Filling fin tube slots

[slipperyfrog]

What is the best/easiest way to fill in fin slots on a tube so that I can change the arrangement?

It is for a Fat Boy kit and want to change the fins from 3 to 4. I was going to use some removable vinyl to make a backing and fill the slots with wood filler? epoxy? Then just remove the vinyl after it drys and sand down. I could then just make 3 new slots.

I found one other post that used cut out cardstock but I don't want to do that.

 

[rstaff3]

That's pretty much what I've done. Coupler (or a piece of sectioned tube) + wax paper + filler. I've done it with fill'n'finish and epoxy filler. If I remember right, the wood filler tends to form cracks along the length of the slot during normal landing stresses. A permanent backing helps. As I think about it, I may have used a permanent backing.

 

[gpoehlein]

I filled in the slots on a Big Daddy tube so I could turn it into a tube fin model. I glued a piece of cardstock (110#) to the inside of the tube, then glued strips of cardstock the width of the slot and trimmed to the length (rounded on the ends) into the gap. It took about three layers of cardstock to bring it up to the same level as the outside of the tube. I then used Fill-n-Finish to fill the small gaps that were left - the cardstock filler kept me from having to use a whole lot of filler and made sure there weren't any depressions where the filler shrank or got sanded away.

 

[dixontj93060]

I wouldn't use wood filler as it would likely crack over time. I would back the inside of the tube with vinyl tape as you suggest and use slow cure epoxy with a good dose of filler like West System 406.

 

[slipperyfrog]

Thanks for the quick response. I think I'll just mix up some epoxy and fill them in. The thought of cracks from wood filler doesn't turn me on.

 

[MarkII]

My approach would have been to chuck the Fat Boy's tube into my spare parts bin and replace it with a fresh new unslotted length of BT-80. But that's me. My hat's off to those who would go through the trouble of filling in the slots. I would have had my doubts, but you all have proven that it can indeed be done successfully. The extra little bit of wall thickness that is added to the inner wall can have the extra benefit of supporting the centering rings that are installed above and below it as well.

 

[powderburner]

slipperyfrog (and we're definitely gonna make you explain that one sometime),

A big part of your answer is going to involve whether the re-built (ex-slotted) portion of BT length is going to be pressurized at ejection in your new configuration. That is, is your new design going to keep the fin slots behind a centering ring (and isolated from ejection gas pressure)?

If not, you need to restore the 'hoop strength' of the BT cross-section by lining that zone with another (internal) BT doubler. Cut a short length of scrap BT80 to cover the length of the existing fin slots plus maybe an extra half inch ahead and behind, cut a slot down the side of your BT80 patch and remove a 1/4 inch wide strip, roll the patch down to a smaller diam and slip it inside your original BT (with gobs-o-glue, of course). Keep the lengthwise cut of your patch away from the existing slots.

If you are using a CR (like in the original Fat Boy) to keep ejection gas out in front of the slots, you should be OK with cardstock reinforcement on the inside and filler material in the external slots.

 

[Pat_B]

Some .5oz fiberglass and one layer of jap tissue will give you a really strong fix.

 

[bradycros]

The best fix would be to get a new tube. Simple, yes?

 

[gpoehlein]

The best fix would be to get a new tube. Simple, yes?

Sure, if you want to do it the EASY way! But would that be "The Cowboy Way?"

 

[slipperyfrog]

Sure, if you want to do it the EASY way! But would that be "The Cowboy Way?"

:w::w::w:

Where is the fun in buying new stuff.

 

[rstaff3]

I agree. My motto is 'Use what ya' got.'

 

[bradycros]

Where is the fun in buying new stuff.

Read this answer carefully. You already have a body tube slotted for the three finned Fat Boy, build it that way. Then get a new 8" BT-80 & nose cone from semroc and build your four finned Fat Boy.

The fun begins when you have finished building and end up flying a Fat Boy and a Fatter Boy, neither of which has a body tube cut to hell and then repaired.

 

[bradycros]

I agree. My motto is 'Use what ya' got.'

Sooner, rather then later, your going to run out of what ya got.

Then your going to need to replace your "what ya got " parts. That falls into the catagory of "new" parts.

Pay for them now or pay for them later, you still pay to get 'em. Or have already paid to have them.

 

[slipperyfrog]

Read this answer carefully. You already have a body tube slotted for the three finned Fat Boy, build it that way. Then get a new 8" BT-80 & nose cone from semroc and build your four finned Fat Boy.

