straightening splined shaft
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  1. #1
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    Default straightening splined shaft

    So,ordered material months ago,,now customer is in big ass hurry to machine it.Talking about 316 SS-1 1/8" OD with 20 splines.Ordered it from Grob.This is to be used as the Transom Shaft for a boat.Basically I need to machine 6 places about 2 inches long down to 1 inch diameter,,,right below the root of the spine.The bar is 6 foot long and has about a 1/8 inch bow to it.Never occurred to me to check it when material came in months ago,as got straight shit before,,,I ASSumed !
    Like I said,,big ass hurry
    These machined spots need/should be all in the same plane
    SO
    I have no big press,etc.,etc.
    Is flame straightening a viable option ?
    Or best just to do the best I can with what I got ?
    Oh yeah,big ass hurry,,like one way or another got to be done by daylight tomorrow,ughhhhhh....
    Thanks in advanced,,,

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    if you have a heavy table available, or at worst a Bridgeport, take a couple stout C clamps and fix them to the ends of the table to act as stops. For a BP, clamp some step blocks to the ends of the table.

    Now take a Kurt style vise, and set up its moving jaw such that you can use it as a load/press when a bar is put in between the moving jaw and the ends of the bar are against the stops you set up.

    Take the high bow, put it against the moving jaw, and gently move the jaw to induce a counter stress to the bow. You can tape a cheapo digital caliper to the moving jaw and fix the slider to a stationary part (or vise-versa) to give yourself a readout for how much you've moved the bent shaft. Once you get a decent number of shafts straightened you'll have an idea of how far to move the jaw to effect a good counter bend.

    Aluminum or brass jaw pads on the contact surfaces to protect the SS, even plywood would work, but you don't want too much compliance. Maybe polycarbonate is the best compromise.

    You want to minimize how many times you bend a bar, each bend introduces a little stretching to the shaft, which also strain hardens it a bit. That makes it more difficult to re-bend, so the new bend is adjacent to the old.

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    How about try the small ass press? That's not a very big shaft, however, SS is pretty springy, so takes quite a bit of overbend to make it take on a new alignment.

    It's also extremely soft and easily crushed, so only support it where you plan to machine the teeth away. If you happen to have spline couplings that you can slide over it to protect the teeth, do that.

    Flame straightening won't work very well on a solid piece of shafting. While it works great on tubing, I've always found it very difficult to make a solid shaft pull very far by flame straightening. Since you have to upset the metal in little circles, which in this case have teeth passing through them, you'll get even less draw when cooling the hot spots quickly. Give it a go, though, just in case it works. You need to get one spot, maybe 1/2" diameter red hot as fast as possible (probably within 15 seconds) on the high side of the arc. Cool it quickly with an air blast. The most effect is achieved by the first 2 or 3 seconds of cooldown. Essentially, you want to make a dark cooler spot in the middle of the red area before it all goes dark. Stainless cools slowly, and you need to cool it completely (to uniformity) before drawing conclusions about how much you were able to pull it in one session. If you need to try again to pull it some more, then pick another spot maybe 3" away, and try it again.

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    316 is soft. Put it in the crotch of a tree, slip a pipe over the end and pull. Have v-blocks and indicator ready to check your progress. You did not tell us how straight it needs to be. Hopefully the places you need to turn down are at the ends, or the turning is likely to let it warp again.

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    I've done a variation on Millards method. Two vee blocks on the " Bridgeport " table and a clamp in the middle of the shaft. Put a DTI on top and weigh up how much force you need. Go carefully, a little bit at a time.

    On place I worked at had been a " Millwrights " in the old days of the Cotton Mills around here. There was loads of old stuff in the back of the tool stores. I was having a look around one day and I came across the perfect tool for shaft straightening. It was a forged bar about 1.5" thick by about 3" deep and about 24" long. In the centre it had a circular area about 3" dia that was drilled and tapped 1.25" BSF with a strong hex head bolt in it. A bit like an old fashioned bearing puller.

    It came with two more forged items that fitted on either end of the bar. They were slotted so you could slide them in and out along the bar. The ends of these items had been forged into hook shapes.

    The idea was to slide the device down the bent shaft with the hooks supporting the bar, position the bolt on the bend and then tighten the bolt. It worked great on shafts up to about 1.5". Simple idea but very effective.

    Regards Tyrone.

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    Quick thought if you aren't committed to a plan yet and If you have a lathe long enough. Setup in Chuck, 4 jaw if really critical. Remove tailstock if in the way. Set other end in a steady rest. Get indicator setup on carriage. Use a heavy ratchet strap to start pulling bow out. Adjust steady rest down the length of Bar for best results as you start working the bow out. I mentioned ratchet strap because it came to mind first but what ever method to pull that fits the situation. Work puller sparingly as you understand how much pull is required to straighten. Check often, good luck.

