Cutting hole in body tube for internal filets

[RocketSquirrel]

I Shouldn't have set the Aft ring on MMT, but this way i can ensure good filets on fwd side of middle ring too... (trying to see the bright side) If i cut these square/rectangle pieces out to apply the epoxy, how should i put the piece back in place? Im thinking about using masking tape to make it sit flush and tack thick/mid CA on the corners. Then maybe use thickened epoxy to fill the gaps before sanding. Or thick/mid CA. Does that sound like a plan? How do you normally cut into the body tube then glue it back? Ive seen it done, i just cant find the threads.

 

[RokitFlyr]

Not exactly sure what you're trying to do. If you mean the cutouts behind the fins, put a short piece of coupler on the inside, then glue them to that. Also strengthens the aft end of the tube to resist landing damage.

 

[RocketSquirrel]

Not exactly sure what you're trying to do. If you mean the cutouts behind the fins, put a short piece of coupler on the inside, then glue them to that. Also strengthens the aft end of the tube to resist landing damage.

No that makes sense, but what happened was i epoxied the aft centering ring on the fin can, so there is no other way to epoxy the middle cr (or international fin filets) without cutting a hole in the body tube. I normally leave the aft ring off so i can epoxy the fwd ring first, then take out the aft ring to epoxy the middle ring and internal filets before setting the aft ring in place.

 

[RokitFlyr]

Oopsie. Well......maybe drill a hole (3) in the centering ring between the fins. Say 3/8". Pour epoxy in, rotate the rocket around to get it where you want. Easy to patch them up. Won't hurt the strength of the ring.

 

[OzHybrid]

Cut the tube back flush with the motor mount centering ring. Then tidy it up.
Edit: now you've changed the photo......

 

[RokitFlyr]

That's not the photo I was referring to.

 

[RocketSquirrel]

Oopsie. Well......maybe drill a hole (3) in the centering ring between the fins. Say 3/8". Pour epoxy in, rotate the rocket around to get it where you want. Easy to patch them up. Won't hurt the strength of the ring.

Wait, drill IN the cr? And yeah i saw your comment about the pic, i loaded the wrong one.

 

[David_Stack]

You may want to visit the Wildman Rocketry site, in the Downloads section Tim has posted build instructions for the "Booster Assembly (Injection Method)". The biggest hurdle you will likely have is that with your fins already installed drilling holes immediately adjacent to the fin is going to be a bit of a challenge.

If you insist on cutting a large hatch like you've drawn on the body tube, you could glue strips of balsa or similar on the inside surface of the body tube that would serve as a shelf to affix the cut out piece of body tube to.

All that said, how hard are you intending to push this airframe? Do you really need additional adhesive (weight at the wrong end of the rocket) at those existing bonds?

 

[RokitFlyr]

Wait, drill IN the cr? And yeah i saw your comment about the pic, i loaded the wrong one.

Yes.

 

[RocketSquirrel]

how hard are you intending to push this airframe? Do you really need additional adhesive (weight at the wrong end of the rocket) at those existing bonds?

its for my L2, I chose this one because its a little heavy. My clubs altitude limit is 4k AGL and im trying to keep it under 3k and i dont plan on pushing it too hard. Maybe a J250? Depends on whats available from my local supplier.

 

[lakeroadster]

Wait, drill IN the cr? And yeah i saw your comment about the pic, i loaded the wrong one.

Three fins, right? You can drill (6) holes in the centering ring... no worries. Makes it appear you did this on purpose for inspection purposes. ​

 

[RocketSquirrel]

Three fins, right? You can drill (6) holes in the centering ring... no worries. Makes it appear you did this on purpose for inspection purposes. ​

are you guys talking about the underside of the Aft ring and inject? Or through the body tube down into the cr...

I got several people on the LOC fb group saying to drill holes in the body tube where the external filets will go, inject epoxy and rock back and forth to ensure its evenly spread. Ive seen this done, and ive seen people drilling holes in the aft ring to inject but never down into the cr from the bt.

 

[lakeroadster]

are you guys talking about the underside of the Aft ring and inject? Or through the body tube down into the cr...

I got several people on the LOC fb group saying to drill holes in the body tube where the external filets will go, inject epoxy and rock back and forth to ensure its evenly spread. Ive seen this done, and ive seen people drilling holes in the aft ring to inject but never down into the cr from the bt.

Drill through the rear centering ring.​

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[Zbench]

This is too late for this application, but I got this idea from Apogee components. Make the upper ring with divots around the circumference. Apply a good amount of epoxy where the middle centering ring is and when you push the assembly in it will leave an evenly spaced amount of epoxy for the middle ring to adhere to.

This application below is for gluing into a nose cone where I wanted increased gluing area but the idea is the same. Solves the “how do I get glue to the middle centering ring” problem. Something to consider next time.

 

[JimByrne]

Drill a small hole next to the fin then use a springe to inject epoxy (I use Bob Smith 30 minute), tilt the body tube so epoxy builds up next to the fin when done the fillets will cover the hole.

 

[rcktnut]

Put good fillets on the top of the top and rear of the rear centering rings, do external fin fillets, good to go.

 

[mundayr2]

As stated before, I drill holes in the BT next to the fin slots and inject Bob Smith 30 minute epoxy with syringes and blunt needles you can get at Amazon. Has always worked for me.

 

[rcktnut]

Internal fillets are also over-rated. The fillet at the inside of the airframe is the least bending stressed element in the structure. Fillet the outer fin attachment and the fin to MMT are you are good to go. Especially if using a FG airframe.

I'm not the only one that feels that way about it!

 

[RocketSquirrel]

I decided to cut into the Aft CR like some of you mentioned, im less concerned with the internal filets as i am the middle CR. Here's what i came up with
Might have made the holed a little bigger than needed, but shouldn't be a problem.



This tool i rigged to plung the epoxy should work great. I plan on using west system thickened with 406. Never done it before, so im thinking about getting it to honey consistency and going up from there if needed. Applying a thinner layer first might be better to let it soak in any gaps.

Thanks for the advice, i over thought this one which caused problems.

 

[RocketSquirrel]

This is too late for this application, but I got this idea from Apogee components. Make the upper ring with divots around the circumference. Apply a good amount of epoxy where the middle centering ring is and when you push the assembly in it will leave an evenly spaced amount of epoxy for the middle ring to adhere to.

This application below is for gluing into a nose cone where I wanted increased gluing area but the idea is the same. Solves the “how do I get glue to the middle centering ring” problem. Something to consider next time.

View attachment 636861

I like this for a nose cone, ive been wanting to get the eggtimer mini and do this for a nose cone