I need a better tube sanding technique

[4regt4]

Backstory: I'm building a 2.6" rocket with PML phenolic tubing. It has world class spirals. If you yell into them, you can hear an echo. They seem to have a square cross section. I filled them with Elmer's CWF, and, yes, I completely filled them. It was mounded up above the tube surface. However....

When I sanded them down, it seems that the sandpaper "dipped" into the crevasse, er, I mean spiral, and sanded away some of the CWF. Probably due to uneven pressure from my hand or fingers. So I still have spirals, but just not as deep. I need a better way.

It would seem that some rigid sanding block would help, but a flat block on a curved surface isn't likely to provide even results. At least not in my unskilled hands. What would be perfect is a contoured sanding block, with curvature matching the tube diameter. Nobody seems to sell them, and I don't really want to try and make something just for this one rocket. I tried a foam backed sanding block, not much better results.

Ideas?

Hans.

 

[OC-Patrick]

...thinking out of the box (and maybe someone has already done this), but we paper wood fins not only for strength but also to eliminate the wood grain and help in finishing. How about papering the entire body tube?

 

[4regt4]

That's certainly an idea. But if I'm going to laminate it, I might as well go with fiberglass. It's past the stage now where any laminate would be reasonably easy to apply - fins are on, and there is an initial coat of primer.

Hans.

 

[SolarYellow]

If you sand with any flexibilty to the paper and the surface you're sanding has differing hardnesses, the softer areas will have more material removed than the harder areas. This is even evident when sanding filler-primer into lower layers of regular primer/paint/plastic.

In the situation you're dealing with, I'd just use a hard, flat sanding backer, like a piece of wood or an aluminum sanding tee. Once you get to where it's close to level, rock or roll the sanding block around the tube as you move it. Never just hold the sanding block at a fixed angle relative to the tube as you move it or, as you surmise, you'll end up putting flats on the tube.

Once you have primer on the tube, I'd try this, for $5 at Walmart:
https://www.walmart.com/ip/Bondo-Glazing-and-Spot-Putty-00907ES-4-5-oz-1-Tube/16927984

I wouldn't expect CWF to stick very well once any paint is on the tube.

A further option for the bare phenolic might be to try to get the CWF closer in hardness to the tube by mixing it with wood glue before application. I've never tried this, I just made it up as I'm typing. But might be worth trying if using CWF on harder materials than paper and wood.

 

[Hobie1dog]

Get a black foam sanding block made for auto body called Dura-Block, they come in lots of sizes but I have found that the 12 inch one seems to work best.
https://www.amazon.com/dura-block-sanding-blocks/s?k=dura+block+sanding+blocks
they make adhesive backed sandpaper that is the same width that comes in rolls and all different kinds of grits. I use 220 0r 320,
You move the sanding block in an arc that follows the tube and usually you rotate the tube with your left hand and make the arc with the dura-.block with your right hand. Having the flat surface of the foam block makes it even with the surface. When you use your fingers like you have been doing, the curvature of your fingers and sandpaper creates a divot. I use only Timbermate filler because it sounds like baby powder and it's water-based so you can thin it like soup.

 

[kalsow]

There are several ways to create a sanding block that matches your tube diameter: 3-d printing, wrap sandpaper around your tube with the grit facing out and sand something soft-ish (balsa, hard foam, etc) to form a block, wrap your tube with parchment paper and lay up a curved section of fiberglass. After you've made a block, have fun sanding!

 

[4regt4]

If you sand with any flexibilty to the paper and the surface you're sanding has differing hardnesses, the softer areas will have more material removed than the harder areas. This is even evident when sanding filler-primer into lower layers of regular primer/paint/plastic.

In the situation you're dealing with, I'd just use a hard, flat sanding backer, like a piece of wood or an aluminum sanding tee. Once you get to where it's close to level, rock or roll the sanding block around the tube as you move it. Never just hold the sanding block at a fixed angle relative to the tube as you move it or, as you surmise, you'll end up putting flats on the tube.

