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center drills vs spotting drills

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  • #31
    I broke a 1/8" bit I often use to pilot holes (its only got like 3/4" of flutes so its rather rigid) off inside some mild steel when it was only like 3/16" deep, really looked like a pain to remove from that side. thankfuly I could drill through the backside but I agree, removing a small drill from a hole is a big pain.
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


    • #32
      If it is in a drill press or mill I have very little problem removing the broken drill you describe without flipping the work over. I use a carbide drill of my own making.
      It's only ink and paper


      • #33
        Originally posted by oldtiffie
        There was an excellent video (U-tube) posted here not all that long ago about a bloke who was using a lathe at a pretty good speed to drill very small holes in a brass jet for an IC engine of some sort or another.
        I believe this is the URL you are looking for:

        However, on my computer it is now a dead link
        Dave A.


        • #34
          Originally posted by Scishopguy

          Another issue that comes up a lot is picking up a center punch mark accurately. One of the old diemakers told me, after the boss had left, that I would have better results if I used a really small drill and just touch the dimple left by the punch. You can see which way it deflects and correct with the BP table until it lines up. Then you step up by drill size and the hole comes out on the money.
          That's exactly what I do...... Didn't know it was a "recognized" method... it works very well, but obviously depends on the accuracy of the layout.

          Keep eye on ball.
          Hashim Khan


          • #35
            center drill???

            for center drills to work really well,not only does the drill tip need to be sharp, and accuratly ground but the angle part of center drill needs to be sharp and free from nicks and dings also. to get precise center hole in home shop, its best to use steady rest, and finish center hole by cutting, with HSS in coumpound toolholder.and also make sure pilot hole is deep enough so live center doesnt bottom out in pilot hole ,and create wobble.i have never bought center punch, i always use broken taps,reground by hand, good hard steel, free too.
            FORD BEATING JAP CRAP SINCE 1941!! CAROLYN JONES(1930-1983 actress)may this lady never be forgotten.


            • #36
              How many people are actually running a centre drill at the recommended speed for the pilot diameter?
              Paul Compton


              • #37
                Originally posted by Carld
                From my experiences locating from a center punch mark is marginal at best. The issue of getting the center punch mark in the exact place is a hit and miss affair.

                I use three ways depending on the needed accuracy of the location. For within 1/32" accurate I use a center punch and a wiggler. For within a 1/64" I use cross hairs marked on the work and a wiggler. For within +/-.001" I use home on the corner of the work and the DRO on my mill.
                What Carl said!!!

                Boilermakers use center punches, machinists use DRO's. I do both so I use both but at the appropriate time.

                One reason a center punch will break is that just because it hasn't broke yet doesn't mean it isn't dull. A dull bit will break just when it is the worst time. When ever I get a new center drill out I dunk one end into the layout fliud to mark it as unused and then I only use the other end until I feel it is dull. After that I grind the dull tip off so I don't confuse it with the other end.

                If you want a spotting drill but can't find them (they are not the most commonly found bit ) then take a broken center drill and regrind it to the right angles, a make-do spotting drill.
                The shortest distance between two points is a circle of infinite diameter.

                Bluewater Model Engineering Society at

                Southwestern Ontario. Canada


                • #38
                  Technology marches on

                  When I started out in T and D, DRO's and CNC machines were not available. Everything was layout lines taken from part models, sent down from the "big three" in Detroit, and transferred to slabs of tool steel. Trace and profile of male and female halves of dies was done on Hydrotels that were older than I was. The boss would calculate the proper diameter of tracer finger and cutter to use to get the correct clearance for metal thickness to be used in the die. Center punch marks made in the layout department were pretty close to dead on (by those days standards) and we had to pick them up by wiggler, center drill, or tiny drill bit. Of course, when you are drilling a series of 3" spring pockets into a dieset, on a Fosdick 4' sensative radial drill, a couple thou either way is lost in the noise level.

                  We produced some amazing tooling and I will never forget the cars that we made tooling for. The headlight bezel for the 73 Camaro was particularly interesting because the design required a sheet of .032" aluminum to be drawn about 6" deep in one hit. Reality sank in and we ended up having to draw it in 3 seperate operations to keep it from splitting out. Each draw left a shock line and that is why the inside of that bezel had a flat black coating from the factory, to hide the shock lines. OOPS...Engineering change!!!

                  Sorry, didn't intend to ramble and hog the thread.
                  Jim (KB4IVH)

                  Only fools abuse their tools.


                  • #39

                    Originally Posted by oldtiffie
                    There was an excellent video (U-tube) posted here not all that long ago about a bloke who was using a lathe at a pretty good speed to drill very small holes in a brass jet for an IC engine of some sort or another.
                    Originally posted by koda2
                    I believe this is the URL you are looking for:


                    However, on my computer it is now a dead link
                    Dave A.
                    Thanks for the try Dave - appreciated.

                    No result here either.


                    • #40
                      Pecking order

                      After Dave went to the trouble of looking, I thought I'd better get off my freckle and look a bit further.

                      I wanted some proof or verification that the extended ("floating") and "self-centreing" of a drill in a chuck in a tail-stock method worked on small holes - as I said in one of my earlier posts in this thread.

                      Further, it works just holding the drill in a pin vise/chuck in your hand and "peck-drilling" as well. The higher the speed and using preferable carbide drills is much better than slower speeds.

                      I first saw and used this in the Instrument Shop and Tool Room - over 50 years ago. I have had occasion to use it since.

                      It is all counter-intuitive and it looks as if it won't or can't work - but it sure can and does.

                      Very sharp drill are essential as the drill has to cut and not push its way through.



                      And a spade or centreing bit - similar to what I posted a pic of earlier:

                      Pin chuck (there are several types):