Announcement

Collapse
No announcement yet.

Converting rotational pull of a bolt to direct pull.

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

  • Converting rotational pull of a bolt to direct pull.

    I’m still looking for a way to pull a tone of loaded ammo. No make that close to 4 tons of loaded ammo. We have been playing with the standard RCBS collet type puller and it works quite well. And the change out to different calibers is only $15.00. So expanding on this I want to put an air cylinder on the screw that pulls the collet tight. I tried getting a mesherment with a torque wrench. But my wrench only go’s down to 10lbs. and I’m less than that maybe a pull scale on the handle of the collet closer. It is only a handle 3” long. Question is once I get a value how do I convert it to pull force? The collet closer is a 3/8”X16tpi bolt. I know there is some mechanical advantage with the screw. So I need to add this to the equation. It only takes about 90deg turn of the collet closer from contact of the bullet tell tight enough to pull the bullet without slipping out. An air cylinder bigger than I need would be ok. I could fine tune the closing force with a regulator. I tried a 2” bore cylinder with a 3/4” rod at 100psi. It might have closed the collet just a little. Anyway it didn’t work. I could go with a lever arm if it is going to take a 6” bore cylinder for direct pull.

  • #2
    If you want to work out how much force your closer, your bolt, is exerting when you hit the handle with a certain force, this is what you do. You treat the system as a lever. When you pull the handle, 3" long, round a full circle, you move it a distance of about 18" - 2 times pi times the radius. When that happens, the closer moves 1/16" - the tpi.

    The ratio of that lever system is 18 divided by 1/16, or 288. So if you exert a force of 10lb at the end of the three inch handle, the closer is closing with a force of 2880lb, or 1 1/3 tons.

    But this assumes a frictionless screw. Lets say that friction eats up one third of your effort. In this case a 10lb pull gives you a closing force of 1900lb.

    I hope this is what you were after.
    Richard - SW London, UK, EU.

    Comment


    • #3
      http://www.spaenaur.com/pdf/sectionD/D48.pdf
      From the chart...
      400 in lbs torque = 5,000 lbs pressure = 1:12.5

      edit; pressure on a 3" handle is 3x for conversion to in. lbs.
      10 lbs. on a 3" handle is 30 in. lbs. x 12.5 = 375 lbs of force
      Last edited by Abner; 10-18-2012, 07:30 AM.

      Comment


      • #4
        Originally posted by jeremy13 View Post
        I tried a 2” bore cylinder with a 3/4” rod at 100psi. It might have closed the collet just a little. Anyway it didn’t work. I could go with a lever arm if it is going to take a 6” bore cylinder for direct pull.
        A 2" bore air cylinder with a 3/4" rod will not have much force at all retracting at 100psig due to the rod size. For an air cylinder Force = Pressure x Effective Area. Using a PHD CRS cylinder with a 2" bore as an example you get 304 pounds of force at extension and 260 pounds of force at retraction with the rod diameter of 3/4. Up that to a 2.5" bore CRS and you get 483 pounds at extension and 439 pounds at retraction. Quite a difference for just 1/2" bigger bore because of the area.

        One trick I use when designing automation equipment to get more force into a small area is to stack two cylinders together. The bottom one a double rod cylinder and the top one a single rod cylinder.

        John
        My Web Site

        Comment


        • #5
          Have you thought of using a stepper motor to tighten the screw? This thread describes using a stepper motor for a power drawbar setup: http://www.cnczone.com/forums/mechan...r_drawbar.html

          bob

          Comment


          • #6


            Ever use one of these when torqueing head bolts on a Texas puickup?

            --G

            Comment


            • #7
              Yup - confession - forgot that little factor of twelve.

              Well, it was the middle of the night, and it looked like no one was going to reply to Jeremy till todaqy, so I wiped the sleep out of my eyes... Just not enough.

              Now if only the question had been in metric... My error would probably have been less, like, ten ?
              Richard - SW London, UK, EU.

              Comment


              • #8
                Rohart's reply is right on and exactly how I do it. But do remember his warning about friction.

                As for measuring torque values smaller than a regular torque wrench will allow, there are smaller versions. In the past I have purchased torque screwdrivers in various ranges, some quite low. McMaster has some. I would also think that larger torque wrenches are available too.

