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  • silly Q - how do you bore?

    and I'm not talking about explaining the value of indexable cutters to the wife

    I finally ground my first boring bar from a HSS blank and it works beautifully, even on steel. But I couldn't figure out the best way to use it. Am I supposed to start at the mouth of the bore and cut a constant depth towards the headstock? Or should I use it like I'm facing the work, starting a fixed distance inside the bore and increasing depth of cut radially?

    I was cutting a relief on the back of my new chuck so that it would thread onto the lathe spindle properly and register properly, so I only needed to cut perhaps 1.5mm towards the headstock (ie. into the chuck) and 2mm radially. I don't have any measurement devices at all on the lathe yet (working on that though) so I could only tell when I'd cut a pass to the correct depth by ear as the sound would change from a sssss to a squeak. Got it done eventually, but it took a while!

    What I need to do some time in the future is bore two 14mm deep by 20mm wide holes in a lump of alu. Do I drill to approximately the right depth then bore longitudinally from that hole or is there a better way of doing it? This is all completely new to me, so some way of skipping at least a few of the screw ups would be neat

    thanks!

  • #2
    Originally posted by mattthemuppet View Post
    start at the mouth of the bore and cut a constant depth towards the headstock

    What I need to do some time in the future is bore two 14mm deep by 20mm wide holes in a lump of alu. Do I drill to approximately the right depth then bore longitudinally from that hole or is there a better way of doing it? This is all completely new to me, so some way of skipping at least a few of the screw ups would be neat


    thanks!

    This is the correct approach

    Rough in the holes with a 17 or 18 mm drill bit to depth. Then take an end mill of the same diameter to flatten the bottom, preferably a single end 2 flute EM.

    Comment


    • #3
      that infamous squeak or squeal is always a reliable sign that you've reached the bottom

      I'm sure everyone's got their way of doing it but I like to (in no particular order)
      1. mark the depth on the boring bar itself.. with a sharpie, for example. maybe 0.020" or so shy from the bottom
      that'll at least give you a visual.

      2. use a carriage stop. if you don't have one use a beefy c clamp.

      3. if the hole isn't so deep that you must use your carriage (or carriage feed).. there are always the
      divisions on your top slide. if its deeper, then use the above tricks to get within 5-10-20 thou, measure,
      then clean up the bottom using your top slide graduations.

      better yet, if its really important, rig up a dial indicator against your carriage somewhere to clean up
      those last few thou.

      wait.. does no measurement devices on the lathe mean no divisions/graduated dials?

      Comment


      • #4
        [QUOTE=mattthemuppet;879841] distance inside the bore and increasing depth of cut radially?

        I was cutting a relief on the back of my new chuck so that it would thread onto the lathe spindle properly and register properly, so I only needed to cut perhaps 1.5mm towards the headstock (ie. into the chuck) and 2mm radially. sound would change from a sssss to a squeak. Got it done eventually, but it took a while!

        1.5mm isn't very deep for a chuck backplate register, most spindle registers are at least 1/4" (6mm) long. What lathe have you got? Any chance of a photo?

        Richard
        'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

        Comment


        • #5
          Originally posted by Dr Stan View Post
          This is the correct approach

          Rough in the holes with a 17 or 18 mm drill bit to depth. Then take an end mill of the same diameter to flatten the bottom, preferably a single end 2 flute EM.
          that's an interesting approach, I hadn't thought of that. Only downside would be that I don't have a tail stock that I can put a drill chuck in, although I'm working on a ghetto milling attachment that I can make to hold one. If I used a large drill, do I still bore to the correct diameter with the boring bar, before finishing the bottom with an end mill?

          Originally posted by Tony View Post
          that infamous squeak or squeal is always a reliable sign that you've reached the bottom

          I'm sure everyone's got their way of doing it but I like to (in no particular order)
          1. mark the depth on the boring bar itself.. with a sharpie, for example. maybe 0.020" or so shy from the bottom
          that'll at least give you a visual.