Once you have primer on the tube, I'd try this, for $5 at Walmart:
https://www.walmart.com/ip/Bondo-Glazing-and-Spot-Putty-00907ES-4-5-oz-1-Tube/16927984

I wouldn't expect CWF to stick very well once any paint is on the tube.

A further option for the bare phenolic might be to try to get the CWF closer in hardness to the tube by mixing it with wood glue before application. I've never tried this, I just made it up as I'm typing. But might be worth trying if using CWF on harder materials than paper and wood.

Actually, I have Bondo drying on the tube as we speak. One section will get chrome paint, and I suspect it will show the phenolic Grand Canyon more so than the other parts. So I'm paying more attention to that area.

Hans.

 

[4regt4]

Get a black foam sanding block made for auto body called Dura-Block, they come in lots of sizes but I have found that the 12 inch one seems to work best.
https://www.amazon.com/dura-block-sanding-blocks/s?k=dura+block+sanding+blocks
they make adhesive backed sandpaper that is the same width that comes in rolls and all different kinds of grits. I use 220 0r 320,
You move the sanding block in an arc that follows the tube and usually you rotate the tube with your left hand and make the arc with the dura-.block with your right hand. Having the flat surface of the foam block makes it even with the surface. When you use your fingers like you have been doing, the curvature of your fingers and sandpaper creates a divot. I use only Timbermate filler because it sounds like baby powder and it's water-based so you can thin it like soup.

The Dura Block looks worth a try. But for now, I think I'll use my aluminum "T" and carefully rotate the tube as you suggest. I'd like to button up this project to start the next one. Seems I'm building roughly one a week.

Hans.

Hans.

 

[OzHybrid]

Soft sanding blocks are for blending small imperfections. Hard sanding blocks ( wooden block with a quality sandpaper contact cement glued to it or aluminium if you've got the budget) are where you want accuracy. With a hard block you shouldn't go into the spiral slots. A hard block in the shape of the tube diameter will give the best result.

 

[mh9162013]

You could try priming the rocket with a filler/primer after applying the CWF, but before sanding. The added height from the primer on the non-spiral portions of the tubing might reduce the chances of sanding down into Valles Marineris that's supposed to be filled with CWF.

I encounter this problem regularly with my LPR builds. I apply the CWF seemingly so the spiral I'm trying to fill is overflowing, yet the spirals are still evident after priming and sanding. I deal with this problem by priming and sanding again...and again, if necessary.

 

[4regt4]

You could try priming the rocket with a filler/primer after applying the CWF, but before sanding. The added height from the primer on the non-spiral portions of the tubing might reduce the chances of sanding down into Valles Marineris that's supposed to be filled with CWF.

I encounter this problem regularly with my LPR builds. I apply the CWF seemingly so the spiral I'm trying to fill is overflowing, yet the spirals are still evident after priming and sanding. I deal with this problem by priming and sanding again...and again, if necessary.

Thanks.

Actually, on most of my regular cardboard rockets, I don't use any CWF, but instead I put on 5 or 6 VERY heavy coats of Duplicolor Filler/Primer, then sand with a foam backed sandpaper. Works quite well, but not perfect. The remaining spirals are more obvious with some colors than others. But not real noticeable from 3 or 4 feet.

On this project, just a little while ago I filled the remaining grooves with Bondo. It seemed to sand more evenly with my foam sandpaper. Must be that the Bondo is harder than CWF. I'll find out shortly how it works, as I just put a coat of regular primer in prep for the finish coat - probably tomorrow. If it looks like crap, I will make sure everybody stays at a distance from my table at the next launch.

Hans,

 

[mh9162013]

I don't use any CWF, but instead I put on 5 or 6 VERY heavy coats of Duplicolor Filler/Primer

I've used that technique too, but I found it to be cost prohibitive.

