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How to fill spirals with the least amount of sanding?

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Buckeye

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Spirals never bothered me until now. I am working with a 7.5" LOC cardboard body tube on my current build, so I want to hide the spirals this time. I tried a couple techniques, I am sanding my ass off, and I don't like any of it!!!

Water-diluted wood filler: Does not adhere very well and falls out of the spirals in places during sanding. Causes the paper to peel up on the edge of the spiral (probably from the water)​
Bondo: Adheres very well, but my application technique with a putty knife leaves much to be desired. I am coating the entire tube, not just the spirals. Lots of excess Bondo and lots of sanding. The finish is very nice, though.​

I am probably doing both methods incorrectly. Still, I want an easier method with less sanding. I am thinking that a coat of laminating epoxy is the way to go. Is that enough to hide spirals, or is a filler underneath still required?
 

Zertyme

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If you are patient, you can apply masking tape on both sides of the spiral.
Then fill the spiral with the filler of your choice.
Once everything is filled, you can remove the masking tape.
1611320012649.png

I used rocketpoxy on this one.

This technique takes longer to prep, but you won't have to do any sanding.
 

hobie1dog

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I wouldn't be filling anything more than just the spirals as you're drastically increasing the amount of work. I refuse to build anything made of cheap cardboard with spirals, see my signature.
 

Spitfire222

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I use the wood filler myself, and it seems to work fine. I do spray a coat of filler-primer before I add the filler. I figure this helps to begin filling the spirals so that less filler is required, and it improves adhesion. Don't forget that the wood filler will shrink a bit as it dries, and this could be contributing to your adhesion problems.

Covering the whole body tube with any filler is a bit overkill, as it will all get sanded off anyways, if done correctly. Filling the spirals is tedious enough, but it can be streamlined a bit for those of us who have plenty of time in life to enjoy nicely finished, smooth rockets.
 

dr wogz

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My go-to has always been to not fill them in the first place (20' rule). but I have discovered that a few coats of 'sandable primer' can go a long way. Not only for spirals, bur for all the slight imperfections in cardboard tubes. Fins too..
 

Buckeye

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If you are patient, you can apply masking tape on both sides of the spiral.
Then fill the spiral with the filler of your choice.
Once everything is filled, you can remove the masking tape.
View attachment 447426
I used rocketpoxy on this one.

This technique takes longer to prep, but you won't have to do any sanding.
Me likey this idea.
 

BABAR

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If you are patient, you can apply masking tape on both sides of the spiral.
Then fill the spiral with the filler of your choice.
Once everything is filled, you can remove the masking tape.
View attachment 447426
I used rocketpoxy on this one.

This technique takes longer to prep, but you won't have to do any sanding.
Interesting idea. I’ll raise the bar a bit further. Electrical/ vinyl tape will stretch to shape the helix required, so two pieces ( one each side of spiral) should be easy to smoothly and contiguously apply.
 

sandeja1

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Interesting idea. I’ll raise the bar a bit further. Electrical/ vinyl tape will stretch to shape the helix required, so two pieces ( one each side of spiral) should be easy to smoothly and contiguously apply.
Wouldn't/doesn't electrical tape have too much "stickyness" or does it come off easily without affecting the paper tube? Genuinely curious as I had never considered using that type of tape before. Great idea!
 

Pem Tech

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There have been a few cases in the past years where tube spirals where filled. It wasn't fun and was endowed with much adult language. The methods include diluted wood sealer, drywall/plaster mud, heavy coats of primer and epoxy clay, but the effort outweighs the results. IMHO... If I'm building a Hanger Queen I would do it, but for a flying rocket, nah, the 3 foot rule is good enough for me. By the by, I love Quantum tubing for this reason but homey's pockets just ain't that deep.
 

Zertyme

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I used normal clear tape because it's thin.
Thin masking tape should be fine too.
If the tape is too thick the filled spiral will have to be sanded down.
 

dr wogz

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Wouldn't/doesn't electrical tape have too much "stickyness" or does it come off easily without affecting the paper tube? Genuinely curious as I had never considered using that type of tape before. Great idea!
I have used electrical tape to mask off paint, but I have patted in on my jeans to remove some of the stickiness / ensure the stickiness has been "contaminated" (Dust, dander, pet hair, cake crumbs, Holley 4-barrel re-furbish crud..)
 

hball55

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If you are patient, you can apply masking tape on both sides of the spiral.
Then fill the spiral with the filler of your choice.
Once everything is filled, you can remove the masking tape.
View attachment 447426
I used rocketpoxy on this one.

