Luke, do you sand with a block or just with the fingers?
Do you recommend wrapping the tube with sandpaper, gripping it, and moving it up and down as you twist the tube?
How do you treat a plastic nosecone?
Also, do you recommend any brands of paint?
Sanding is both an art and science... it's not difficult to master with some practice, but there's a few things to know going in. Part of it depends on how well you work with your hands. Some folks are more comfortable and do a better job with a sanding block or rubber sanding sponge or whatever-- if it works for them, good, they should use it. For "newbies" to sanding, using a sanding block or sponge is a good idea, simply until their techniques improve.
Personally, I just use my hands/fingers. I prefer to cut my sandpaper into approximately 2 or 3 inch wide by about 4 inch long blocks... Sometimes I use a sheet or half-sheet flat on the table, for stack-sanding fins and flat sanding edges of parts (fin roots, etc). This works very well for those parts where you need them to be straight and true.
For sanding rockets after priming, there's a few tips to remember...
1) ALWAYS sand in small circles if at all possible... almost like you'd use glass cleaner and a paper towel to clean the screen of your computer. DO NOT sand in straight lines, straight up and down the tube, straight across the tube in a back and forth motion, etc... try to sand in circles right up to the edges of fin fillets and launch lugs and stuff for the best results. If you MUST sand in straight lines (like sanding fillets themselves) try NOT to sand the surrounding fin or body tube... The reason for this is, sanding in small circles prevents deep sanding scratches, which are ESPECIALLY noticeable if they're in long, straight lines... it also removes material UNIFORMLY across the surface, avoiding sanding in flat spots or creating hot spots in the sanding process...
2) Use LIGHT PRESSURE-- let the sandpaper do the work! Sanding with too much pressure on the sandpaper merely generates heat, which is wasted energy and softens the primer or paint being sanded. It also clogs the sandpaper as too much material is being shaved away from the surface too quickly, and the space between the grit particles where the sanded off material would escape between the grit particles is largely squeezed out down to nothing when the paper is pressed hard against the surface being sanded, so the material simply packs in between the grit particles and clogs the paper to the point that it can't take material off-- it simply slides back and forth without cutting. The heat generated "welds" the sanded off particles together and can ruin the paper as it makes it impossible to clean out of the grit. Plus, sanding with too much force causes the grit to cut into the surface too deeply at one time, creating DEEP sanding scratches that will be very hard to remove later on... Never sand with more force than you'd use to say clean your nose with a Kleenex after a sneeze, or apply a Band-Aid to a cut, basically...
3) KEEP THE ROCKET MOVING AT ALL TIMES. This is important to prevent heat buildup, prevent sanding flat spots into the surface and keep from making sanding scratches... what I usually do is hold the rocket or nosecone in one hand, and sand with the other hand, using the paper over my fingertips, going in small circular motions, like if you were cleaning the screen of your cell phone or something like that... I rotate the rocket in my left hand as I sand with the right hand, by simply moving my fingers like if you were rotating a bottle or something in one hand to read the back label or something like that, rotating very slowly. I also overlap my sanding as I gradually move up the length of the rocket while I sand in these continuous small motions, so most of the rocket is sanded in this completely overlapped, constantly moving method... when you get near the fins or around the launch lugs, you have to modify your technique a bit to sand around them, but the same basic motions apply.
It sounds a lot harder than it is... but it's the best way I've found to get a mirror finish on a rocket. Wrapping sandpaper around the tube and sanding up and down will only create sanding scratches and irregular sanding-- some spots oversanded and others undersanded and still rough... so I wouldn't recommend that. If you're doing some early construction-type sanding, that will be finished over with primer, filler, and sanded out later on, then it's not so critical... but for finish sanding prior to paint, DON'T sand the tube this way!
