Dealing with body tube edges

[AstroAbaqus]

Dear all, I am relatively new to this forum and I hope to have not replicated any previous post I did some search but nothing popped out. I am currently in the process of building my first HPR from scratch, I have a full design on Open Rocket and a decent cad on Fusion 360 and if you can point me to the proper section where I can share it would be nice (I guess scratch build or build plan but not sure).

Anyway my issue is with my LOC 4 inch body tubes, they are nice solid, I love them . However, I noticed that the ends are a bit ruining inside, I did not handle them a lot since I am acquiring material slowly for this built. But I am concern that they could ruin even more in the future. I had a similar problem when I did my first ever cut on the motor mount tube, and I used a small amount of CA and then sanded with fine paper. Results was okish, but I am afraid to do the same on the body tube for looking and fit reason.

Do you have a better solution to this apparently silly issue? I am over thinking as many of new comers to rocketry? I had other builds but they were much simpler and did not required me doing significant alteration and I was more focused on developing the electronics. Thank you very much for any help. I really enjoyed being on this forum and learning from many of you

 

[prfesser]

Not certain what you mean by "a bit ruining inside." Can you post a picture?

 

[AstroAbaqus]

Not certain what you mean by "a bit ruining inside." Can you post a picture?

I know probably is nothing, but my worry is that it could be worst in future.

 

[Steve Shannon]

That fraying is normal on thick cardboard tubing. What you did is right: soak the ends in CA or wood gardener and let it dry, then sand to the finish you want.

 

[manixFan]

That fraying is normal on thick cardboard tubing. What you did is right: soak the ends in CA or wood gardener and let it dry, then sand to the finish you want.

In addition to using the CA, I also 'chamfer' the edge first, either by just running something smooth and roundish along the inside while pressing firmly to the outside, or if I have a hard fiberglass nosecone of the right diameter I'll insert that backwards and use it to compress the fibers along the inside edge of the tube. Then apply thin CA and sand it smooth after it has cured. On big tubes sometimes I'll use a thin CA followed by a medium CA that I will spread thin with a popsicle stick or something similar.

I always have to wear a mask when I sand anything, especially with CA. It seems to bother me more than most things.


Tony

 

[teepot]

Ditto above. Put the CA on the inside edge of the tube, let dry and sand. I do that on every body tube and the bottom of the motor tube.

 

[AstroAbaqus]

Thank you all for your advices! Will do this today!

 

[AstroAbaqus]

I have carefully done what all you suggested and worked amazingly. I used CA with a brush let it dry and sanded gently with 150 sanding paper. Thanks a lot for the advice about the mask, since the dust was way more thinner than usual. I dry fitted everything and I am happy since all my drawings reflect nearly perfectly in real life. I also dry fitted my fins and after a small work with the precision knife they slide in with just enough friction. My only issue is that I realised that probably between the fin tab and the motor tube there is something like 1 mm gap, probably even less. Now if I apply some pressure, which should be the case when I use the fin jig, the fins go into contact without any visible distortion of the airframe. Now my question is, do you think I have to add a layer of FG, very thin one, to just be sure or is fine since during curing I will apply pressure and this will be ok and I am just overbuilding as all new hpr rookie ?

 

[OverTheTop]

The CA glue works well on cardboard tubes but do it in a ventilated area. The fumes are not good for your health. Incidentally it also works when cutting holes in fiberglass to keep the little sharp ends of the fibers in place after you cut or drill a hole. The hole can then be filed or sanded nicely.

What motor are you looking at flying it on?

 

[AstroAbaqus]

The CA glue works well on cardboard tubes but do it in a ventilated area. The fumes are not good for your health. Incidentally it also works when cutting holes in fiberglass to keep the little sharp ends of the fibers in place after you cut or drill a hole. The hole can then be filed or sanded nicely.

What motor are you looking at flying it on?

Totally agree regarding fumes, I worked with lot of composite at Uni and we always worked with air suction system when cutting and you could see literally fibres flying.

Regarding the motor as you can imagine the 54 mm is not ideal for a lvl 1, especially due to its dimensions and weight, so I will use an adapter to scale back to 38 mm. From Open Rocket, adding some uncertainty on the mass it will be 2.8 kg (6.2 pounds). I will go for CTI since is much more available here in UK atm, and from simulation the best I could use is a I216. But also other I impulse motor could be ok. Is a bit large and heavy because my idea was to have a training built to prepare something capable of doing Lvl 1 and lvl 2 ( not in the same year ).

 

[jqavins]

Now if I apply some pressure, which should be the case when I use the fin jig, the fins go into contact without any visible distortion of the airframe. Now my question is, do you think I have to add a layer of FG, very thin one, to just be sure or is fine since during curing I will apply pressure and this will be ok and I am just overbuilding as all new hpr rookie ?

I'm not sure I understand the issue. If the root edge is in good contact with the MMT while the glue is curing then you shouldn't need any special measures. You'll need normal fillets, of course. A well glued root edge and good fillets are all you need. But if you want to put a strip of thin FG cloth in the fillet, extending a little way up the fin and onto the tube, there's no harm in it.

 

[OverTheTop]

Totally agree regarding fumes, I worked with lot of composite at Uni and we always worked with air suction system when cutting and you could see literally fibres flying.

Let's hope the suction was sufficient .

Did a tour of a Boeing plant a while back. All the CF machining was done under water.

 

[manixFan]

Let's hope the suction was sufficient .

Did a tour of a Boeing plant a while back. All the CF machining was done under water.

Exactly why I only use a wet tile saw to cut CF and always wet sand it. I'm sure not as safe as doing it under water, but as close as I can get. That and never go near it with any kind of tool without wearing a mask.


Tony

 

[AstroAbaqus]

I'm not sure I understand the issue. If the root edge is in good contact with the MMT while the glue is curing then you shouldn't need any special measures. You'll need normal fillets, of course. A well glued root edge and good fillets are all you need. But if you want to put a strip of thin FG cloth in the fillet, extending a little way up the fin and onto the tube, there's no harm in it.

I did a silly mistake in the cad, when I generated the dxf file for the laser cutter I neglected did not saw a small overlap between my fin and body tube, less then a mm. Well I sorted out by carefully cutting out a slot where the fin touch the airframe bodytube, and now it snug in like a charm. Exacto knife and some time and I fixed it. Now waiting for the resin. I am also fixing my workshop so I can work in a more proper space hehehe. The fins looks so loose because they are not glued but once all assembled they are pretty nice and straight. The rings have some notch to centre them, but I have also a jig for the bonding step.