Case blister, is it toast?

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Zyzzyva1000

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Have never had this happen before (did have a burn through, but not this). Brand new 29-180 case. Used an H238T, flight was perfect. Didn't notice anything wrong until I got home and noticed the slight blister on the case (in the photo the forward closure is there, but this was after the aft end of the motor when it occurred) when I was unloading it to clean. You can just barely feel the blister, and you can see some discoloration inside. I had made sure to grease the outside of the liner tube well after my last issue. The liner was burnt in a small triangular pattern extending up from the nozzle to this area (forgot to get a picture of that), but was otherwise intact, as as the aft o-ring and the nozzle itself.

So, question: is the case toast now? (my suspicion is that is the case, but I figured I would ask before I toss it since Ive never seen this before with my 38 mm HW)
 

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Have never had this happen before (did have a burn through, but not this). Brand new 29-180 case. Used an H238T, flight was perfect. Didn't notice anything wrong until I got home and noticed the slight blister on the case (in the photo the forward closure is there, but this was after the aft end of the motor when it occurred) when I was unloading it to clean. You can just barely feel the blister, and you can see some discoloration inside. I had made sure to grease the outside of the liner tube well after my last issue. The liner was burnt in a small triangular pattern extending up from the nozzle to this area (forgot to get a picture of that), but was otherwise intact, as as the aft o-ring and the nozzle itself.

So, question: is the case toast now? (my suspicion is that is the case, but I figured I would ask before I toss it since Ive never seen this before with my 38 mm HW)
Email Karl at aerotech and send pics. I dont think a case blister in that location would have been due to assembly error. More likely a void in the grain. Aerotech may warranty and send you a new one. Karl has always been great to deal with when something popped up.
 
Well, apparently it was not ok. I sent it back to AT, and was sent a new case. Threads are borked on the new case (can't thread either closure onto the forward end of the tube, both thread fully and easily onto the other end).


Edit: closure inspection it appears the lip where the smooth bore of the case starts and the threads end is too large on the one Side. Anyone ever run into that? I think that is abutting the end of the closure and preventing it from continuing forward. Some light dremel work?
 
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Ok, so it's not the threads (I was able to thread a forward closure from a 29 mm 40-120 case onto this case. And since the previous forward closure worked with the blistered case, I can only assume it's the 'lip' on the inside of the new case. Is it safe to take a Dremel to this lip?
 
I would take an exacto knife with new blade and scrape any burrs down. Knife does a great job deburring aluminum. More control than a dremel.
 
I would take an exacto knife with new blade and scrape any burrs down. Knife does a great job deburring aluminum. More control than a dremel.
Good thought. Just tried that, no real burr there. Not sure what the deal is, both closures thread onto one end of the casing without issue (smooth as butter). Neither make it more than a turn on the other end without the whole thing binding. Guess I am just not meant to use 29 mm motors.
 
Ok, so it's not the threads (I was able to thread a forward closure from a 29 mm 40-120 case onto this case. And since the previous forward closure worked with the blistered case, I can only assume it's the 'lip' on the inside of the new case. Is it safe to take a Dremel to this lip?

The threading on the 29 40-120 hobby line case and the 29 180 high power case are completely different. Did you send in a 180 and receive a 120 back ?
 
The threading on the 29 40-120 hobby line case and the 29 180 high power case are completely different. Did you send in a 180 and receive a 120 back ?
But the threads seem to be the same? No it’s a 180 case. I realize the closures are completely different but the threads seem to be the same
 
Got a thread gauge? If yes, check the pitch on both the closures and the bad end. If no, brush a light coat of grease on the bad thread and melt a blob of wax into the thread, remove, then check the pitch of the wax blob against the closure's thread.
Got a vernier caliper? If yes, measure the inside diameter of the threads of both ends and compare. If no, maybe cut a square (as in parallel sides) piece of cardboard out to the exact inside diameter of the bad thread and compare against the good end. If the piece is looser in the good end, the ID on the bad end is too small and the whole thread form could be undersize.
Check the bad thread with a magnifying glass and inspect the cleanness of the thread & the depth compared to the good end. Also check for damage towards the end eg. is there a section of thread pushed in or pushed down?
It can happen where the threading insert used to cut the thread breaks during a job. More unusual for softer Al-alloy components though (I'm used to it with harder materials like SS).

TP
 
The threads are different .
Do not try to use that case and never mix the 2 closures they are close but under pressure it will fail.
Sent a note back to Karl and let him know .
Wasn't planning to use it that way, just didn't have anything else the same diameter, and was curious.

Edit: Apparently the thread issue is a recently discovered issue (new machinists) and Karl is taking care of it.
 
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