Frame #2 Four Months of Testing

It's been far too long since I last posted.  In the mean time I completed frame #2 about three weeks after the first one and I've been test riding it ever since.  It has about 2700 km on it on mostly paved roads, rollers, some gravel roads and some less than gravel twin track roads in the Appalachians of North Carolina near West Jefferson.

I built the bike with an EDGE 2.0 fork, Shimano Dura-Ace Di2 groupo, Ritchey WCS stem and post, a Pro carbon bar and Shimano 7900-C24-CL wheels. 

It has internal Di2 wiring and an under down tube battery mount.  The frame has a "lugged" look to the joints rather than the smother finish on the first frame.  The finish on this is spray can automotive clear coat.  I have an interesting finish idea for the next frame and it will have the proper logos etc (now that I know the frames work).

It's been ridden hard and has held up well.  No frame related issues of any kind.  At first I though the back end was a bit too harsh but I think that was just in contrast to the True Temper S3 frame I'd been riding for years.  I used the BB86 or press fit Shimano standard for the BB.

I'm planning the next version of this frame with a lighter chain stay assembly and thinner individual seat stays.  This should bring the weight down from the current 1060g for a 58.5cm frame.  I'd like to do internal rear brake cable as well as Di2 wiring.

Finished Carbon Frame #1

Neil's frame is finally finished.  It's the first full carbon frame and it turned out well.  Still need to work on the cosmetic finish etc and see how test riding goes.  Without further ado here it is with integrated seat post, PF30 BB, ChrisKing 44mm Inset compatible head tube and a final weight of 990g.

Frame Load Test

I took the first trial frame and loaded it to failure.  It took a lot of force to get it to fail.  In most cases it took almost double the load I've applied in the past to cold set OX Platinum frames and accidentally destroy an S3 frame.  For example, the side load test where the head tube is supported, I was suspending my full body weight on the end of a 4' bar and bouncing slightly.  Is the frame "strong enough"?  It's hard to say yet but this does give me confidence.

More Cable Guides

I finished the cable guide through the chain stay yoke of Neil's frame.  It turned out well, see for yourself.

A little more finish work and it should be ready to clear coat.  Here are the down tube mounted derailleur guides.  I'm going to work on carbon versions that bond on to avoid the drilled holes in future frames.

Next up, a real treat (here is a hint).

Cable Guides

The next and approaching final step was to position the cable guides and drill the holes.  Here is the frame with the derailleur and one brake cable guide in place.

 I put a modified 1/2 cable guide on the chain stay next.

The next step was tricky.  I had to position and drill a hole through the frame behind the BB for the front derailleur cable.  After placing a Shimano BB guide on the frame I marked the entrance hole on the bottom.

After drilling through the far side guided roughly by eye I glued in a 1/8" dia brass tube.

I'll trim and sand the ends flush once the glue cures.  Here is another photo for Neil, the weight prior to cable guides.

I have to modify my rivet gun to reach down into the cable guide pockets.  Once that's done the guides will be glued and riveted in place.

Sanded Finish

Here are a few photos after the joints have been sanded.  First I rough sanded the joints to get the high spots and bag joint wrinkles off trying to remove as little carbon as possible.  Next I painted the joints in a thin layer of laminating epoxy.  This was followed by another sanding and another coat of epoxy etc.  The end result looks quite nice when wet or I assume under clear coat.

Unwrapping and Sanding

When the frame comes out of the oven you have to strip all the bag, bleeder and release cloth off.  Sounds like no big deal except the excess epoxy has soaked through the release cloth and into the bleeder.  It forms a lovely crust around the joints that does not come off willingly, visible as the dark areas around the joints.

Next we have a guest frame building assistant, in this case Neil.  He's been tasked with peeling off the above mentioned crust which he does with the maniacal glee of a 4 year old at Christmas.

Look, you can see the mania in his eyes I swear!

Anyway, with the bag and crust removed it was time to inspect the joints for good compaction etc.  In this case everything turned out quite well.