When I'm finishing a rocket, I usually do several steps. Balsa fins usually get papered using white glue spread EXTREMELY THINLY over the fin, and pressed down onto printer paper, which is folded over the leading edge. This is before the fins are glued to the rocket, but after they've been sanded to whatever airfoil shape you desire. By folding the printer paper over the leading edge of the fin, this ensures that the paper cannot eventually tear loose from the fin from the 200 mph plus airspeed of the rocket, with this tornado-force wind ripping past the fins... the secret here is to apply the WHITE glue VERY thinly, just a few drops spread out as thin as you can spread it with your finger works great. Press the fin down to the paper, apply another VERY VERY THIN layer of white glue to the top surface of the fin or to the other half of the paper where the fin will be folded over the leading edge, and then holding the paper taut, gently roll it over onto the other half of the paper. Use a sharpie marker to "burnish" the paper down tightly to the fin, by rubbing out the excess glue and pressing the paper down firmly against the wood. Work from the center of the leading edge of the fin towards the outside edges and rear of the fin, flip, and repeat. Lastly, go all the way round the edges of the fin with the blunt rounded end of the Sharpie marker opposite the cap... this will pull the paper tightly over the edges of the fin and glue it to itself, encapsulating the fin. Flip the fin and repeat this last step, then set the fin aside to dry overnight. Next day, cut the excess paper off with scissors down to about a quarter inch of the fin edges, then switch to a SHARP hobby knife (new blade is preferable) and gently "shave" the paper off the edges of the fin down flush with the balsa fin core along the tip, trailing, and root edges of the fin-- the leading edge should be perfectly smooth, tight, and ready to go. Draw the fin edges across a piece of sandpaper on the table at a slight angle to "shave" any remaining "paper hairs" off the edges of the fins, and voila-- papered fins-- which are MUCH stronger than unpapered fins, and the paper and glue COMPLETELY covers the pores in the balsa wood, meaning no pesky filling and sanding and filling and sanding steps to cover the balsa grain on the fins! Works great... (for more info, see my "Dr. Zooch Vanguard Eagle Beta Build" thread.... there's a complete step-by-step explanation of the process and also pictures of each step to guide you through it...)
For balsa nosecones and transitions, I first CA harden them, using pink-bottle ultra-thin CA glue from Hobby Lobby (cheap) applied outside and allowed to "soak in" as much into the wood of the cone or transition as it can possibly take... but be careful-- the fumes can get mighty strong doing this, and sometimes the balsa can get quite hot if it's got any moisture in it (moisture activates CA). Make sure your CROSSWIND to the parts and doing it OUTSIDE in a well-ventilated area! (If the wind is in your face, you'll get fumes from the parts, if it's at your back, your face will be in the turbulence of the wind whipping around you, which can STILL pulls fumes into your face... hence CROSSWIND). ALSO, be very careful to NOT glue the nosecone or transition to your fingers! Set the parts down on WAX PAPER when you're done and allow to dry (if you set them on cardboard or anything else but wax paper, you'll probably return to find the parts securely glued to whatever they're sitting on!!) They should be fully cured in 30 minutes or so.
