removing blind taper pins
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  1. #1
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    Default removing blind taper pins

    i have several blind taper pins that i have to remove. they
    are down inside the apron of a VDF lathe that the hand wheels
    were crashed by a dumbshit who had no business moving a lathe, but insisted he could .

    i have a slide hammer with the appropriate 6mm threads, but
    the pins are so tight that the screw breaks off in the pin.
    the shafts are too bent to remove , and i suspect the pins
    are bent in their mating holes. there's very little access to
    try to drill them out . any suggestions?

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    Oxygen lance?

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    Use a big hammer.


    On the guy that crashed them.

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    Try a stack of washers taller than the protrusion of the pin, then screw in a hex bolt or cap screw and tighten it down to pull the pin. The gentler pull might work. If no go on that I'd probably try the flame wrench with a quick application on the pin to red hot while the surrounding surface was protected (a piece of sheet metal with the appropriate sized hole should work). Then try to pull again. If worse comes to worst, drill it out and re-ream for an oversized pin at reassembly.

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    Weld a stout washer to the pin, then weld a hex nut to the washer. Thread a bit of all thread into the nut and use slide hammer or bushing and wrench to pull. Small impact works well. You can buy threaded taper pins to replace what you remove.

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    I would apply a liberal amount of Kroil and let it sit overnight. Then try the slide hammer again, but with multiple LIGHT blows instead of doing it hard enough to break the screw.

    Oh, and replace that broken screw with a high grade stud.

    Another idea would be to put a longer screw in the hole. Then heat the whole area with a heat gun. Then, while shielding everything but the screw, blast the screw with freeze spray and pull on it as soon as possible. In other words, expand surrounding material with the heat, shrink the pin with the freeze spray and then pull.



    Quote Originally Posted by tnmgcarbide View Post
    i have several blind taper pins that i have to remove. they
    are down inside the apron of a VDF lathe that the hand wheels
    were crashed by a dumbshit who had no business moving a lathe, but insisted he could .

    i have a slide hammer with the appropriate 6mm threads, but
    the pins are so tight that the screw breaks off in the pin.
    the shafts are too bent to remove , and i suspect the pins
    are bent in their mating holes. there's very little access to
    try to drill them out . any suggestions?

  9. #7
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    Needn’t be blind. Try to clean the other side and make pictures with smartphone, if feasible. I am quite confident that the bores go through. Can you turn the shafts?

  10. #8
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    can't weld in there . can't get to the other side, a dozen gears
    in the way . these pins are only 8mm or so on the end, and butted against gears and shafts that don't rotate more than 90 deg.
    no room in there to get my hands in . just the tips of my fingers. been spraying around the pins with crc 2-26 everyday.

    the screws i broke were Allen brand 12.9 5mm shcs.

    tomorrow i will heat what i can get to and try again, otherwise- i have some 12" NYTD m-42 cobalt drills i'll try.

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    I had a taper pin that bent in the tapered bore that was one of the hardest things to fix I have had in years. Same situation basically. Not enough room to really get at it etc. I hate blind tapers. I personally would never design something that had a blind taper. There is no need for it and makes everything harder when things go south. I ended up sitting in front of the machine for well over an hour with a Foredom and a carbide "dental" burr. I just ground out the pin. Real pain in the ass but it did work and was the only way I could figure out how to get it out.

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    Forget about using any kind of lube, it won't work on taper pins. They are soft and conform with the bores,zero clearance for any lube to enter.
    A hand wheel shaft sounds like maybe 25mm or less which should be a 6 or 7mm.I have never ran into any hardened ones, they drill easy. I have had to make extended drills to get to some on machines by just drilling some rod and welding or brazing or s/solder the drill in place.
    Bear in mind that they are measured by the small end so a 6mm on the big end could be 7mm or more, depending on how long it is. The taper is 1/50.I always order the longest available in any size to make what I need.

    Take some short scrap round stock(large enough to fit your lathe chuck) drill and ream it to hold the pins to cut to size and thread.
    Only takes a few minutes and if you clean up the bore you will have to make up a new pin anyway.

    I have to deal with them quite regularly, just had to make some up today. All the European equipment we have uses them, I don't recall any late model US stuff that uses them.

    I have had to drill quite a few out on the bench because whoever set them last got carried away.

    Since you already have a threaded hole for a pilot I would use a pilot drill and drill through then follow with ,if a 6mm pin then use a 5mm drill and tap to 6mm. You will have just a shell that should come out easy. You can make a tap extension same as a drill.

    Not sure if you are trying to get the handle off a shaft or a shaft out of a bore in a casting.

  14. #11
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    Hoo boy, tnmgcarbide, you have my sympathy. I have utterly failed at getting steel pins out of aluminum castings to the point of scrapping a valuable steady rest, selling the lathe and starting over.

    I know a guy who had a Polamco lathe which needed spindle bearings. He bought the bearings no problem but he couldn't get the machine apart because of the [email protected]#$%^&*() taper pins so he wound up selling the machine and buying another.

    In other words, stuck taper pins in very tight quarters can be nearly impossible.

    Let me get completely unreasonable for a moment. If you took a cutting torch and cut all the shafts that all those gears are mounted to and got them all out of the way so you could actually get at your taper pins, do you think it's conceivable you could remake the gear shafts later?

    metalmagpie

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    Might consider drilling the taper pin all the way through, tapping it, then using a longer screw against the end of the blind hole to push the pin out. The screw is probably a lot stronger in compression than it is in tension.

    Put a dog point on the screw so that if you mushroom the end you’ll still be able to unscrew it.

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    I've had occasional luck drilling through, filling the hole with grease using a hypodermic and slipping a dowel pin into the hole and hitting it with a hammer. That can break the pin out from the hydraulic force. It works better with a reamed hole for the pin but I'd bet it'd work in a threaded hole.

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