The fun begins when you have finished building and end up flying a Fat Boy and a Fatter Boy, neither of which has a body tube cut to hell and then repaired.

Exactly! ......except I only wany the one Fat Boy and not two.

 

[bradycros]

Exactly! ......except I only wany the one Fat Boy and not two.

Why don't you just tell us what your going to do?

 

[slipperyfrog]

Why don't you just tell us what your going to do?

It is for my "Sumo Boy“ idea. :horse: or thinking more that "Sumo Daddy" sounds fun. I have a Big Daddy kit laying around as well.

Bah I may just pick up some new tubing and let the kids have the Fat Boy kit to build.:y:

 

[bradycros]

It is for my "Sumo Boy“ idea. :horse: or thinking more that "Sumo Daddy" sounds fun. I have a Big Daddy kit laying around as well.

Bah I may just pick up some new tubing and let the kids have the Fat Boy kit to build.:y:

It's good to know your decision making skills are so finely honed. :wink:

 

[MarkII]

It's good to know your decision making skills are so finely honed. :wink:

:wink: :wink:

A 34" length of BT-80 from BMS costs $6. An 8" long section cut from it would effectively cost $1.41. Uncle Mike sells a single 18" long BT-80 for $2.50, so an 8" long section cut from it would effectively cost $1.11.

Or you can just get a BT-80WH (same tube as in the Fat Boy, but unslotted, I presume) from Semroc which, with the NAR discount, would cost $1.98.

How do those prices compare with the combined cost of, for instance, some lightweight fiberglass plus some Japanese tissue plus laminating resin plus your time and effort? :confused2:

 

[UPscaler]

I was drilling the holes for my rivets in my darkstar last night, and realized one was completely off center. So I taped some masking tape (sticky side down) inside the body tube covering up the hole from the bottom with the non-sticky side. Filled it with CA, sanded, good as new!


Of course, this was a fairly small hole.



Braden

 

[Stymye]

you can do the same thing with balsa and glue for filling slots
,, fill the slot with a sliver of balsa ..slather it with glue ..sand

before it dries remove the internal tape backing .
quick and easy
go over it with some filler later if needed

 

[green dragon]

years back I bought a CASE of 5.54" x 34" tubes from Ron at LOC ( Iroc 'seconds' ). all slotted.

Been using those for years, for repairs, etc - filled the slots with 1/8" x 1/8" spruce ( 1/8" wide slots ), ca'd in place and sanded to match the tube contour...

been used in the 'presurized' part of airframe ( chute compartment ) amd also , repairs on my Wolverine is like 3 sections ,al with filled slots ), NO issues with one ever cracking or blowing out.

filling slots is easy..... although might be a lil trickier to sand out on a thinner walled tube, but the ca will wick into the tube and the filler will stay in place.

have at it

~ AL

 

[bradycros]

:wink: :wink:

A 34" length of BT-80 from BMS costs $6. An 8" long section cut from it would effectively cost $1.41. Uncle Mike sells a single 18" long BT-80 for $2.50, so an 8" long section cut from it would effectively cost $1.11.

Or you can just get a BT-80WH (same tube as in the Fat Boy, but unslotted, I presume) from Semroc which, with the NAR discount, would cost $1.98.

How do those prices compare with the combined cost of, for instance, some lightweight fiberglass plus some Japanese tissue plus laminating resin plus your time and effort? :confused2:

Good points, I absolutly agree with them.

 

[o1d_dude]

Or you can just get a BT-80WH (same tube as in the Fat Boy, but unslotted, I presume) from Semroc which, with the NAR discount, would cost $1.98.

And it will arrive the day before you place the order.

 

[slipperyfrog]

:wink: :wink:

A 34" length of BT-80 from BMS costs $6. An 8" long section cut from it would effectively cost $1.41. Uncle Mike sells a single 18" long BT-80 for $2.50, so an 8" long section cut from it would effectively cost $1.11.

Or you can just get a BT-80WH (same tube as in the Fat Boy, but unslotted, I presume) from Semroc which, with the NAR discount, would cost $1.98.

How do those prices compare with the combined cost of, for instance, some lightweight fiberglass plus some Japanese tissue plus laminating resin plus your time and effort? :confused2:

Sometimes we forget half the fun of a hobby is not saving a buck or two but spending some time & effort doing something new/out of the ordinary. :wink:

 

[Pat_B]

I was also thinking that this was a rocket he was building right now and was looking for more of a patching solution rather than having to wait for new tubes to be ordered.

Still think glass and jap is the way to go. No filler to get knocked out.