Results 1 to 6 of 6

Thread: Drilled Hole positioning query on threaded bolt

  1. #1
    Associate Engineer
    Join Date
    Feb 2014
    Posts
    3

    Drilled Hole positioning query on threaded bolt

    Hi All,

    I've just joined and have a specific question, that I hope you can help with;

    I'm up-issuing a drawing at present, relating to a machined block with a machined bolt going through it.

    The bolt has an M12 Thread on it, but there is no indication of what pitch the threads are (I don't know much about that anyway). I don't have any thread gauges available, only a vernier caliper.

    On the existing 'assembly drawing', there is a note which states:- Screw bolt in to block face, hand tight only. Then back off 1/4 turn.

    Then drill a 1/8" hole on the center line (of the bolt), completely through the assembly.

    The threaded end protrudes through the other side of the block, and a cap nut is fitted to it, with the same instructions as above.

    The 2x 1/8" holes are then pinned with slotted roll pins.

    The crux of my query is;

    How can I determine the bolt length, and the positioning of the 2x holes on the bolt? (1 on the shank near the bolt head, and the other through the threaded end).

    I want to add reference dimensions for the benefit of the machinist who will manufacture these items.

    How do I work out what distance the head of the bolt is from the face of the block?, after turning it back a 1/4 turn, from being hand tight against the face of the block?

    I can only guess at this at present, but there should to be a way to work it out, should there not?

    I would appreciate any help, that any of you can provide.

    Thanks & regards,

    Brian.

  2. #2
    Project Engineer
    Join Date
    Oct 2013
    Posts
    92
    well you need to know the pitch. every turn of the bolt will produce 1 x pitch. (or fraction of) I suspect that no pitch means it's a m12 x 1.5 (coarse) but could be 1.75 too but that should be noted on the print. you said machined bolt (to me that means an inhouse made part) is the pitch on the print for the bolt?
    Last edited by GlennD; 02-05-2014 at 06:21 AM. Reason: spelling corrected an omission

  3. #3
    Associate Engineer
    Join Date
    Feb 2014
    Posts
    3
    Quote Originally Posted by GlennD View Post
    well you need to know the pitch. every turn of the bolt will produce 1 x pitch. (or fraction of) I suspect that no pitch means it's a m12 x 1.5 (coarse) but could be 1.75 too but that should be noted on the print. you said machined bolt (to me that means an inhouse made part) is the pitch on the print for the bolt?
    Hi Glenn,

    Thanks for the prompt reply.

    Yes it's a part that may originally have been made in-house, but we now get them machined elsewhere, as we don't have a machining facility here. Unfortunately, there is no information on the original drawing in regard to the thread pitch.

    The thread on the manufactured part is about 25mm long and in that length, I've counted 14 threads - if I divide that into 25, it gives me 1.79, which is closer to a 1.75 thread pitch.

    I've also set the verniers to 1.75 and sighted it on 2 of the thread 'points' and it appears to fit.

    If this is the case, then am I right in assuming that a 1/4 turn is 0.44mm? (If that's so, then 0.5mm would do for all intents and purposes).

    Incidentally, I am studying towards a B Eng in Mechanical Engineering, with the Open University (but currently getting my maths up to scratch, rather than studying engineering modules) ... is there any specific courses or experience that you could recommend, to teach me all of this sort of stuff? - I'm not in a position to do an apprenticeship in a machine shop at present, though that would probably be the best thing.

    Thanks,

    Brian.

  4. #4
    Lead Engineer Cake of Doom's Avatar
    Join Date
    Aug 2012
    Location
    UK
    Posts
    435
    bolt threads.jpg

    This should help you out a bit.

    As soon as you can, get your hands on a copy of The Machinery's Handbook. It can't replace hands-on experience of course but I've found it one of the most valuable reference books to own.

  5. #5
    Associate Engineer
    Join Date
    Feb 2014
    Posts
    3
    Thanks Cake of Doom :-)

    I may have an older pdf version of the handbook somewhere - must have a look for it.

  6. #6
    Lead Engineer
    Join Date
    Aug 2013
    Location
    Houston TX USA
    Posts
    417
    As per Cake of Doom's reference, I checked my Machinist Handbook and found that a 1.75 pitch is what is shown as the standard for M12 metric Cap Screws.

    At the same time, your instructions are to drill both the block and nut x-holes "after assembly" and, from a practical standpoint, I believe that is the prudent method to use to insure you get a clean matched set of holes for the pin insertions. If you try drilling the holes before assembling the bolts into the block and nut you run a large risk of either a linear or lateral offset of the holes' alignments.
    Last edited by JAlberts; 02-05-2014 at 02:44 PM. Reason: added required M12 designation for std 1.75 pitch

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •