P-40LUVR

Im on my first kit...and wondering how smooth do I have to get the fuse so that it looks ok to apply the monocoat?
I have some places that I had to put putty in to cover cracks and low spots.
Thanks!

CafeenMan

The answer is how good do you want it to look? A finish does not fix or hide defects. More often than not, the finish makes defects stand out more.

Fix anything obviously wrong. Sand, sand, sand, sand and sand some more. Always use a sanding block. Start out with 120 grit and sand until everything is flat, smooth, flush, level, etc. Tilt parts so that light hits it at different angles to help show low spots and other blemishes.

Do not switch to finer grit until the only thing left in the wood is the scratches put there by the 120 grit.

Switch to 220 grit and sand until all the 120 grit scratches are gone. Switch to 320 and do the same.

You should be able to run your hands over the entire structure without looking and not feel anything. Before you cover, remove ALL the sanding dust. I use an air compressor to blow dust out of the structure. After that I use a shop vac with a brush attachment to vacuum the outside. A final wipe with a tac cloth gets it ready to cover.

Finishing a plane takes as long or longer than building it. It's not a "last minute" item to do in a few minutes and then cover. It's obvious some people think that way and it shows in the finished product.

P-40LUVR

MERRY CHRISTMAS!!!!
THATS RIGHT...THATS WHY CHRIST IS IN "CHRISTMAS!
CELEBRATE HIS BIRTH,THATS WHY!
DON'T ASK OTHERWISE!

submikester

My Feedback: (6)

What airplane is that you're building there?

Gray Beard

My Feedback: (-1)

Like most of us I just hate sanding but Caf is correct in the hows and whys. In my case I sand until I get sick of it and say it's good enough and it feels smooth. Anything you can feel will show up after covering so you just have to decide how well you want it to come out. Make sure the plane is clean when you are covering, every little piece of crud that you missed will come back to haunt you. Nice looking plane your building too, sure is A lot of planking.

TexasAirBoss

My Feedback: (22)

I generally sand 4 or 5 times, the last 2 times with 400

When you think it looks perfect, walk away and come back tommorrow. You will see something you don't like.

voyager_663rd

And then make sure you get all the dust and loose stuff off. Putting on mono or ultra, those little hunks of crap will cause the cover to stand up like a pimple and you'll see and feel the difference.

Time spent now is cursing saved later.

John Murdoch

My Feedback: (11)

That way, it'll only take five or six years to get done.... LOL

MadScientist

A good trick I picked up not long ago is after your fine sanding is done, take a single square of toilet paper, and hold that between the sanded surface and your fingers as you check the surface for flaws. i don't know why this works, but you seem to feel the bumps and hollows a whole lot easier than with your bare hand. try it- it's amazing how more sensitive your fingers appear to be!

Bob Yeager

My Feedback: (5)

This is a takeoff on the old bodyman's trick of wearing a thin pair of cotton gloves to check a repaired panel for defects not readily apparent to the eye.

P-40LUVR

Sub,im building the Airsail Piper Tomahawk.

Sense963

My Feedback: (10)

These are all great ideas from people who obviously know what's what. Finest compliment I ever received was being a newbie at my field and the best craftsman in the club coming up and looking at my Kavalier and saying, "this was built by someone who knows what sandpaper is..."

splais

My Feedback: (25)

I am beginning final prep on a fully sheeted 35% Edge. This is going to be my "baby" and I want to do a great job. I have read a lot of stuff on covering prep. Have any of you used or feel it is worthwhile to use Balsarite film prep on your models. I have read that it will improve the covering job and help the covering to stick better. For those not familiar with it, it is a liquid that you paint on the wood. I guess it is suppose to seal and strength the surface supposedly. Can anyone comment. thanks.

PS: While I am at it - is there any trick to building a fillet between the vertical stabilizer and fuselage, or is it just a matter of filling in with the appropriate filler and then sanding to shape.

Bax

My Feedback: (11)

One step missed was after sanding with 300-400 paper; you should take a mildly-damp rag and wipe down the balsa surface. Any added fuzz and 'hair' will now stand up and be apparent. It will also remove dust. You can then sand with the next finer grit.

As was stated above, the better the base, the better the finish. An old comment was that quality of your finish was directly proportional to the weight of sandpaper used up.

For film coverings, many people are satisfied with stopping at 250-grit paper. Winning finishes involve sanding to 600-grit or finer...and then not putting dings in the model with the sealing iron!

splais

My Feedback: (25)

So in a nutshell, what would your recommended progression of sanding grits be from start to finish. thanks.

120
220
320
400
600 optional

Do you need this many steps? Actually, for balsa, 120 seems a little strong.

CafeenMan

120 is very coarse for balsa. Coarse paper will bring everything to shape a lot faster.

[link=http://airfieldmodels.com/information_source/model_building_tools/sandpaper.htm]Sandpaper[/link]

CafeenMan

By the way, I take back the 120 grit suggestion. I would only use 120 grit if I were tearing a block down. Normally I start with 180 if I'm block sanding something that has a lot of joints to be brought flush such as truss fuselage sides.

Sorry about the mis-disinformation.

Sense963

My Feedback: (10)

Rob's Rules of Sanding:
1. It's an art, there are no rules.
2. If in doubt, see rule 1.

