Modifying Er40 collet wrench
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  1. #1
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    Default Modifying Er40 collet wrench

    So I want to add a square hole to my er40 collet wrench. This will allow me to use a torque wrench. The collet wrench width and thickness is beefy enough that this subtraction shouldn’t weaken the wrench. I have another identical wrench that will not be modified so that can be used when not needing to torque it down.

    I have a few questions.

    How would you create this 1/2” square drive hole?
    How does the distance of the square drive hole to the center of the nut effect my actual torque application compared to what is dialed in on my torque wrench? Techniks specs 140lbft for their Er40 nuts.73523063-f38b-4e9d-9aae-87dc3cc41ac6.jpg


    The tightening of the collet nut will be in a CAT40 fixture. I think I will mount this fixture to a board and that will be clamped in a vise. Hopefully the torque application doesn’t tip the vise and stand over. But that’s another issue.

    Thanks in advance for the help.
    Attached Thumbnails Attached Thumbnails a251ee08-64b1-49f3-998d-35da5387fbe2.jpg   80d7f338-8da1-4d7e-bf99-0da278a8c4cb.jpg  

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    If you attach the torque wrench at 90 degrees to the spanner wrench, no correction is required. Otherwise, if the wrench is effectively longer than the standard torque wrench, the applied torque will be higher than the wrench reading by the ratio of approximately the distance from the center of the torque wrench handle to the center of the spanner opening divided by the distance from the center of the handle to the center of the square drive. Probably about 21/18 or so.


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    You can make the hole any number of ways.
    For a 1 off I’d just drill it and clean it up with files.
    If it’s too hard I’d have it edm.

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    Drill a suitably sized hole and weld square drive socket to it.

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    Quote Originally Posted by PT Doc View Post
    So I want to add a square hole to my er40 collet wrench. This will allow me to use a torque wrench. The collet wrench width and thickness is beefy enough that this subtraction shouldn’t weaken the wrench. I have another identical wrench that will not be modified so that can be used when not needing to torque it down.

    I have a few questions.

    How would you create this 1/2” square drive hole?
    How does the distance of the square drive hole to the center of the nut effect my actual torque application compared to what is dialed in on my torque wrench? Techniks specs 140lbft for their Er40 nuts.73523063-f38b-4e9d-9aae-87dc3cc41ac6.jpg


    The tightening of the collet nut will be in a CAT40 fixture. I think I will mount this fixture to a board and that will be clamped in a vise. Hopefully the torque application doesn’t tip the vise and stand over. But that’s another issue.

    Thanks in advance for the help.
    I would highly recommend the bolting of the tightening fixture to an old milling machine table. I have a 4000 lb mill that has been in this service for years, and it hasn't shown any signs of movement or tipping


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