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Best method to turn between two shoulders

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  • Best method to turn between two shoulders

    I would like to turn a part between two shoulders. What I have been doing is to use my parting tool to turn a grove wide enough at the right shoulder to get my right turning tool in between the two shoulders and turn to the desired diameter. Then finish with a left turning tool. This would be for a fairly deep reduction in the diameter between shoulders.

    THat is how I have been doing the job. How should I be doing this job?
    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    I made a tool to do that. Using a 1/4 in sq tool bit, I ground into the end to create a bit of a hollow, then ground on both sides for side relief. The tool is intended to plunge straight in like a cutoff tool. Basically it's a left hand and a right hand tool in one. If the distance between shoulders is 1/2 inch or more, this bit will cut both shoulders square and the bottom flat. If the groove is less than 1/2 wide, but more than 1/4 wide (obviously) then you can leave some flat points on both sides of the end when you grind the hollow. Actually, I like to leave a couple of flat points anyway, just to give the cutting edges better support. The only reason for the hollow is to lessen the length of the cutting edge where it makes the flat bottom. This helps to reduce chatter. You have to work the tool left and right in order to get the bottom fully cut to one diameter.

    The reason I don't like using cutoff tools like that is that unless they are quite thick, they flex sideways, mucking with the shoulders. Sometimes the groove must be narrow, and then you don't have much choice.

    Of course, if your cutoff tool is 1/4 inch wide, you already have this sort of tool. It might also already have side relief. You can grind the slight hollow like I do, or if your machine can handle it, just leave it squared across the tip.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


    • #3
      Same Method

      Darryl's method is exactly what I would do. He beat me to the reply.

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      • #4
        This is what I use. I plunge cut with a V nose tool first to get the groove close to size.

        It's only ink and paper


        • #5
          I should have been more clear. I want to know how you do it if there is three inches between the shoulders. Not just a grove.

          something that looks like this.

          How to become a millionaire: Start out with 10 million and take up machining as a hobby!


          • #6
            For a groove (?) that wide I'd simply use a regular RH (or LH) turning tool; start at one side and make progressive cuts, stepping in deeper each pass. You'll end up with a taper that runs down to the bottom. Change to an opposite hand tool and cut away what's left, leaving a bit of material all around for finishing. Switch to your double-sided tool, plunge in to the final dia. and finish the cut, doing the two shoulders last. Depending on how much material you're removing it'll take about the same time to do it as it took me to write this--not counting tool-grinding time...
            Just one project too many--that's what finally got him...


            • #7
              Depending on how square the spot where the center portion and the bottom of the shoulder meet [makes a difference if it really is square or if a small radius will work], but you can do the bulk of it with a single bit, a "round nose" turning tool, sort of a combo of left and right hand turning tool all ground on one bit...designed for exactly what you want to do (move in either direction)...if you can get away with a radius at that shoulder/center meeting place, it may even be possible no other tool need be used, but if you want a truly square shoulder the nature of the round nose does not really allow for that...then that second tool others suggest will do the job...I would use the round nose back and forth, then use both a left and right hand facing tool to do the job described [I have not had much luck grinding those fine/detailed tools previous posters illustrate]


              • #8
                BlackForrest - What Carld shows and Darryl described will work for long distances, too, not just grooves.

                I've done by all three methods described here. For a very great reduction in diameter, I usually plunge in with 1/4" tool square nose bit and then finish the job with LH or RH cutters. On a heavy machine, this presents no problems and it increases productivity in the sense that I can sharpen a square nose bit and ordinary RH or LH cutters in much less time than I can sharpen more complicated cutters.

                When the shoulders are closer together, I use a tool very similar to the one pictured by Carld but like I said, I try not to use those ordinarily since they are more trouble to sharpen.


                • #9
                  Black Forest...

                  I believe you now have a top-quality grooving/parting tool. You can use can that tool to "multi-plunge" the groove. Start with the first groove to leave .02" (0,5mm) per side (.040"/1mm on the O.D.) for finishing, then make your step-overs be 90% of the insert width. Don't baby it, use the same heavy feed rates you would for parting off.

                  On the finish pass, you can use the same tool to plunge the flange to width, reach the final diameter, traverse across at a finishing feed rate, back out, then plunge the second inner flange face to finish width.

                  You'd have to run one each way to see what is faster, but in general I think you'll find that the aggressive rates that you can use with the parting/grooving tool will actually be much faster.
                  Last edited by PixMan; 11-21-2011, 06:03 PM.


                  • #10
                    I use a Manchester dog-bone type parting/grooving tool for making such grooves. This tool has no problems with a plunge followed by a turning move. It helps to feed aggressively, as this actually bends the tool to the side a little during the turning move, creating front clearance accordingly. I get chatter if I under-feed or dwell. The manufacturer specifically recommends this technique.


                    • #11
                      Yes, rklopp, that's EXACTLY the reason I encourage our BF friend to try using the 4mm Walter parting tool that I believe he's got. It would be better if he was using their GX24 double-ended tools, but the FX single-ended style should also work.

                      I have the Valenite VTG (double-ended) and VSG (single-ended) systems and several different style of toolholders for them. They show that practice you describe in the catalogs, as does the Walter catalog.


                      • #12
                        Take part and blue it up, scribe the lines where you want the groove to be.

                        Chuck the part in the lathe and use a live center in the end because obviously it's too short and needs support.

                        Put a V nose cutter in the tool post and plunge cut in several steps to get the groove to almost the width and depth you want.

                        Install the tool in the photo in my post in the tool post and align it so each tip of the cutter touches the surface of the part.

                        Make a plunge cut on the left side and move the carriage to the right. Keep doing that until the left side is almost finished to the scribe mark. I like to leave about .030" to clean up. I also leave about .030" on the minor diameter of the groove.

                        Do the same on the right side of the groove. When both ends are done with about .030" left to remove begin to remove the metal until it is to the desired size.

                        I have done that so many times I can almost do it in my sleep. It's so simple it's hard to believe everyone doesn't do it that way. You can use less relief in the center of the cutter and you can put radius's on each side of the cutter tip. The configurations of the cutter are numerous and only limited by your imagination. In fact imagination has a large part in being a machinist.

                        EDIT: I am not being snarky, you asked for instructions on how to do it and here they are.
                        Last edited by Carld; 11-21-2011, 10:37 PM.
                        It's only ink and paper


                        • #13
                          It's interesting that this thread popped up today. I was making a couple of parts just like this last night and was wondering the same thing as the OP. My ancient 1919 F.E. Reed lathe is the opposite of ridged and none of my attempts at grinding a cutter that would allow me to make the part with one cutter worked. I ended up using the left and right cutter technique.

                          As I was finishing up the last part I started to wonder if I wouldn't have been better off mounting the part in my vertical rotary table on the mill and cutting the grove with an end mill.


                          • #14
                            Not really. If you made the part as I described it would go faster than you think. There's to many variables using the mill but it would work.
                            It's only ink and paper


                            • #15
                              This is how I like to do it, though I have to do it by hand as I don't have a CNC lathe (yet.)