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  • Shaft straightening

    I have two shafts from a 1950’s Brown and Sharpe surface grinder that are bent… These are about 15 inches long and about ½ to 7/8 diameter inch where bent. I haven't had a chance to put these in V blocks etc, but they appear to be a "simple" bend in one location. In the pics below, the threaded shaft is bent just before the junction of the narrower section - the threaded portion appears straight. The splined shaft seems bent closer to the middle.

    I have a couple of choices… try to straighten them myself, or send them out to someone who might know what they are doing… These are not available., and would cost a bunch to get remade. They don’t appear to be hardened, but it’s unclear what steel they are made from. It has fine surface finish even where turned and could even be leaded steel.

    I imagine a lot of electric motor and other shafts get bent… and fixed… Anyone know companies that do this work? I might get enough courage to try this myself, but I’m not really sure where to start… any hints? I have a surface plate, v blocks, lathe for center, arbor press, and shop press. Would this be done cold or with some heat?




  • #2
    If there are center drilled spots in the ends, stick it between centers in the lathe and find the high spot w/ a dial indicator and mark it; note how much the shaft is bent at that point If there aren't, I'd use a tool in the toolpost and a steady rest to put an accurate center in both ends, and proceed from there.

    Once you know where it's bent and how much, set it up in the press w/ the
    "bump" up, centered between supports and clamped in place. Use that dial indicator and watch the deflection as you bend it back. The less distance
    between the supports, the less springback... but the more force required.
    Half the distance will make for 8 times less deflection for the same load, while the bending force will only drop by a factor of 2.

    I'd do all the bending cold, and support the shaft on some scrap copper or brass to prevent marring. Same w/ where the press arbor bears on the shaft...

    You should practice w/ some similarly sized scrap to get a feel for the exercise.

    - Bart
    Bart Smaalders
    http://smaalders.net/barts

    Comment


    • #3
      I agree with what barts said. Have straightend polished rods, axle shafts, and jet engine parts this way.

      Keith

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      • #4
        When I worked in the sawmill in McCloud, CA there was one particular piece of log handling equipment (called the "charger") that had a pair of ground 3" ball screws 8' long. This gadget carried logs through a scanner in order to position the log on the head-rig carriage. A lead screw was mounted on each side of the machine and moved the charger past the scanner. The screws were driven by a common servomotor through a pair of right angle gearboxes.

        Because of a minor engineering oversight, the machine was somewhat flexible, but there was no provision in the drive chain for this sort of movement. The end result was that one of the shafts in one of the gearboxes would flex until it broke, which in turn would allow the machine to twist said precision ball screws into pretzel-like shapes.

        Since the screws were so difficult and costly to replace, and we had to keep the mill running, the twisted screws were hauled to the machine shop. For starters, they were chained down to a large planer table, and a chain fall was used to straighten them out to the point where they could be mounted on a lathe . Then the machinists used a somewhat smaller chain-fall, and an assortment of BFHs and brass blocks, and maybe some come-alongs, to finish the straightening process. (Shudder!)

        And the most wonderful part of all this was that they did a fine enough job that you could barely see any wobble when they were re-installed. Which just goes to show that somebody who really knows what he (or she) is doing can accomplish tasks that us mere mortals cannot distinguish from magic.

        I finally came up with a way to stop the servo when the charger started to get more than a few hundreds of an inch out of square, but that's another story.

        -bill

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        • #5
          Then the machinists used a somewhat smaller chain-fall, and an assortment of BFHs and brass blocks, and maybe some come-alongs, to finish the straightening process
          I never heard of any of the term 'chain-fall' before. I guess BFH is big effing hammer?
          Peter - novice home machinist, modern motorcycle enthusiast.

          Denford Viceroy 280 Synchro (11 x 24)
          Herbert 0V adapted to R8 by 'Sir John'.
          Monarch 10EE 1942

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          • #6
            Originally posted by Peter.
            I never heard of any of the term 'chain-fall' before. I guess BFH is big effing hammer?
            Peter--"Chain fall" is a commonly used term in my part of the world also.-It is simply another name for a chain hoist with pulleys at both ends.---Brian
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

            Comment


            • #7
              Years ago this elderly gentleman who was an armorer inWW2 and was the most respected machinist in our town used his lathe and torch to straighten things like engine push rods etc.When the indication looked right he would speed up the lathe to cool it a little quicker and that was it.Never had any problems with push rods etc.---As an aside he was "with it" in his old days till his cardiologist told him "No more welding" because of pacemaker.This apparently destroyed his image of his ability to do certain things and all went downhill from there and he became confused etc.Seen this type of things in other people when something changes such as loosing the ability to drive etc which triggers the downward deterioration.Used to think of old people as "them".Now I'm one of "them".