 

[4regt4]

I've used that technique too, but I found it to be cost prohibitive.

Yes, I do use way too many cans of the stuff....

Hans.

 

[JimByrne]

Backstory: I'm building a 2.6" rocket with PML phenolic tubing. It has world class spirals. If you yell into them, you can hear an echo. They seem to have a square cross section. I filled them with Elmer's CWF, and, yes, I completely filled them. It was mounded up above the tube surface. However....

When I sanded them down, it seems that the sandpaper "dipped" into the crevasse, er, I mean spiral, and sanded away some of the CWF. Probably due to uneven pressure from my hand or fingers. So I still have spirals, but just not as deep. I need a better way.

It would seem that some rigid sanding block would help, but a flat block on a curved surface isn't likely to provide even results. At least not in my unskilled hands. What would be perfect is a contoured sanding block, with curvature matching the tube diameter. Nobody seems to sell them, and I don't really want to try and make something just for this one rocket. I tried a foam backed sanding block, not much better results.

Ideas?

Hans.

If you or a friend have a wood lathe mount & spin it while sanding---works great for me.

 

[jdsmith39]

I designed a tube chuck/lathe. If you or you know someone who has a 3D printer, this could be very useful.
I posted it in the 3D printing forum.
https://www.rocketryforum.com/threads/tube-sanding-made-easy.182165/

The post has a link to the printables page. Which explains what you need to use it and a video of me using it.

I used it for my L3 project last year, which I fiberglassed all of the tubes.

 

[Capt. Eric]

I am working on a 4" Frenzy with similar spiral canyons. I filled and sanded with results similar to yours. Then after 3 good coats of filler primer, sanding between them, I'm happy. Sometimes you just gotta grind it out. I did use a finishing palm sander, but not much different from a block, just faster.

I like the idea of a 3D printed curved sanding block, but I don't have ready access to one of those. If you do go that route, make sure you start designing one using the actual outside diameter and also add the paper thickness so you get as accurate a curve as possible.

 

[cwbullet]

Sanding is a slow and tedious process. Speeding it up can make the result less than desirable.

 

[jahall4]

Several posts here, have not read them all so my suggestion may be repetitive, but radially sanding light coats of Duplicolor filler primer it the ticket!

Spray the red first then the gray sand back to red and repeat as many times as necessary. Not only will this hide the spirals it will level the entire tube resulting in a "glass" finish which is obvious in the 2nd pic. Compare below and above the black ring.

 

[4regt4]

Sanding is a slow and tedious process. Speeding it up can make the result less than desirable.

Certainly true.

But for me, there has to be some sort of trade off / cut off. I can sand and paint to perfection, or go "good enough" and be 2/3 into finishing the next rocket in the time it takes to hit perfection on the 1st one.

I'm just hoping to find techniques to either speed things up, or improve results given the same amount of time. e.g. Mask and paint stripes, or use vinyl tape. Tape is faster and good enough (for me).

Hans.

 

[RokitFlyr]

Try getting some "sanding sponges". I've had good results. I cut them into various thicknesses . Cut the sides off about 1/4" thick, and the flats 1/2" or so. DO NOT use your ( or wife's/significant other's) fancy scissors!!! I use my bandsaw. They curve nicely around the tube.

Mark

 

[4regt4]

Try getting some "sanding sponges". I've had good results. I cut them into various thicknesses . Cut the sides off about 1/4" thick, and the flats 1/2" or so. DO NOT use your ( or wife's/significant other's) fancy scissors!!! I use my bandsaw. They curve nicely around the tube.

Mark

I have some sanding sponges, but never thought to try and make them thinner. That should work well.

Hans.

 

[Astrobuf]

Backstory: I'm building a 2.6" rocket with PML phenolic tubing. It has world class spirals. If you yell into them, you can hear an echo. They seem to have a square cross section. I filled them with Elmer's CWF, and, yes, I completely filled them. It was mounded up above the tube surface. However....