                Originally posted by Guido View Post


                Ever use one of these when torqueing head bolts on a Texas puickup?

                --G
                This device appears to show an angle in degrees. How do you use it to find a torque value? Is there a table? If so, why would they do it that way instead of just calibrating it in ft-lbs or some other torque unit?
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there IS a penalty for trying!

                Comment


                • #9
                  This power drawbar is super neat. Do check it out.

                  I have wondered if there was a simple way to power/automate the lock down screws on things like a RT for CNC operation. Perhaps a simpler version of this?

                  Originally posted by rowbare View Post
                  Have you thought of using a stepper motor to tighten the screw? This thread describes using a stepper motor for a power drawbar setup: http://www.cnczone.com/forums/mechan...r_drawbar.html

                  bob
                  Paul A.
                  SE Texas

                  Make it fit.
                  You can't win and there IS a penalty for trying!

                  Comment


                  • #10
                    Originally posted by Paul Alciatore View Post
                    Rohart's reply is right on and exactly how I do it. But do remember his warning about friction.

                    This device appears to show an angle in degrees. How do you use it to find a torque value? Is there a table? If so, why would they do it that way instead of just calibrating it in ft-lbs or some other torque unit?
                    thats for 'torque past yield' fasteners I believe.
                    The idea being that your torque to X ft-lbs with a typical torque wrench, then turn them X degrees past that to actualy strech the bolt.. (And never use that bolt again if you reinstall the cylinder heads)

                    PS: rohart: That is a great method you came up with. Lots of websites out there use some calculation based on the *diamiter* of the bolt while not taking TPI into account at all!
                    Some people keep telling me this is correct.. Although none can exactly explain why the TPI has no effect, Clearly TPI provides a ratio for movement.
                    I am 100% convinced the TPI *has* to matter. Maybe those websites use the diamiter to lookup the TPI for a typical bolt (or whatever the TPI formual is for course bolts) but that can't be the same as for fine threaded bolts.

                    By reducing it to 'Move X, Z amount, results in moving Y, Z/R amount, Where R is the ratio of input force to output force, and ratio of distances moved' is very simple and can't really be wrong, based on my limited understanding of physics.
                    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                    Comment


                    • #11
                      OK I had some time to dig up a screw that I can replace the screw with handle. Now I can get a better reading on the torque required to pull the collet closed. I friend of mine has a up to 100 in-lbs. torque wrench well try it out to night and get a better reading.

                      Comment


                      • #12
                        You might think about making a simple cam lock handle. That would be like a socket head cap screw (grade 8) with the head cut off, a handle with a cam on either side of the bolt and a 1/4" hardened steel dowel pin through the cam and bolt.
                        You would lift the handle to release the collet and push down the handle to tighten the collet. When the cam is at or just past center it will stay locked. You can adjust the tightness of the cam by screwing the bolt in or out.
                        Kansas City area

                        Comment


                        • #13
                          One more suggestion?
                          How about something set up like a air driven wedge type system, A bit like a morse taper collet only steeper so it's self releasing. Say 3 fingers inside a steep taper that are pulled or pushed up and down by an air cylinder on each finger. With 4 tons of ammunition to break down into it's components, your going to need something as automated as possible. And with that many cycles, the threads would wear fairly quick even if they were well lubricated. Acme would be far better of course.

                          Pete

                          Comment


                          • #14
                            Friend came over with his very nice Snap-On torque wrench that went to 200 in-lb. And came up with 120 in-lb. or 10 ft-lb being about right. This is for what I’m considering to be the hardest of the rounds to pull apart. So 1800 lbs. of pull force is about right. This is just staggering to me never would have guessed that a screw can exert that much force with just a 90deg turn. Looks like it will take a 4” bore cylinder running at 150psi. To do the necessary clamping force. That will make things rather large. Fitting in all the cylinders will make this at least 30” wide. I’m thinking I would like to do 5 to 6 bullets at a time.

                            Comment


                            • #15
                              This is what I'm using.
                              http://www.midwayusa.com/product/680...-bullet-puller
                              and the collets
                              http://http://www.midwayusa.com/prod...vc=sugv1680804

                              Comment

                              Working...
                              X