Tool Tips -- rectangular holes

Jon Titus, KZ1G
 

Perhaps a bit off topic, but here goes...
In a recent post, looking for a 40M QRP SSB kit, Fred (K3TXW) explained, "...I have problems making a rectangular hole in a piece of aluminum of exactly the right size, with the edges exactly parallel to the edges of the case. I inevitably make the opening too big or slightly wavy. The result screams "homebrew carelessness" though I'm not careless. Maybe there is a rectangular punch or something to do this right, but I don't have such a tool; I use a set of files."

In addition to files for work on front panel fabrication, I recommend an electronics shop include:

1.  A drill press with a chuck that will accept 0.50-in.-diameter bits.  Harbor Freight sells a couple of bench-top units for under $100.  Put a magnet on the base as a place to keep the chuck wrench.  (It's usually best to clamp work to the drill press table.)  Once you have a drill press you'll find many other jobs for it.
2.  A good set of sharp drill bits.  Bits with a titanium nitride coating remain sharp for a long time.
3.  A step drill bit.  I use an Irwin Tools Unibit 3/16-Inch to 7/8-Inch Step-Drill Bit with a 3/8-Inch shank.  Great tool when you need to make larger holes for controls or to start a rectangular cutout.
4
.  An Adel-brand metal nibbler.  They show up on Ebay.  Or buy a new one at https://www.adelnibbler.com.  I've used one since I was a teenager and couldn't work on chassis or panels without it.

Lay out your hole with masking tape around the outside.  To make a rectangular hole (see attached image) I use a step bit and smaller bits to make round holes that remove a lot of metal.  Just don't get too close to the rectangle's edges.  Next I use the nibbler to remove remaining metal close to, but not at, the rectangle edges.  Finally I clamp the panel or chassis in a bench vise so an edge of the hole aligns with the top of the vise jaws.  File away any remaining metal until the edge is parallel with the vise jaws.


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Jon Titus, KZ1G
Herriman, UT USA

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