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Thread: Miniature 4 mm ratchet wrench

  1. #1
    Supporting Member mklotz's Avatar
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    Miniature 4 mm ratchet wrench

    These inexpensive 4 mm precision screwdriver kits, e.g....

    https://www.amazon.com/Syntus-Precis...11&s=hi&sr=1-9

    are great when working with miniature equipment. A bit for virtually every screw type (with the possible exception of JIS Pozidrive) is included along with metric sockets in the 2.5 - 5.5 mm range. All these bits have a 4 mm hex shank that fits the included handle and extensions therefor.

    The one thing that isn't included is a 4 mm ratchet wrench, a tool that allows access to fasteners in locations that prohibit use of the screwdriver format handles. Commercial 4 mm ratchets are almost impossible to find. The only one I could locate is this...

    https://www.amazon.com/Lisle-14540-H...8191086&sr=8-3

    gadget for adjusting Ford headlights. Its head is rather bulbous and the ratchet isn't reversible; to reverse the action one must remove the bit and reinsert in the other direction - not a deal killer but not ideal given that there are better solutions.

    Chris Rueby, one of the genius-grade modelmakers over on MEM, designed and fabricated a scratch-built 4mm ratchet...

    https://www.modelenginemaker.com/ind...topicseen.html

    George Britnell, another genius modelmaker, made his own version...

    https://www.modelenginemaker.com/ind...html#msg239454

    I didn't want to take the time to do a complete build as they did, but still wanted to have the capability for the rare occasions where it might be needed.

    This style offset screwdriver...

    https://www.amazon.com/MulWark-Profi...191343&sr=8-20

    has the advantage of a small, thin head as well as a switch to reverse direction. I have one I picked up cheaply at HF a long time ago.

    The problem is that it takes only a 1/4" hex, not 4 mm. An adapter is needed. Wiha makes a 1/4" to 4 mm adapter, e.g. ...

    https://www.amazon.com/Wiha-75802-In...8958965&sr=8-1

    but its length nullifies the advantage of the thin offset screwdriver head...

    Miniature 4 mm ratchet wrench-4-mm-1.jpg

    Miniature 4 mm ratchet wrench-4-mm-2.jpg

    Miniature 4 mm ratchet wrench-4-mm-3.jpg

    Miniature 4 mm ratchet wrench-4-mm-4.jpg

    I have some 1/4" hex steel but carving a 4mm hex into it would test my patience. This is a really low torque application so a simple hole with a setscrew acting on the 4mm hex flats would work so I made this...

    Miniature 4 mm ratchet wrench-4-mm-5.jpg

    A half inch length of hex has a turned down section (to slip between two retaining tabs on the wrench) which has a cross-drilled and tapped 0-80 hole for a setscrew to lock the bit in place. The hex is drilled through with a #16 drill (0.177" ~= 4.5 mm) that is a slip fit on the 4 mm hex shanks on the various bits and sockets.

    Fully assembled, it looks like this...

    Miniature 4 mm ratchet wrench-4-mm-6.jpg

    and can fit into a crevice less than an inch wide.

    I abandoned the idea of a 0-80 setscrew early on; they're just too tiny. A 0-80 SHCS works much better; it can be held on the end of a 0.050" Allen wrench for mounting.

    Yes, this is all rather fiddly but it will only be used very rarely, if at all, so I'm willing to live with it.

    173 Best Homemade Tools eBook
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  2. The Following 3 Users Say Thank You to mklotz For This Useful Post:

    Jon (Aug 16, 2021), Tonyg (Aug 17, 2021), uv8452 (Aug 22, 2021)

  3. #2
    Supporting Member NortonDommi's Avatar
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    Chapman make a very good gunsmith driver kit that has one of the nicest wrenches I know of and it is rated at 200 pounds/inch. Bits have a collar on them to stop them being pushed through the head.

  4. #3
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    Thanks mklotz! We've added your Miniature 4mm Ratchet Wrench to our Fastening category,
    as well as to your builder page: mklotz's Homemade Tools. Your receipt:




  5. #4
    Supporting Member mklotz's Avatar
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    mklotz's Tools
    When I was making the adapter for 4mm bits, I noticed that the headroom needed to use the wrench was limited by the length of the bit. If the bits were shorter, they could be inserted into a smaller free space above the fastener. Not a real problem; when necessary, simply cut the 4mm bit shorter and gain a little clearance.

    Then it occurred to me that the same thought applies to the 1/4" bits commonly used with this style wrench. I was ready to get out the disk grinder and make a set of amputated bits when it occurred to me that I couldn't be the first person to notice the occasional need of short bits. A quick check on Amazon proved this true...

    https://www.amazon.com/dp/B07YCP213C...roduct_details

    This set is shown in the photo along with a short 3/16" hex bit compared with its normal sized brother.

    Normal size length = 0.98"
    Shortie length = 0.59

    Headroom gained = 0.98 - 0.59 = 0.39"

    Something to keep in mind if you do a lot of work in close quarters.

    Miniature 4 mm ratchet wrench-short-bits.jpg



    173 Best Homemade Tools eBook
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    Regards, Marv


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  6. The Following User Says Thank You to mklotz For This Useful Post:

    Frank S (Sep 15, 2021)

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