Announcement

Collapse
No announcement yet.

Don't trust them!

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Don't trust them!

    I was working on the connecting rod to a model steam engine today, and was drilling a 19/64" (about .297") hole before reaming to .302". Same as an N drill, but the drill would have made too big a hole. Turns out, so did the fractional, hole .303" diameter, and I thought I had plenty of room to spare. Don't trust 'em! Shoot a test hole first, before you have to make the sad face.
    I'm here hoping to advancify my smartitude.

  • #2
    Its yer own fault sir!
    Most of the sources suggest a 3% smaller drill than the size of the reamed hole.
    In your case drill should have been .293 or 0.009" smaller
    FSWizard - Free Online Speed and Feed Calculator

    Comment


    • #3
      It's always my fault! No 'bout adoubt it. It just amazes me how many ways there are to get it wrong, and I seem to find 'em too. Not complaining, just didn't see this one coming. Very avoidable tho', you are right.
      I'm here hoping to advancify my smartitude.

      Comment


      • #4
        Twist drills are a roughing procedure. Never expect one to drill on size.

        Comment


        • #5
          Yea its just annoying how much they drill oversize at times, almost never undersized. And no need to kick the clumsy bastard while hes down gizmo2, im sure hes going to be down there kicking himself for awhile looking for those couple thou that fell outta his hole. :P
          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

          Comment


          • #6
            Best method is to get those fancy 3-flute "drills" (don't know their english name), they make the hole round(er) and straight(er) after a twist drill and leave the needed size for a reamer. For example, if I want 16H7 hole, I drill with 15 mm drill, then use the 3-flute to get to 15.75 mm and then shove a 16H7 reamer down the hole. Works everytime and provides expected results.
            Amount of experience is in direct proportion to the value of broken equipment.

            Comment


            • #7
              Called core drill here as their main use is in opening cored holes up in castings without grabbing.
              Downside is, not saying they don't exist but I have not seen any under about 1/2"
              .

              Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



              Comment


              • #8
                OK then, I will not be finding anything except basic twist drills in my local suppliers' in .5mm sizes, anything more sophisticated would have to be ordered in for me, and of course I would have to know what to ask for!

                So, supposing I need 6mm hole, how close will I be if I drill 5mm then 6mm? Maybe 5.5mm then 6mm?

                Comment


                • #9
                  3% smaller than the size of the reamer
                  ...
                  ...
                  FSWizard - Free Online Speed and Feed Calculator

                  Comment


                  • #10
                    I often wondered what the rule of thumb was for drill size before reamer size. I always assumed as long as the drilled hole was within the tapered part of the reamer I was good to go.
                    Andy

                    Comment


                    • #11
                      Brownells has some 3 flute bits in small sizes.

                      JL.....................

                      Comment


                      • #12
                        If I'm picky about a hole dia, I drill about .010 smaller and finish with the proper size. Checking the drill dia at the tip is a good idea to make sure the drill is actually the right size. Where ther are multiple users, you can never count on a drill being in it's proper storage slot. Bob.

                        Comment


                        • #13
                          The way I understand it Macona is responsible not only for drills cutting oversize but global warming, sun spots, and flat beer. The man carrys a heavy burden. ;-)
                          Last edited by Forrest Addy; 05-27-2013, 06:09 PM.

                          Comment


                          • #14
                            A new (good) drill, and/or a well sharpened drill, is less likely to drill oversized. Dull, poorly sharpened, a little bent, oversized every time.

                            doug

                            Comment


                            • #15
                              Me too. It seems that with no center point for it to swing around it's more difficult for the second drill to drill oversize. It kinda acts like a "roughing" reamer.

                              Phil

                              Originally posted by Bob Fisher View Post
                              If I'm picky about a hole dia, I drill about .010 smaller and finish with the proper size. Checking the drill dia at the tip is a good idea to make sure the drill is actually the right size. Where ther are multiple users, you can never count on a drill being in it's proper storage slot. Bob.

                              Comment

                              Working...
                              X