My feeling is 100-120 is about as coarse as you need, and 320 or thereabouts is as fine as you need. After that, you get into points regarding covering. (I'm assuming an iron-on) There are schools of thought that say you shouldn't iron your covering to large areas, but use a heat gun and some tissue to heat/wipe, thereby avoiding the all-too-common "covering iron marks." Faye Stilley, one of the premier covering gurus will tell you to "polish" the balsa until it shines with fine grade paper, then only attach covering with an iron around the perimeter, as ironing into the wood only brings out the grain (no good) and really doesn't add any strength. Read all you can then decide what works for you.

Kirk RC

My Feedback: (4)

Agree on the sanding. I always go down to 400, and apply Balsa-rite. Also I use a tool called the Wood Pecker, helps miniize air bubbles on the full sheeted surfaces. All that said, the bigger challenge is not to rush the covering. After all the time spent building its natural to want to GET IT Covered NOW. I do a little bit at a time, if Im in the groove Ill cover longer, if its not working out I turn the iron off and take a break. Im currently covering a TF GS P-47 and keep reminding myself that it will take a month so dont rush= cant fly when its snowing anyway.

Sunny_B

Kirk RC
How do you use the woodpecker and not get the multitude of little indentations showing through the covering? I have yet to see a plane where the builder used one of those, that can't be spotted in a heartbeat. I've got one of these treasures, but have yet to use it for that reason. If you have overcome this obstacle, please tell me how. The idea of lessening bubbles is very attractive.
Sunny_B

gow589

My Feedback: (1)

I lean a little more toward using coarser paper to start. I have built a lot of Ziroli and Royal airplanes which require a fair amount shapping. Any time you are doing much shapping (even with balsa) the more coarse the better to start. The reason is something like 120 will leave low spots durring shapping. It is no where near coarse enough to cut down planking without "wallering it out" (I understand that phrase, does everone else?). If you are going to monocoat it or fiberglass it I see no reason for 400. 200 is quite adequate. The grooves in balsa are coarser than 200 grit. I know some will disagree but you will have to experiment and find out what works for you. Try different grits so you can make up your own mind.

Also, always use a block or something to control the surface. Never sand with paper alone!

gow589

My Feedback: (1)

I am also a big fan of Balsa write but a light coat of cheap spray adhesive works well too. For it to work you have to iron to the fues/wings not just the perimeter. This forms a bond and if done right you will see little or no shrinking/wrinkling over time. Great stuff!

Kirk RC

My Feedback: (4)

Sunny,
Heres my process, first sand down to 400 grit, clean off surface put on balsaRite. I then run the pecker over the surface using very light pressure. I have found the teeth will do most of the cutting so dont force the tool or you get to deep/course cuts, use a light touch and let the tool wt do the cutting. I dont overlap each pass, but leave a inch or two space between each pass. I have found that you want each pass to be in the same direction with the grain when ever possible,dont cris-cross this becomes critical because after you "peck" the plane go back and lightly sand. The last sanding (very light) removes those little particals of balsa the pecker pulls to the surface. It sounds like alot of time but I just did a TF-GS-P-47 last night and it only took slightly over an hour. I think the key is that the cuts dont need to be very deep at all. We just need to break the surface so the O2 will disipate. The results are night and day in how the Monokote lays down and you cant see the cuts at all. I have done atleast 10 planes like this with the same excellent results. The part that always surprises me is how shallow the cuts can be and still allow the air to flow, my hypothosis is that we basicly sand the balsa surface closed with 400-600 grit and air cant flow into/through the balsa. The pecker breaks that "surface tension" and allows the air to flow into the balsa, we dont need each cut to be completly through the surface to get the effect.
It works for me.
Kirk
Sorry about the typos cant get spell check to work

DamonTX

Is "wallering" the result of using paper alone or a sponge sander then finding that the balsa was smoothened but the glue joints are still sticking out? I guess a spot where this would be common is on a rounded nose sheeted with say 1/2" wide planks. If this type of area were sanded with a block or bar then the glue joints would be flattened along with the sheeting.

gow589

My Feedback: (1)

Wallering is the result of part of the surface being harder than the other. This could be epoxy glue joints, where hard wood meets balsa, or even harder sections of balsa. It doesn't matter if you are using a block. This came really aparrent when I was block sanding my car for paint. As soon as I hit metal, sanding stopped. If I continued to block sand, it would still "waller" (if you can come up with a better term let me know). With a sharp 60 grit paper it cuts through harder areas such as wood and epoxy glue joints without creating low spots. It is much easier to come up with a final shape.

Added: this is greatly effected by the underlying structure, where the wood flexes and where it does not. Even if you think it's not.

It also cuts down on the work load. Here Is my write up on fiberglassing:

http://www.rc-tech.net/fiber/fiber.htm

I cut the finish with 40/60 grit. It makes fast work and it makes it real even. You just have to smooth it for paint which is not a problem. Cuts the sanding time down by 1/3. Still had an "Automotive" finish when done.

I learned this the hard way years ago. I bought a Royal C-310. When I was building it the plans had me glue several big balsa blocks together. Afterwards it said sand to shape. I spent 30 minuts looking for the missing part in the directions till I figured that they really did mean sand it. I cant tell you how many hours I spent sanding that buger with 100 grit. After that I started experimenting with rougher sand paper. I found everone trying to push 100-120 grit for shapping and everywhere I turned all I could see was surfaces that look like waves and people who had sanded for hours. When I plank the Ziroli airplanmes I wouldn't even think of using 100 grit for shaping. I have also put iron on covering over sport planes sanded 60 gritt. You know what? No one could tell. I think if your sanding 600 grit, your wasting your time.


If I built smaller park flyiers, I might feel differently. The scale of things would make a difference.