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little holes becoming big holes - drilling, boring, two sided boring, mega reamer ?

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  • little holes becoming big holes - drilling, boring, two sided boring, mega reamer ?

    Hi Guys

    Recently I've been making some larger holes (1" - 3") using my lathe. I go through the standard procedure - center drill, small drill, medium drill, bigger drill, boring bar, maybe bigger boring bar. My problem is going from "bigger drill" to "boring bar". My biggest drill is a really short 1" drill (which thanks to you guys, I've figured out how to sharpen). My smallest boring bar barely fits in a 1" starting hole. It's a real squeaker !!!

    So, I have to buy a larger and longer drill bit, or a smaller boring bar. But while contemplating that purchasing question, I've also been thinking about this problem of drilling larger holes and boring them out. This led me to some questions, and I haven't found an answer on the intertubes yet, so I thought I'd turn to you guys for the answers.

    Do they make larger drill bits that have carbide inserts on the cutting edges? In fact, wouldn't that be sort of like having two boring bars welded back to back? Wouldn't that eliminate some deflection (although torsion might increase)? Wouldn't it be easier to replace two carbide inserts as compared to sharpening by hand or with a jig? In fact, if one had 4 inserts wouldn't it be approaching an indexable reamer in cutting action (although not as smooth of a finish) ?


  • #2
    What size machine? There is tooling galore, but the size of the machine will dictate...can drill some big holes with a 5mt tailstock.

    Yes there are carbide/indexable large drills.. often with coolant through.. see above. can be quite $$$.

    Boring bars are pretty easy to 'cowboy' yourself in a pinch.. some solid bar and either braze or use a set screw on a hard pointy bit.

    Double cutting would be interesting... off side would need to be upside down and projected twice as far as front cutter.. suspect the doc would be limiting.. may as well just double it on one tool maybe...

    Have a mill or big drill? Opens up some options. Rig something up on apron and use power feed?


    • #3
      How deep are you needing to go? If less than 2 inches, the easy answer is an annular cutter (generic term). Also known as Rota-Broach (brand name). This is a hole saw for steel, comes in many diameters, cuts a pretty clean hole quickly. For use on lathe, mill, drill press, mag drill. Run 200 RPM or so.


      • #4
        Get yourself set of smaller boring bars, they are very cheap compared to indexable drills.

        After getting to 18mm or so a insert boring bar is faster way to remove metal than HSS drill assuming you won't need very deep holes.
        With 16mm boring bar max 40mm deep holes the limit on material removal rate is the 1.5hp motor on my smallish lathe.


        • #5
          It takes a lot of power to turn serious amounts of steel into chips. So unless you're running a hefty size machine you'll likely find that you're stuck with at least a few steps from small to large to spread out the conversion of solid into chips.

          But if you have such a machine and want to drill to such sizes instead of boring a smaller drilled hole then carbide spade bit inserts and a suitable drill body is what you want. Here's a rather impressive display of such a drill in use

          Big twist drills get REALLY pricey. But if your boring bar is a squeaky tight fit into a 1" hole I'd suggest that a 1 1/8" drill bit would not break the bank. Just use it as a dedicated final drill size before going to the bar. And a 1 1/8" size is not so pricey that you'll want to be sitting down for the shock like they get at around 1.5" and up.

          Or break down and buy or make a smaller size boring bar to open up the 1" hole far enough to then switch to the big bar. At some point you will need to buy or make smaller diameter boring bars than your present size. Drilling is OK but drills wander. And sometimes the holes aren't totally round or parallel from drilling. Boring after drilling undersize is the only way to ensure that the ID is axial and of consistent size to small tolerances. So eventually you're going to NEED boring bars in a variety of sizes.

          Depending on what holders you have or are willing to buy you can either put them in separate holders or make a split sleeve for your holder that you use with the 1" bar to allow the use of smaller diameter bars. There's lots of options.


          • #6

            I have this set, and the smaller 3/4 set. They are great for smaller HP machines, drill presses, Magnetic drill presses , lathes etc.
            I did a lot of work on forklifts, and these are also great for counterbored holes on fork carriage bars, for chain anchor pins, stub shafts, etc.
            They were a lot less expensive when I purchased mine 30 some years ago, also have a fixture for sharpening on a surface grinder.


            • #7
              You need smaller boring bars. If you do ebay, you can look for Bokum or Criterion, both of which I like... I got a set (25) of them of mixed sizes for about $20 or $30 a few years ago, and I use them by preference, unless they are totally unsuitable. They work very well.

              I would stay away from the "sheep's foot" style, they kinda work, but the import ones tend to have very thin shanks, and they flex a lot.

              This is a carbide type of "sheep's foot" bar. Thre are HSS ones as well. They are OK for certain things, but IMO not for general purpose use.


              I find this style with thin shanks flexes way too much. Contrast those with these


              Keep eye on ball.
              Hashim Khan


              • #8
                I like to take advantage of the fact that no real accuracy is required until the last few cuts. On anything larger than an inch or so, I'll start out with either an annular cutter (referenced above) or a cutting torch and then finish up nice and accurate with a normal boring bar. I've even seen guys do it with a bi-metal hole saw on shallower holes.


                • #9
                  Originally posted by softtail View Post
                  What size machine?
                  Have a mill or big drill?
                  I have a Rockwell 11/42 with a 2 HP motor. I could have had a Leblond 18 for cheap, but after moving the Battle Shaper I decided against moving another industrial sized tool this year.*

                  I have a Bridgeport. My drill is just a Delta 14".


                  *Next year is another story.


                  • #10
                    Treat yourself set of boring bars:


                    • #11
                      Well, depending what you are drilling, running a hole saw or annular in the mill gets you up to size pretty quick. Not great for longer round stock though...


                      • #12
                        I guess the other question is how often you do stuff like this. Big size twist drills, annular cutters and the like are pretty specialized. AND pricey. You'd want to be doing a lot of the same size job needing the one tool to justify such things. And hole saws or the annular cutter is only good for through holes in limited thickness materials which makes their use even more specific.

                        But it does come back to if your ONLY boring bar for use in the lathe needs a minimum 1" hole before it'll work then the one truly missing tool in your arsenal is a smaller size boring bar or even two or three smaller sizes.


                        • #13
                          I have a BP and a 13" lathe and occasionally use different kinds of boring bars, but the style I use most is this:

                          You do need a carbide grinder to sharpen and reshape as necessary.



                          • #14
                            Originally posted by softtail View Post
                            Well, depending what you are drilling, running a hole saw or annular in the mill gets you up to size pretty quick. Not great for longer round stock though...
                            If you are drilling through holes softtail's right. Annular cutters are awfully quick ways to drill larger thru holes in relatively thin material. They work in the lathe as well. An added bonus is you get to keep the inner slug for other projects - the material isn't wasted in chips.

                            But don't just take my word for it - Stefan shows it on Youtube:

                            I've made up a set of steel boring bars that use old HSS or carbide centre drills. They work great in the home shop and are easy to make. If you are production turning anti vibration bars from Sandvik, indexable carbide tipped drills, or similar are where it is at, but not worth the cash for home shop type jobs.

                            Glanze CCMT boring bars are fairly well made indexable carbide solutions that go down quite small. I have 2 and I use them when carbide is required.
                            Last edited by enginuity; 12-09-2017, 02:22 PM.