This technique takes longer to prep, but you won't have to do any sanding.
So somebody else who has used rocketpoxy, lol. Usually, I use rocketpoxy to fill holes that I drill in the wrong place, rocketpoxy works great, as it sands away so well.
 

afadeev

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Spirals never bothered me until now.
You must be getting old, or turning into a perfectionist, or a bit of both!
:p

I am working with a 7.5" LOC cardboard body tube on my current build, so I want to hide the spirals this time. I tried a couple techniques, I am sanding my ass off, and I don't like any of it!!!
Water-diluted wood filler: Does not adhere very well and falls out of the spirals in places during sanding. Causes the paper to peel up on the edge of the spiral (probably from the water)​
Bondo: Adheres very well, but my application technique with a putty knife leaves much to be desired. I am coating the entire tube, not just the spirals. Lots of excess Bondo and lots of sanding. The finish is very nice, though.​
I've switched to using Bondo for spirals, exclusively. Both for the ease and speed of application, and the durability.
Wood filler takes too many applications, and occasionally falls out of the spirals during sending, requiring a complete multi-step redo.

Once spirals are filled, I spray sandable primer over the body tube, and sand everything even.
They key is getting a quick drying primer, as all Krylon and cheap WM/HD primers clog up the standing paper unless you wait 1-2 days to let them fully dry.
For this purpose, the best I've found is "Krylon Industrial Tough Coat Light Gray Sandable Primer".
It dries in under 15 minutes, sands easily and quickly. You can apply and sand multiple coats in under one hour.

I am thinking that a coat of laminating epoxy is the way to go. Is that enough to hide spirals, or is a filler underneath still required?
Epoxy would add a lot of weight.
If that's not a concern, you would go with fiberglass tubes to begin with.

Have fun!
 

Buckeye

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Once spirals are filled, I spray sandable primer over the body tube, and sand everything even.
They key is getting a quick drying primer, as all Krylon and cheap WM/HD primers clog up the standing paper unless you wait 1-2 days to let them fully dry.
For this purpose, the best I've found is "Krylon Industrial Tough Coat Light Gray Sandable Primer".
It dries in under 15 minutes, sands easily and quickly. You can apply and sand multiple coats in under one hour.
Good tip on the Krylon primer.

I have Rustoleum Filler/Sanding primer from the auto parts store. I will try that on the bare spirals as well to see if it truly "fills" them. These LOC tubes have pretty narrow, tight spirals, so the primer may be good enough, but I have been fooled before.
 

neil_w

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I have Rustoleum Filler/Sanding primer from the auto parts store. I will try that on the bare spirals as well to see if it truly "fills" them.
That certainly works, if you use enough of the primer. But based on my experience it will take a lot of filler/primer to completely fill the spirals, and you'll end up doing a lot of sanding.
 

dbpeirce

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I wrap the tubes in fiberglass!!! Smooth like butter!!!
 

kevin.mcgee

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This is exactly my technique. I use wood filler that has been barely diluted.

If you are patient, you can apply masking tape on both sides of the spiral.
Then fill the spiral with the filler of your choice.
Once everything is filled, you can remove the masking tape.
View attachment 447426
I used rocketpoxy on this one.

This technique takes longer to prep, but you won't have to do any sanding.
 

Nathan

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Instead of spreading the Bondo with a putty knife, try using your finger (with nitrile gloves). You get much better control. But personally for filling spirals in cardboard tubes I would use diluted CWF. It sounds like you may be diluting it too much. You only need a tiny amount of water to give it the consistency of toothpaste.
 

Arsenal78

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There have been a few cases in the past years where tube spirals where filled. It wasn't fun and was endowed with much adult language. The methods include diluted wood sealer, drywall/plaster mud, heavy coats of primer and epoxy clay, but the effort outweighs the results. IMHO... If I'm building a Hanger Queen I would do it, but for a flying rocket, nah, the 3 foot rule is good enough for me. By the by, I love Quantum tubing for this reason but homey's pockets just ain't that deep.
Not directly related to filling spirals but filling still but how in the hell do you get a nice surface on the inside of the Kraken tube fins? I tried once and it was a disaster.
 

nelie61

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I like to use the Elmer's wood filler in the orange tub. Put it on with a old credit card and wipe back off with the card back into the tub. Apply to the entire tube because there are small dimples in the tube also and it takes care of that. Easy to sand and apply another coat. Sand and apply Primer and sand. This method adds almost zero weight and tube is very smooth. Although I have never done a 7" tube, Just another way out of the hundreds of ways people like to finish
 

DES

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I have had really good luck with the "smear and wipe" technique using the Bond Glazing putty. Basically you smear a thin film of the solvent based glazing putty over the body tube, let it start to dry a bit so it gets thicker, then quickly wipe it all off with a paper towel, scrubbing across the spirals. It leaves the filler in the groves, but very little on the surface of the tube. The putty dries fast, so you have to do a section at a time and not get carried away. You can repeat the process a couple of times if the groves are deep, or you can apply the putty directly to the grove, and use a plastic scraper to level it off. It goes really fast.

