Sunday, November 21, 2010

Out of the Oven

Here is the joint out of the oven. It sat at 200F for 2 hours after ramping up for 30 minutes. The bag, release ply etc peeled off fairly clean but I'll use some flash break tape next time to keep the tubes clean in the first place. You can see in the photo below I had some bag pressure issues. A small hole developed right at the inlet tube and the pressure was 15-20inHg (or about 10pis) when I it took it out of the oven. The shiny area is where the release ply was not being pressed into the joint.

On the top side though, the joint is well compacted and solid. I found that tapping on the joints tells you a lot. You can tell the uncompressed areas by sound alone.

While not pretty yet (these are un-sanded) and not fully compacted the main tube joints feel strong and stiff. Destructive testing and cutting it apart will tell the whole story though.

Joint Test Vacuum Bag

Here is a BB test joint I've prepped for the oven. I used 3 pieces of Stretchlon 250 bag material and 350F rated bag tape. Under the tape is release cloth with a very fine weave, then the carbon prepreg layers. You can see the UHMW plugs I use in the BB to run the bag and seal tape onto.

It took about 10 minutes to get all the leaks sealed and I was able to pull 26mmHg on the pump. The bag did it's job and stretched nicely into the fillets. The release cloth appears to be enough of a bleed layer on a bag this small, everything was pulled down tight.

Friday, November 05, 2010

Head Tube Cure and Finish

After applying 10 layers on the mandrel I used the lathe to hold the it in place and slowly turned it by hand to apply the release coated shrink tape. I'm carefully overlapping 75% with the previous turn for better compressive force and a smoother ridge free finish.

Into the oven it goes...

Here it is straight out of the oven with the shrink tape removed. Notice the left hand end, that's where the masking tape holding the shrink tape in place let go and allowed it to slip. Good thing I made the tube a little longer than required.

Back in the lathe I hand wet sand the outer surface and square the ends with the lathe tooling. Wet sanding eliminates the dust issue (as long as you protect the lathe from the splashing).

The finished headtube. It is ridiculously stiff and weighs 50.3 g.

Head Tube Layup

After calculating the thermal expansion of UHMW for the temperature delta of the cure process I decided to layup a headtube for Chris King InSet headset press fit ID of 44mm.

You can see the layers below, 10 in total, alternating between 0 deg and 90 deg.

The next two photos show the wrapping process as the carbon sticks to the previous layer and the backer is peeled away. Working in the shop around 50F I had to use a heat gun to increase the tack level of the prepreg in order to get the wraps to stick and conform.

The finished layup ready to shrink tape.