Sand the parts with 220 grit to get rid of the hard crusty stuff that CA seems to raise from balsa-- hardened sanding dust from the factory shaping of the cone or part, stray balsa "hairs", etc... sand til fairly smooth with 220 grit to get rid of this stuff. Then apply filler if needed, usually I go with a coat of Elmer's Carpenter's Wood Filler thinned with a few drops of water worked into a dab in a baby food jar until it's about the consistency of hot dog mustard, then brushed onto the cone or transition (or fins, if you don't want to paper them-- harden with CA if desired and then brush on the CWF) and after it's dried a couple hours, sand as much of the filler off as you can with 220 grit, followed by a lite sanding with 400 grit to smoothe the surface out nicely... or go straight to primer, giving it about 3-4 good coats, starting off fairly light and getting a little heavier with the successive coats. Allow to dry thoroughly (usually several hours to overnight, but under certain conditions might take a couple of days, if it's cool and humid). Then sand with 220 grit paper to take about half to 3/4 of the primer off, wipe down with a damp paper towel to get rid of the dust, then switch to 400 grit and sand it again, to smooth the part out and take the primer down a bit more. Then, with a bowl of water handy and some paper towels, dip the 400 grit in water and shake off the excess, and sand the part lightly again-- remember to use LITTLE PRESSURE and SAND IN CONSTANTLY MOVING CIRCLES, and keep the part moving/turning in your hand. Sand as much as you can until the paper starts getting dry-- as it does, you'll notice that the sanding dust is now "sanding mud" since the dust is mixed with water and will get thicker and drier as you sand... the paper will also start to "clog up" and you'll see that the sanding is getting less and less productive... wipe the excess "sanding mud" off with a damp paper towel, dip the paper in the bowl of water, and rub your thumb across the face of the sandpaper underwater to release the trapped paint particles stuck in the grit... they'll wash out fairly easily if you're not pressing down too hard while sanding. Then shake off the excess water and continue sanding where you left off, until the entire part has been sanded smooth. Wipe off the sanding mud, and hold the finished part up to a distant light source, a bright window or light across the room... look at the REFLECTION of light off the part-- you should see that the primer is almost shiny after you've "damp sanded"... the reflection should make a "glint" of light off the part as you slowly tilt it in relation to the light source... slowly turn the part in your hand while observing the "glint" of light reflected off the part... the reflected light should be smooth and straight, even, and unbroken... if it's twisted or appears wavy, or if it changes at a sharp angle or appears to break and move over a bit from the broken end, then you have a flat spot or uneven surface... you can either sand some more in the affected areas to try to level it out, or reprime if necessary... or you can just go with it... up to you! If you see pits or "holes" in the reflected light, you have pits or holes in the surface-- a little more sanding might take them down perfectly smooth. If the reflection is very "hazy" or "scattered" looking, you have sanding scratches and probably need to sand some more to get rid of them-- sand LIGHTER with LESS PRESSURE on the sandpaper... using this technique, you can find MUCH smaller imperfections in the surface than you could EVER feel or see by looking directly at it... essentially this is exactly how a DVD player works... reflecting laser light off tiny imperfections burned into the disks surface, and observing the reflected "holes" and "glints" to transmit data...
For plastic nosecones, it's usually helpful to wash them in soapy water and allow to dry thoroughly, to ensure that the plastic is clean and free of oils or other contaminants that would cause paint adhesion problems. Sand off any "parting lines" from the molding process-- sometimes it's more helpful to just "scrape them off" using the edge of a sharp hobby knife scraped over the parting line like a razor would be... Once the cone is smooth to your liking, prime and sand normally as with the balsa cones.
For the body tubes, first I fill the spiral groove most of the time with Bondo Glazing and Spot Putty... this is the "red stuff" in a tube from the auto-parts store that works VERY well to get rid of surface imperfections too deep for primer alone to take out. Not every tube needs this-- some more than others, depending on the tube size and manufacturer... it's a case by case thing. BGSP is basically just a VERY thick red oxide primer solids (basically, the dust you sand off the primered surface) with JUST ENOUGH lacquer thinner to make it the consistency of toothpaste... FAR too thick to spray on... just daub a little into the groove with your finger, turning the rocket as you go. If you have some big imperfections in the balsa cones, before priming them but after CA hardening them, this stuff works great for filling that too... Allow it to dry for at least 30 minutes, then you can sand it down smooth with 220 grit followed by 400 grit. Works great and the spirals will disappear... I like BGSP better than say Elmer's Carpenter's Wood Filler, which is a fine product for filling the balsa grain in nosecones and transitions when thinned to the consistency of hot dog mustard and brushed onto the parts and allowed to dry for an hour or so, and then sanded down smooth with 220 grit followed by 400 grit... but for some reason every time I try to use it on tube spirals, it seems to sand out of the grooves COMPLETELY and leave them just as unfilled as if I'd done NOTHING AT ALL. The BGSP leaves them filled and smooth, so that's what I use... Once the spirals are filled and the fins on and filleted, and the launch lug glued on and filleted (Don't forget that one!) then I prime the rocket as described before, without the nosecone (which I prime and sand seperately) and then sand it just as I described before...
