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I'm working on a case design. There is rectangular switch. I am trying to open a rectangular hole on the metallic case to fix it in there. I'm not doing a good job, if it goes on like this it looks like I'm going to ruin the case at all.

How do I open this hole?

Switch and the imperfect hole #1
Picture #1

Switch and the imperfect hole #2
Picture #2

Dimensions of the rectangle is 20.0mm x 25.4mm.

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    \$\begingroup\$ Once you get the hole roughed out by drilling, you can use a file to clean it up and make the hole square. But it will be a tedious job. For production, this kind of job would be done with a punch or a mill. With a mill you won't get square corners. \$\endgroup\$ – The Photon Jun 22 '12 at 20:26
  • \$\begingroup\$ To drill a square hole, use a square hole drill! youtube.com/watch?v=9qEhyQfbImY \$\endgroup\$ – Wouter van Ooijen Jun 22 '12 at 21:47
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    \$\begingroup\$ @WoutervanOoijen Did that guy make one of these: youtube.com/watch?v=rI-15fovYEY \$\endgroup\$ – embedded.kyle Jun 22 '12 at 23:02
  • \$\begingroup\$ @embedded - How does the drill know which way the square should be orientated? \$\endgroup\$ – stevenvh Jun 23 '12 at 5:55
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    \$\begingroup\$ @stevenh: As fa as I can see a square drill is not put on a simple rotating axis. Part of the magic is in the sideways movement of the axis. You can not simply clamp the drill, without regard for its orientation with respect to that sideways movement. \$\endgroup\$ – Wouter van Ooijen Jun 23 '12 at 7:26
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There is the tool exactly for this, named nibbler. They sell it for $10 in Radioshack.

enter image description here

enter image description here

Specialized hole punch for specific shapes:

enter image description here

For most advanced holes there is a special drill even For most advanced holes there is a enter image description here

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  • \$\begingroup\$ Nibbler may be hard to get outside America, unfortunately. In my experience, nibbler is pretty much local to America. \$\endgroup\$ – Nick Alexeev Jun 22 '12 at 21:47
  • \$\begingroup\$ but but. The whole panel mounting culture is a lost cause then. The switch on a picture is possibly sized in even fractions of inch. There are even special hole punchers for switches, rheostats, connectors, like DB9/DB25 etc. Unfortunately the sets of hole punchers in US are very expensive and rare as well. \$\endgroup\$ – user924 Jun 22 '12 at 22:02
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    \$\begingroup\$ I have never seen one of these before. Now, I need one. \$\endgroup\$ – embedded.kyle Jun 22 '12 at 23:00
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    \$\begingroup\$ Agree. Everyone needs one. More rocket surgery for masses \$\endgroup\$ – user924 Jun 22 '12 at 23:10
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You are doing fine. If you don't have an expensive punch, or even a nibbler, you can do a perfectly acceptable job with a drill and file. I have done many cutouts like this.

The secret is patience. Start each dilled hole in an indentation made by a pin punch so that the drill bit does not wander, and don't try to drill right up to your line. One of the first exercises I did as an apprentice machinist was to file something to within 0.001 inch tolerance. It's not as hard as you may think, but it can't be rushed. Use a good file and clean it from time to time with a file card. Aluminum in particular, being soft, will tend to gum it up.

You'll note that the switch has a flanged edge. Any slight imperfections in your hole (perhaps up to 1 mm, but you can do MUCH better than that) will be covered by this if your original layout lines are good and you are careful not to make the hole any larger than it needs to be.

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    \$\begingroup\$ +1 for patience. Getting frustrated and then become a little bit sloppy ruined some prototypes for me. Seems that I'm no mechanics guy. \$\endgroup\$ – 0x6d64 Jun 23 '12 at 8:02
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I installed a very similar switch (single not dual) into an Altoids tin. I used a Dremel with a cutoff wheel. Very easy, it took two minutes.

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As always, it's all about having the right tool for the job. Without tools it's impossible, and with better and better tools, it becomes easier and easier.

You're not doing badly so far, but you seem to have drilled some of the holes quite far from the line. That didn't help.

Option 1. Keep drilling, preferably with holes nearer the line. Use side cutters to damage the metal between the holes, then man-handle the metal out with a screwdriver and / or hammer.

Clamp your panel upright in a vice, and use a coarse file to square up the hole.


Option 2. Drill a large hole at two opposite corners, and use a small saw blade to cut each edge. Then file it to shape.


Option 3. Use a dremel with circular cutting disc, then file to shape.


Option 4. If you want to spend some money on tools, you can do a lovely job with a hand operated milling machine. You can get nice little ones on eBay for a few hundred bucks.

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Depending on how perfectionist you are, this way it will take somewhere between a long time and a very long time.

I would have my front panel made by a service like Front Panel Express. With hobbyist tools you can't get the same quality and accuracy. (I noticed your fixing hole is off center.) They can work with aluminium up to 10 mm thick, or acrylic or a custom material. You can download a front panel designer software from their site to create your design.

(Disclaimer: I'm not affiliated with FPE)

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Fretsaw in use

I agree that a jig saw is the best method if the panel allows the frame to swing, and I recommend the type in the picture, with an adjustable frame, rather than one that has to be squeezed to tension the blade -- I find that type very difficult to control. This one is easy as you can undo the wing nut and shorten the frame, loosen the clamp screws and insert and clamp the blade, then extend the frame and tighten the screw.

Drill a small hole, just big enough for the blade, in each corner, so that you can turn the blade easily for the next side.

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  • \$\begingroup\$ Thank you, Stevenh, for that helpful tip. Silly me assuming that "image" ... \$\endgroup\$ – Harry Weston Jun 26 '12 at 13:16
  • \$\begingroup\$ take that from someone who did lots of cases in product design major... this is better than the nibbler. it works for several kind of materials. So it's one skill to learn \$\endgroup\$ – gcb Jul 6 '12 at 19:13
  • \$\begingroup\$ For reference, that type of jig saw is commonly called a "Jeweler's Saw" \$\endgroup\$ – Steven T. Snyder Aug 20 '12 at 21:23
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I would have went for:

  • Starting by drilling holes just like you did, at the corners of the designated box.
  • Using a jigsaw I would have cut the main lines of the box, careful not to pass the lines. Slightly less is fine - that's handled by the next step
  • Using a (file tool, I would have completed the cut rectangle to fit the exact shape/size

good luck and enjoy it!

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