Then you sand and prime. Two coats of a primer, with sanding between usually fills all the spirals. This will depend on your body tube and how deep the groove are. I don't like "spray fillers". They are soft and gummy, don't sand well, and don't really seem to fill spirals well.

DSCF1156.JPG
DSCF1162.JPG

DSCF1173.JPG
DSCF1174.JPG


DSCF1159.JPG
 

tjgray693599

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Sir, you are a genius! I ended up making my body tubes fuzzy after sanding down the Bondo filler.
 

neil_w

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I have had really good luck with the "smear and wipe" technique using the Bond Glazing putty.
That looks great, and I would definitely try it if the Bondo didn't stink up the house (and that's a lot of Bondo which I would guess translates into a lot of stink.) I do something similar with CWF, but there's no way to cleanly wipe all of it off like that while still wet, so there's still plenty of sanding to do. I still find it easier than filling and sanding only the spirals.

However, I will note that a 7.5" airframe will consume a *lot* of filler if you're going to cover the entire tube.
 

hcmbanjo

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Here's way too much information about my two-step fill process.
CWF then Duplicolor Filler/Primer -
 

Michael L

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Evercoat Z-Grip. Better than bondo, sands easier, etc. I haven't tried it yet (it's on order) but a reputable experimental aircraft builder switch to Z-grip from Bondo on his builds. He uses it for his carbon fiber molds (Mike Patey on YouTube)
 

RocketTree

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+1 on masking the spiral and filling it. I brush on filler primer for shallow spirals. Wood filler or automotive glazing putty for deep ones. Very little sanding required after.
 

DES

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Might be a minor confusion here - "Bondo" - typically a polyester resin with a hardener you mix in. Two component. Very strong, suitable for filling really deep defects, like 1/2 inch or more dimples in your fender, but stinks to high heaven, somewhat hard to spread and harder to sand.

The product I'm using for spirals is "Bondo Brand Glazing Putty". This is a one component, solvent based filler. Finishing filler for very minor defects. Spreads and sands very easily, but I would not use if for anything thicker than 1/8 inch, or less. I buy it at the auto parts store.

I've tried the water based wood fillers. Okay on the body tubes, but I've had trouble with warping on plywood fins, even if I spread the filler on both sides at once. The solvent based glazing putty won't warp the fins.
 

Buckeye

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Might be a minor confusion here - "Bondo" - typically a polyester resin with a hardener you mix in. Two component. Very strong, suitable for filling really deep defects, like 1/2 inch or more dimples in your fender, but stinks to high heaven, somewhat hard to spread and harder to sand.

The product I'm using for spirals is "Bondo Brand Glazing Putty". This is a one component, solvent based filler. Finishing filler for very minor defects. Spreads and sands very easily, but I would not use if for anything thicker than 1/8 inch, or less. I buy it at the auto parts store.
Well, the Bondo, err plot, thickens!

I have the "Professional Glazing and Spot Putty." It includes the red hardener. It smells slightly less than Bondo Body Filler, but pretty much behaves the same. Are you saying there is another "Glazing and Spot Putty" that does not require mixing in a hardener? If so, then 3M has a horrible marketing department.

This is what I have:

20210125_080325.jpg
 

prfesser

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Well, the Bondo, err plot, thickens!

I have the "Professional Glazing and Spot Putty." It includes the red hardener. It smells slightly less than Bondo Body Filler, but pretty much behaves the same. Are you saying there is another "Glazing and Spot Putty" that does not require mixing in a hardener? If so, then 3M has a horrible marketing department.
This is the one-part stuff. It's available in smaller tubes as well, but I go through it pretty quickly so I get the 1 lb. size:


It sands the way that primer/filler is supposed to sand (but often doesn't). Dries quickly (solvent evaporates), no clogging of sandpaper. Considerably more expensive than the two-part filler.

Mix with a little acetone or lacquer thinner to make a thinner version for painting on the spirals.

Best -- Terry
 
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