Remember that a paint job is NO BETTER than the PREPARATION WORK done before hand... IOW, if you do a lousy job priming and sanding, you WILL have a lousy paint job when you're done-- no matter HOW expensive or fancy a paint you use... Paint DOES NOT "cover up" poor finishing techniques and surface preparation-- it MAGNIFIES them! So the primer should look as good as you want the finished rocket to look BEFORE you ever paint the color coats on it!
Now the hard part... You CANNOT get a great finish with poor preparation, BUT you CAN certainly screw up good preparation by doing a poor or sloppy application of the finishing color coats... be sure you paint LIGHTLY, EVENLY, and DO NOT put on HEAVY coats when color painting... practice when you're priming-- try not to make ANY runs, drips, or sags in the primer coats... but don't get "comfortable" just because you can shoot primer without runs, sags, or drips... primer is MUCH easier to apply, as it's thicker and sticks better and dries faster, whereas color paints are thinner, "wetter", and flow easier, thus making it easier to run, drip, or sag... SO BE CAREFUL... if in doubt, better to shoot a little too little paint and have to make another coat or two to cover well, than to spray too much and get a run, drip, or sag...
Remember with ALL this stuff, "practice makes perfect"... you WILL get better with every build, if you practice your techniques, try different things as they occur to you to find the best techniques for your individual style, and pay attention to what you're doing-- what works and what doesn't...
Brands of Paint?? Hmmm... that's an ever evolving thing. I've had some of my best luck with Walmart Colorplace 99 cent a can stuff... I stocked up on it a year or so ago, and I've been recommending it for years... but recently I've heard folks having bad experiences with it, so I don't know if they changed the formulation or what... So buyer beware... it's cheap enough to get a can and experiment on spare tubing or whatever to see if it works for you... Krylon I DO NOT recommend, though I DO occassionally use it as the "paint of last resort", primarily for thier "Bauhaus Gold" which is a VERY close match for shuttle tank foam for scale builds... but I've read TOO MANY horror stories to recommend it... IMHO there are MUCH better paints. I've had EXCELLENT luck with Rustoleum-- it seems very consistent in quality. I used to like Valspar paints until 1) they switched to those gawdawful "twist lock" can atomizers, which belong on AIR FRESHENER more than paint, because they atomize TERRIBLY... (same with the stupid flat-fan twist-nozzle crap on Krylon-- flat fans produce coarser droplets and worse coverage than cone-pattern spray nozzles, ESPECIALLY hollow cone spray nozzles... in point of face, the "el cheapo" button nozzles on the "cheap paints" are actually MUCH better for painting droplet size and consistency and delivery than these so-called "fancy" nozzles). The second thing was, Tractor Supply Company USED to carry Valspar paints with REGULAR button nozzles rather than twist locks, but TSC discontinued carrying Valspar and has switched to "Majic" brand paints, and I have no experience with them. Have to give them a try and see what I think. Probably the best paint is Rusto or Dupli-Color... but be careful... these paints come in BOTH lacquers AND enamels... DO NOT mix the two, or you'll regret it... You CAN apply an enamel OVER a lacquer, but NOT the other way around-- DO NOT try to put a lacquer over an enamel or you'll most likely have a RUINED paint job on your hands-- completely alligatored. IN fact, the fastest way to take off a ruined enamel paint job? Wipe it off with a paper towel soaked with lacquer thinner! (beware of melting plastic or foam parts though!) You CAN apply a lacquer over an enamel IF you're an absolute painting ACE... but it's NOT a beginner or average painter technique, so I WON'T recommend trying it!
That's pretty much it... Good luck! OL JR
