridden steel and c/f coupled tandems too.
Been following your posts and you are dong a terrific job on that frameset . . .
Enjoy the ride TWOgether!
Rudy and Kay/zonatandem
To answer your question, my carbon tubes are standard stock from Rockwest. They are Unis layered at 0,45, and 90 degree designed for longitudinal stiffness. The top tube OD is 34.8 and ID is 28.8. The Chain stay OD is 22.6 and ID is 18.4.
Regarding their stiffness, that would depend on where you take the measurement. Below is a longitudinal cross section of my top tube design:
The red part is the top tube ferrule,the green parts are the couplers and main frame, and the yellow is the PLA core. The stiffness of the tube varies along the length of the tube depending on its material, thickness, and surrounding structures.
I can calculate the stiffness at any given point using the formulas:
Stiffness = EI
Where E is Young's Modulus of Elasticity and I is the Moment of Inertia.
Plotting the stiffness along the top length of the tube I get the following graph:
Using the graph, I can visualize the effect of changing each component on the final stiffness profile of the tube.
How does this alter final riding characteristic of the bike? I really don't know. The problem is I do not have a reference point. If I was building several hundred bikes, I could empirically determine the ride characteristics of each components by altering each component individually on a reference standard bike. As this is a one of a kind, I do not have that luxury. Moreover, I am not sure it makes that much of a difference to me. Some people like their bike stiff, some like it flexible. Personally I am happy either way as long as it is not in either extreme.
My main concern with this bike is strength and durability. It is pretty hard to reach ultimate tensile strength limit of carbon fiber on a bike. What I am more concerned about is failure from low cycle strain damage. The purpose of this exercise is to mitigate that damage by relieving the high stress point gradually and avoid any abrupt change in stiffness (notch effect). That I think is the advantage of the bulb or wrapped joint design. Rather than a single stress line as seen in a welded joint,the joint wrap redistribute the stress over a wider surface area. My internal carbon fiber lug add additional surface area not only for adhesive bond but also for diffusion of stress.
I would venture to guess that this is probably one of the stiffer top tube design. The problem with this of course is that it exposes the vulnerability of other weaker or more flexible areas. So everything else on the frame must also be strengthen. Hence the choice of wider and thicker chain stay.
The end result is a stiff and more durable frame. The price of course is weight and reduced flexibility. I have used a few design elements to mitigate these effects and help improve ride comfort. Eliminating the lateral beam,compacting the frame, lengthening the exposed seat stem, and lengthening the chain stays for examples should help the carbon fiber frame soften the ride. Additionally, tire, wheel, spoke and saddle choices are made with consideration to comfort, light weight, and durability.
My goal is for a 9-10 lb frame and a ~30 lb bike. Any lighter than that, I would worry about it not being strong enough, any heavier than I would have negated the light weight benefit of using carbon fiber.
Thank you for the detail response including the formulas. When comparing steel double butted tubes I usually just calculate the stiffness of the thinner center section and ignore the butted ends. This is of course an oversimplification but has worked pretty well in predicting the stiffness when compared to the seat of the pants feel when riding the bikes. I can see that the complexity of the carbon tubing structure make such estimations very difficult.
For comparison to your bike, I think that many Calfee tandems use a 2 inch diameter top tube but other than that I have no idea of its construction. Possibly some Calfee owners or someone from Calfee can chime in with some more data. Your top tube diameter of 34.8mm is much smaller. The smaller diameter would indicate a much more flexible tube but without more data on the Calfee tube I am not sure if a valid comparison can be made. Personally I like the look of thinner tubes but beauty is in the eye of the beholder.
As you may know from my previous posts I like wide tires and the idea of a carbon tandem that allows for big tires is very interesting to me. I look forward to watching your build continue. Please keep us posted with as much information as time allows.
According to the stiffness formula,there are 2 ways to increase the stiffness of a hollow tube.
Stiffness = EI
Where E is Young's Modulus of Elasticity and I is the Moment of Inertia.