When I sanded them down, it seems that the sandpaper "dipped" into the crevasse, er, I mean spiral, and sanded away some of the CWF. Probably due to uneven pressure from my hand or fingers. So I still have spirals, but just not as deep. I need a better way.

It would seem that some rigid sanding block would help, but a flat block on a curved surface isn't likely to provide even results. At least not in my unskilled hands. What would be perfect is a contoured sanding block, with curvature matching the tube diameter. Nobody seems to sell them, and I don't really want to try and make something just for this one rocket. I tried a foam backed sanding block, not much better results.

Ideas?

Hans.

I'm guessing you sanded free hand. Never sand freehand if you want to make something flat. Use a sanding block.

If you used a block, then you pressed so hard you deflected the tube. When clearing excess I find using a coarse paper works best to clear most of the humps. Start with 80grit, then on to finer grits to remove the ghost and level.

I'm not a fan of using anybodys drywall or wood filler. You likely will have better luck using an autonomy material meant to level and fill bonds. I use 3M's glazing putty. It dries extremely fast, & does not shrink. You apply it with a squeegee. There are less expensive glaze products that would, for a rocket. Work just as well. Go to O'Reilly or a NAPA.

https://www.zoro.com/3m-glazing-put...Rw5pM4Bllz_Yg0Ddb9oaAl-_EALw_wcB&gclsrc=aw.ds

 

[manixFan]

I've used that technique too, but I found it to be cost prohibitive.

I use the non-aerosol cans of the primer-surfacer. It’s much less expensive than the spray cans and can be thinned with acetone to get it the right consistency. I’ll use a chip brush to apply it and then sand most of it off.


Tony

 

[mh9162013]

I use the non-aerosol cans of the primer-surfacer. It’s much less expensive than the spray cans and can be thinned with acetone to get it the right consistency. I’ll use a chip brush to apply it and then sand most of it off.


Tony

View attachment 637970

I am intrigued. Seems like a can like that costs about $30, but might be able to last several dozen (or even hundred) BT-60 sized LPR rockets.

I'm on a building hiatus right now, but when I resume, I'll look into that. Right now, I'm using Rustoleum primer (about $6 per can) and one can probably lasts about about three to five BT-60 Estes Patriot size rockets.

 

[Back_at_it]

My PML IO rebuild had these deep spirals that needed to be filled. I started with two coats of SEM high build primer. I wasn't concerned with runs as the stuff dries quickly and is easy to sand. Once dry I knocked it down with 100 grit then went back and coated the rocket in DAP wood filler. The sanding was then done with Dura Blocks with various grits of sand paper. I like the Dura Blocks as they have just enough flex that they don't sand grooves into your materials. Hard sanding blocks like the aluminum stuff tends to sand flat spots when used on rounded surfaces.

Ideally I would have used a scrap piece of body tube the same diameter as the rocket cut lengthwise with some sandpaper glued inside but the IO was an oddball tube size that I didn't have laying around.

In a perfect world you'd have a sanding block the exact shape as the materials you're sanding but that isn't always possible.

 

[ep29030]

When I had a nosecone area to repair and I needed a rounded shaping, I took a short piece of PVC (can also use a coupler)) and cut it lengthwise to make a curved piece that was about 1/8” of the tube’s circumference. Then spray the inside of the piece with 3M Adhesive 90 and laid a piece of sandpaper inside. This makes a curved, straight and rigid sanding block for a curved surface. You can use this technique on tube to make a curved sander. The closer to the sanded tube diameter it is, the better it works.

 

[4regt4]

Just found this on Amazon. I ordered a set, we'll see how well it works.

https://a.co/d/825IU95

or if that link doesn't work, this might:

https://www.amazon.com/dp/B0CPDY1KGQ?ref_=cm_sw_r_cp_ud_dp_DWEREDJ854M3YYJEA9YB&th=1

Hans.