how to get a highly-polished exterior

I'm not very interested at this time with constructing rockets with a nice paint job (or any paint, for that matter), decals, etc. Judging by the exquisite detail shown in a number of build threads here, this may be a radical statement.

:wink:

However, I'm very interested in learning how to modify a spiral-wound craft-paper airframe to make it lighter, stronger and highly polished - i.e. I don't care what it looks like, as long as it performs well.

Reading around on the forums, a number of people appear to smooth/polish/strengthen their body tubes via the application of various types of glue, putty, etc. Obviously, there are many methodologies here, but I'm specifically looking for some that isn't geared towards setting up the rocket for eventual painting and finishing.

Any tips or advice in this area would be appreciated.

Searching around the forums, a common technique for strengthening appears to be coating the inside/outside with CA. One polishing tecnique made use of floor polish. I wonder if these are the best strength-to-weight mehods? I wonder how effective they might be without intending to paint the rocket?

Marc_G has an exellent thread on using Future/Simple Green to get a shine on a rocket in here somewhere.

Someone will chime in on using progressively finer grits of sandpaper that can give you a mirror finish.

First one must define "polished'' as far as your end use. Are you talking about just a shiny mirror like finish or a aerodynamic finish. What are you trying to accomplish?

For me it was the smoothest aerodynamic finish I could attain for an altitude related project. To do this I wanted all imperfections filled and a true and smooth, slick surface. I thought of it like this: don't add and fill as much as sand & remove.

Fillets were epoxy and made slightly larger than needed, then sanded to final shape. No filler or spot putty. When the final shape was attained a light coat of flat high temp paint was applied to see where I was. Then more sanding, to the point of only paint was needed to fill the scratches left by sanding. It was then painted with several coats of high temp paint & wet sanded with 400 till it was smooooth as a babies butt. There is no gloss coating I know of that can get you a smoother or better than this "polished finish" . It looks like crap but run your fingers over it, then any high gloss finish. There is NO comparison over which is smoother. Note the shine/reflection in the picture.

It may not look good but it is smooth/polished and in no small part helped the rocket go over 22,000 feet.

So if this is the type finish you're after, wet sanding & minimal fill and paint is the ticket.

Bear in mind polished and structural strengthening are accomplished 2 different ways.

You might look into a product called Micro Mesh. I use this stuff for fine woodworking projects and it's like magic. I polish hard woods (ebony, hard maple, etc.) to pretty much a mirror finish - even without ANY finish applied. Most folks can't believe they are looking at bare, UNfinished wood.

Now this is assuming a reasonably hard surface to begin with that CAN be polished. I doubt that paper airframe tubes would work. You would need to put some type of filler/finish on first - thinned epoxy would likely work. Then you "finish the finish". One method I've used in the past is to grain fill with System 3 Epoxy mixed with silica thickener (similiar to what rocket folks do for fin fillets). I scrape the majority of it back off before it hardens with a plastic scraper). Then I LIGHTLY sand the high spots with normal 220-600 grit sandpaper. Then go through the grits using MicroMesh. Absolute mirror finish when done.

All that said, I've never applied any of this to rockets. I've never needed to get my birds that smooth. But you do, so this might work for you.

The product is basically super tough sanding sheets. They are cloth backed and the grit itself is embedded in a type of rubber I believe. You start with the coarsest grit - which is 1500! - and work your way through up to 12,000 grit. Not a typo - yes that's 12,000. It's definately an "elbow grease" type of effort, but after the first couple of grits, the polishing actually goes pretty quickly with each finer grit. The supplied foam/rubber backing block really helps. If taken care of, each sheet lasts quite a long time.

I get mine from luthier's & woodworking supply houses, but I believe Amazon carries the product. Get the kit that has individual sheets and a seperate foam/rubber block - not the smaller individually padded sheets.

Post pics when you're done!
s6

Or.....Method Two:

Do the "grain filling" procedure like what I described above the same way. (SLOW cure epoxy mixed with silica thickener to provide a solid, hard base to be polished).

Then use automotive polishing compounds and buffing wheels. The best way to buff would be actual buffing wheels on a bench grinder, but most folks don't have the infrastructure. Next best is foam type wheels that you can use with a cordless drill. Most auto paint supply houses that sell the liquid compounds (I use Meguiar's) also sell the wheels.

The two main tricks to know with this method:
1) Make SURE that your work is secured - it's really easy to catch a tip the wrong way and send your piece flying. Not good.
2) It's also really easy to burn through your finish and make a mess of it. Go slow, check your progress constantly, keep your wheel "wet", and don't push too hard. Power tools can save you a lot of effort, but they can really screw things up fast if you don't watch out.

Again, more effort than I've put into a rocket project, but I'd love to see your results.

good luck, s6

judo said:

Marc_G has an exellent thread on using Future/Simple Green to get a shine on a rocket in here somewhere.

