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  • Parting off relatively large diameter stock

    I'm a relative machining newbie and need to make several aluminum "discs" 3.336in diameter by 0.25in thick.

    I know enough to keep the parting tool stick-out to a minimum, but in this case the stick-out will need to be nearly 2in. I also know that with this much stick-out parting tools like to "bow", creating a convex or concave cut, depending on your perspective.

    Being so thin, just cutting them off rough with a saw, then milling the faces flat and perpendicular is also problematic.

    Any tip and tricks, special tools, or alternative methods to make these discs?

    My lathe is 12in x 36in with a 1.6in bore spindle, and I have a Bridgeport.

  • #2
    I'd consider cutting them from 0.25 plate. Or start bit thicker and facing on both sides to get correct thickness.
    Use pressure plate and tailstock. 12x36 lathe should be enough sturdy for this sort of thing.

    https://www.youtube.com/watch?v=bODk7QPBpYs
    Location: Helsinki, Finland, Europe

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    • #3
      You could probably use parallels to get the discs gripped in the jaws, without parting.

      1. face the end
      2. cut disk off on bandsaw
      3. use parallels to mount in chuck against faced surface
      4. clean up and face to final thickness

      I hate parting.

      Comment


      • #4
        Originally posted by jmarkwolf View Post
        I'm a relative machining newbie and need to make several aluminum "discs" 3.336in diameter by 0.25in thick.
        The easiest way is to rough cut the disks from 1/4 inch plate with a saw, then mount the rough cut blanks on the lathe to clean up the edges and make them round. This works best if you have the luxury of making a hole in the middle of the blank to hold it while it's in the lathe.

        If you can't make a hole, you can make a temporary face plate that fits in the chuck, then use two sided tape to give it some traction. Finish your mount by trapping the disk between the faceplate and a live center in the tailstock. Then you can turn the edges lightly.
        At the end of the project, there is a profound difference between spare parts and left over parts.

        Location: SF East Bay.

        Comment


        • #5
          And if you really want to part the disc from a 3 inch round...

          You can do it with a HSS blade or a carbide insert on a holder. Make the stickout 1.5 inches. Make sure that it's perpendicular to the lathe's axis. Make sure that it moves at exactly 90 degrees to the axis. Any deviation will cause it to bind and break.

          A carbide insert is often wider than the holder, so there is less chance of binding.

          Use the side by side cut technique. That's where you cut 1/4 inch deep, then pull out the blade and move it over just under 1 thickness and plunge it in 1/2 inch deep. Pull it out and return to the original position over the first cut and plunge 3/4 inch deep... Repeat over and over, going 1/4 inch deeper each time. The end result is a single groove twice as wide as the blade's cutting edge. When you get close to the center, cut only at the right side.

          Easy peasy.
          At the end of the project, there is a profound difference between spare parts and left over parts.

          Location: SF East Bay.

          Comment


          • #6
            Originally posted by danlb View Post
            And if you really want to part the disc from a 3 inch round...

            You can do it with a HSS blade or a carbide insert on a holder. Make the stickout 1.5 inches. Make sure that it's perpendicular to the lathe's axis. Make sure that it moves at exactly 90 degrees to the axis. Any deviation will cause it to bind and break.

            A carbide insert is often wider than the holder, so there is less chance of binding.

            Use the side by side cut technique. That's where you cut 1/4 inch deep, then pull out the blade and move it over just under 1 thickness and plunge it in 1/2 inch deep. Pull it out and return to the original position over the first cut and plunge 3/4 inch deep... Repeat over and over, going 1/4 inch deeper each time. The end result is a single groove twice as wide as the blade's cutting edge. When you get close to the center, cut only at the right side.

