SonexBuilders.net

I hope the photo came through…I haven't tried this before. I have a feeling it didn't so I'll put it on the Expercraft website too. (websites.expercraft.com/cdgundy)

I started to polish with F9, using the instructions from Sonex and watched the EAA video. After 1 hour the results were so disappointing I figured I must be doing something wrong. The photo shows dark spots on the surface. Did I use too much and if so how do you fix the problem? Did I not use enough?

I polished the recommended 30-45 seconds on a small area and after no noticeable change, kept on buffing. After about another 30 seconds, the dark splotches began to appear. After wiping them off with mineral spirits, I tried again using less F9. Same results. Wiped off and tried again using less. Same results.

I'm not using much pressure on the buffer which is the Harbor Freight model with adjustable speed. I'm only guessing on the RPM based on seeing the video. After an hour of trying I gave up. Yes it is a bit brighter than the other untouched side of the tail, but not much. Also, I had a few scratches before I started which I thought had been sanded out with 600 grit then 1200 grit, but the buffing really shows up ANY small scratch. It really looks crappy.

Any pictures and suggestions would be most appreciated.
Darick Sonex #1646

/Users/darickgundy/Desktop/polishing.JPG

Personally I have not had any luck sanding out scratches. Just makes things worse. Nuvite says their polish "lays over" the grain of the aluminum, rather than removing material. So sanding removes the grain and there is no longer material to "lay over" with the polish.

As for the polishing, as a reference you should be able to do a good first pass with the F9 of a 2'x2' area in just 10 minutes. Some hints:

- For the initial F9, polish everything while the sheets are flat, before you bend or form them. This will save you a lot of grief and time. It's hard to polish right to the edge of a piece since the polishing head wants to grab the edge, so you might consider rough-cutting your sheets about an inch larger (when you can), so you don't have to go to the edge. After polishing you can draw the final part of the aluminum with a Sharpie and cut it out. You can't always do that, but when you can, it helps.
- Use the real lambs wool polishing heads. Nothing else seems to work nearly as well. You can reuse them by cleaning with TSP in the washing machine (but run a couple of extra cycles of the washing machine before you attempt to put any clothes back in!).
- Dab the F9 on in small areas 4" to 6" apart. More is not better.
- Start with low speed to spread the polish and avoid slinging it around.
- Word on an area maybe 6"-8" high 12" to 18" long. You can modify those number to go larger once you get the hang of it.
- I hold the polisher (same one you have) at about a 45 deg angle so only the edge is touching.
- Once the polish is evenly spread, turn up the speed to medium-high.
- Move slowly back and forth and do NOT stay in one spot. You will overheat the metal and the polish. Keep moving, slowly.
- Now you can angle the polisher a little less, like maybe 20 deg to 30 deg.
- After a couple of passes you should see the F9 start to go away and the shiny aluminum appear.

No "one" technique is "the" technique. You will get other opinions on the above, and they will likely work as well. These ones have worked for me, and I've polished every bit of exposed aluminum skin (except under the fuselage; who's going to see that?).

http://www.mykitlog.com/users/category. ... egory=5563

Mike Smith
#439

Same here -- I've sometimes had polishing efforts that quickly showed results, and other times just like Darick described where it seems to get worse and nothing helps. It can be frustrating trying to get it to work as easily as the video shows.

I completely agree with all of Mike's points (an excellent write-up), but the one thing in particular he said that seems to matter most is the bonnet type ("use the real lambs wool polishing head"). It's a night and day difference between the synthetic and wool bonnets. And in addition to that, even with the right polishing head, there seems to be a magical point where the bonnet has the right amount of polish loaded in it. I still haven't figured out when is the ideal point to clean with the spur, but for me the polishing seem best somewhere around 15 minutes after starting. Also, heat buildup definitely seems to affect the results as well: I get the dark splotches you described if I go too long or too much pressure. If the polish turns to black tar with a heavy consistency, you've already gone too far.

-Steve #1363

When things start going wrong for me while polishing, I get out the mineral spirits and clean the aluminum with a microfiber towel until all the old polish (and other contaminants) are removed. There could be oils or wax build up on your parts. Given that you sanded, I would spend some time cleaning first. Keep practicing, it will eventually become second nature. After you have a nice polish job, nuvite makes a cleaning product that I use to get the bugs off and right before I do maintenance polishing.

-Jim W0162

Thanks Jim, Steve, Mike. I tried again today and had a lot more success...pictures and comments are on my website (websites.expercraft.com/cdgundy).
I polished the vert. tail skin after all the rivet holes were drilled and disassembled for deburring. The aluminum skin was laying flat on my work bench. As the buffing wheel moved over the holes, the holes collected or grabbed the fibers and polish leaving streaks behind each hole. In order to prevent contamination with the finer compounds, I had to make sure all the F9 was cleaned off, even on the backside of the skins where the polish came through the holes. I'm thinking it may be easier to polish after the skin is riveted to the framework, which is how I'll polish the rudder.
Darick
Sonex 1646, TD, CS, AeroVee

Darick,
I polished my tail prior to riveting. I had streaks around the holes, but hit the holes from all directions and afterwards it buffed out nice with a cloth. I did not clean the back side until I was ready to rivet. I used cheap HF 7" bonnets, they claim wool, but may be a wool-like substance. They worked good as long as you switched to a new one when they got gunked up. I went through 5 of them for the stabilizers (2 for the Waiex). I did 2-3 passes of F9 and 1-2 passes of C. I was not looking for perfection, just most of the heavy work prior to riveting. We leaned in pretty hard on the skins. They did heat up, but not so much that they would warp, and waaaaay below the temperature where material properties would change.