          2. use a carriage stop. if you don't have one use a beefy c clamp.

          3. if the hole isn't so deep that you must use your carriage (or carriage feed).. there are always the
          divisions on your top slide. if its deeper, then use the above tricks to get within 5-10-20 thou, measure,
          then clean up the bottom using your top slide graduations.

          better yet, if its really important, rig up a dial indicator against your carriage somewhere to clean up
          those last few thou.

          wait.. does no measurement devices on the lathe mean no divisions/graduated dials?
          great advice, especially marking the boring bar, thanks! Yes, no measurement devices means no graduated dials. No lead screw either, so a carriage stop doesn't help much either It's a very small old lathe - small as in it can sit on the passenger seat of my car, old as in the indeterminate age of the very old. Still, it's what I have! I'll be posting up a strip down + "refit" thread sometime soon, once I've got my digital tire gauge "DRO" set up...

          Comment


          • #6
            Once you have the flat bottom in the hole, put the boring bar inside the hole and bring it to just touch the side of the hole. Then back out and dial a few thou. for the first cut and zero the dial or DRO. Make a cut starting from outside the part and feeding toward the chuck. Measure the newly bored hole, move the difference and make a finish cut. Depending on how much material needs to be removed, you may have to bore several times in small increments to get to the finish size. Always use the shortest stiffest boring bar that will do the job. A set of brazed carbide ones is not that much and works great on most projects. Plan on sharpening them yourself as they wear with a green wheel or diamond wheel.
            Kansas City area

            Comment


            • #7
              Originally posted by Richard P Wilson View Post

              1.5mm isn't very deep for a chuck backplate register, most spindle registers are at least 1/4" (6mm) long. What lathe have you got? Any chance of a photo?

              Richard
              I do, it's kinda embarrassing though:



              (it's an old picture, so I don't use that file on the lathe anymore)

              here's the spindle, although for some reason I didn't remove the adapter plate



              the whole spindle nose including threads is about 20mm long, give or take

              Comment


              • #8
                1. Drill about as deep as needed.
                2. Use bigger drill (this might save time.
                3. Expand hole as needed.
                On my 3 1/2 inch ML7 lathe my routine with carbon steel is, after center drilling use initially 13 mm drill, then 22 mm drill (this is highest diameter available on MK2 taper) then bore to size.
                Of course there are *smaller* bores as well but imho anything worth boring must be wider than 13 mm.
                Smaller holes are just drilled & reamed.

                Hint.
                For final cuts sharpen your boring tool or put in sharp carbide insert, or your bore will be tapered.

                Comment


                • #9
                  For shallow cavities, I often find it easier to use a facing cut than a boring bar.
                  Byron Boucher
                  Burnet, TX

                  Comment


                  • #10
                    fyi no lead screw required for carriage stop. in fact its better as you have no nut to strip.

                    imagine just using a c clamp on your rails.. gives the carriage something to crash into before it gets
                    to the bottom of the bore.

                    might look something like this:
                    1. lathe off
                    2. touch tip of boring bar / drill / reamer / etc to face of your work.
                    3. measure, say, 1" down your ways and clamp a block of something there. brass/alum/steel.

                    now your tool can't bore a hole deeper than 1" because your carriage can't physically get it there.

                    Comment


                    • #11
                      Originally posted by Toolguy View Post
                      Once you have the flat bottom in the hole, put the boring bar inside the hole and bring it to just touch the side of the hole. Then back out and dial a few thou. for the first cut and zero the dial or DRO. Make a cut starting from outside the part and feeding toward the chuck. Measure the newly bored hole, move the difference and make a finish cut. Depending on how much material needs to be removed, you may have to bore several times in small increments to get to the finish size. Always use the shortest stiffest boring bar that will do the job. A set of brazed carbide ones is not that much and works great on most projects. Plan on sharpening them yourself as they wear with a green wheel or diamond wheel.
                      thanks for the tips! I can't make deep cuts with this lathe as it only has 1/6hp motor (!), so it just stalls, plus the amount of flex and backlash in the cross slide/ compound doesn't help. Multiple shallow cuts it probably the way to go. I tried a brazed carbide bit, but either it was crap or my lathe doesn't spin fast enough for it to work. HSS or the cheap indexable cutters I got for Christmas seem to work really well though.

