Saturday, December 9, 2017

Chapter 25 Finishing - Wings & Canard

I've been doing finishing work interspersed with other tasks.   My short term goal is to get the epoxy wipe done to protect the surfaces.  Then before priming, sand with 220.  I'm using West Systems and read several of their instruction manuals several times. I think a there's a few paint jobs that didn't last very well because bad advise was given.  West states that the last sanded epoxy coat over the filler makes an excellent substrate for polyurethane paint.   Logically, the sooner the surface can be made smooth, the better.   Primer is heavier than filler.  A smooth glass surface takes less filler.
I tried to do most of the sanding outside, but occasionally the wind would cause the air to flow out the large doors.  Applying the epoxy at night outside tends to draw bugs, so having the lights up high and working indoors reduces contamination.

Sanding outside at night has a benefit of making it easy to find the low spots by shining a shop light down the surface.   It also reduces the huge mess the dust makes.   The granularity of the dust from 36 grit isn't bad, but 80 and 120 grit starts to make really fine powdered sugar type dust.  Fans placed off to the side help keep the bugs and dust from being a nuisance. 
I applied a "cream coat" to sand off before doing the epoxy wipe.  Most of this gets sanded off but since it is epoxy rich, helps fill in any pin holes, drag marks and low spots.  Where the light is shining off the surface, you can see a smudge from my finger wiping on the surface.   This indicates amine blush.   If left on, it tends to load up the sandpaper, can cause problems with epoxy curing if applied over it and also cause yellowing.  It cleans off with a little soapy water.

Two padded saw horses, an output table and a shop light stand with a pad helped position the wing so the bottom could be sanded on without any rocking.
One of my Paulk work benches with 3/4" pegs works nice to hold the canard on the trailing edge so the leading edge can be worked on easily.   The shop light shining down the surface reveals some low spots that are probably only .004".   I'll do another fill/sand.
I watched a bunch of Eastwood videos on prepping and painting and decided to clean the dust and debris off with a mix of water and alcohol and let it dry.  Without doing this, when micro or epoxy is applied over a more dusty surface, the dust thickens up the micro as it is squeegeed and the excess is reapplied to bare areas.

Chapter 21 Strakes - Fuel caps

These are not the plans Usher fuel caps.  Several folks recommended the Newton caps because they don't leak and you can use just your fingers to remove them for fueling.  Locking versions are available.  The two hole saws (2 1/4 and 2 1/2) worked well.   Cut the 2 1/4 hole through the top layer first but not through the inside skin.   Then make a cut with the 2 1/2 hole saw just through the top skin and then clean the foam and micro off the glass where the flox needs to bond.  In retrospect, installing these caps before glassing the top skins on is probably better.   You can more easily decide where you want the caps to be.   Also you'll have less debris in your tanks.  I'm not sure how well the caps would hold pressure for the leak test.   
Don't try to clean the debris out with a vacuum.   The air rushing into the opening will scatter particles everywhere in the tank.   Vance recommended this duct tape trick.  I also used some wet paper towels to mop up the junk that fell in.  A long skinny dowel worked good for dabbing with duct tape and "mopping" with the damp paper towels. 

Flox filled in the gap between the skins for a glass to glass bond.  Then the neck was cleaned with alcohol and then buttered.   A short piece of pop sickle stick with electrical tape just long enough to catch the inside flange was wired to the longer stick.   The neck was buttered with flox and gently allowed to settle down through the flox.  The extra that squeezed through dropped onto a paper towel inside the tank.   Visible flox that was dripping was carefully extracted before it hardened.   The neck needs to be oriented properly.   The top surface of the cap will slightly higher than the strake surface when they're installed.