Thursday, December 30, 2010

Test Frame

It's time to build a test frame.  I collected some appropriate tubes and substituted some 1.75" OD for the BB and head tube.  Step one (well, actually about step 17) is to miter the tubes to fit in the jig.

Here I fit the head tube to the jig with the new oversize locating cones.

Below you can see the mill mounted belt sander in action cutting the DT to HT joint.  I hold a shop vac with a fine particle bag installed next to the belt/tube to catch the carbon and epoxy dust.

I built the mitering fixture so the tubes could be removed with both the holding blocks locked in place, one on each end of the tube.  This allows me to test fit tubes in the jig and return them to the mill in the same location if further cutting is required.  Here you can see the DT with it's holding block in the jig.

The finished BB joint with the other miter block shown.

The front triangle fit in the jig.  Next step will be to miter and fit the rear end.

Sunday, December 12, 2010

Break Time II

After the side load I tested the in plane bending (trying to pull the joint apart in the the plane of the frame).  I used split blocks to support the ends of the tube and a 4' solid steel pry bar to apply the load.

 I applied almost 1/2 my body weight to the joint about 4 feet from the support block.  So, the joint was under 300+ ft-lb of torque.  After alternating this load in opposite direction a few times there was a cracking sound and this small flap of carbon pulled free.  Also, a small crack curved under and along the joint fillet..

One good hard heave (probably over 400 ft-lb) and the joint cracked further.

Eventually if failed completely...

Break Time

First you'll notice the custom patent pending "distributed loading system" employed for this test.  I stood on the test joint suspended between two frame tube blocks.  This resulted in 170lbs being applied.  Nothing happened.  I then pulled up on the nearby work bench and applied more load...and more until I could not pull any harder.  Other than a tiny deflection there was no damage.  Repeating this later with a bathroom scale sent the needle off dial over 340lbs.  So, 350lb sideways load test passed.

Sunday, December 05, 2010

Finished Finishing?

I hand sanded with 240grit emery strip then used a cloth buffer wheel to smooth out the surface. Not perfect but good enough to prove I can produce a good looking joint with practice.

When it's wet you can see the uni-directional carbon finish. It would look good if it was clear coated.

Epoxy "Painted" Joint

Here is the test joint after initial sanding with a coat of clear laminating epoxy "painted" over the surface. I will sand this down until it's smooth or I hit carbon (when the sanding dust turns from white to black).

Friday, December 03, 2010

Sanded Joint

I quickly sanded the joint to take off the epoxy flash and the high points etc. I didn't take too much off so I would not cut away fibers.

I'm going to "paint" the joint with clear epoxy and sand that to get it cosmetically smooth. The top side of the joints turned out well with little sanding. The underside had a void in one area that will have to be filled.

Once I make it all pretty it's time to break it...

Unsanded Joint

Here is the joint after pulling off the vacuum bag and unwrapping the release cloth and tape. Seems to be good compression this time with a just a few small voids at the root of the underside fillets.
This side (that was facing up in the oven) did not seem to be as compressed. It lacks the even pattern from the release cloth you can see on the other side. It appears well consolidated though.

Thursday, December 02, 2010

Vacuum Bagging

After reading about Nick Crumpton's methods here
I decided to try to bag the whole joint this time and not seal off on the tubes. You can see little wood caps taped on the tubes I put there to keep the bag from sucking in and breaking.
This is at 20 inHg and it went to 26.5 inHg before it went in the oven.

Here it is resting on a block of wood ready to bake.

Seat Cluster Test

I'm trying larger fillets (Aeropoxt Light fairing compound) over the glued joints to see how the carbon layup works with them.

Here are the first few layers of 150g/m^2 unidirectional prepreg being applied.

And here is a the finished joint. I tried to be aware of the final cosmetics of the joint as I went. Time will tell how it looks and performs after it come out of the oven.