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  • Welding and rethreading

    I have a Cub Cadet with a 50" mower deck. I stripped a blade holding spindle. It's a 5/8-18 thrd. I want to weld over threads or turn it down and put on a threaded sleeve and weld that fast. The blade itself is located on a star shaped lock at the end of the thread. I think it's a forging made probably of 4140 type steel. I plan on maching the threads off before I weld. Don't get me wrong I will buy a new one ,but I would like to have this one as a spare. $19.95 for new one on Jim's Small Engine Supply + shipping. How would you repair this ? It slides out of the bearing housing. I cleaned it and I'm ready to procede.

  • #2
    I would not even think about it after seeing the damage done by a flying lawnmower blade.Almost any mom & pop lawnmower shop will have that spindle for the same money through the Oregon brand replacement parts label.Chances are that CubCadet is an MTD or Murray in disguise.
    I just need one more tool,just one!

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    • #3
      Have done just that many times, no failures that I know of.

      Use 7018 if using stick, or E70 something if wire. I have never taken extraordinary measures to let it cool slowly, it will get red with the multiple passes. Let it cool on it's own.

      Dave

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      • #4
        You should be able to build up the threaded area with MIG and ER70S-6 wire. That should be machinable Then it's a matter of getting a good, well centered thread on it (die or single point )

        Dan
        At the end of the project, there is a profound difference between spare parts and extra parts.

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        • #5
          I used to do alot of build up work when I worked for a strip mine outfit. When I built up something that had to be machined after, I would preheat until spit boiled off (technical I know but the way I was told to do it lol) and I started to weld. Didn't stop welding until the part was built up or the day was over. I was told if I didn't heat it up that much, the machinist would snap bits left and right. It's was all 7018 btw.

          Hope that helps,
          Chris
          Last edited by Tamper84; 07-19-2012, 10:25 PM. Reason: Forgot to add some details

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          • #6
            Well, I will say that rethreading a welded up area is not an easy task. You want to have the right rod or wire for the job and you want to make damn sure you keep everything clean as you build it up. Hitting a slag inclusion or a porous section while single point threading sucks. Also, watch your interpass temperature. You want it the whole part to get good and hot so it cools slowly.

            I think a much easier repair is to weld on a threaded sleeve but I'm not convinced this is a safe thing to do. By the time you turn down the existing threads and bore a hole in a threaded sleeve, you don't have much area to weld. If it was a 5/8 - 30 or some really fine machine thread, then you might get away with hit.

            Also, if it is 4140, you'll have to be careful how you weld it and what material you weld to it. When welding mild steel to 4140, I preheat to about 450* F before welding and I use a 309 SS rod. If welding 4140 to 4140, use low hydrogen rods (e.g. 7018) and remember to keep the rods in an oven before use. Keep the bead fairly narrow - not wider than 1/2". 4140 is supposed to be welded only after it has been annealed and should be stress relieved at about 1000*F, IIRC, after welding. Then, once you've done the stress relief, you can re-harden and temper it.

            :Edit: Looks like other's beat me to the punch.
            Last edited by Fasttrack; 07-19-2012, 10:33 PM.

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            • #7
              I've threaded welded shafts (my own & others) and the key is making sure it is soft enough to thread. However, as Weird pointed out the potential hazard of having a mower blade flying off is more than offset by a $20 part. There are some things I just will not work on such as trailer hitches,
              w a y to much potential liability.

              However, if you're dead set on making the repair I'd consider completely cutting off the mangled threaded diameter and drilling & tapping the shaft for a 5/8-11 stud made from a grade 8 bolt. Of course this is only possible if there is enough material in the shaft. I'd also Loc-tite and cross pin the stud.

              Just my $0.02

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              • #8
                For $20 I wouldn't phuk with it, but if you want to fix it....
                Cut the threads off flush with the star, drill and tap 1/2" 20 and use a bolt. That's how most of the decks I've seen are anyway (john deer, grasshopper, etc.).

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                • #9
                  Thanks for all the good advise. I'm out the door to buy the new spindle this morning. I think I will try welding and single pointing new threads on it. I like the idea of using
                  7018 rods on it. I'll let you know how it turns out and I'll post pictures. It may take me a while to do this so be patient. Thanks again , Boot

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                  • #10
                    With all due respect,reconsider the situation.The welding process will affect the heat treat condition of the base metal.The original threads are rolled threads which are 30-40% stronger than cut threads and the machine is spinning a 3-4 lb mass at 3,000 rpm which is known to occasionally strike objects.

                    After 20+ years as a machinist what you are considering is something I would not do for myself.Just because it can be built up and rethreaded doesn't mean it should be.Not harping on you,it's just not a good idea IMHO.
                    I just need one more tool,just one!

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                    • #11
                      Originally posted by wierdscience View Post
                      With all due respect,reconsider the situation.The welding process will affect the heat treat condition of the base metal.The original threads are rolled threads which are 30-40% stronger than cut threads and the machine is spinning a 3-4 lb mass at 3,000 rpm which is known to occasionally strike objects.

                      After 20+ years as a machinist what you are considering is something I would not do for myself.Just because it can be built up and rethreaded doesn't mean it should be.Not harping on you,it's just not a good idea IMHO.
                      Weird is absolutely correct about this. Throw that piece in your junk pile to be taken to the scrapper on your next trip.

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                      • #12
                        I've got a bunch of those spindle shafts protruding from my Kazoo but none, that I recall, with the star mount. (I'd have to look again.) If I had it, you could have it for postage. I bought the inventory from a mower service center at auction a few years ago and still haven't gone through all the stuff. I know there's complete spindles and a load of shafts but don't recall seeing the star type.

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                        • #13
                          I agree that a lawn mower blade shaft is not a good place to experiment. Besides, I think there have been enough replies that I can now tell my " related" story without highjacking the thread ! Many years ago, I " fixed" the thermostatic engine fan on my '62 Oldsmobile by welding it solid. I used three or four short pieces of angle iron, and had them welded in by a welding shop. The arrangement worked for a few hundred miles. Then, one day out on the turnpike, there was a violent vibration from the engine, followed by terrible noises, and steam and coolant spewing everywhere. I opened the hood, and found that the cast iron water pump housing was broken in two, and the now unattached fan had flown around and eaten up lots of things in the engine compartment ( radiator, hoses, wires, etc.) What apparently happened is that one of the welds holding down one of the angle iron pieces had broken, caused an imbalance in the fan and pulley assembly, and that shook the water pump casting apart. I've been a little reluctant to weld parts that rotate at high speeds and loads ever since.
                          Last edited by Bill736; 07-21-2012, 10:14 PM.

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                          • #14
                            Some "fixes" should not be done , like the one above , however I have repaired my trailers , and manufactured a coupling or two for rotating machinery , if you are not confident or competant then by all means dont do anything . However many people are imtimidated into not attempting to repair a machine part by the growing "what if " group which is popping up everywhere. I for one will not be intimidated because I would not be able to earn an income .
                            Michael

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                            • #15
                              A lot here may have had their confidence boosted to a "of course I can do that" level by reading John Stevenson's many posts on just this sort of work.

                              If you can't control your ego just leave it alone.

                              John has a huge store and knowledge of and about such things as well as a vast skill and ability doing it and may make it look easiet than it might be for others less skilled.

                              I certainly would not try it and I certainly would not "farm it out" to some self-proclaimed expert either.

                              If I could not get a replacement part - preferably new - or in very good "used" condition - I'd probably scrap the mower and begin again with a new(er) and perhaps better one.

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