Announcement

Collapse
No announcement yet.

machining a tailstock feedscrew.

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

  • #31
    if you're going to the effort of making a new screw and a nut insert, why not go one step further and make an extension to increase the quill travel? There's a good 3 part Youtube series on it and I'll be getting back to mine shortly. Just need to finish off the extension that goes between the casting and the screw holder. That'll net your friend another 1" and a bit, which can make a big difference for awkward set ups with a center or deep hole drilling.

    Comment


    • #32
      How would this setup work. If I were to do a a 12x2mm trapezoidal thread but if I set the nut up in a line bore method. I think the advantage of this would be many. Firstly because its such a small bore any internal threading bar would want to bend. Say I did a 10mm bar that is cross drilled .If i set the nut up on the top of the saddle, as if I were to line bore it . I could then pre thread it with a v shaped single point tool in the cross threaded shaft. Then I could swop it out for a trapezoidal shaped tool.
      I would think the advantage of doing it supported in the chuck and on the tailstock would give it better rigidity. Also I can see better as I dont have to look inside the chuck to see whats going on.
      Okay ,i see the minor diameter is 9,5mm so if I used a 9mm shaft it might just fit.
      Last edited by plunger; 08-31-2021, 05:29 PM.

      Comment


      • #33
        Click image for larger version

Name:	southbend nut setup.jpg
Views:	126
Size:	123.6 KB
ID:	1959575 If I clocked the nut up perfect to the spindle in this milling attachment. The stainless tube in the vice is simulating the nut. I was too lazy to take out my rotary broach for the pic but swop it for a running center .Would this work.

        Comment


        • #34
          A few things that may help.
          For a Acme thread nut , as said already----you should do it in several stages and start with a deeper square cut ( larger OD than Acme major Diam) .
          Then switch to a Acme style tool bit.
          One trick I have used is to take the existing LH leadscrew and grind groves/slots in the very end ( which has the least wear by the way) and use the screw to do the last cleanup pass in the nut. it is snug ,But, works well in the normal middle of travel.
          Another trick
          Picking up a thread properly with two different tool bits can be tough, especially when you can't see the result of the second tool, so the solution is as follows
          Say the needed nut is 30 mm deep-
          Make one 40 mm deep and drill the ID out as normal, then remove the nut and mill the first 10 mm half off so it becomes a "half a hole" for 10 mm.
          Reset in the lathe with the half hole in front and start your thread cut and you can see the thread form easily when you set up the second or third cutter as it is exposed and can time the tool feed location dead nuts. When done, cut off the 10 mm "trainer"

          Rich
          If you make a new screw, just make it longer and use the end like a tap, and the thread form does not have to be to any standard but yours .
          Last edited by Rich Carlstedt; 08-31-2021, 06:02 PM.
          Green Bay, WI

          Comment


          • #35
            You don't have to line bore anything. Just put the spindle in a 3-jaw. Make your LH bronze nut and press it into the bored out spindle.

            Comment


            • #36
              Originally posted by Rich Carlstedt View Post
              A few things that may help.
              Rich
              If you make a new screw, just make it longer and use the end like a tap, and the thread form does not have to be to any standard but yours .
              Yep, pretty much what I was saying before -- just do the screw and tap all in one go from the same rod. Much easier that way.
              25 miles north of Buffalo NY, USA

              Comment


              • #37
                If you make a new screw, just make it longer and use the end like a tap, and the thread form does not have to be to any standard but yours .
                While true about the standard idea this won't work. The tapped hole in the nut would tend to come out at the same or slightly smaller size. There would be no clearance and likely even a little interference.

                Anyone that has used a cheap tap or made their own and used it in steel knows how snug the tap fits even with repeated passes. It's bad enough on a small size and would be unworkable on something like this lead screw and nut. Some clearance for both the thread form and OD's is essential.

                BUT... IT's still a neat idea but with a slight change. Machine the OD down and leave a slight step larger on one end of the shaft to prepare that end for functioning as a tap. Then cut the thread form passing over both the screw and tap section. Finally once down close to what you need do the final very light passes only on the lead screw portion and leave the tap form a little wider than the screw area. This would give the clearance between the nut and the lead screw so essential for a smooth running thread.

