Cracked Tail-stock Casting
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  1. #1
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    Default Cracked Tail-stock Casting

    Recently, a couple months or so, I got a new to me Victor 1640B. I know, I know, Peoples Republic or Trash, but that's beside the point. So there I was, minding my own business, cutting a length of 7/16-10 Left hand Acme thread. Nothing too difficult, machine is cutting nice and true and there's no sign of any issues. I turn the lathe off and step aside to grab some water. As I'm walking out of the shop I hear a loud crack come from the lathe. I look around for a bit and then I see it, a sizable crack running about 2.5" inches in length from the operator side alignment bolt. Now I haven't adjusted center in around a week and a half, haven't needed to as it's been cutting within .001/ft but I do admit to getting a little torque happy trying to get that last little bit out.

    Anyways, a pleasant call to Machinery Solutions in Cali later and I get the great news that yes, I can get either a complete assembly or just the top half casting. For $2500 and it'll need to be machined to match the ways and sit on center... So add about, oh I don't know, $1000 is my rough estimation to have it fit. I paid $4800 for the machine, not about to pay $3000-4000 just to replace a tail-stock.

    I attached some pictures of the damage as it happened and some after I'd removed a small Chinese fortune worth of auto body filler and throat and eye destroying particulate and paint. It looks nowhere near as bad without the ashes of 1000 Chinese ancestors plastered all over the casting. But it's still broken and I'd like it to be less broken. Anyone have any suggestions on how best to repair it? I'm afraid just fixing the crack isn't going to be enough. The crack is on both sides of the bore for the alignment bolt and originated at the thread in the casting. I'm not really opposed to anything that prevents me from buying a new one and having it fit. I've been suggested drill and tap it to the base place and use bolts to lock them together once I get it aligned. I'm not opposed to this but I would still prefer to do anything I can to either prevent the crack from getting worse or the casting warping off center.

    Any help is appreciated as I'm kind of dead in the water till I get it back in a usable state.

    Stephen

    I'm either terrible at working the image system on PM or it just sucks, possibly a combination of the two. I put them in an imgur album to make them easier to see.

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    My approach would be to blue up mating surfaces for misalignment. My guess is that there was an alignment problem and the stress of clamping caused the cracking. As as repairing what you have, I would "V" out the crack on both sides and braze it. Then refit the parts. Might require shimming.

    Tom

    Edit Forgot to say to drill a hole at the end of the crack to keep it from progressing.

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    Something ain't right there. The crack is huge with the adjustment screw in it but closed with it out. Is the hole tapered? Crooked? Something causes it to spread when the screw is in. I would braze it and tap it to be sure that it is straight and as cylindrical as that will make it. What made you think that it should be so tight? It is adjustment, not a lock. adjust it to where you want it and lock it with the gib.

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    Quote Originally Posted by tdmidget View Post
    Something ain't right there. The crack is huge with the adjustment screw in it but closed with it out. Is the hole tapered? Crooked? Something causes it to spread when the screw is in. I would braze it and tap it to be sure that it is straight and as cylindrical as that will make it. What made you think that it should be so tight? It is adjustment, not a lock. adjust it to where you want it and lock it with the gib.
    Mostly lack of experience among other things. I knew it was tight but the cam wasn't binding for the table lock, and it was holding on center. I just didn't expect the casting to let go with under 40ft/lb pressure.

    The openness of the crack you see is just the body filler making it look worse than it was. Keep in mind there's almost .25" of body filler on there.

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    Life is a cruel cruel teacher.

    But the lessons are well learned.

    Quite your crying, get a life, this is a machinists forum, $2500 for hard parts flows like water.

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    Quote Originally Posted by CalG View Post
    Life is a cruel cruel teacher.

    But the lessons are well learned.

    Quite your crying, get a life, this is a machinists forum, $2500 for hard parts flows like water.
    I don't think I'm crying.. just looking for advice on making repairs. I understand that $2500 is a drop in the bucket for (most) shops, but it'd be kinda silly to just cave and buy it, besides it's a week and a half delivery time, I've got a whole week in a half to make it worse! OR fix it, if possible.

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    no repair is needed in my opinion.

    you likely cracked the casting because you didn't back the other screw off before torquing the one in the front to push the tailstock towards you.


    if that crack actually dynamically degrades the stiffness of the tailstock enough to be a problem, you've got what looks like at least 1.5 inches, you can mill a slot to the right of the crack, drill and tap the baseplate of the tailstock for a bolt/stud, and bolt the two together, leaving room for at least an inch of travel/adjustment for taper turning.

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    Mechanical repair/reinforcement.

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    I think there may be a large unfused inclusion in the iron ........the is crack from an edge,which is not stressed dynamically.................drill the crack end,and attach a top plate with socket screws............I suspect any heating to braze will reveal a serious fault in the casting.