After a bit of sanding to take the high spots and wrinkles out it looks like this.  With a few thin coats of epoxy and sanding it will look quite nice.  Neil requested that the lugs blend into the frame which these do nicely.

Last up is a "baby picture" of Neil and his new bundle of carbon joy.

Next up is the joint finishing, cable guide attaching etc...

Bagging and Baking Neil's Frame

With all the joints wrapped in Carbon it was time to "bag'n bake".  First step was to close the frame openings with the UHMW plugs.  The plugs also serve to keep the BB and head tube "round" under heat and vaccum.  The UHMW actually expands in the oven and are tight when hot.

Next step was to carefully cover the carbon wrapped joints in release cloth.  I use an Airtech product that has a very fine weave.  I try to make it smooth and wrinkle free but it turns out it does not matter that much.

After that it's time to cover each joint in bleeder material which serves to distribute the vacuum over the joints and soak up excess resin pulled out of the prepreg under vacuum during cure cycle.

The final step before baking it to apply the vacuum bag.  I choose to enclose the frame with a fold between the stay.  It's a bit more work to get the bag sealed but does not apply extra side load to the stays.

Here it is post cure in the oven.  It was hung from the top of the oven but it fell down during cure.  Note to self, get a right angle air fitting for the vacuum seal.  I think the bend in the air hose pushed the frame off when the door closed.  Next oven will have a window!

In the above photo you can see the heat dissipating plate I installed after the first test frame stays failed under vacuum due to localized overheating.  This time there were no issues.

Carbon Wrapping Neil's Frame

With the joint fillets sanded and the frame thoroughly cleaned with isopropyl alcohol  it was time to start wrapping the joints in carbon.  I start with a few pieces that will wrap along one tube and around the other.  This should set a good solid foundation for the joint.

Here is the first piece going on.  It looks nice and easy but this stuff is sticky and fragile and it's being draped over 3D contours.  Working in a cool shop (+12C) the prepreg often needs to be heated lightly with a heat gun to make it sticky enough.

After many overlapping layers you end up with this which I hope turns out cosmetically pleasing (and of course structurally sound) after the oven.

The BB wrapped.

And the Seat Tube Junction.

Tomorrow I hope to get it at least in the vacuum bag if not in the oven.

Alignment Check and Fillets

Once the epoxy had cured I check the alignment of the frame.  I have a fixture that holds the frame horizontally by the BB.  I use a height gauge to check everything.  First I check the seat tube comparing one end to the other. This is how much it was out by...in other words almost nothing (0.008" over 23").

Next I check the head tube using a straight steel rod and cones to center it on the head tube.  I compare the ends of the rod 16" apart to magnify any error on the head tube.  It was not out by much, 0.012" over 16", so I am not complaining.

Next I added the fillets to the frame joints.  I use mixture of DP-420 and glass micro spheres that forms a thick paste.  Here they are prior to and then after sanding on the head tube.

 Since this is the first frame using a Press30 size BB I had to make new UHMW plugs for vacuum bagging.

 Prior to adding the fillets the frame weighed 894g.  With the fillets sanded it was 906g.

Gluing Neil's Frame

The time has come, Neil's frame is taking shape.  I mitered the rear end and prepared all the tubes for gluing.  They've all been sanded with 80G and wiped down inside and out on the ends with isopropyl alcohol.  First step was to install the water bottle bosses.  I applied a little epoxy to the inside of the tube around the hole before inserting the Rivnuts.

Here is the BB joint ready to cure over night.

The dropouts plugs were sanded rough, cleaned and coated in glue.  I also coated the inside of the stays after roughening them up.  I used flash breaker tape to keep excess epoxy off the ends of the stay.

The seat tube junction turned out well.  I used some tape to lightly hold the joint while it cures.  It's important that everything sit at rest in the jig, anything forced could lead to misalignment.

The head tube joint is critical.  I'll check alignment tomorrow and if it's not good enough I'll have to break the front triangle apart and try again.

Finally the whole frame.