What steel to use for cross pins joining two shafts?
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  1. #1
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    Default What steel to use for cross pins joining two shafts?

    I get the weird jobs nobody in this area wants to mess with. I swear ten guys will come into my shop and they don't have a full set of teeth between them. Anyway I have to cut two pto shafts and join them together. The reason being that one of the splines in no longer available. Anyway I've been looking into ways of joining two shafts which include a keyed coupling, a welded coupling and a cross pinned coupling. I want to go with something that if it does fail, I can go to plan B without destroying the shafts. I am leaning towards cross pinning with 1/2" pins (shafts are about 1.5" D. If the pins shear I just move on to something else. My question is what type of steel should I use for the pins? I don't want anything real brittle but plenty tough. I have some 4140 but I'm just not sure. I also have O-1 and various tons of mystery metal.

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    Are they the same shaft knuckles? Then you can just change out the knuckle and be done.

    It seems as you want to add in a shear pin in between the knuckles to connect both different PTO shafts. That doesnt sound like a good idea because a PTO spinning at 550 rpm or 1080 rpm is going to do some damage when that goes. A pto shaft is also made 2 pieces so it can slide in and out so tilt has play for going up/down and what not.

    Your best bet is to tell them- Go to a farm store or online and purchase a spline adapter and it is no longer your problem.

    Sent from my SM-G960U using Tapatalk

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    4140 HT if you go pin route, I'd personally make a keyed spline adapter.

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    Why not something like this?

    When/if it breaks they can replace it themselves.

    https://www.tractorsupply.com/tsc/pr...bolt-pack-of-5

    And this page from McMaster gives some hints on what type of steel to use and what weakening grooves look like.

    McMaster-Carr

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    Thought of a keyed coupling but that is a bit more work. Have to broach the keyway in the coupling and mill keyways in the two shafts, I had not thought of a bolt. I like that idea. I could safety wire the nuts on to add a bit more security. Bondo...there are no knuckles on this. Think of two shafts that just have to be coupled together end to end. This is an internal PTO shaft. In other words one end goes into the transmission and the other end is a standard 13/8 six spline affair. The problem is that the spline that goes up in the transmission is no longer available. I could make a new shaft but the guy doesn't want to spend that kind of money. If I can get them coupled together then I am good to go. There is very little room up in the differential because of a ring gear so the coupling can only be two inches long but most any diameter as there is plenty of room behind the ring gear.

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    Perhaps this will help getting an idea of what I am trying to do.

    shaft1.jpg


    shaft2.jpg

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    That helps, and makes a lot of sense now.

    It depends on the strength needed. If it's just turning a light load. You could do shear pins. But if you are doing a heavy load with minimal angular displacement, I would think a keyed sleeve would be better. If you drill a 1/2" shear pin hole, then you weaken the shaft itself. So do that on the shaft that can be easily replaced.

    Sent from my SM-G960U using Tapatalk

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    Both shafts will need to be cross drilled. I hope it doesn't weaken them too much. I will turn the coupling for an interference fit so I hope that will help support the drilled portion of the shafts. Again, my wish is to make it so that if the pins do shear there will be minimal damage to the shafts so I can take another approach. If the pins do shear one of the shafts should just spin in place. At the suggestion from Scottl, I think I will use bolts although I don't think grade 2 shear bolts would be the best option. I would want to go to something a bit stronger. I had originally thought I would just use some 1/2" shafting and cut some pins and tack them to the coupling. The bolts sound like a good idea. If they go tits up I can just take them off which eliminates having to grind the tack weld off to get sheared pins out. I will safety wire the nuts to the bolt.

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    Your fix is miss engineered, .5 pin will not pack the load.Vee the two shafts and weld them, then machine round and press straight...Phil

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    a keyed coupling would be the best bet. if need be, find a way to drill a hole in the middle for a bolt in the end of the shaft and just put keyways in it. super easy even in a lathe. 1-2 hr tops/

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    I'm sorry but you lost me there BT.

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    sorry, a bit mis explained. id say drill and thread a piece of threaded rod in the center of the shafts and v then weld it all to keep it fairly straight or sleeve it.

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    ahhhhh. Now I gotcha.

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    Phil in MOntana beat me to the punch. Prep for full penetration, preheat, weld, straighten
    If there is room, a mechanical shrink coupling(Ringfeder or similar) would work with less hassle but more $ up front

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    When considering cross pins the most important question to ask is "what is the torque?".

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    I can only really guess at the torque requirement. It all depends on what implement this PTO is going to drive. I can investigate what the HP is at the PTO and perhaps that would help.

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    Quote Originally Posted by magneticanomaly View Post
    Phil in Montana beat me to the punch. Prep for full penetration, preheat, weld, straighten
    Me three on this. Don't like the pin idear at all.
    If there is room, a mechanical shrink coupling(Ringfeder or similar) would work with less hassle but more $ up front
    Or similar but cheaper, make up a tube of decent wall thickness that is snug on both shafts. Stick them together then weld around it on both ends. Pretty easy lathe job and keeps the shafts straight and lined up.

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    What you describe was my original design something like what this guy did.

    img_7257.jpg
    img_7256.jpg
    img_7273.jpg

    The collar is no problem. Keeping it all straight is going to be an issue at least for me. I do not want to weld this in my lathe. I thought of putting it on V blocks and tacking it to keep it from bending and then weld all the way around. There is also very little room between the collar and the flange bearing. I may have enough room if I bevel the end of the collar to get my MIG gun in there but it is going to be close.

    This is what I mean about not much room. I had to cut the shaft where I did because the collar needs to be this far back to clear the ring gear. The collar itself can only be 2" long so it will not do much as far as keeping the shafts aligned (or at least I don't think so). I don't mind welding it up and then putting it in the lathe to make sure if it is straight. If not I guess I could tweak it with a bottle jack.


    shaft1.jpg


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