Keyed Battery switch: How to drill a hole with flat sides?

[claycookiemonster]

My Master/Battery switch has a threaded body with a diameter of .750 inches.
However, the sides of the switch body are flattened, and those flattened sides are only 5/8" apart.

My initial plan is to drill a hole 5/8" in diameter and then file the flat sides into the hole. After the flat sides are right, I can file top and bottom to get the 3/4" diameter for the overall switch body.

I know that will work, but I'm wondering if there's a simpler and better way?

 

[BobTurner]

If you google "washers with flats on the inside" you'll see what you want (also called "double D" washers). I'd find a way to pin such a washer on the back side of your panel (maybe a double countersunk rivet?) to keep it from rotating. Filing certainly will work but it's tedious.

 

[Desert Rat]

If you have room behind the panel to make this fit, it would be easier to do your funky shaped hole on the bench on a doubler and then either rivet or glue it behind the panel to be lined up with a nice round hole in the panel that easy to drill without goofing

 

[JonJay]

In the time it takes to read all the responses to your post, you might be done filing it by hand. If you have the right size half round or round file that comes close to the finish “arc” of the hole, it will go fast.
Hand filing aluminum panels isn’t hard if you have the right files. You can also speed things up with a nibbler to rough out the flat sides, then file smooth.
This isn’t a hard job.

 

[jliltd]

If you can make a drawing of the hole on CAD or other program mark the center mark and periphery. Print it out 1:1 on Avery address label paper on a laser or inkjet printer. Poke the center hole mark with a scratch awl. Use this hole to locate the label paper template on the panel with a drilled hole where you want it located. Stick the label to the panel and then drill, nibble, grind and or file at will.

 

[gasman]

You can drill the 3/4' hole needed and then pinch
the four edged of the flat spot. Use a 1/8" pin punch and
tap the aluminum down to make a Mickey Mouse ear at
the start and end of the flat spot. It will intrude into the hole.
Those tabs will not allow the switch body to turn.

Practice on scrap.

 

[PaulvS]

The most satisfying way to do this is to draw the outline with a fine marker pen, drill a couple of holes with a step drill, put on a Beethoven waltz and then file away to the music. Takes about 15-20 minutes and you should feel much better afterwards.

 

[RV6_flyer]

The most satisfying way to do this is to draw the outline with a fine marker pen, drill a couple of holes with a step drill, put on a Beethoven waltz and then file away to the music. Takes about 15-20 minutes and you should feel much better afterwards.

IF I could not find an inexpensive punch or borrow one to make the required hole, I would do as Paul suggests.

I had to enlarge the AI and DG holes like Paul suggests when I switched to two G5s from vacuum operated AI and DG.