                      Originally posted by Martin0001 View Post
                      1. Drill about as deep as needed.
                      2. Use bigger drill (this might save time.
                      3. Expand hole as needed.
                      On my 3 1/2 inch ML7 lathe my routine with carbon steel is, after center drilling use initially 13 mm drill, then 22 mm drill (this is highest diameter available on MK2 taper) then bore to size.
                      Of course there are *smaller* bores as well but imho anything worth boring must be wider than 13 mm.
                      Smaller holes are just drilled & reamed.

                      Hint.
                      For final cuts sharpen your boring tool or put in sharp carbide insert, or your bore will be tapered.
                      Never thought about it like that, makes sense though and it'll be a whole (see what I did there?!) lot quicker too. Resharpening prevents tapers because the cutter won't be pushed out of the cut?

                      Originally posted by Boucher View Post
                      For shallow cavities, I often find it easier to use a facing cut than a boring bar.
                      thanks, that's pretty much what I ended up doing.

                      Still, with all these tips I should be able to pick the best set of tools/ approaches for a particular job. I'm learning as I go, but some stuff I just don't know that I need to know it!

                      Comment


                      • #12
                        Originally posted by mattthemuppet View Post
                        Never thought about it like that, makes sense though and it'll be a whole (see what I did there?!) lot quicker too. Resharpening prevents tapers because the cutter won't be pushed out of the cut?
                        That is a reason.
                        Final cuts (for example last 2-3 mm) always with sharp tool.
                        Otherwise there will be a taper, a considerable one.

                        Finally:
                        Resharpen and hone tool before last few thous cut - that makes all the difference in terms of surface finish.

                        Comment


                        • #13
                          Originally posted by Tony View Post
                          fyi no lead screw required for carriage stop. in fact its better as you have no nut to strip.

                          imagine just using a c clamp on your rails.. gives the carriage something to crash into before it gets
                          to the bottom of the bore.

                          might look something like this:
                          1. lathe off
                          2. touch tip of boring bar / drill / reamer / etc to face of your work.
                          3. measure, say, 1" down your ways and clamp a block of something there. brass/alum/steel.

                          now your tool can't bore a hole deeper than 1" because your carriage can't physically get it there.
                          now I understand that's a really neat tip, thanks! I could even just clamp the cross slide (ooh, a new project) as long as I have enough clearance with the carriage to advance into the work. Hmm, thinking now...

                          Originally posted by Martin0001 View Post
                          Finally:
                          Resharpen and hone tool before last few thous cut - that makes all the difference in terms of surface finish.
                          does a faster spindle speed also help? I've been doing most of my turning at the lower of the 2 speeds, otherwise the tool sometimes seems to "skate" over the material. I've read that higher speed = better finish.
                          Last edited by mattthemuppet; 10-14-2013, 06:16 PM.

                          Comment


                          • #14
                            Originally posted by Boucher View Post
                            For shallow cavities, I often find it easier to use a facing cut than a boring bar.

                            I agree!

                            You want more fun, locate and cut a groove for an internal O-ring.

                            Andy

                            Comment


                            • #15
                              Speeds and feeds are best to be found experimentally because not all what books say will work exactly as specified on your particular machine.
                              Too many factors at play.
                              I am finding it easier to get nice finish on internal bore than on external bar turning.
                              Carbon steel doesn't like high speeds too much.
                              I would stay with lower speed and finer feed but you must check it yourself.

                              Comment

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