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You picked the wrong bit and now you’re stuck with a hole that’s too big — or are you?  Depending on the application you might be able to salvage the piece with these reducing punches from Micro-Mark.

To use these punches, pick one with a ball larger than the hole size, put the ball over the hole, and tap with a hammer.  You deform the edge of the hole inward which reduces the diameter — at least at the edge — and that might be just enough if, for example, you’re trying to press-fit a shaft into the hole.  These can also help you make domes or dimples in sheet metal.

Sized 1/2″, 5/8″, and 3/4″ in diameter, the three punches can be used for holes sized 1/16″ to 5/8″.  The hardened steel heads come attached to 1/4″-diameter, 4″-long steel handles.

The three-piece set will make your wallet $28 lighter.

Reducing Punch Set [Micro-Mark]

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7 Responses to Make A Big Hole Smaller

  1. Dave says:

    Now I know why I save old ball-bearings!

    You can also centerpunch deeply several times around the hole.
    If you are pushed far enough into desperation, you will also centerpunch the sides of the hole as deep as you can with your skinny punch.


  2. @Dave:

    You’re right on both counts, but I think the advantage of using a tool like this (or ball bearings) is the hole should be reduced uniformly — important if you’re trying to press fit something onto a high speed rotating shaft.

    Another thought that crossed my mind while writing this:

    If you own a welder and the material was thick enough maybe you could fill the hole and try again.

    Anybody have any luck trying that?

  3. Dave says:

    Filling a drilled hole with a weld bead might be tough.
    Some expert out there will claim it’s easy, though…

    easy for *them*!


  4. Anne says:

    I’m no expert, but did manage to get hole-filling to work, as our welding instructor recently made us do exactly that (with a MIG welder) for practice.

    It is not easy – there’s a trick to it, hard to describe, with little bursts of the welder – but it does work. Looks pretty awful unless you grind it down afterward, it makes a blob that looks a lot like the outside of a tiny mudwasp nest. (I suppose a real expert could make it look nice from the start…) If you do it carefully, with no voids, you pretty much are back to square one and can re-drill, with nothing worse for wear. Well, subject to the whole “don’t overheat the piece or you can change its strength/hardness” issue. So, it probably depends on what the piece is for, what it’s made of, all the usual stuff.

  5. matt says:

    Good trick for filling in holes with weld is to clamp a “different metal” plate under the original piece to hold the welded metal while it cools. By “different” I mean use aluminum to back steel and stainless and use steel to back aluminum. The two different metals don’t get along well and don’t stick.

  6. SuperJdynamite says:

    I’ve filled small holes with welding rod. To fill a larger hole I would try filling it with a steel rod cut so that it’s slightly proud of the plate, welding, and grinding it down.

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