T-Nuts And Motor Retention

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judo

judo

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This one comes up frequently. I took the recent posts by Spannerman about motor retention and Doggonewild and his beveling jig and popped out of my rocket slump. Here follows a thread on using t-nuts for motor retention. (Cat not appearing in this thread.)
 
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The centering ring, t-nuts, screw, retainer (washers in my case), epoxy (mine's 30-minute), mixing stuff, tape, and a center-finder or rule if you feel lucky.
T-nuts01.jpg
 
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Start with the aft CR. This one is a Semroc BT-80 to #9.
T-nuts02.jpg
 
Yeah, ok, it was marked in the other picture already. This ain't Industrial Light and Magic. I did find out that by rotating my CR 180 degrees that my center finder is actually a bit off. Thank you Chinese tools from Harbor Freight. You get what you pay for. But, as I'm only putting rockets into air, not space, I'll cut the rant off now.
T-nuts03.jpg
 
Ace Hardware's finest. These #8 t-nuts plus two washers and two screws set me back $1.45. I've bent two of the barbs down and one off. The CR's are not all that thick.
T-nuts04.jpg
 
I've filed one edge down so I can place it closer to the MMT. The washers just fit over the edge of the MMT and the next size up washer reaches too far and weighs more.
T-nuts05.jpg
 
This is where the t-nuts will fit together against the MMT.
T-nuts06.jpg
 
Here's where the holes go. Mark with a tap or nail so your bit does not wander. Drill gently. Don't crack the CR.
T-nuts07.jpg
 
Clamped for safety. No, you are not strong enough to hold down the ring by hand. Your drill will out-torque you.
T-nuts08.jpg
 
Mix just a little bit of epoxy. You just need enough to put into the holes you just drilled.
T-nuts09.jpg
 
Make sure that your MMT fits cleanly into your CR.
T-nuts10.jpg
 
Put some masking tape around the inner and outer diameters of the CR. This will prevent epoxy from going places you don't want it to. I hope.
T-nuts11.jpg
 
Put some oil or light grease on your screws and thread them into the t-nuts. Mix up some more expoxy and cover the t-nuts. Be generous but not crazy. The screws keep the epoxy out of the threads and the grease lets you remove the screws after curing.
T-nuts12.jpg
 
Should be even easier for me to do because I have a 4'' airframe so i shouldn't need to file the nuts down :)

Il get some pictures of my attempt :D

Sam.
 
Nice tutorial -- that will help answer questions for folks!

FWIW, when I do this, rather than put the screws in with grease on them (nice idea, btw), I just pack the threads of the T-nuts with Vaseline. It serves the same purpose.

-Kevin
 
just another option is to use threaded inserts instead of T-nuts the work the same but require far less flange room. I generally set them solid in epoxy with the machine screws in place simply covered with a layer of masking tape.
 

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