Announcement

Collapse
No announcement yet.

Spring Loaded Follow Rest

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

  • Spring Loaded Follow Rest

    I was just thinking about the fact that some metals seem to finish better if you take a bigger depth of cut. 4140QT and most stainless come to mind.

    Now, I have some more modestly long tapers to cut. I can't really use a follow rest, and no matter how careful I am using a steady rest in the middle always seems to leave me worry away at a slight mismatch where the first and second half of the turning meets up. If I could cut it all in one pass from your stock a follow rest would work, but the diameter difference is enough that just won't work. If I try to cut the full length with enough DOC to get that good finish I'll get a little chatter in the middle. Would a spring loaded follow rest that engages the work pieces a little before the chatter chows up be able to give enough to finish to the end of the cut and have enough spring force to prevent chatter in the middle of the cut? Ideally it would be finished based on measurements taken from previous heavy cuts, and the follow setup based on chatter marks from previous cuts.

    The only other thing I can think of is taper turning fixture paired with some sort of scissor mechanism that moves a follow rest the opposite direction the same amount as the cutting tool. I'm thinking still spring loaded to take up an variance, but then it would be constant back force the length of the cut.

    Or is this just another one of my overly complicated dumb ideas?
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  • #2
    I already made one like that for turning tapered and contoured rifle barrels and similar long projects. I used roller blade wheels to contact the workpiece and made the spring loaded part adjustable for pressure. This allows you to turn the entire length in one setup instead of doing short segments, then trying to blend them together. I turned a straight taper on a barrel and it worked really well.

    I also made a lathe jig for the manual lathe to turn contours to match an existing part or a flat template. It worked out pretty well too.
    Last edited by Toolguy; 03-26-2018, 03:00 PM.
    Kansas City area

    Comment


    • #3
      Would leaving a couple of thou on and getting the tapers finish ground be the answer?

      Comment


      • #4
        I think I have seen pneumatic cylinders used as a springs somewhere.
        Something with rather high friction in the moving "piston" element would help to dampen possible vibrations. Hydraulic or mechanical friction type damping perhaps?
        Location: Helsinki, Finland, Europe

        Comment


        • #5
          Originally posted by MattiJ View Post
          I think I have seen pneumatic cylinders used as a springs somewhere.
          Something with rather high friction in the moving "piston" element would help to dampen possible vibrations. Hydraulic or mechanical friction type damping perhaps?
          Pneumatic with a fast acting regulator might do the trick. Then pressure from the follow could be "fairly" constant.
          *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

          Comment


          • #6
            Originally posted by Toolguy View Post
            I already made one like that for turning tapered and contoured rifle barrels and similar long projects. I used roller blade wheels to contact the workpiece and made the spring loaded part adjustable for pressure. This allows you to turn the entire length in one setup instead of doing short segments, then trying to blend them together. I turned a straight taper on a barrel and it worked really well.

            I also made a lathe jig for the manual lathe to turn contours to match an existing part or a flat template. It worked out pretty well too.
            Do you happen to have photos or drawings of those?
            Mike
            WI/IL border, USA

            Comment


            • #7
              Unless I'm missing something or not understanding what your saying, How would you control the spring tension on a spring loaded follower rest??
              The tension is going to constantly change as you move down along the barrel and the taper gets smaller.
              Too much spring tension and your pushing the barrel into the cutting tool, too little and the cutting tool is pushing the barrel away.
              Pics would help.

              JL.............

              Comment


              • #8
                Originally posted by JoeLee View Post
                Unless I'm missing something or not understanding what your saying, How would you control the spring tension on a spring loaded follower rest??
                The tension is going to constantly change as you move down along the barrel and the taper gets smaller.
                Too much spring tension and your pushing the barrel into the cutting tool, too little and the cutting tool is pushing the barrel away.
                Pics would help.

                JL.............
                I think the point is it doesn't matter that much. An 1/8 inch of taper is a lot, but a 10 lb per inch spring is only going to vary by 1.25 pounds of force over its entire length of travel. Its about taking out the vibration and eliminating the chatter. Near the tail stock (if that's the small end) spring pressure is less. In the middle where chatter occurs spring pressure increases, and near the head/spindle the work piece is thicker and its better held by the chuck is where the spring force would be the highest. Relatively. Since this is for a manual application you might even want to remove the follower as it approaches the chuck so you don't crash it.