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I did find this, thank you. For those who read this, you can find it here.

blackjack2564 said:

First one must define "polished'' as far as your end use. Are you talking about just a shiny mirror like finish or a aerodynamic finish. What are you trying to accomplish?

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I'm looking for ways to polish the exterior of the rocket to maximize aerodynamic performance while adding a minimal amount of weight, if any.

blackjack2564 said:

For me it was the smoothest aerodynamic finish I could attain for an altitude related project. To do this I wanted all imperfections filled and a true and smooth, slick surface. I thought of it like this: don't add and fill as much as sand & remove.

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This is exactly the approach I was looking for, thank you. I think that this is a pretty darn good mantra, to wit "don't add and fill as much as sand & remove".

blackjack2564 said:

There is no gloss coating I know of that can get you a smoother or better than this "polished finish" . It looks like crap but run your fingers over it, then any high gloss finish.

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My current hypothesis is that the more finishing products - i.e. primer, paint, etc - added, the heavier the rocket, and the lower overall performance. So looks 0 and performance 10 is definitely where I'm currently headed.

stealth6 said:

You might look into a product called Micro Mesh. I use this stuff for fine woodworking projects and it's like magic.

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Found it here. Given the range of featured applications, this seems very applicable to my problem.

stealth6 said:

Now this is assuming a reasonably hard surface to begin with that CAN be polished. I doubt that paper airframe tubes would work. You would need to put some type of filler/finish on first - thinned epoxy would likely work.

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I was actually thinking of preparing several sample body tube segments with differing structural strengthening methods, such as epoxy, thinned epoxy, epoxy mixed with carbon-fiber and/or cellulose-fiber, various combinations of CA, and finally wood glue. Then perform weighing and crush-testing on each to determine weight versus strength ratios for each methodology.

However, it remains to be seen if I have enough free time for this experiment.

stealth6 said:

It's definately an "elbow grease" type of effort, but after the first couple of grits, the polishing actually goes pretty quickly with each finer grit.

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One problem I'm currently pondering is adding surface irregularities to the exterior of the rocket via repeated applications of, say, epoxy / sanding / flat-coat painting, etc. which would in turn affect aerodynamic performance.

Currently, I'm guessing one way to mitigate this factor would be by using a guide - such as a body tube section cut in half, longitudinally through the axis (resulting in a U-shape) - then glue the sanding medium to the section as a sanding guide.

Anyone every try something like this?

stealth6 said:

Then use automotive polishing compounds and buffing wheels. The best way to buff would be actual buffing wheels on a bench grinder, but most folks don't have the infrastructure. Next best is foam type wheels that you can use with a cordless drill. Most auto paint supply houses that sell the liquid compounds (I use Meguiar's) also sell the wheels.

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I have done something similar using a hand drill on another project, however, I would be highly concerned about putting too much pressure on what, in the end, is a rolled paper tube.

stealth6 said:

Again, more effort than I've put into a rocket project, but I'd love to see your results.

good luck, s6

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Thanks s6, I really appreciate the lengthy and insightful replies.

Depending on how much money you feel like putting into a rocket you could go with a catalyzed clear coat.... I'm a model maker by trade and I do model rockets in my spare time, so I have access to some nice paint. If you want light, idk how light it would be but throwing down a light coat of some tamiya model primer or sparvar primer followed by a nice coat catalyzed clear can make it perfectly smooth.

Tamiya model primer and Sparvar primer spray a very thin coat which would add little weight (I've never cleared something with no form of paint so I don't know how well it would work to clear a cardboard tube). Then spray some catalyzed clear (that's the expensive part). Spray a tack coat (not super heavy) and then wait 5-7 min and spray a nice coat, wetsand that coat smooth and spray one last coat and you can have it be like glass. The catalyzed clear gets much harder for extra strength compared to regular lacquer clear but the price shows.

That advice is a waste though if you don't have a spray booth and nice paint. If you want to go no paint at all you can buy some 3m sanding sponges, fine, superfine, microfine, and a 3000 grit for like $10 on ebay for 1 of each and then some 4000 and 12000 grit to make it like glass with the help of some polish. Hobby lobby sells a nice finishing kit if you go this route.

g3d said:

One problem I'm currently pondering is adding surface irregularities to the exterior of the rocket via repeated applications of, say, epoxy / sanding / flat-coat painting, etc. which would in turn affect aerodynamic performance.

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You will have to add something though. That paper tube itself is likely about as smooth/aerodynamic as it can be already. And it really can't be polished itself. Some sort of "polishable" medium is required, be it epoxy, paint, CA glue, or whatever.

g3d said:

Currently, I'm guessing one way to mitigate this factor would be by using a guide - such as a body tube section cut in half, longitudinally through the axis (resulting in a U-shape) - then glue the sanding medium to the section as a sanding guide.
Anyone every try something like this?