                For a one time use on brass I'd want to use something more durable than mild steel for the one piece screw and tap "just in case". But it would not need to be a fancy tool steel and receive heat treating. Just something a little tougher than mild. For example, an anti sway bar from a car or truck would work well as is.
                Chilliwack BC, Canada

                Comment


                • #38
                  Reveling how rough I am, when I make a tap like this, I don't clean the burrs off after machining. That way the tap cuts slightly large and creates the necessary clearance.It works for a single use tap like this one will probably be I tend to use silver steel (I think thats drill rod to you guys) for the leadscrew and the tap, that way I can harden and temper the tap.
                  Yes, there should be clearance at top and bottom of the thread, I tend to aim for about 0.005" top and bottom (0.010" on diameter) by overboring the nut by 10 thou, and skimming the leadscrew crests by 10 thou compared to the tap
                  '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


                  • #39
                    Wow there's some good points being raised in here. I never would have thought to leave the burrs on the tap. Gonna have to remember that one.
                    25 miles north of Buffalo NY, USA

                    Comment


                    • #40
                      It only works once though, maybe twice, but no more.
                      '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


                      • #41
                        Seems as if making the section intentionally bigger is much more controllable than depending on the burrs.

                        The good news is, though, that the burrs (probably) make all portions of the profile larger. That's more trouble to do on a part of the regular thread.
                        2730

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

                        Comment


                        • #42
                          Wow, that is a great tip! Things like this are why I read these posts.

                          Thanks!



                          Originally posted by Rich Carlstedt View Post
                          A few things that may help.
                          For a Acme thread nut , as said already----you should do it in several stages and start with a deeper square cut ( larger OD than Acme major Diam) .
                          Then switch to a Acme style tool bit.
                          One trick I have used is to take the existing LH leadscrew and grind groves/slots in the very end ( which has the least wear by the way) and use the screw to do the last cleanup pass in the nut. it is snug ,But, works well in the normal middle of travel.
                          Another trick
                          Picking up a thread properly with two different tool bits can be tough, especially when you can't see the result of the second tool, so the solution is as follows
                          Say the needed nut is 30 mm deep-
                          Make one 40 mm deep and drill the ID out as normal, then remove the nut and mill the first 10 mm half off so it becomes a "half a hole" for 10 mm.
                          Reset in the lathe with the half hole in front and start your thread cut and you can see the thread form easily when you set up the second or third cutter as it is exposed and can time the tool feed location dead nuts. When done, cut off the 10 mm "trainer"

                          Rich
                          If you make a new screw, just make it longer and use the end like a tap, and the thread form does not have to be to any standard but yours .
                          Paul A.
                          SE Texas

                          And if you look REAL close at an analog signal,
                          You will find that it has discrete steps.

                          Comment


                          • #43
                            I would like to try start this .Iam going to try make an offset internal boring bar. I dont have drillrod this size but have en8. I dont know the American equivalent. It is a medium carbon steel I think.Do you think this could work on brass to make a nut .

                            Comment


                            • #44
                              Originally posted by plunger View Post
                              I would like to try start this .Iam going to try make an offset internal boring bar. I dont have drillrod this size but have en8. I dont know the American equivalent. It is a medium carbon steel I think.Do you think this could work on brass to make a nut .
                              Should work ok, I imagine a medium carbon rod would be equivalent to something like C45 or 1040.. good enough for 40-50 rC for a single use
                              25 miles north of Buffalo NY, USA

                              Comment


                              • #45
                                Speaking of leaving the burr on..... Back when I did my Myford ML7 restoration I had to replace the two bronze bearings in the jackshaft frame as they were worn out of round. I found and inserted stock bushings. But due to shrinkage from being pressed into place and a slight warp of the frame the shaft, some cold rolled steel, ran tight in the bearings. Like VERY tight. The CRS stock was over length so I made one end of the shaft into a "D" bit reamer on one end and a stub to fit my hand drill on the other end.

                                This took out a few shavings that almost fixed the issue. But because it was directly on size it still was running snug. So I used a trick from my wood working and burnished the lip of the "D" out a little much like sharpening a card scraper. That extra size from the burr did the trick and now the shaft ran with just the right fit. But the resulting edge only lasted long enough to do this one extra cut in the two bearings bearings. I could feel it dulling with the second bearing. But it was enough and the shaft spun freely at that point. I smiled at my cleverness on that one....

                                Two lessons here. First is that leaving a burr can work... for a very short while. Second is that mild steel will cut something softer such as brass or bronze for a short while.

                                So depending on how tough and hard this EN8 steel is you might need to tough up the sharpening a few times by stoning or lightly grinding the upper face. Lightly enough that the tool lives long enough to get the job done But it should work. Plus being softer metal I'd suggest you run at a pretty slow cutting speed. That might help with reducing heat build up and hopefully keep the edge for a few more turns.
                                Chilliwack BC, Canada

                                Comment

                                Working...
                                X