                An 1/8 of taper would result in a piece 1/4" smaller at one end than at the other.

                Of course you have to think it through, and maybe take some "guess cuts" to see what happens before you get to your final cut.

                It would also be possible to make a setup using a constant force spring, but that's more complicated and constant force springs are more expensive, have a more limited life, and tend to be more for low force applications like a pocket watch.
                *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

                Comment


                • #9
                  Originally posted by JoeLee View Post
                  Unless I'm missing something or not understanding what your saying, How would you control the spring tension on a spring loaded follower rest??
                  The tension is going to constantly change as you move down along the barrel and the taper gets smaller.
                  Too much spring tension and your pushing the barrel into the cutting tool, too little and the cutting tool is pushing the barrel away.
                  Pics would help.

                  JL.............
                  That was my thought as well. So I was nodding at the idea of a regulated pressure cylinder. But it also occurs to me that if a strong spring can be used through levers so the support wheel only sees a fraction of the force but can move more then by nature of working the spring over only a small portion of its stretch it SHOULD be somewhat more constant a force at the idler wheel.
                  Chilliwack BC, Canada

                  Comment


                  • #10
                    I have limited experience at this, as I have only done one barrel so far. From the one I did, it seemed that the amount of force needed is neither that much or that critical. You only need enough to dampen the harmonic vibrations. The barrel is strong enough to deal with cutting forces on it's own. I was able to just turn the entire length several times without any problems, just like making a cut on a short piece. The exact depth of cut didn't seem too critical either, as long as you don't try to hog it off. I will try to find time to replicate the setup, get pictures, and get the Shop Wench to help me post them sometime soon if anyone is interested.
                    Kansas City area

                    Comment


                    • #11
                      Originally posted by BCRider View Post
                      That was my thought as well. So I was nodding at the idea of a regulated pressure cylinder. But it also occurs to me that if a strong spring can be used through levers so the support wheel only sees a fraction of the force but can move more then by nature of working the spring over only a small portion of its stretch it SHOULD be somewhat more constant a force at the idler wheel.

                      On another forum one fellow said he would just finish it on a cylinder grinder. Here was my response:

                      That's perfectly fine if you HAVE a cylinder grinder, but if its possible to get a finish quality cut on the lathe why wouldn't you. One less setup means its more cost effective to make the part.

                      Now think about this. There are several ways to tackle such an application.

                      Remember:
                      1. A follow rest also exerts force against the work piece, and the work piece can bow away from that force more in the middle than at the ends.
                      2. The only stated goal is a finish quality cut. I didn't say anything about accuracy or precision, although it might not be as bad as you think.

                      Options:
                      1. The most complicated would be a mechanism using a constant force spring. Add on that constant force springs typically have a finite life and cost more it hardly seems worth it.
                      2. Regulated pneumatic cylinder. In theory it could be pretty good, but in practice a regulator that will be closer force tolerance than option 3 would be quite expensive.
                      3. A simple compression spring in a tube that is easily adjustable relative to the axis of the work piece. (two actually)

                      Now #3 is most likely what you thought of when you "pooh poohed" the idea, but it might be the easiest and have the least amount of variance if you think it through. Here is a simple example. An 1/8 inch of taper travel gives you a 1/4 inch of total taper. That's not the most extreme taper you might see, but its a lot of taper. Now if you have the small end of your taper on a center in the tail stock the spring pressure is lowest at that point. At the middle where you are most likely to get chatter the spring pressure increases, and as it approaches the chuck where the work piece is thickest and most firmly held against deflection the spring pressure is at its highest.

                      (Theatrical interjection) AURGH! SEE MY POINT EXACTLY SPRING PRESSURE CHANGES ALONG THE WORK PIECE !!!!!!!!!!!!!

                      Um, yeah, a little, but think about it a little differently by putting specific numbers on it. If you use a 10lb compression spring (it can be any practical length) the total variance in pressure is only 1.25 lbs over the entire length of travel. If the spring is 3 inches long you can vary your overall pressure from zero to 30 lbs, and its a pretty simple mechanism anybody could build. Certainly any "real" machinist. Add something like a rubber wheel (using the term rubber broadly) to roll along the work piece and it will help level out and dampen the vibration a little more I think.

