Test Priming Day 3

Woke up this morning and checked the 2K epoxy primed pieces. No question that this primer is tough! Resists scratches. When I got home from work...tough as nails (after 23hr dry time). The only concerns that I have had all day was with respect to metal prep. I phoned a friend who owns a local autobody shop. He confirmed to me that the two part epoxy primer was his recommendation for the job, however he indicated that he saw no need to apply alumiprep, but was fairly certain that Alodine was a good idea. He said that is the process used in aviation that he was used to seeing. He indicated that the process helps open up the aluminum to accept the primer. I am convinced that it is superior, however I have serious concerns with applying this method at home. Alodine is extremely nasty stuff, and the application process requires Alodine to be washed with clean water. How do I do that in winter? Do I want to Alodine in the house???

I've been looking at Endura Paints under aviation primers and they have two recommended methods for preping thin aluminum. The Alodine method, or a Biodegradable method using a cleaner and a Metalink product. According to the data sheet the metalink is waterborne "Endura MetaLink is an environmentally friendly, chromate free, pre-bond adhesion promoter for bonding metal alloys such as: Aluminum (#2024, #5052, #6061, #7071 and #7075)". The only concern I have is a lot of parts are alclad....not alloy....So how will this work? Hmm. Geezze my head hurts.

Update - 10:00pm Epoxy test pieces are great. Can't scratch a thing on them. I have tried to wipe them with MEK and virtually nothing comes off! 

Test Priming Day 2

Just after midnight  (about 7 hrs after spray) I checked the primer, scratch test has improved greatly but I was able to scratch it although considerable pressure was required (See bottom left corner). I work up this morning and checked the sample primer pieces. The primer has hardened to a point where it is really difficult to scrap with a finger nail (See bottom right corner). Almost no primer was scraped off the aluminum despite great effort.  When I got home from work (23hrs after spray) the test piece was not able to be scratched with a fingernail (see right side). Only when a screwdriver was used could the primer be scraped. (see center)

After 28 hours, I tried to remove the primer with a moistened towel. MEK and Acetone took the primer of the Aluminum very easily. The degreaser took a bit of rubbing in order for the primer to be removed. Gasoline had no effect on the primer. using a light colored cloth there was no transfer of dark primer onto the cloth...Didn't expect that. I prepped four new pieces of aluminum with Acetone, MEK, Degreaser and one just plain scuffed and wiped dry. Acetone seemed to evaporate almost immediately, more so than the MEK. I let the pieces dry outside for a while.  Then I sprayed two coats of Spray Max 2K epoxy primer. The primer application was really smooth and covered well. It occurred to me that in comparison, the Dupli-color required 2 heavy coats to cover, while the 2-part epoxy covered a bit better with only one pass. I waited 30min for the second coat. I noticed that the pieces took time to be dry to touch, after 30min the pieces where still a bit tacky.  (Note: The placement and timing of the scratches is the same as the sequence above.)  After 1 hour, the primer was able to be scratched with a fingernail. It seemed more like I was removing the top layer of the coat as I could not scrape down to aluminum. After  4 hours, the scratch test is similar to the Dupli-color after 24hrs. You have to press extremely hard to scratch with a fingernail, even then you only seem to be distressing the top layer....not quite breaking through the top layer.

Test Priming

Stopped by Southtown Auto/Napa and Canadian Tire today to pick up some test priming materials. Southtown was a good source of 3M scotchbrite and ProFrom professional paint supplies. I picked up a bunch of scotchbrite reloc pads and a reloc holder. I picked up a roll of aluminum from Canadian Tire as well as a can of Dupli-color Self Etching primer.

I begin with cutting up the aluminum into roughly 6" pieces. My first test was to see how the scotchbrite pads worked on the aluminum.  I used a 3" reloc scotchbrite wheel on the test aluminum, and it seemed to really scuff the aluminum with deep scratches. I immediately sensed that this is not the answer to prepping the aluminum. I then used some maroon scotchbrite hand pads to scuff the aluminum. Much better results. The surface preparation is more smooth and gentle. 