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    Should have mentioned, slide shaft in Chuck and move steady rest as needed to isolate bow and pull said bow without inducing more curvature

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    From my archives:

    "I have straightened many shafts. Your press should work fine. It appears from
    your description that the shaft protrudes from the gear enough on the pulley
    side to support in vee blocks. So here's the method:

    Saw a couple vee blocks out of aluminum.

    Support the shaft on these blocks in your press.

    Mount a 1 inch travel indicator beneath the shaft under the bend.

    Rotate the shaft such that the high spot is up.

    Press against the shaft with a piece of aluminum between the ram and the shaft.

    Deflect the shaft about .100".

    Rotate the shaft and see if it has gotten any straighter.

    Once the shaft starts to become straighter lessen the deflection increments. It
    may take a .250 deflection to make the shaft move .001 but only .260 to make the
    shaft move .002.

    "Use the indicator to monitor the deflection and be careful once the shaft starts
    to straighten because it will be easy to over bend it. The aluminum vee blocks
    will indent to fit the shaft and will work better as the pressure rises. This
    indenting also protects the shaft. Steel vee blocks will damage the shaft. It
    takes a long time to tell you this but straighteneing the shaft will be quick."

    If you don't have a press then get one, borrow one, rent one or hire a properly equipped shop to straighten the shaft.

    Flame straightening stainless is a REAL BAD idea. Stainless moves quite a bit more than steel with heat (ever try welding it?) and you'd be completely hosed in no time.

    metalmagpie

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    I have straightened many a thing by peening ,,grind a 1/2" wide cold chisel to a radius just smaller than the root of the spline . determine if the warpage is local to one area or bow across entire piece if it is over entire length, locate inside of bow suporting shaft on something forgiving like a wood 2x4 and hammering light ly on chisel and moving down and reeating the full length of shaft recheck for warpage if no progress hit harder repeating till progress is made, it will move be patient and progressive . peening works it cumpresses the metal making it grow everso slightly , to straighten is subtlework but gratifing when mastered , it take not a lot of tools just the rtight know how .

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    I have straightened shafts and tubes between centers in a lathe.

    I use heavy steel across the ways and an enerpac cylinder.

    I like doing it in the lathe because it makes it real straightforward to check progress.

    Probably obvious, but use a dead center. Hopefully you have 5MT.

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    Quote Originally Posted by Garwood View Post
    I have straightened shafts and tubes between centers in a lathe.

    I use heavy steel across the ways and an enerpac cylinder.

    I like doing it in the lathe because it makes it real straightforward to check progress.

    Probably obvious, but use a dead center. Hopefully you have 5MT.

    I once had to go to a broken down lathe were the operator had been straightening ( stretching was the term used in my neck of the woods for some reason ) a pretty decent sized shaft using that method. I can't recall the make now but I do know it had " Gamet " bearings on the spindle.

    When I got the spindle out some of the hollow rollers in the " Gamet " bearings were broken and more or less just fell out onto the floor ! You can imagine the cost of the new " Gamet " bearings and there was quite a serious debate as to wether or not to scrap the lathe there and then. Eventually the company decided to stump up the money for the new bearings. They also had to stump up the money to have the spindle nose re-ground as it was running out about 0.008".

    I will add that the operator who wrecked the lathe was a bit of a know-all and an all round idiot. I have seen shafts straightened the same way without anything being broken lots of times but you do need to be really careful.

    Regards Tyrone.
    Last edited by Tyrone Shoelaces; 03-10-2018 at 07:27 AM.

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  17. #12
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    Quote Originally Posted by Tyrone Shoelaces View Post
    I once had to go a broken down lathe were the operater had been straightening ( stretching was the term used in my neck of the woods for some reason ) a pretty decent sized shaft using that method. I can't recall the make now but I do know it had " Gamet " bearings on the spindle.

    When I got the spindle out some of the hollow rollers in the " Gamet " bearings were broken and more or less just fell out onto the floor ! You can imagine the cost of the new " Gamet " bearings and there was quite a serious debate as to wether or not to scrap the lathe there and then. Eventually the company decided to stump up the money. The also had to stump up the money to have the spindle nose re-ground as it was running out about 0.008".

    I will add that the operator who wrecked the lathe was a bit of a know-all and an all round idiot. I have seen shafts straightened the same way without anything being broken lots of times but you need to be careful.

    Regards Tyrone.
    lol. I love it when those kind of people come unstuck. Did he admit his error and apologise or blame the lathe?

