Rivets or screws on internal aeropack retainer?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

rderstadt

New Member
Joined
Aug 29, 2014
Messages
2
Reaction score
0
I'm building my first minimum diameter model (Madcow Tomach) and was wondering if it is necessary (or a good idea) to screw or rivet the internal aeropack motor retainer in place (i.e. through the wall of the body tube and into the retainer) rather than use JB Weld. My thinking is this might be more secure and would also allow me to remove it in the future if needed. Has anyone done this? What kind of screws or rivets should I use and how many would you suggest? Or, should I just stick with the JB Weld and not worry about it? Thanks.
 
I've heard of people doing it, but I'm not sure what screws they used. I'm not sure rivets would hold up so I would go with screws. Hopefully someone else can weigh in.
 
I also did not feel the idea of bonding the retainer in place was cool so I used three 6-32 screws on a Mongoose 38 and it seemed to work rather well. The only issue is the retainer is rather thin and as such there was not much for the screws to bite into. I used button head cap screws as I did not feel the need to us countersink (I was not of the opinion it would make that much difference as I was not using a tower and had buttons on the outside). Unfortunately the motor failed on the first flight and actually pushed the retainer forward distorting the holes. As such the idea of bonding nuts to the inside never took shape. I had planned on asking Aeropack if they would consider a custom one where the walls were about .187 thick so I could tap the holes in the body. Never got around to it.
 
Last edited:
Build up a small area inside the retainer where the screw(s) go through with JB Weld. Then drill and tap.
 
Considered that, however never got to it. Does JB-Weld hold a thread pretty good?

Yes. I used this in a Blackhawk 38 to attach the shock cord. You can see the built up area. If you go screw route instead of epoxy (which makes sense), tap through both the body and retainer for best retention. A variation is wood plates with blind nuts epoxied inside the retainer. I used this on my L3 ebay.

4.jpg

006.jpg

010.jpg
 
Last edited:
I built a minimum D 38 from scratch...........
I drilled and tapped 4/40 into the Aeropac internal retainer...
Be certain that you have it at the correct depth
so that the aft motor closure is up against the aft of the airframe
so the motor isn't pushing against the screws to propel the rocket...
Those are beautiful pics by Titan of the way he did the blind nuts....
I did mine a bit different... But the same principal..... Same end result.......
Mine are turned upside down,, large flat steel surface against the airframe wall,,,, put the screw in to hold firmly in place,, then bury in any good epoxy that won't run... make a small mound around the blind nut....
Such as Aeropoxy 6209 or Rocketpoxy or West mixed with milled glass to stiffen it up..

The epoxy carries no load,, just holds the blind nut in place,, and you are screwing your steel screw into steel threads....

You can't get much stronger then that..........

Teddy
 
Might be possible to drill holes in the retainer large enough to epoxy/press PEM nuts into them and then contour the exposed part the PEM on the OD of the retainer. PEM nuts are available from McMaster-Carr in steel, stainless steel, in sizes down to 2-56
 
I am in the process of building the 54mm MD carbon Tomach and I also opted for the internal Aeropack. Like you I wondered how to mount it and after a talk with Teddy (one bad hawk) I opted to use the self clinching nuts and machine screws. So far I installed them for the payload tube to the altimeter bay. For the aeropack I was hoping to use the same machine screws in the pic and simply tap the aeropack.

View attachment 247481

As you can see I used three, not a very scientific formula...3 fins, three screws.

View attachment 247483
 
I am in the process of building the 54mm MD carbon Tomach and I also opted for the internal Aeropack. Like you I wondered how to mount it and after a talk with Teddy (one bad hawk) I opted to use the self clinching nuts and machine screws. So far I installed them for the payload tube to the altimeter bay. For the aeropack I was hoping to use the same machine screws in the pic and simply tap the aeropack.

View attachment 247481

As you can see I used three, not a very scientific formula...3 fins, three screws.

View attachment 247483


I agree completely Michael,,, ( you really do some clean,, neat work )......
On a 3 fin rocket of mine,, all screws and rivets go inline with the 3 fins...
The reason for this is so I have 3 spaces 120 degrees apart around the airframe to put vent holes that will be in smoooooth air flow,,,
airflow uninterrupted by screw or rivets.......

Teddy
 
I haven't used this system so...

After a flight using 75/98mm motors has anyone had problems with the aft closure, the forward closure, or both loosening before the retainer's bolt comes free from the 3/8" tapped forward closure's threads? It seems highly likely that lubed motor casing threads would loosen first leaving the remaining casing parts inside the tube. I think I'm a fan of the bolt method as an insurance policy against stranding casing parts.

Thanks,

=G=
 
Back
Top