I cleaned one piece with MEK and one with the Proform Wax and Grease remover. I noticed that the MEK seems to evaporate quickly, while the degreaser/cleaner stays more wet. (Using an individual microfiber cloth for each, I wiped all excess liquid off and set them outside to dry for 20min (~23deg C and sunny). The Dupli-Color self etching primer was applied in two coats, the second being applied 10min after the first coat (as per the directions). The result is that after 45min dry time, both are easy to scratch with a fingernail (top right corner). After 3 hours the primer is becoming more hard, both are becoming difficult to scratch. It took a few tries and lots of pressure with the thumbnail to scratch the primer (top left corner).

More Tools!

I noticed that Canadian tire has some tools on sale this week. I picked up a digital caliper for $14.00 and a 5" vice for $44. Great deals! Looked on the internet at paint schemes. A bit early to be looking at that, it's just fun though. Reading some more builders logs on the Empennage construction. Getting a sense of the construction order. Metal prep work, drill debur, etc.  Clean, Prime, Dimple.  Been researching more on primers....wow, my head is spinning. There is no end to figure out a decent priming job. Some guys swear by rattle can primers. Aircraft spruce and Canadian Tire both sell the same Dupli-color self etching primer. Epoxy primers seem good, but reading Endura Paints process on cleaning the aluminum prior to application is nearly a full days process! I think I may be wise to conduct my own priming tests. I see Canadian Tire sells rolls of sheet aluminum, I guess  I have a project to work on before my tools and kit arrives.

Also been trying to find a 3M cut and polish wheel for a pneumatic die-grinder as well as a 6" wheel for the bench grinder....The search is on! (P.S. The problem with reading all the forums on building the RV is that most of the products are only available in the US, or available from Aircraft.ca with huge shipping charges!!!)

Tools to look at buying: A pneumatic cleco gun, a 3M cut and polish wheel for a die grinder, and #40 and #30 drill bit reamers.

Buying more tools!

Have set up the garage more. Went to home depot and IKEA. I bought a small table on rollers and also bought a bench grinder and sanding station. I have been reading up on methods of sanding. To my surprise folks seem to be using a course grit sandpaper (60-80) but the FAA Acceptable methods indicates 150 or finer. More reading suggests that Aluminum Oxide sandpaper is acceptable. However silicon carbide abrasives are not good to use as the silicon can contaminate the aluminum. Black sandpaper contains carbon, which can accelerate corrosion. Steel wool on aluminum is not acceptable either.

Ordered the Empennage!

Well, today is the day. I ordered the RV-7A Empennage with electric trim and some practice projects and some tools (Boelube, 3m tape and scotchbrite wheel, 2 practice kits, Aluminum Tool box).  Getting excited!

Been researching deburring methods. Seems critical that all aluminum edges are properly deburred. The rule of thumb is that no metal edges should cut fingers. There is debate on the forums about deburring lightning holes.

Found a great chart

SCOTCHBRITE GRIT CHART

7445 - White pad, called Light Duty Cleansing - (1000)
7448 - Light Grey, called Ultra Fine Hand - (600-800)
6448 - Green, called Light Duty Hand Pad - (600)
7447 - Maroon pad, called General Purpose Hand - (320-400)
6444 - Brown pad, called Extra Duty Hand - (280-320)
7446 - Dark Grey pad, called Blending Pad (180-220)
7440 - Tan pad, called Heavy Duty Hand Pad - (120-150)

Still getting organized

Stopped by Sherwin Williams today on my way home from work to ask about primer. The girl behind the desk said that the person to talk to (Chris) was away and should be back next week. I stopped by Home depot and princess auto to look at more tools (Drill Presses, Parts Bins, Paint guns, etc.) So far princess auto looks like it has a ton of tools for metal working. Looked at vices, dollys, air hoses, everything. I need to go back and by some parts bins. Worked on organizing the basement storage room. Threw out old tools (old pop rivet gun, old pop rivets, etc). Want to make sure no old sub standard parts filter into the build inadvertently.