Announcement

Collapse
No announcement yet.

Quick Opinion on Line Boring Bar

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

  • Quick Opinion on Line Boring Bar

    Hey all,

    So I'm finishing up a 24"x1.25" line boring bar today. I wanted some opinions on whether to drill the holes before finishing it. Pros being that any distortion can be removed in the finishing cuts, cons being that it will be an interruppted cut. I'm also not sure if I can keep the deflection acceptably low. I got about 10 thou diametrical deviation turing the whole 29" on my Sidney, but it has a lot of wear and I was taking off about .1" from the diameter. But I'm not sure if even with a skim pass I can get close to .001 on the diameter the full 24" down. For lathe work it doesn't matter but I'd like to be able to use it on my Royersford drill press eventually. Maybe best to leave it and finish it up when I have a follow or bigger TPG? I guess I could always toss a steady in the middle.

    TIA,
    MB
    Last edited by The Metal Butcher; 06-12-2021, 12:37 PM.
    21" Royersford Excelsior CamelBack Drillpress Restoration
    1943 Sidney 16x54 Lathe Restoration

  • #2
    Originally posted by The Metal Butcher View Post
    ........So I'm finishing up a 24"x125" line boring bar today.
    ....
    24" x 125" ??

    TMB, I hope that's a typo.
    Lynn (Huntsville, AL)

    Comment


    • #3
      A 24" Dia. bore 125" deep (-:
      Last edited by Bented; 06-12-2021, 12:30 PM.

      Comment


      • #4
        Yep. That is a typo. 24" L x 1.25" D. I will fix OP.

        I basically stopped using my school laptop some months ago and the keys oxidized. So the rarely used ones don't hardly work anymore. I should get rid of it...
        ​​​
        21" Royersford Excelsior CamelBack Drillpress Restoration
        1943 Sidney 16x54 Lathe Restoration

        Comment


        • #5
          Support that bar with the same style running bushings you plan to use when it is in service. ON A STEADY!
          Lap to fit the bearing journals as required.

          Comment


          • #6
            Originally posted by lynnl View Post
            24" x 125" ??

            TMB, I hope that's a typo.
            Well, somebody has to rebore the shaft bushings for the propeller shafts in the museum's battleship
            Attached Files

            Comment


            • #7
              Welp, I guess I should have asked this a few days in advance to get any help. I drilled my holes first. Didn't cause any runout. Big mistake though. Thing is wicked chatter prone now. I was roughing 29" long at .1" off the diameter now with the MT4 straight in the spindle. I'm getting crazy chatter just taking off .005". Bodes I'll for use as a line boring bar.

              I tried it on the Rockwell but was getting wierd results. I'm setup with a steady and am 8 thou over in the middle and on size on the end. Of course I was ****ing with the TS alignment to try to correct it. Ugh I should have quit while I was ahead. I'm gonna have to make a box tool and finish it in the Lagun and hopefully get it straight. What a mess. I need a follow rest or 4.
              21" Royersford Excelsior CamelBack Drillpress Restoration
              1943 Sidney 16x54 Lathe Restoration

              Comment


              • #8
                A lot can be done with rock maple when the job is only one piece. MAKE THOSE RESTS! You need them!
                In example, I have been known to run oiled leather pads between the steady pads and the work to keep from scoring the shaft. If the steady were made from aluminum, there would still be no wear... Be resourceful!

                A box tool won't straighten anything.. Too short!

                Comment


                • #9
                  You ought to be able to turn a 24" long piece of steel at 1.25" diameter without any kind of steady or follower rest, though it will take a little doing. I'd be looking at your tool geometry very closely if getting chatter, the holes probably have nothing to do with it, though I would have done them after the turning was finished as standard practice. You need a very sharp edge and minimal radius. You may not be able to do it with an off-the-shelf insert.

                  Comment


                  • #10
                    A traveling box tool. M2 tool steel guides (unless I can find roller bearing elements) and I'll be GTG.
                    21" Royersford Excelsior CamelBack Drillpress Restoration
                    1943 Sidney 16x54 Lathe Restoration

                    Comment


                    • #11
                      Would any distortion in the bar itself even be a problem? Unless im missing something, since the bar is just holding a single-point tool and the rotation accuracy is coming from the lathe itself, the bars straightness shouldnt matter, no? Id cut to size before drilling because of that, to avoid the interrupted cut.

                      To clarify my train of thought, the only way that ive seen a line boring bar used is by spinning it between centers on a lathe. Long as the lathe was aligned, nothing about the bar really mattered other than the position of the bit in the bar, which set the diameter of the hole. I have no idea if thats how line boring is always done or if i misunderstood something somewhere, so if im wrong i always enjoy learning more

                      Comment


                      • #12
                        I think TMB wants equal diameter end to end to aid in setup measuring.

                        Box tool will take out the chatter, but I don’t think it will help the straightness unless you make repeated small cuts on the high spots and then a final pass.

                        Comment


                        • #13
                          Epic has nailed it, the bar need not be dead straight and the cutting tip is outside the bars diameter anyway. Using the bar to measure the bored hole would be difficult even if the bar was perfect.

                          Comment


                          • #14
                            Originally posted by old mart View Post
                            Epic has nailed it, the bar need not be dead straight and the cutting tip is outside the bars diameter anyway. Using the bar to measure the bored hole would be difficult even if the bar was perfect.
                            It’s less about measuring the hole & more about measuring cutter stick out and thus the size hole that WILL be produced.

                            Comment


                            • #15
                              I want the bar dead straight for use with a bearing in my drill press like a real line boring setup. Otherwise I'd have stopped after roughing it in. Maybe I should have...
                              21" Royersford Excelsior CamelBack Drillpress Restoration
                              1943 Sidney 16x54 Lathe Restoration

                              Comment

                              Working...
                              X