            Easy peasy.
            Not to forget the most important ingredient when parting aluminium: Cutting fluid.
            WD-40 works reasonably well.
            Location: Helsinki, Finland, Europe

            Comment


            • #7
              seems to me tbat soct jaws would be in orxdr for tbis job. Part tbem off with room to face them while holdi g them in soft jaws.
              Location: The Black Forest in Germany

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

              Comment


              • #8
                To get all surfaces machined......face and turn the OD. Bandsaw. for the final op, the trick is to us a chuck spacer. The machined face goes against the spacer while you face the second face.

                i make my own spacers, three pieces of metal welded to a hub then ground flat and parallel (or milled or filled). They're contained within the jaws so are safe. I've used parallels as well for setup , but make darn sure you don't leave them in!

                http://cdn1.bigcommerce.com/n-yp39j5...0.1280.jpg?c=2
                in Toronto Ontario - where are you?

                Comment


                • #9
                  Originally posted by Black Forest View Post
                  seems to me tbat soct jaws would be in orxdr for tbis job. Part tbem off with room to face them while holdi g them in soft jaws.
                  happy hour?
                  in Toronto Ontario - where are you?

                  Comment


                  • #10
                    Originally posted by Black Forest View Post
                    seems to me tbat soct jaws would be in orxdr for tbis job. Part tbem off with room to face them while holdi g them in soft jaws.
                    I type just like this on my phone when I forget my glasses. Translation: "Seems to me that soft jaws would be in order for this job. Part them off with room to face them while holding them in soft jaws."



                    Dan
                    At the end of the project, there is a profound difference between spare parts and left over parts.

                    Location: SF East Bay.

                    Comment


                    • #11
                      Originally posted by danlb View Post
                      I type just like this on my phone when I forget my glasses. Translation: "Seems to me that soft jaws would be in order for this job. Part them off with room to face them while holding them in soft jaws."



                      Dan
                      Thank you Dan. That is exactly what I did.
                      Location: The Black Forest in Germany

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

                      Comment


                      • #12
                        "the stick-out will need to be nearly 2in. I also know that with this much stick-out parting tools like to "bow", creating a convex or concave cut, depending on your perspective."

                        If you were to look up recommended blade thickness versus diameter in a book on automatic screw machines I bet you'd find 1/4" blade or thicker would be about right.

                        (I'd look it up myself if I hadn't got ridden of my B&S books.)

                        Comment


                        • #13
                          Originally posted by Mcgyver View Post
                          To get all surfaces machined......face and turn the OD. Bandsaw. for the final op, the trick is to us a chuck spacer. The machined face goes against the spacer while you face the second face.

                          i make my own spacers, three pieces of metal welded to a hub then ground flat and parallel (or milled or filled). They're contained within the jaws so are safe. I've used parallels as well for setup , but make darn sure you don't leave them in!

                          http://cdn1.bigcommerce.com/n-yp39j5...0.1280.jpg?c=2
                          I stumbled across this video that details mounting spacers to the chuck face for the same effect. I like the idea, seems like it would be very versatile, and should work perfectly for the OP's needs.

                          https://www.youtube.com/watch?v=U3x8H1Xb-jg

                          Comment


                          • #14
                            Originally posted by Yondering View Post
                            I stumbled across this video that details mounting spacers to the chuck face for the same effect. I like the idea, seems like it would be very versatile, and should work perfectly for the OP's needs.

                            https://www.youtube.com/watch?v=U3x8H1Xb-jg
                            it is a good idea, I'd forgotten about it. if someone wants go right to it.....8:25
                            in Toronto Ontario - where are you?

                            Comment


                            • #15
                              Iif you do parallels, and of course remove them, the part can shift in the jaws unless only the lightest of touches is used to machine it.

                              With the 3 leg chuck spacer, the part can be turned in a fairly normal way without much fear of shifting. It is very unlikely to come out like a tiddly-wink piece without the user doing some fairly violent things. Essentially it is the same as if the part were resting on a chuck jaw step.
                              CNC machines only go through the motions.

                              Ideas expressed may be mine, or from anyone else in the universe.
                              Not responsible for clerical errors. Or those made by lay people either.
                              Number formats and units may be chosen at random depending on what day it is.
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                              Generalizations are understood to be "often" true, but not true in every case.

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