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I hide imperfections around a rectangular hole in the front panel with a bezel. Those will hide a lot of sins. They are also easier to fabricate with straight, clean edges. Riy=ugh edges that might show a little on internal panels of chassis - who cares.
Your use of the bench vise to keep the edge straight during filing is good but will eventually damage the vise. I use a sacrificial piece of steel like a piece of angle iron clamped up along with the workpiece. In woodworking we call that a "fence".
On 10/30/2018 11:50 AM, Jon Titus, KZ1G wrote:
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.
Jon Titus, KZ1G
Herriman, UT USA
bark less - wag more