Announcement

Collapse
No announcement yet.

center drills vs spotting drills

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

  • center drills vs spotting drills

    Originally posted by mochinist
    Now that you got that fixed, here is some helpful advice for the future. Put the centerdrills away unless you need to drill a center hole for some lathe work, and buy yourself a spot drill.
    I would love to see a thread about that. I have seen advice ranging from "center drills are also used for starting holes" to "center drills are for drilling centers, that's why they are called that." The latter opinion seems to make sense to me.

    I don't even have a lathe ( some day...). I bought a set of 4 center drills from littlemachineshop.com because I was already ordering some other stuff from them, so it was convenient.

    So, for starting holes, center drills vs. spotting drills. What think you? For added fun (and my edification) what size spotting drill relative to the final hole size?

    -Pete
    I just like to make stuff.

  • #2
    The little center portion on center drills are weak and are easily damaged, so yes, spotting drills are for starting holes.
    James Kilroy

    Comment


    • #3
      Spotting drills do seem to center up a little better when starting and are less prone to breaking the tip. The center drills will wander a little and the tip does break off causing some issues.

      I haven't tried but I guess if your drilling a center in the shaft and want a center to be real close you could start with a spotting drill and then finish with the center drill, just don't drill to deep with the spotting drill.
      It's only ink and paper

      Comment


      • #4
        When you try to drill a hole with any sense of precision it ( the chosen drill that is) tends to wander (try it) .So you use a very firm bodied centre drill which is less likely to wander this starts a hole of correctly then change to standard drill of your choice which when inserted into prederilled hole, will not wander, and drill following the started hole which makes it more accurate .These can be used in a milling machine and drill press or a lathe so you can still use yours without a lathe .Alistair
        Please excuse my typing as I have a form of parkinsons disease

        Comment


        • #5
          center drills are an (oldish) progression to improve productivity. They combine the countersink with a small pilot drill. Originally you centered a workpiece (as in drilled a center) in 2 operations, one with small pilot drill, and the one to create th 60 degree hole for the center. Combining the ops into a single drill saves time in production.
          To start hole use spotting drill to center a shaft use a center or slocum drill.
          Tip to make them last longer - cut down the center bit, especially if you use a bearing center, as the little pocket is for a reservoir for the lube used with dead centers, and generally the pip is what snaps off in use.
          Dave
          Just south of Sudspumpwater UK

          Comment


          • #6
            I've used both

            Center drills are intended for putting in centers for turning on a lathe. The reason they work as well as they do for spotting is that they are usually short and very stiff.

            Spotting drills are intended to be used for accurately putting a hole in location without using a guide bushing. They are usually longer than center drills, but are still very stiff. They are ground for a thin web at the point that is accurately ground so that they do not wander. In addition to locating the hole I used spotting drills on the CNC mill to locate the hole and go deep enough to leave a chamfer on the finished hole. The spotting drills I used were a 90 degree included angle point, so I could set the OD of the chamfer by spot drilling half the drill diameter deep less half of the web thickness.

            As far as using a spot drill to get an accurate center before using a center drill: If the center drill won't put the center on center, then there is a problem with either the holding of the center drill or with the sharpened geometry of the center drill.

            Comment


            • #7
              the centre drill will work, but the spotting tool is the right tool for the job as they guys have stated....aside from the fact that you can't bust the pip off a spotting drill, the resultant spot is the right angle (if you use a 118 degree one) for the drill. This will start the drill with less chance of chatter

              i've always found a bit odd how prevalent the practice of starting a hole with a centre drill is....I suppose just expediency, if its all you've got sort of thing...buy a good quality 1/4 and 1/2 and they'll last a life time as will your centre drills.

              what to do with the 4 centre drills? why buy a lathe of course
              in Toronto Ontario - where are you?

              Comment


              • #8
                I look at it as a matter of tolerances.

