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  1. #1
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    571

    Single all-thread rod to secure av-bay sled?

    Most sleds are secured in the av-bay by a pair of all-thread rods. I was getting ready to drill holes in the av-bay bulkheads for 2 rods. Both bulkheads already have holes drilled in the center. This made me wonder, instead of drilling 2 holes in each bulkhead for two all-threads, why not just use the existing center holes and use just a single all-thread? I've used a single all-thread successfully for NC-mounted altimeters, why not do the same in the av-bay? Just need to devise some method of keeping the altimeter from spinning around the rod.

    Any thoughts on whether a single all-thread will work?
    Happy New Year,
    Bill


    L1 3/25/17 H135
    L2 8/12/17 J180

  2. #2
    Join Date
    13th June 2014
    Location
    Cocoa Beach, FL
    Posts
    3,551
    Ive done that on 3 rocket with 1/4 threaded rod. Used forged eye-nuts to secure lids/shock cord. Look up crazy Jims Punisher build


    Sent from my iPhone using Rocketry Forum

    Tim
    L3 NAR 98225

  3. #3
    Join Date
    11th January 2012
    Location
    Commonwealth of VA
    Posts
    1,561
    I only use a single 1/4" all-thread in my 3" through 5" air frames. I use stainless, or Grade 8, depending on the design.

    -Bill Riley

    TRA: 12294
    NAR: 89196

    A good rule for rocket experimenters to follow is this: always assume that it will explode.
    Astronautics, issue 38, October 1937.


  4. #4
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    571
    Thanks for the replies. How do you keep the sled from spinning?

    L1 3/25/17 H135
    L2 8/12/17 J180

  5. #5
    Join Date
    27th May 2015
    Location
    Charleston, SC
    Posts
    151
    An excellent discussion of how to do a 1/4-20 single all thread AV bay is found in the "Hints" section of doghouse rocketry ( http://binderdesign.com/pdf.html/BUI...IMETER_BAY.pdf ). I have used that approach successfully. Of note, 2 caveats apply: 1. a cotter pin is epoxied to the bulk plate and a wire is then twisted around the eye nut and connected to the loop of the cotter pin (see pictures in attached link). This prevents the eye nut from loosening due to the wind/shock cord twisting after chute deployment. and 2. Having an all thread adhering to the center of one surface of the altimeter sled decreases the available space to attach a tracking transmitter or GPS unit within the AV-bay. The advantages of this approach are less AV-bay weight and a simpler way to open & close the AV-bay.

    Fred,L2
    KG4YGP
    ICBM member, S.C.

  6. #6
    Join Date
    13th June 2014
    Location
    Cocoa Beach, FL
    Posts
    3,551
    Quote Originally Posted by billdz View Post
    Thanks for the replies. How do you keep the sled from spinning?
    Size the sled up to the bulk plates or secure the sled with nuts. Lots of options.
    Tim
    L3 NAR 98225

  7. #7
    Join Date
    3rd February 2012
    Location
    So Cal (ROC, TRASD, SCRA)
    Posts
    2,562
    I do almost all of my sub-4" rockets with one 1/4" allthread, and I generally use U-bolts for the shock cords. Tighten them up decently and they won't spin.

  8. #8
    Join Date
    9th October 2013
    Location
    San Jose, CA
    Posts
    659
    I do this on almost every rocket I've built. Though I don't use any all-thread, but a pair of 1/4"-20 forged eyebolts, with a coupler nut to join them together. I also use the coupler nut to hold my sleds (3D printed) in place, so the sled typically captures the nut and the upper eyebolt (also keeps the sled from turning), bulkhead and nut remain together along with the sled, and the lower bulkhead and eyebolt are removed to insert the works into the coupler, and the bottom eyebolt is then screwed-in to close-up the bay. My local hardware store carries Stanley forged eyebolts in both 2" and 4" lengths, so I can do bays up to ~7.5" with just the two bolts and coupler nut, I could do longer with two nuts and some all-thread, but I don't have any bays likely to be that long on the roadmap. These eyebolts also have shoulders just below the eye, so I don't need any nuts/washers on the outside, on the upper bulkhead a nut/lock/washer set locks the eyebolt to the bulkhead. I use the longer coupler nuts (~1 3/4") to ensure several complete turns on each side, haven't had an eyebolt even start to come loose on almost 50 flights this way (and no swivels). On 54mm and greater bays I tend to just leave the eyebolts centered, on a 38mm rocket I shifted the eyebolts as much as I could while keeping their loops from hitting the airframe, to leave enough room for my altimeter and battery.

    The only ones I have that aren't this way are my Binder Excel's bay, which is built the stock way with a pair of all-threads running top-to-bottom and shorter eyebolts on-center at both ends (but if I ever re-build that bay I'll consider converting it, I have another 4" in the works I plan to do the above way, though I may use 5/8" eyebolts instead), and a GLR Firestorm 54 which was built their stock way, a single offset all-thread running top-to-bottom and shorter eyebolts on-center at both ends, but after an early ejection split one of these (wood) bulkheads in half separating the rocket into two pieces I decided to go with the above approach on the rebuild so that the bulkheads themselves are not carrying any shock loads (beyond holding the avbay coupler itself). FG is probably strong enough that the load transfer wouldn't be so bad, but on a wood bulkhead I'd rather not have it carrying any significant load.

    Last edited by woferry; 2nd January 2018 at 05:49 PM.
    Will Ferry (Launches & Videos) NAR #96512 (L2) / TRA #15328 (L2) / LUNAR #2759
    L1: 9/2013 @ XPRS, GLR T-Bolt "Thunderbolt" (R.I.P.), H148R
    L2: 4/2016 @ TCC Helm, Binder Design Excel w/DD "dd2.xls", J315R
    Impulse flown (flights): 2013: 767Ns (2), 2014: 4298Ns (8), 2015: 7486Ns (16), 2016: 11693Ns (18), 2017: 11138Ns (16)

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