Tube Spirals

[tjtx]

As a beginner, I am perplexed by a very consistent observation of tube spirals. It appears to me that there are two different kinds of spirals: 1. the very obvious "open" spirals that have a definite separation between the adjacent pieces of paper (glassine?) covered cardboard which we fill with our personal favorite technique, and 2. Underlying spirals which are paper covered but observable. It is this category of spirals that I need help with. This morning I was filling the open spirals of a BMS Big (BIG) Bertha clone and I noticed that in several areas the paper covered spirals had "bulged" outwardly creating raised ridges. On a previous model, I tried to sand these ridges off which created more open spirals which severely weakened the structural integrity of the body tube. I tried to fill these self-induced open spirals, but the over all strength of the body tube was compromised. Is there a "secrete hand shake" method of dealing with second category of spirals?
I thank you in advance for any or all replies,TJ

 

[foose4string]

I don't usually fill around or sand the raised spirals. They usually disappear well enough after a couple coats of primer, and especially after the top coats are applied(sanding between coats).

On the other hand, the grooved spirals are a bit harder to conceal with primer alone (although I understand there a some high build spot filling primers that will do the job). I usually use some lightly thinned(with water) Elmer's fill n finish brushed into the tube seams and then sanded until I get everything level with the top of the seam. This takes a little time and patience, but isn't too bad if you do it before you start building. Regular Elmer's wood filler will work too. Don't thin the filler too much or make it watery as that will soften the tube when it's applied.

If you can find the spot filling primers I would recommend going that route as it might save some time and less overall work.

 

[Pat_B]

On my nicer models I'll cut away the glassine cover from the underlying spirals then squirt some CA on it, followed up by th normal Fill 'N Finish. I'll actually cut on both sides of the spiral which results in a small piece of the glassine being removed.

On larger tubes you can just put one slice in the center of the spiral then fill with CA.

Changes in atmospheric pressure result in those underlying spirals becoming more and less visible with changes in temp/pressure, and the spirals will appear and disappear unless you pierce the glassine.

 

[Micromeister]

I find the easiest and fastest way to take care of both spiral problems is with the use of High build primers.
I haven't fooled around with FnF or other fillers for years, preferring to spend a little more time just spraying on filler coats of primer.
Generally I use 3 coats without sanding between, let them dry for an hour or so depending on the Lable instructions. Sand these three layers starting with 120 or 240 grit DRY sandpaper. when I reach paper, spary on another 3 coats of primer, let dry and sand starting with 240 or 360grit. Unless the Spirals are exceptionally deep that all it takes, finish sanding with 400 or 600 grit wiping the dust with a tack-rag and checking the body and joints by holding it up towards a light, If no imperfections are seen its on the the basecoat Paint.
Even on my Interceptor-E I only needed 2 sets of 3 coating of very Cheap Grey Auto (Not Hi build) Wal-mart primer to completely fill all the Raw Balsa grain and tube seams at the same time. Some folks prefer to use fill N finish (FnF) on body tube seems and grain as they don't have a decent place to spray on primer. If that's your situation I'd still suggest only filling the deep inward seams. The slight overlaps on the glassine layers will even out just fine with a coat of two of primers as others have mentioned.
Have to disagree with Pat B on this point. Once these overlaps of glassine are primered over and sanded smooth and/or the tube seams primer filled and sanded I've never had or heard of anyone before this having a seam reappear in the finished model due to atmoshperic pressure changes. I keep most of my fleet in an unregulated Heat/cold Shed, where the temp and Humidity vary with the outside climate, models built in the 80's show no more sign of seam lines then they or the models built last week. I think Pat may have some other problem with the method or materials used if he is seeing his seem lines reappear.
Most of us rough up the surface of the glassine layer before the first primer coat is applied but even that is only done Lightly with 320 or 360girt sandpaper just to give the paint and primer a little more "tooth" for adhear to as it dries. excessive harsh sanding or removal of the glassine can result in totally unsatisfactory end finish with lots of fuzzy fibers or rough looking finish.

 

[Pat_B]

I got the idea for cutting the glassine from the spirals from someone's website a few years ago. The Mar/Apr issue of Sport Rocketry also showed the same technique. Clearly, it's an issue that others have also encountered.

It all depends on how picky someone is when finishing their rockets. Cutting out the hidden spirals, then filling, assures that they'll never reappear. By 'reappearing' I don't mean a significant bump in the rocket's surface, but rather a obvious surface defect that can be visible in an otherwise flawless finish.

 

[Micromeister]

I got the idea for cutting the glassine from the spirals from someone's website a few years ago. The Mar/Apr issue of Sport Rocketry also showed the same technique. Clearly, it's an issue that others have also encountered.

It all depends on how picky someone is when finishing their rockets. Cutting out the hidden spirals, then filling, assures that they'll never reappear. By 'reappearing' I don't mean a significant bump in the rocket's surface, but rather a obvious surface defect that can be visible in an otherwise flawless finish.

Pat:
I'm unsure there really is an "Issue" at all. I'm sure something has caused some to have some sort of reaction, I see lots of things on web sites and unforunaturely published in Sport rocketry that really haven't be all that helpful and in some cases simply pass-on not so good habbits or techniques. Without having seen such an effect I find it hard to understand how such a blemish could or would occur. My guess if you had a very deep sub-surface seam covered by a single wrap of glassine I suppose if the applied primer and finish were thin enough there might be something over time but man..all those if's?
Just to make it clear; Many of my later models are of the Semi-flawless finish variety; People constantly want to know what I built them out of as they can't tell. But as there are no flawless finishes produced by anyone anywhere, do to the fact there was only one perfect person on this earth your assertion is a bit overstated.
I too have been cursed as a perfectionist, but have learned over time where to draw the line
That being said; My earlier remarks about having models from the 80's that still show no signs for the conditions you've discribed remain. Many of these models were museum display models later flown and retired. I suppose if one's models are stored in a very humidy area for very long periods they could pickup some cardboard expansion over time, but then again, I live in DC, a very high humidity area and to date, have never seen such an effect.

Do you have a photo of the effect discribed that could be uploaded? I'd really like to see what this defect looks like, and prehaps visit the website to discuss it's cause with the author.

If it's as subtle as your suggesting; prehaps it's not something beginners and folks just starting out in finishing really need to worry about?