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    Watch a Keith Fenner video on youtube......he is a master at straightening stainless shafts.

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    Quote Originally Posted by Demon73 View Post
    lol. I love it when those kind of people come unstuck. Did he admit his error and apologise or blame the lathe?
    No not a bit of it, he was a bit of a " golden balls " with the management because he would work literally any hours they asked. He just thought " It was one of those things, I got a bit carried away with the " Enerpac ".

    He was a prick of the first order.

    I was working on an installation there in the period between Xmas and New Year. He was turning some sort of big crankshaft in a large lathe. Slowly facing along the side of the crank. It was really cold in the shop, no heating on, so he goes to the little maintenance shop where I was based and puts the fire and radio on. Drags a chair over to a bench and puts his feet up on the bench !

    Well out of sight of the job that's still running in the next bay.

    I said " Shouldn't you be out there on the lathe ? " He says " Nah, it'll be alright, I know how long it'll take to turn down ".

    About half an hour later I'm back in the maintenance shop and he's there again. This time he's obviously had some sort of crash and he's trying to disguise a big gouge in the four way tool post with an angle grinder.

    Like I said a complete prick.

    Regards Tyrone.

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    Honestly, just use a press and some lumps of nylon or wood, splines will dig into ether with no harm once the V's are imprinted too it is pretty easy, especially as you get a feel for it.

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    Quote Originally Posted by Garwood View Post
    I have straightened shafts and tubes between centers in a lathe.

    I use heavy steel across the ways and an enerpac cylinder.

    I like doing it in the lathe because it makes it real straightforward to check progress.

    Probably obvious, but use a dead center. Hopefully you have 5MT.
    I wouldn't apply ANY jack directly against the spindle and tailstock as opposing supports. That's just not respectful of the machine.

    I have built a self-contained double sided cradle with Vees that capture the shaft, and with the jack sitting opposite on a backbone attached to the cradle. All the bending forces are inside this cradle, the lathe is never abused. I used a short height 20 ton jack, but it does still take up a fair amount of space, so you'd need an 18" swing lathe to get this contraption in there.
    As you say, it is very convenient to then check the progress of the bend.

    I've found through experience that the supports for pressing need to be spaced apart about 6x diameter of the diameter being straightened. Otherwise you might get a 'straight shaft' with an opposite hump in the center, essentially a crankshaft which is a bitch to straighten because you have to do at least 3 bends to fix that hump: basically you have to undo that hump or you'll have one hell of a mess.

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    Out of curiosity did you get the shaft straightened?

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    Quote Originally Posted by Hodge View Post
    Out of curiosity did you get the shaft straightened?
    said "f" it figured I do more harm than good.
    That said,I know a lot of ways,but who was it,? Hung that throws Dung ?,,,for one simple bow you usually have to bend 3 spots to even begin to get straight,,,that has been my past experiences too.
    I don't have a big enuff lathe or press to tackle this at zero hour so I 4 jawed it at the end.Made a delrin bushing for the ass end so I did not become a youtube idiot star.
    Center drilled that and made my first "bushing" spot for the Transom Lever.
    Next I moved the shaft out about 18 inches or whatever,and indicated next to the jaws with the 4 jaw,and used my center to help persuade the sob to run true,,machined my 2nd bushing spot for the next Transom Lever.
    Did a 180 and rinsed and repeated for other end
    That makes 4 of the places
    Then I used the 4 jaw,steady rest, and center to do the remaining 2 spots to somewhat machine concentric
    Bossman said it would be fine,,,after I wrapped his head around what I was doing.

    Still warped,but all in same plane since bushings will keep it straightened,,,the drag should not be to bad on how it works for we use Hydraulic Assist Down Pedal


    and thanks for input all

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    Quote Originally Posted by HuFlungDung View Post
    I wouldn't apply ANY jack directly against the spindle and tailstock as opposing supports. That's just not respectful of the machine.

    I have built a self-contained double sided cradle with Vees that capture the shaft, and with the jack sitting opposite on a backbone attached to the cradle. All the bending forces are inside this cradle, the lathe is never abused. I used a short height 20 ton jack, but it does still take up a fair amount of space, so you'd need an 18" swing lathe to get this contraption in there.
    As you say, it is very convenient to then check the progress of the bend.

    I've found through experience that the supports for pressing need to be spaced apart about 6x diameter of the diameter being straightened. Otherwise you might get a 'straight shaft' with an opposite hump in the center, essentially a crankshaft which is a bitch to straighten because you have to do at least 3 bends to fix that hump: basically you have to undo that hump or you'll have one hell of a mess.
    I agree. That idiot should have been fired. Lathe is NOT a straightening press.

    JH


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