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Yes, this is a good idea, and worth doing. However, DON'T glue the sanding medium in - you will need to either replace it often or clean it out as bits of rolled up finish will ball up on it, and put scratches/gouges in the surface you are trying to polish. DO put some type of padding between the sandpaper and the inside of your sanding caul/tube though - the hard surface of the tube will cause you problems.

g3d said:

I have done something similar using a hand drill on another project, however, I would be highly concerned about putting too much pressure on what, in the end, is a rolled paper tube.

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If you are worried about crushing the tube, you are leaning too hard into it. You can polish a pretty delicate structure with this method if you are careful. The bigger worry is having the wheel catch an edge or point and throwing your workpiece across your shop space.

g3d said:

Thanks s6, I really appreciate the lengthy and insightful replies.

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Yer welcome.....It's what this forum is all about as far as I'm concerned.

One more tip if you decide to use MicroMesh: Make sure that whatever "finish" you end up using (epoxy, etc.), you mix it precisely and wait until it is absolutely bone dry before polishing. Otherwise, you will end up just ruining the MicroMesh and making a godawful mess of your piece.

s6

As an initial test, I performed the following:

1) Obtained a 6" section of 24mm body tube that was left over from scavenging parts from my last build after flight #7 caused the sustainer to buckle.

2) Wiped down the interior & exterior with a damp paper towel, and let dry.

3) Wiped down the interior & exterior with a paper towel, moistened with acetone, and let dry.

4) Lightly sanded with 200 paper, wiped down, and re-cleaned with acetone.

5) Used a cue-tip to apply CA as evenly as possible across the exterior surface, and as far is it could reach into the interior, allowed to dry.

6) Lightly sanded with 200 paper, wiped down.

7) Used cue-tips to apply a second coat of CA.

8) Lightly sanded.

At this point, I could no longer feel the ridges from the spirals in the paper tube. However, I did note a vertical streaking pattern resulting in minor variations in CA application, even though the exterior was highly smooth to the touch. In order to test this, I made a number of cuts using a hobby knife and noted that certain areas of the tube were slightly harder to cut than others, indicating a variation in CA thickness.

By making comparable cuts in a similar section of tube, I was able to easily determine that the treated tube was much harder to cut. From a quick tactile analysis, the treated tube was much more resilient to deforming, and would return to its previous shape, as well as being more crush resistant.

g3d said:

As an initial test, I performed the following:

1) Obtained a 6" section of 24mm body tube that was left over from scavenging parts from my last build after flight #7 caused the sustainer to buckle.

2) Wiped down the interior & exterior with a damp paper towel, and let dry.

3) Wiped down the interior & exterior with a paper towel, moistened with acetone, and let dry.

4) Lightly sanded with 200 paper, wiped down, and re-cleaned with acetone.

5) Used a cue-tip to apply CA as evenly as possible across the exterior surface, and as far is it could reach into the interior, allowed to dry.

6) Lightly sanded with 200 paper, wiped down.

7) Used cue-tips to apply a second coat of CA.

8) Lightly sanded.

At this point, I could no longer feel the ridges from the spirals in the paper tube. However, I did note a vertical streaking pattern resulting in minor variations in CA application, even though the exterior was highly smooth to the touch. In order to test this, I made a number of cuts using a hobby knife and noted that certain areas of the tube were slightly harder to cut than others, indicating a variation in CA thickness.

By making comparable cuts in a similar section of tube, I was able to easily determine that the treated tube was much harder to cut. From a quick tactile analysis, the treated tube was much more resilient to deforming, and would return to its previous shape, as well as being more crush resistant.

Click to expand...

What was the weight of the tube before and after treatment?

Build cleanly

Fill spirals with whatever works for you.

Use primer . . . several coats, sanding in between.

Paint carefully. Wet sand thoroughly dry paint, esp. to remove drips, curtains, runs and other imperfections.

Use polishing compound on the final coat of paint. AMAZINGLY cheap, easy, and effective way to get a glossy polished surface.

Performance preferenced flying would dictate the use of Other airframe forms then spiral wound craft or phenolic paper tubing, simply in the persuit of optium mass.

Many competition flyers have for years used several other media very successfully in this effort in motor classes 1/4a through G. If your intent is to stay within these thrust guidelines where are you going with this?

Many of these alternate airframe materials involved tracing papers, vellums, mylars and 1/2oz/yd single wrap fibreglass body tubes, with Nosecones of equally light weight construction.
Fins as thin as .005" of materials such as fibreglass, carbon fiber, graphite sheet, mica, and some composite combinations with ultra thin competition weight balsa or other core materials. Many of the various fin forms are still indeed painstakingly airfoiled to the unth degree.

The majority of these materials are/were left un-polished while some are highly polished through a hi-speed rotory polishing method involving CA soaked applicators.
This process by the way is a rudimentory method of producing a sort of Phenolic "Plastizied" tube for airframes.

I guess my question is what is the goal in this excercise? If we knew where you'd like to end up prehaps we'd be of more help as much of this stuff has been looked at several times in the past.