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    Quote Originally Posted by john.k View Post
    I think there may be a large unfused inclusion in the iron ........the is crack from an edge,which is not stressed dynamically.................drill the crack end,and attach a top plate with socket screws............I suspect any heating to braze will reveal a serious fault in the casting.
    That was one of my concerns as well. The casting was very poor quality once I removed the filler, trust me it was a quarter inch for a reason. There were numerous voids that weren’t very deep that my initial grind took out, the ones you can see still there were too deep to safely remove and the crack runs right next to it. I have a feeling if I’d gone a little deeper the crack would’ve made it into the inclusions. That said, the bore for the bolt is almost 2” deep with maybe .375” of threading at the end. Not exactly a rigid design, they could’ve just as easily tapped the whole length and used a long sec screw for a way stronger design.

    Then again, not over torquing it is a good solution as well.

    I am kind of on the mindset that there’s no large forces acting upon the area under normal use and as johansen said, probably doesn’t need repairing. But I’d hate to be turning a large heavy piece and have the crack expand or cause severe vibration mid cut. I do like the idea of lock bolts into the base plate but maybe one on each side of the crack. I do have some nickel 55 rods but I’m afraid the web is too thin to reliably repair it with anything beyond a light braze just to seal up the crack.

    Thanks for the suggestions people.

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    I don’t think an inclusion in the casting or some taper in the tapped hole caused the crack. The designer of the part is the main problem. Given cast iron’s very poor tensile strength and the fact that a standard 60 degree thread is simply a neat little row of wedges,(ever see how granite is split with wedges and shims?) the outcome is no surprise.

    Why not just drill an end hole to hopefully stop progress and see how it goes? That thin bit of iron wasn’t doing much before it cracked.

    My 2c
    Denis

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    It looks like you have plenty of room on top of the casting across the hole. Could you add a strap across the crack from side to side to take the force off the casting? I think you could put the casting in a vice to draw the crack together and then add say a 1/4" thick strap across it using some bolts drilled and tapped into the casting while it is squeezed together. Just an idea. You could of course braze it up but you may have to preheat the casting and I'm not sure what that would do to the alignment. I have never had much of a problem with cast iron warping if done right, but I would not want to take a chance. Usually on something that I don't want to heat up much, I will stitch weld it with a nickel rod giving it plenty of time to cool between "stitches" . I agree with others that there is not a ton of force on this area and I would take the minimal heat approach. Of course you should drill the end of the crack as others have said to stop the progression. One thing is for sure in my mind. I would not pay that kind of money for a new one. I think this is very fixable given the circumstances.

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    Quote Originally Posted by iwananew10K View Post
    Mechanical repair/reinforcement.
    Amen. A hefty steel strap with ends that fit over extremes of casting, and a set screw one end or other (think custom "C" clamp). I mean it lays there on the big flat surface. Then a nice photo to send over to the folks that pretend to be in the making machine tools business

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    If in fact that the adjusting screw was wedging the base apart, then that has to be corrected before strapping or other mechanical fixes. 40 ft-lb is a bit for an adjusting screw.

    Tom

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    Quote Originally Posted by iwananew10K View Post
    Mechanical repair/reinforcement.
    This. Lock-N-Stitch it then refit. Metal Stitching & Thread Repair Inserts. - Turlock , CA - LOCK-N-STITCH, Inc

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    Let it be noted that there are a number of shops in the US that perform Lock-N-Stitch-type repair of iron castings, and most of 'em are closer to the OP's east-coast location. Continental Field Services may be the closest big shop, but that job isn't a big job . . . I suggest a quick search using your favorite search engine, looking for "metal stitching" and "cast iron repair" to look for a local shop that can do the job.

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    From what I see, if you brought it to me I would: Put a stout C clamp on the part closing the tailstock crack. Mill the top of that piece of the tailstock flat. Find a suitable piece of flat steel to bolt and dowel to the face, and install. Then fix the fitment between the adjusting screw and the tailstock bottom. Fix the cam that made you overtorque the screw in the first place.

    A photo of the bottom would be very useful.

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    Just before the castings are poured ,the foundryman tosses in a number of shovels full of old nuts ,bolts and punchings to cool the melt to correct pouring heat......when the melt is OK to pour ,the moulds are poured ........sometimes castings have unfused steel bits in the iron...........if not visible from the surface ,then the casting is sound.............if visible in a finished surface ,out comes the chalk filler.

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    Quote Originally Posted by John Garner View Post
    Let it be noted that there are a number of shops in the US that perform Lock-N-Stitch-type repair of iron castings, and most of 'em are closer to the OP's east-coast location. Continental Field Services may be the closest big shop, but that job isn't a big job . . . I suggest a quick search using your favorite search engine, looking for "metal stitching" and "cast iron repair" to look for a local shop that can do the job.
    I think for a project that small I would try to do it myself. Lock-N-Stitch provides a lot of info and instruction on using their products and I wouldn't be afraid to take a swing at it. I haven't used these products but I plan to. I have a Farmall Super C with a windowed block and I plan on attempting to patch a piece in using Lock-N-Stitch. If I fail, I'm not out much and I'll move on to getting a different engine.

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    Can you run one or two through bolts front to back? If you can, no other repair is required except scraping the top part to thee base.


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