                If you want kind of close enough. use a drill (in a drillpress)
                If you want close, use a center drill(in a drillpress)
                If you want closer yet, use a center punch W/ a well sharpened drill(in a drillpress)
                If you want very close use a spotter W/ a well sharpened drill (on location in a mill)
                If you want perfect, plunge a ball endmill, just undersize, W/ a well sharpened drill, then ream (on location in a mill)

                Comment


                • #9
                  It is a futile argument, some hate them others don't.
                  They will break the nib off no doubt when you least want it to happen, however more times than not they function just fine.
                  Some say for use in a lathe only, for making centerholes only... Well, being in a horizontal plane does not make them function any differently then if vertical....

                  Comment


                  • #10
                    Originally posted by smalltime
                    I look at it as a matter of tolerances.

                    If you want kind of close enough. use a drill (in a drillpress)
                    it's not just a matter of tolerance, starting a drill without at least centre punch in metal is not a good idea because they can wander, especially for small drills which could bust

                    If you want close, use a center drill(in a drillpress)
                    Smalltime, can you share your reasoning for recommending a centre drill in the second point? There are two very good reasons for not using the centre drill and instead using a spotting drill....you won't bust the pip and the cone will be the right angle....what are the reasons why would you recommend using using a centre drill to start a hole? We've all done it and made it work, but imo its the wrong tool for the job.\


                    Some say for use in a lathe only, for making centerholes only... Well, being in a horizontal plane does not make them function any differently then if vertical....
                    of course not, its a matter of number of times its used...they won't last as long starting 20 holes and drilling 1 centre hole, vs just drilling 1 centre hole.... AND that the cone they create is the right angle. every had a drill chatter as it starts in a centre drilled hole? spot drill reduces that. As I said, in light of these two facts, I've always been perplexed why someone would use a centre drill for starting a hole, maybe I'm missing something
                    Last edited by Mcgyver; 12-30-2009, 06:16 PM.
                    in Toronto Ontario - where are you?

                    Comment


                    • #11
                      I use my center drills to start holes because I havent gotten around to buying spot drills yet.. Stupid local stores don't carry em and I keep forgetting about them when I order online.
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                      Comment


                      • #12
                        Originally posted by Uncle O
                        It is a futile argument, some hate them others don't.
                        They will break the nib off no doubt when you least want it to happen, however more times than not they function just fine.
                        Some say for use in a lathe only, for making centerholes only... Well, being in a horizontal plane does not make them function any differently then if vertical....
                        I was really hoping tiffie would have posted some sketches, wiki links and long thought out post by now on why the spot drill is better for starting holes, but I guess he is busy.

                        First off I dont say they are for lathes only, although I do say to just use them when you need a center hole for a center, which more often than not tends to be on a lathe. Using some sort of indexer and a center on a mill or grinder would be the other alternatives that come to mind.

                        Like said a center drill will work fine a lot of the times, be sure to use a lot of cutting oil and choose your RPM's wisely and you should be ok. If not have fun removing the broken center drill tit from your part. I would rather just use a spot drill and have zero worry about that happening.

                        Lastly I do this for a living and time is money, I have full drill indexes with screw machine length drills and I use just those when the hole isn't that deep to be drilled, no spot drill.

                        Comment


                        • #13
                          Originally posted by Black_Moons
                          I use my center drills to start holes because I havent gotten around to buying spot drills yet.. Stupid local stores don't carry em and I keep forgetting about them when I order online.
                          Take an old 1/2" or 3/8" drill and shorten it and resharpen it.

                          Comment


                          • #14
                            I don't have any old drills of sane sizes... Everything but a few small drill bits was pertty much lost beween the period my dad worked and I started up my shop.
                            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                            Comment


                            • #15
                              Originally posted by Black_Moons
                              I use my center drills to start holes because I havent gotten around to buying spot drills yet.. Stupid local stores don't carry em and I keep forgetting about them when I order online.
                              now thats a reason i can't argue with
                              in Toronto Ontario - where are you?

                              Comment

                              Working...
                              X