I pretty much followed Kerry's video to a T, using F9, Nuvite brand wool pads, and a spur to clean/fluff the pad regularly.

It took me 3-4 hours to really feel like I had a handle on it.. one thing I was doing before was using too much polish, and reapplying it before it was actually used up. It seems to me that the best polishing is actually had when the polish is just starting to dry up and pick itself up... i.e. when you're polishing at the point where it's just starting to look clear as you move across the surface. If you stop and reapply before that point you're missing out.

My results in the following link. It took me 7 hours to polish both Waiex ruddervator skins, the rudder skin and both turtledeck skins (this includes setup/cleanup time.) I went slow and probably got the most out of what F9 can give before moving on to C grade (don't have any yet.)

http://www.rynoth.com/wordpress/waiex/2 ... polishing/

I also had the hole streaks, but I paid special attention/got the most polishing done around the holes since that's a spot it'll be tricky to polish once riveted. Mineral spirits cleaned everything up (a messy process in itself.)

I polished one flap and spent about 5 hours on it to polish 3 sides (even the short hinge side is polished) with an Harbor Freight polisher. I did revisit the Kerry Fores Hombuilders polishing video as well for a refresher.

Previously, when polishing my elevators and Horizontal stab and vertical stab, I polished the skins before riveting with clecos in them, moving the clecos as needed to polish. This time I riveted first and then polished. I can definitely tell the difference with the small area around the rivet being much better when polished before riveting.

After 4 or 5 passes (I really was not counting, only working the areas as they needed more work) with the F9 polish and a few passes of C on the top side of the flap, I have a good distortion free finish, but you can still see swirls in the finish, which hopefully the S grade will take care of after the polishing. I think some of those fine swirls from the C grade are when your bonnet starts to load up with polish, so I am a believer in using the spur to clean it regularly while polishing.

I had some deep scratching on my skins from the skin slipping in my metal brake when I bent them, those scratches are still there, but not so noticable with the polish unless viewing from an angle. I did work them a considerable amount of time as well. Some of the minor scatches did seem to go away also. I am hoping with continued polishing they will improve. My plane is not being built to be a show plane anyway, but a frequent flyer, so I can live with blemishes in my finish. Those may not be as noticable as possibly some other oofs in my build anyway. ;)

I have to say, polishing is no doubt a long and tedious process, but I feel the results are worth it. I really don't dread the work either as it has the reward of seeing improvement as I go. So as not to spend so much time on my feet and helping save my back a little, it helps me to have a stool to sit on when you are working on the smaller parts to make the process a little more comfortable, which that will only happen on the wing while working on the edges, which will save your back for when you have to reach over to do the middle.

Another thing I do during the long hours of polishing, is think about the next part of my build I will be working on, or details, or think how nice my plane will look all polished up at the places I want to fly it, maybe glancing at a reflection of the clouds in my wings, and other times possibly hiding from the suns reflection on it. what ever helps make the time go faster. I am sure everyone has their own methods. :)

Here are a couple of pictures of todays experience.


This is the before and after view, one flap raw and unfinished.


This is the closer view. Nice reflection of my hand, but there are still some swirl marks and imperfections. This is after the C grade on the top side of the flap. Lower sides not readily viewable will only have F9 polish and that is all.

That looks great Vic! Job well done!

Do yourself a favor and ploish the bottom well before assembly. Trust me, you do not want to polish laying on the ground holding that polisher above you. Ask me how I know!!

Just to confirm what others have said: Polishing sheets in the flat is the way to go. You can use quite a bit of pressure when sheet is laying flat on table, enough to deflect the backing pad when held at an angle. Confirmed this with Nuvite rep at Oshkosh, Do not expect them to recommend higher pressure as someone will try it on an assembled part and end up with all the ribs showing. Do clamp the sheets to table when polishing especially the smaller ones. Not good to have polisher throw these across the room.

One think i did not see mentioned, the polishing pads. These must be the twisted wool type, like found in carpets others do not work. If in doubt get at least one pad from Nuvite to compare. I used total of 4 pads, two for each grit to complete job. Second one of each still very usable.

Working in small areas of about 1 ft x 2 ft. seems best. I dab on compound with throw away 1/2" brush one dab every 5" or so. I then use very slow speed to smear the stuff around then up to about 2,000 - 2,500 RPM until the compound has mostly been rubbed away. Move polishing head slowly, about 5 - 6 seconds for 2 ft. With proper pressure and angle, you will polish about a 2-1/2" swath per pass. After finishing each spot, I lift off and run polisher up to its 6,000 RPM Max to throw off accumulated compound and aluminum. Do this outside, no one said this was a clean job. About three times over with the F9, followed by 1 to 2 times with the C grade. Final polish with orbital polisher, Cyclo or the like does not need as much pressure, and can be done after assembly.

I found polishing in the flat quicker than painting and prep for same. Did paint areas hardest to keep polished, under side of my wings and tail plus all moving control surfaces. Under side of fuselage is polished which meant only wings, tail and fiberglass bits had to go out for painting and no problem hoisting fuselage to paint under it.

David A.