You can either increase the outer diameter or decrease the inner diameter. The more efficient use of weight would have been to build with a wider, thinner walled tube (at the cost of increased aerodynamic profile of course). But, I have another design challenge - the couplers. By design, these things exert tremendous lateral force on the tube. And it is much easier to crush a thin walled wider diameter tube than it is to crush a thick walled narrow diameter tube. Hence my choice of tube size. I have also designed an inner PLA core to buttress against this compressive force. Its shape reinforce the tube where it is needed most and dissipate the stiffness gradually over a wider area.
Calfee, like any good builders, varies their tubing schedule according to the application at hand - altering diameter and thickness according to rider's weight, stiffness, or ride characteristic desired. This bike with its thicker wall tubing and internal support structure, is probably one of the more stiffer bike built. We are a light team (250 lb total), so too much stiffness is not necessarily a good thing. I needed it, however, to help with strength and durability. Again, I am happy either way as long as it not in the extremes.
It has been a beautiful weekend in south Texas. You know you have the good life when morning coffee decision is either biking or building. We did managed to get a couple of long rides in but not much progress in the build.
Here is the jig for the rear triangle glue up:
Here is the frame so far after the glue up:
The crank, pedals, and timing pulley all fit as planned. My only concern is the FSA bottom bracket. If I read the instruction correctly, with a 145 mm dropout spacing, I am supposed to use two spacer on the right and none on the left. Is this correct? The asymmetry just doesn't seem right, especially after working so hard to make sure the frame is perfectly aligned.
Also, sorry to disappoint you on the wheels, those are 26 in. I can fit a 700c but the widest I can comfortably accommodate is a 32 mm.
Why do you need to go with such big tires? Are you making the frame that stiff? My Calfee has a much better ride on 25/23mm tires than the old Santana on 32's.
The bike looks very nice.
as a thought, now that I see how you did the couplers, can you consider a slight mod to the design. I am not sure what diameter the tubes are where coupled, but it may be a worth considering a titanium outer skin over those tubes.
On the internet is a place called titanium Joes. He stock surplus and small quantity titanium tubing and sheet. Possible you could get some thin walled tubing and line the bearing surface of tube.
There will minimize any fretting type wear with carbon on carbon, and will protect the tube ends while dis-assembled.
Obviously I my be entirely wrong because you have mentioned something about what sounds like a core in part of the structure.
Just something maybe worth considering.
Looks very nice though.
I look forward to your report on how it rides. Build looks great.
I like to use different tires for different rides. Skinny tires are great for street only use, but for touring with off road/trail rides I like the fat tires for comfort and durability. With this build I have the versatility of most any wheel or tire I need. For clearance and alignment checks, I want to use the largest tire I have available.
I do get my titanium tubes and rods from Joe's also. That is a good thought about the sleeve, but I am too far along in my build to make that drastic of a change to my design. My ferrules are finished, I would have to completely redo them to incorporate the new sleeve. Maybe in a next revision.
I have the Tacx and Finish Line carbon compound along with the anti-seize lubricant for the bolts. Although I am still waiting for the completion of the build to see if I will need them as the tolerance for the tubes are very tight.
My stoker's right pedal is 5mm more lateral than the left with the spacers as instructed. I must be doing something wrong.
Sorry if I cannot PM anyone back, but the last time I tried, this forum said I do not have that privilege yet. Don't want to seem rude.
Build so far with a few more carbon layers on the joints:
I have also started the glue up for the cable stops and water bottle bosses. Here is my home made jig:
Next up are the cable guides. I was going to bend some titanium tubes for the essentric and bottom bracket shells, but I see that Calfee has a much simpler solution. It seems that they run the cables through groves in the bare carbon fibers. Could anyone confirm? This would save me a lot of work. Thanks in advance.
The bike frame weighs 8 lb. so far. Subtract the weight of the three clay plugs at the head tube, eccentric, and rear bottom bracket shells, and add the weight of a few more layers of carbon and the clear coat and I should be pretty close to target weight.
Barring any major set back, I should be finished ahead of schedule by the end of February. I initially thought about the Houston-Austin MS150, which we do every year, as a good maiden ride. But, the SW Tandem Rally sounds like a lot of fun also.
I believe you need 20 posts to send PMs. I like seeing your responses as it gives a good feel for the project.
The tandem looks great.