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              • #8
                falls

                You are right Brian.

                This may help:
                http://www.weldingmart.com/Qstore/c000231.htm

                I checked because I had the marine/Navy definition in mind.
                http://books.google.com.au/books?id=...esult#PPA88,M1

                This as well:

                As a pilot steamer, John Oxley would steam out into Moreton Bay where she would anchor waiting to collect pilots from outgoing ships and send pilots out to incoming ships.
                While waiting for ships, John Oxley would lie at anchor. To meet a ship requesting a pilot, she would weigh anchor and steam towards the ship. Pilot transfer was by 22’ clinker whalers, which were of a design that was easy to row, manoeuvrable and light enough to be hauled back on board John Oxley.
                Four deck crew were on oars and the Mate was in charge of the boat manning the sweep or steering oar. The pilot would board the whaler as it was being lowered.
                The John Oxley would be steaming very slowly as the whaler was dropped into the water. The crew would release the boat falls (blocks and tackle – pronounced taykel) and row over to the incoming ship.
                Better skippers would place John Oxley so close to the incoming ship, that a pull on the guest warp, or painter that hung down from John Oxley plus a few strokes on the oars was all that was needed to close the distance.
                The pilot would leave the whaler and climb up a rope ladder, clamber over the bulwarks and make his way to the bridge. The whaler would return to John Oxley and secure to the guest warp. The crew would hook the falls onto the lifting hooks in the whalers. Two hands would clamber up lines, get on board and go to the boat deck where they would commence to haul the whaler up under the davits.
                and:
                http://www.navis.gr/safety/general/launch.htm

                Comment


                • #9
                  Originally posted by barts
                  If there are center drilled spots in the ends, stick it between centers in the lathe and find the high spot w/ a dial indicator and mark it; note how much the shaft is bent at that point If there aren't, I'd use a tool in the toolpost and a steady rest to put an accurate center in both ends, and proceed from there.

                  Once you know where it's bent and how much, set it up in the press w/ the
                  "bump" up, centered between supports and clamped in place. Use that dial indicator and watch the deflection as you bend it back. The less distance
                  between the supports, the less springback... but the more force required.
                  Half the distance will make for 8 times less deflection for the same load, while the bending force will only drop by a factor of 2.

                  I'd do all the bending cold, and support the shaft on some scrap copper or brass to prevent marring. Same w/ where the press arbor bears on the shaft...

                  You should practice w/ some similarly sized scrap to get a feel for the exercise.

                  - Bart

                  Hello, Second the above. Also, have used a fixture (jig?) made by Dake which has centers & V's (for shafts without centers) for supporting shaft on a rectangular bar and a gismo to hold an indicator in between the supports to locate and quantify the bend. Mark the high spot & go to press supporting shaft on V's (Dake accesories also). Count strokes on press & check on fixture, see if you need more or if you went too far, then back to press, etc, etc. A little tricky on shafts that have a shoulder. Good luck, Earl

                  Comment


                  • #10
                    Lakeside:

                    As a point of interest, when I worked as a subcontractor at Colt in Hartford (many years ago) the rifle barrels came off the boring machine and went to the barrell straighener.

                    This was a guy with 2 V blocks, dial indicator and arbor press. He twirled the barrell, pulled the arbor press once or twice, and went on to the next one. I have no idea what tollerance they were looking for.

                    The point is, shafts can be straightened this way. I suspect you could greatly improve your shafts likewise, the big question is can you get it good enough. This is quick to set up and at least worth a try; with little down side risk providing good judgement used. (Normal disclaimer,Your conditions may very:yada, yada,yada)

                    Pete

                    Comment


                    • #11
                      If the shaft is hardened, anneal the area where the bend is. I have tried this cold with a feedscrew from a Hardinge lathe, bent just where yours is, and yes I snapped it. So if you are going to anneal it anyhow, might as well try flame straightening. Spot heat where you want the metal to shrink. It will bend the wrong way first, but when it cools off, it will contract. Just like cambering a beam. TIG works great for localized heating for shaft straightening.
                      --Doozer
                      DZER

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                      • #12
                        I'm pretty sure they are not hardened. They mark easily and the set screw left a dent.

                        I put them between centers today - one "simple bend spot on each. Both about 140 thou of run out. The shaft before and after the bend are essentially straight.

                        The shaft with the acme thread is bent right at the junction of the smaller section just before the acme starts. Looks straight forward.

                        The splined shaft is bent right at the point where the spline ends and the threaded section starts. This is more worrisome as the thread may be impacted by any rebending. The press point would be either on or very close to the threads. Right now it appears undamaged as a nut threads on and off with ease.

                        I ran out of time today... a closer look tomorrow.
                        Last edited by lakeside53; 03-15-2009, 03:24 AM.

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