Monday, April 29, 2013

Front Repair

Had a small setback with this frame due to a mislabeled tube and neglecting to measure said tube.  The head tube was not 44mm ID.  I noticed just prior to bagging for the oven, removed the pre-preg and baked the rest of the frame.

After grinding and prying off the wrong head tube I carefully replaced it after cleaning up the joint.  Everything was aligned in the jig to the same location.

Here is the new head tube installed and re filleted.
Below is the complete first layer of joint wrapping.
Here it is later on when I apply a woven layer.
And here is the final finished wrapped joint.
I have the wrapping with release cloth process down to only a few pieces now.
I only vacuum bagged the front portion of the frame this time since the other joints were already cured.  I'm leaving more slack in the bag now to allow for it to pull cleanly into the joint.
In the oven, under vacuum and ready to cure.

Sunday, April 21, 2013

Carbon Wrapping

I start wrapping the head tube joint with uni-directional carbon.  I like to use long fibers that wrap around the front of the head tube to anchor the down tube.
I continue covering both sides of the head tube joint with uni-directional and fill in any small gaps to maintain a smooth joint.
I added a small piece of woven pre-preg under the down tube for a little extra strength.
Next I wrap the entire joint in 45 deg woven carbon using one large piece.  I carefully cut the carbon where it meets the center line of the frame and avoid overlap.
After completing the head tube joint with more uni-directional material I move to the BB joint and complete it in the same fashion.
Unfortunately the heat gun I use to increase the tack level and soften the pre-preg broke on a Sunday afternoon so I had to stop at this point.  Look for the complete wrapped frame and bagging process up next.

Sunday, April 14, 2013

Joint Fillets

After the epoxy set on the joints overnight in the jig I removed the frame, checked the alignment and weighed it.  766g is a pretty good start to having a nice light frame.
Before I wrap the frame in carbon I add fillets to smooth the joints between the tubes.  These are made out of 50 micron glass balloons and DP420 epoxy.  I did a quick test in the oven prior to this build and found a newer, easier to mix laminating epoxy went soft below 250F.  I did not want to risk having it move under vacuum so I used the same method I have on all the frames so far.  Here is the BB sanded.
Another view of the sanded BB joint.  I'm trying slightly larger fillets on this frame.
Similarly on the head tube, larger than normal fillets, mostly because the top and down tube almost touch.
Also trying a web between the seat stays on this frame.  It will help stiffen the joint and make the carbon wrapping a little smoother.  Here it is partially sanded.
Once all the fillets were sanded the frame came in at 788g, ready to wrap in carbon pre-preg.

Saturday, April 06, 2013

Frame Bonded

I continued to miter and fit frame components into the jig.  Below in the ENVE chain stay cut to fit the BB and seat tube.  I'm not that impressed with the molding on the ENVE non-tube parts.  The parting line is rough looking, stepped and grooved.
Here is the head tube ready to be cleaned and rough sanded prior to bonding.  I put 3/4" holes in this time.
I cut off the titanium tube extending from the carbon tube, ground. filed and sanded it flush with the tube.  This is a lot easier prior to being bonded in the frame.
This is how I miter the individual seat stay tubes.  The angle and offset from the center of the seat tube are easy to set this way.

First joint to be glued is the seat tube to BB.  A small bead of glue seals the joint face when completed.
Here is an example of the amount of epoxy used on a tube joint.
Finished BB joint ready to cure overnight before an alignment check is made of the whole frame.
I wrap the dropouts and end of stays in flash breaker tape to reduce the amount of cleanup required after bonding.  I don't want to have to sand away too much glue and possibly scratch the anodized dropouts.