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Question for machinists ?

Discussion in 'Off Topic Threads' started by 635 G, Sep 16, 2009.

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  1. 635 G

    635 G Well-Known Member

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    If you had tow pieces of steel & wanted to attach the pieces of steel with screws which class of screw would you use for the following conditions:

    1) the blocks of steel are 1/2" x 1/2" x 2"
    2) they are subject to different heating & cooling rates
    3) the bottom block is tapped with (2)-10-24 threads
    4) the top block is champfered for a flat head screw (clearance hole for screw)
    5) would you use a class 8-case hardened screws or softer screws

    Phil Berkowitz
     
  2. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Just use a couple Unbrako brand cap screws.
     
  3. yobyllib

    yobyllib TS Member

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    I would use the cap screws mentioned,but with a lockwasher underneath.
    The kind that look like a split ring with a spring bend in them.
    This will keep tension against the threads during rapid heating and cooling,if the
    temps involved would break a good ole Loctite seal on the threads.
     
  4. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    In your 1st. post you mentioned the top piece is countersunk for flathead screws, so how are you going to use lock washers?
     
  5. The Rock

    The Rock Active Member

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    82 Deg lock washers ?

    Rock

    Jim
     
  6. crusha

    crusha TS Member

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    Have them turned out of Invar?
     
  7. yobyllib

    yobyllib TS Member

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    He can,assuming he can,use an endmill to cut a flat pad to nest the washer and
    shcs in place of the flathead.it will look ugly though.
    I just looked at my mcmaster carr catalog,and they do have an "external tooth
    lockwasher" for flatheads.
     
  8. 221

    221 Banned User Banned TS Supporters

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    Flathead's working loose?...... YEAH RIGHT.....That washer just makes them easier to remove.
     
  9. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    If the screws coming loose is a major concern, drill&tap the block for set screws to lock the 10-24 flatheads.
     
  10. chrisg

    chrisg Member

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    stick with the flatheads and use a centerpunch to stake them around the perimeter of the flathead.
     
  11. Quack Shot

    Quack Shot Active Member

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    Drill a small hole around the circumference of the flathead, overlapping the material and tap and install an allen or torx head flush setscrew. Either that or just weld the suckers together and forget about it.

    What stresses are going to be applied and in what directions? That would tell you about what class of fastener to use. Sometimes a grade 5 is preferable to the grade 8, since the hardened fasteners can fail sooner under certain conditions. You might need something heavier than the 10-24 fastener if there is any appreciable load applied.
     
  12. Brian in Oregon

    Brian in Oregon Well-Known Member

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    If sheer stress is an issue, drill the two plates for roll pins. That will help take the stress off of the screws, which can then simply hold the plates together.
     
  13. 635 G

    635 G Well-Known Member

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    The bottom block attaches to the forend wood, the top block is a part of the forend iron. The heads of the screws that attach the the pieces together sheared off. There is no (apparent) lateral movement. I plan on replacing these srews every 2-3k rounds. Just want to get the best screw possible. The top is closer to the heat of the barrel.

    Phil Berkowitz
     
  14. JEB

    JEB Active Member

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    Toolmaker 251 is on the money. Use a QUALITY screw like Unbrako. If my memory is correct, they are made from 4340 steel and heat treated to about Rc 38. That would bring them to around 180,000 - 200,000 psi. You probably should also use red locktite, especially if the threads are a little sloppy. I do not believe that your gun will get hot enough to make a difference. Also for the record, internal tooth lock washers work better than the spring type.

    John Bergman
     
  15. GARMASTERS

    GARMASTERS TS Member

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    Red Loctite?? Use Stud and Bearing mount (retaining compound).
     
  16. JEB

    JEB Active Member

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    Tube red Locktite blue

    JB
     
  17. 221

    221 Banned User Banned TS Supporters

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    IF you Glue in those small FHCS, and you will be drilling them out. Using RED Loctite Type thread locker on small screws "WILL" bite you in the ass. They make a small screw Threadlocker.....Blue and Purple....NOT RED. If you have to glue in FHCS's you have a design problem. We use anti seize or a Bolt Guard material on FHCS to make removal easier. They by design have a smaller and shallower hex than a SHCS.....You have one chance to remove a FHSC and then, never reuse one, especially the smaller sizes. Always use a new screw and a new tool.
     
  18. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Phil, what kind of gun is this forearm for, if you don't mind? Sounds like a heavy duty coupling except for vibrational shear? That may be what's popping the screw heads off. A cut-out in the bottom piece, 111___________111 with the top piece fitted in between that cut out may have prevented the screw heads from popping in the beginning?

    I had a grade 8 tapered head screw pop off on my Carey stock a while back too,no heat involved there. 30 some years of that screw head taking the rebounding of the springs in a straight pull and it finally gave up too! Hap
     
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