Tight fitting motors, how do you solve the issue.

Discussion in 'Low Power Rocketry (LPR)' started by Shade, Jul 23, 2015.

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  1. Aug 5, 2015 #31

    Micromeister

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    Ken:
    Peeling motor is something that shouldn't be done period. Light sanding with 220 to remove the aft mushroom "burr" is perfectly safe as long as it doesn't take of too much

    The slight swelling on the propellant end is I'm told by Estes is in fact caused by the ramming process in manufacturing. Nearly All Estes motors will have this slightly larger OD on the area of the motor containing propellant. Generally this aft end swelling won't cause a problem with standard BT-5, BT-20 and BT-50 size Estes Standard size motor tubes.

    Several have mentioned Wood glue shrinking of centering rings this can cause very tight motor tubes.

    What I've done in the past to correct most Tight MMT tubes is to use a 1/2" wooden dowel to gently enlarge the tight 13mm (BT-5) motor mounts, 11/16" dowel for 18mm (BT-20) mounts and 15/16" dowel for 24mm (BT-50) motor mounts. This process is a little harder if Estes metal motor hooks are present but it is possible to gently stretch the inside of the motor tube to easily fit the motors without splitting the tube. apply to much pressure on the tube ID can split the tube so progress slowly.
     
  2. Aug 5, 2015 #32

    KenECoyote

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    Sorry John, I was just passing on what I've read/heard and another poster also noted the same. Also someone should tell those New Zealanders that! ;)

    Given safety concerns and how some people go overboard with everything (heck, some will sand a hole into the motor tube using your suggested method), I'll acquiesce and say to be safe, just sand the motor tube. :)
     
  3. Aug 5, 2015 #33

    KenECoyote

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    I should add that perhaps a good practice to avoid this altogether is to put in an empty/spent motor into the motor tube as you're assembling the rocket...you can even add 1 layer of masking tape to the motor (if it fits) so that when the glue around the CRs dry, the tube won't shrink smaller than the motor. I'll be doing that from now on. Be proactive! :)
     
  4. Aug 5, 2015 #34

    JERRYR708

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    Just have to be careful that the engine casing doesn't get glued to the motor mount. I have used an empty engine case to push a retention ring inside to make it centered and almost forgot to remove it in time before the glue started to hold it permanently.
     
  5. Aug 6, 2015 #35

    jqavins

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    I think the idea was to have the empty case inside while gluing on the centing rings to prevent "wasp wasting" due to glue shringage, as discussed above. My concern would be if the shrinkage happens anyway you'll have a bugger of a time getting the empty out. It's probably best just to go easy on the glue or use one that doesn't shrink.
     
  6. Aug 7, 2015 #36

    dave carver

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    +1 to this. The cutting of the paper motor tube flares the end out a bit making the motor fit tight in the motor mount tube. a bit of sanding to bring the motor to the same diameter the whole length goes a long way to making the motor fit. I think they use a rolling cutter like a real sharp pizza cutter and because the paper has to go somewhere it flares the end. Just reduce the diameter just enough to ease the fit :)
     
  7. Aug 7, 2015 #37

    Solomoriah

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    Is it my imagination, though, or do the Quest Chinese engines tuck in at the ends rather than flaring out?
     

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