                      You might have to play with adjustment to get it just right, but on the type of part you are gong to need this on you will have to make multiple passes anyway. If you could do it in one pass you could just use a regular steady rest.
                      *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

                      Comment


                      • #12
                        Originally posted by Toolguy View Post
                        I have limited experience at this, as I have only done one barrel so far. From the one I did, it seemed that the amount of force needed is neither that much or that critical. You only need enough to dampen the harmonic vibrations. The barrel is strong enough to deal with cutting forces on it's own. I was able to just turn the entire length several times without any problems, just like making a cut on a short piece. The exact depth of cut didn't seem too critical either, as long as you don't try to hog it off. I will try to find time to replicate the setup, get pictures, and get the Shop Wench to help me post them sometime soon if anyone is interested.
                        I for one would love to see the tools and the setup if you get the opportunity.
                        *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

                        Comment


                        • #13
                          Originally posted by Bob La Londe View Post
                          I think the point is it doesn't matter that much. An 1/8 inch of taper is a lot, but a 10 lb per inch spring is only going to vary by 1.25 pounds of force over its entire length of travel. Its about taking out the vibration and eliminating the chatter. Near the tail stock (if that's the small end) spring pressure is less. In the middle where chatter occurs spring pressure increases, and near the head/spindle the work piece is thicker and its better held by the chuck is where the spring force would be the highest. Relatively. Since this is for a manual application you might even want to remove the follower as it approaches the chuck so you don't crash it.

                          An 1/8 of taper would result in a piece 1/4" smaller at one end than at the other.

                          Of course you have to think it through, and maybe take some "guess cuts" to see what happens before you get to your final cut.

                          It would also be possible to make a setup using a constant force spring, but that's more complicated and constant force springs are more expensive, have a more limited life, and tend to be more for low force applications like a pocket watch.
                          Not really, an 1/8" on a 28 or 30" barrel isn't that much. I've seen rifles that are about 5/8" at the muzzle and 1" at the chamber end.

                          If your going to set something up with a spring and the spring pressure varies about 1.25 lbs. over the entire length of the barrel perhaps break down the force to say.... about 3" of travel. If you could rig an adjustment knob for that spring you could gradually increase the back stop of the spring every 3" or so to keep the pressure more steady.

                          After you get the results of that maybe a final pass or two with out the follower rest using a dead sharp insert to shave any irregularities in the center of the barrel.

                          JL.................
                          Last edited by JoeLee; 03-26-2018, 08:12 PM.

                          Comment


                          • #14
                            I made a similar device for surface/cylindrical grinding of thin rods, pins, drills, etc. It's an arm with a fulcrum. One end of the arm supports the rod from the bottom. The other end of the arm carries a weight. In order to fine tune the supporting force, the weight slides along the arm and then is held by a set screw at a chosen spot. The lever can also be changed by sliding the arm through the fulcrum area. So the spring action is replaced by the weighted lever action.

                            There is a photo of it in the Shop Made Tools thread (post# 1613, posted on 5/31/13): http://bbs.homeshopmachinist.net/thr...123#post854123

                            I guess the same principle can be used for turning too given a proper weight and lever length combination.
                            Last edited by MichaelP; 03-28-2018, 12:49 AM.
                            Mike
                            WI/IL border, USA

                            Comment


                            • #15
                              Originally posted by JoeLee View Post
                              Not really, an 1/8" on a 28 or 30" barrel isn't that much. I've seen rifles that are about 5/8" at the muzzle and 1" at the chamber end.

                              If your going to set something up with a spring and the spring pressure varies about 1.25 lbs. over the entire length of the barrel perhaps break down the force to say.... about 3" of travel. If you could rig an adjustment knob for that spring you could gradually increase the back stop of the spring every 3" or so to keep the pressure more steady.

                              After you get the results of that maybe a final pass or two with out the follower rest using a dead sharp insert to shave any irregularities in the center of the barrel.

                              JL.................
                              That's 3/16 of an inch of taper cutting movement. In my example that would increase the variation of pressure to 1.875 pounds from one end to the other. Sure its 3/8 difference, but the travel is only 3/16.
                              *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

                              Comment

                              Working...
                              X