Precision Wrench Rebuild

Decades ago, one jaw on my little 1/4 inch wrench that fits 4-40 nuts broke off. I brazed it back on, fully aware that one day it would break off again, because brazing isn’t really a suitable repair technique for a wrench, even one labeled as “Precision” in that time-honored manner of all low-cost tools.

Time passes, I’m tightening screws against 4-40 nuts, and the jaw gives way:

Precision wrench - broken jaw
Precision wrench – broken jaw

So I sawed off a strip of bedframe steel that fit the nuts better than the original stamped steel, did a bit of hand filing, and came up with a reasonable replacement:

Precision wrench - detail
Precision wrench – detail

I rammed it into the handle, just as they’d done with the original stamped steel shape:

Precision wrench - rebuilt
Precision wrench – rebuilt

That should last approximately forever…

7 thoughts on “Precision Wrench Rebuild

  1. Super-precision!
    Have you ever messed about with a jeweler’s saw? I’ve had to cut weird proprietary fastener wrenches before and it does a great job of just this sort of thing. Print out a drawing on a laser printer, rubber-cement it to the material, and cut right down the edge of the line, and often you end up with a snap-fit wrench.

    1. jeweler’s saw?

      I have a large frame saw that’s similar to a jeweler’s saw, but no blades fine enough to handle steel.

      I roughed the shape on the bandsaw, cutting very close to the lines, and that eliminated a whole bunch of filing. Eks gave me forced me to take the carcass of a power filer, but … it’s in the garage, waiting for a spot on the to-do list.

      1. ebay will sell you a gross of #4 down to #2/0 (my favorite sizes) for like $5, but they don’t last a long time. Hercules White Label cost 20x as much and worth every penny. Hercules black are intended for silver/gold, but white are intended for fairly high-carbon steel.

  2. I usually don’t need to deal with 4-40 nuts, but I found Craftsman includes 1/4″ wrenches in their stock. The Craftsman is a 1/4″ & 5/16″ dual box. I also have a couple dual-ratchets in that size, as well as larger sizes. Yet another vendor sells an offset screwdriver kit that uses a 1/4″ hex ratchet to drive the bits. The 5/16″ size works nicely for self-drilling sheet metal screws, and there are some that have a 1/4″ head.

    One of the BAEM club members built a die filer from Metal Lathe castings. He said the pull-files were hard to find, but he was brazing a shaft on the tip of a conventional file. (A neighbor offered me an old Shell gas pump for free. I thought it was too expensive…. [grin])

    1. dual-ratchets in that size

      I keep trying to convince myself that I should get some ratchets, but I never need more than a few turns here & there.

      The flat “precision” wrench is vital inside the GPS+voice box, where a 4-40 nut anchors each battery contact stud against the PCB, with less than 1/6 turn available. I didn’t quite outsmart myself on that one, but I still don’t know how to do it any better.

      I thought it was too expensive

      Some things really are white elephants

      1. In comparison to a socket set, I find the flat ratchets more useful for general purposes. If the bolt is a bit long, I don’t have to dig out the deep socket. I have a pine-needle rake (made up from hay rake parts) where access to a socket is horrible, but the flat ratchet fits in. If there’s room to swing the flat wrench, it’s likely to get used.

        My mill-drill drawbar uses a dogleg 17mm ratchet. Handy when changing tooling.

        I have an old Craftsman set, but found more compact ones at various places. Mine was from a near-legendary California hardware store (OSH) before they went downhill, but a decent auto parts store will have them.

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