HS-609PP Finish: Good enough? Better technique?

[John R. Graham]

After what seems like way to long in the "preparing to build" phase, yesterday was day zero for my RV-7 build. I've completed just one thing: I believe I've satisfactorily completed the finishing of one of the two HS-609PP Rear Spar Reinforcing Bars. I rounded the ends pretty evenly with the Scotchbrite wheel but wasn't able to break the edges evenly with it, so I opted to use a file to break the edges and remove tooling marks. Using long overlapping strokes with the file resulted in pretty even work, but the subsequent sanding of the part seemed to take a long time. I started with 80 grit emery cloth and in several steps worked my way up to 400 grit wet or dry, the latter of which is per the plans, resulting in this (click to enlarge):

Furthermore, the inevitable roughness of the filed area sometimes hid that I hadn't removed all the tooling marks, so I iterated back and forth between the file and the emery cloth. Overall, the prep of one bar took me five hours. That leaves me with two questions.

First, am I working to hard? I'm thinking that I should've used one of the little drill-mounted Scotchbrite wheels that came with the Avery kit or else perhaps I should get one of those grinder-mounted flap sanding wheels. I'd appreciate some pointers.

Second, as the parts came from the factory, there were some less than trivial depth (but still pretty small) gouges on the bars that didn't easily sand out. Here's the best picture I was able to get with my macro lens (click to enlarge):

Should I be doing anything more to these?

Thanks in advance for the advice.

- John

 

[CPSONE]

Roloc conditioning disks

I used 3M roloc scotchbrite conditioning disks I bought from a local auto parts store.
1/4 inch shank fits in my die grinders and super fast to change "grit".
I went over the surface by hand afterwards with a scotchbrite pad to remove any swirl marks that were left. Much faster than hand sanding.

 

[Lou]

It took awhile to get the 609 down to an acceptable finish. I used a vixen file to get the rough shape and then used a 6" Scotchbrite wheel mounted on a harbor freight bench grinder. It really knocked down quite a bit of the grunge work.

My 609 looked as if it had been in a sword fight as well. You really need to get those stress risers (scratches) out. After doing as much as I could with the wheel, I switched over to the red 3M scotchbrite pads and used those to smooth out the gouges by hand for the finish work.

The only concern I had after trimming the ends was the edge distance. It was close, but a call to Van's and they said that the end was not that critical. There are plenty of rivets to back up those end holes.

Hope this helps a bit. Bottom line, the 609's required a lot of elbow grease.

 

[Smilin' Jack]

Hey LOU
I am just a head of you by an itsy bit... just putting the rudder together.
I talked to Ken at Vans and he told me a good piece of advice.
any scratch you can get your finger nail to hang up in need smooth out but then he added there is a fine point between being to much of a perfectionist and not getting the airplane done and doing what is correct and flying.

Like you you probably have read all the priming debates. what kind if any, who thick a finish etc. So I decided to prime with Variprime. works good dries fast.

Good luck on the VS... it is one of the easier things from what I heard.

I have about 75 hours total now with the HS and the VS done and the rudders all primed and ready to go back together.... Started the kit on the 28 of January.

Smilin' Jack

 

[John R. Graham]

...My 609 looked as if it had been in a sword fight as well. You really need to get those stress risers (scratches) out. ...

Lou, that's a really apt description of my 609's, although in a limited area. I'll go back to those areas and get to the bottom of the situation, so to speak.

...I talked to Ken at Vans and he told me a good piece of advice. Any scratch you can get your finger nail to hang up in need smooth out but then he added there is a fine point between being to much of a perfectionist and not getting the airplane done and doing what is correct and flying. ...

I like it! Thanks for that as well.

- John

 

[Lou]

For priming, I started out with MarHyde (self etching). Good finish and it was very easy to apply. The only problem I encountered is when two primed parts slid into each other in a tight fit (rib to spar), it would scratch off. The epoxy primers don't have that problem. They are really tough finishes. Just a lot of clean up work afterward.

My latest priming adventure is with Stewart Systems (water based, easy cleanup). Better than the MarHyde (for toughness), so far. Easy to apply with a Harbor Freight touch up spray gun. Still had a little scratch off problem, but I am thinking that the part was either not fully etched or more probably not fully dry. I was playing in the (cold) garage mid-winter and tended to hurry a bit. Also, when I sprayed, I would preheat the garage to 65 or so and then open the door for ventilation when spraying. Temp dropped like a rock and I was pushing the spraying envelope. The temp probably bottomed out at high 20 / low 30 and the worst that happened was a little roughness in the finish. I used a dry rag and scrubbed the surface which smoothed it all out (internal parts of course).

If the warmer weather does not help, I'll give the VariPrime a try. It's all a learning experience.

 

[hendrik]

My latest priming adventure is with Stewart Systems (water based, easy cleanup). [...] Still had a little scratch off problem, but I am thinking that the part was either not fully etched or more probably not fully dry.

Don't want to steal the thread, but just a short comment from my (limited) experience. I use the Stewart Systems ekopoxy, and while it dries within minutes it takes quite a while to fully cure. I didn't have any scratching problems a few days after painting, but it is certainly not completely cured after just one day.