all right let's get straight to the point today we're going to be talking about locating a clearance hole be using GD&T I'm going to walk you through the pick three method what we have here is we have a typical flat plate with a simple clearance hole drill right here you have your front section view and you have your top to you first thing you're going to do we're gonna pick your datums you're David they're your starting point it's the surfaces the features that you want the machine is to locate your hole off of typically there's
three and typically you'll see a B and C which are your datum symbols on the drawing first datum that I'm going to pick is this flat surface here this is a pretty standard what this does is this tells the machinist that you want this holes axis to be perpendicular to that surface second datum you pick this side surface here it's a service that I want to locate the hole across from third day this front surface here for bottom surface so service I'm going to locate the hole up front last thing you want to do you
want to show these datum symbols on your drawing in that order second thing interview depicted dimensions through your design values you're telling the machinist how far over from your second and third datum you want to locate that hole do not use plus or minus dimension that you typically see on drawings so what you usually see is something similar to this if you not do this drop the plus and minus off that then box your dimension and take your dimensions your design values and place them here in this location in this location so the machinist knows
how far to locate that hole from your neighbors one and a half inches box one and a half inches box and now he knows one and a half inches over one and a half inches Oh third thing you're gonna do good picture tolerance your tolerances how much you're allowing the machines to be off when he or she drills this hole notice we eliminated your tolerance here so we have to place it somewhere and where we place that is inside the GMT symbol right here typically an industry you'll see 14 thousands once you now want to
do is you want to take this gbmt symbol that I've generated for you here and just simply place that underneath your size and your size tolerance for that hole then you're going to take your datums in order a B and C first second third you're gonna place them in order inside your D DT single so you've told once again to ashiness to locate that hole perpendicular to your first datum located over from your second datum and locate up from your third DM and that's straight to the point
