The case of the ……

Well Dr Watson, its wobbly metal.

Enough of the Tom Foolery and down to the serious business of an issue that must be fairly common. Drilling larger diameter holes in flexible metal sheet generally found on hobby cases. Just in case you were wondering though Tom Fool (aka Tom Skelton) is apparently a ghost of a Jester at our local castle, Muncaster so here’s hoping he’s had plenty of opportunity to wander round the house and grounds with odd shaped holes in his thin sheet metal parts.

A lot of trouble I have with when its time to put a project in a case is that the 16mm hole needed for an SO239 for example causes me no end of trouble. I have tried a number of different ways to make the holes without giving a figure of 8 or elongated hole. Step drills tend to give slightly better results that piloting and increasing the bit size. I have found that the latter can easily end up with a poor hole if any vibration is imparted into the case.

So what’s the answer, well, I just don’t know. Punching would seem to be a better solution as would routing the holes but in the case of pre folded sheet I’m sure this isn’t too practical. I’m wondering if people have had better results with other ways of making these holes.

Alex Hill, G7KSE, is a regular contributor to and writes from Cumbria, UK. Contact him at [email protected].

5 Responses to “The case of the ……”

  • MIke kv7vzz:

    I’ve had success using two pieces of sacrificial wood to sandwich the sheet metal. Either C-clamps or a vise to hold them tight, then drill carefully. In a pre-formed box you might need a bit of imagination to hold the sandwich. If you can use a drill-press that’s even better. Good luck!

  • Kevin G6UCY:

    As Mike has suggested using using wood to hold the material flat in the form of a sandwich can work well, especially if using a pillar drill which gives a lot more control.

    Another tool if one does have a pillar drill is one called a tank cutter as these can be adjusted to make variable sized holes in thin sheet material. Due to the way they work they are only really any good at making relatively large holes but are great for cutting holes for meters etc.

    Probably the easiest method, at least for the most popular hole sizes is to use hole punches as they make nice burr free holes of exactly the right size. Unfortuately these are not particularly cheap but do have the advantage that they can be bought to punch out holes for IEC, D connectors etc in situ.

    The method I tend to use most often though is to slowly work through the drill sizes in 0.5 mm sizes to the finished hole diameter using a drill speed high enough to prevent the drill bit snatching the panel and finish off if required using a tapered reamer. I have found that as long as one lets the drill bit do the work and avoids rushing things this method works pretty well especially with a decent set of drill bits.

    Hope this has been useful and the best of luck



  • Mike VE3WDM:

    My method is similar to the above suggestions, I place the piece to be drilled on a piece of wood say a 2X4. I use two other smaller pieces of wood like a 1X2 at each end of the metal. This is were I place the hand ratcheting bar clamps

    My method is similar to the above suggestions, I place the piece of metal on wood such as a 2X4 at each end of the metal to hold it in place a smaller pieces of wood (1X2) over each end. I use a hand ratcheting bar clamp to compress the wood onto the metal. So now you have one jaw of the clamp on the top of the 1X2 wood the other end of the clamp is under your work bench. The order is clamp face, 1X2, metal to be drilled, 2X4 and then the work bench. Do this at each end and make sure you use a good sharp bit and the speed on your drill is set to fast. Hope this was not to confusing….if so I can email you a pic of the setup.

  • John K0EBC:

    First choice for holes are chassis punches. Mine have been in my tool box for over 40 years. Second choice, stepped bits.

    John K0EBC

  • The only one I’ve not tried is the punch so I’ve order one and will give it a try. Thanks for the advice


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