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Mounting Hole: 20.2 mm ?????

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  • Mounting Hole: 20.2 mm ?????

    I am looking for a panel mount power switch. I want something that looks nice and also doesn't cost a lot. 115 VAC and current should be less than 100 mA. And I learned a long time ago that electric/electronic parts that mount in round holes are a lot less work. While checking one of my favorite electronic suppliers I found a bunch of snap in ones that are under $2 and that are rated at 20 Amps no less. But they all call for a 20.2 mm diameter mounting hole. Where the heck does that come from?

    20.2 mm translates to 0.795" and, in case you are wondering, that is NOT an even inch fraction. It is 50.9/64". So, I guess 51/64" would be the drill to buy. Not that I am going to, buy I am not even sure where to look for one. Are 20.2 mm drills more common than 51/64"? Is this some common metric size in other countries?

    I will probably drill 3/4" and file or ream it bigger.

    But, how the heck does the manufacturer expect the holes to be made? A custom punch seems to be the only way.
    Paul A.
    SE Texas

    And if you look REAL close at an analog signal,
    You will find that it has discrete steps.

  • #2
    Pragmatic

    a 20.2 mm diameter mounting hole. Where the heck does that come from?
    No, that is NOT a common metric size!

    But if you were to use a 20 mm hole punch, the switch might fit just fine.

    Cheers
    Roger

    Comment


    • #3
      I'd almost bet money (I never bet money unless I'm ABSOLUTELY sure) it's some standard size hole. Either in Metric or fraction inch. What use to "bug"
      me, for 30 years or so, (I retired over 20 years ago so forgive me for not having the right fraction) was the common toggle switch bushing being 1/32
      off a half inch diameter. :-)
      ...lew...

      Comment


      • #4
        I'm guessing it went something like this:

        Engineer: The mounting hole is 51/64".
        Marketing Dick: That number needs to be metric to conform to our ISO blah blah blah certification.
        Engineer: Very well, 51 / 64 = 0.796875. Multiplying that by 25.4 we get 20.240625. Rounding to 1 decimal place gives us 20.2 mm.
        Marketing Dick: Whew, that was close. OK, ship it!
        Location: Long Island, N.Y.

        Comment


        • #5
          If you need a switch that has to handle no more than 100 ma, why are you using a 20 amp toggle switch. A little 3 amp mini will work fine and not require that huge hole. Even high current switches are available smaller than the one you are looking at. Why get involved reaming/ filing a big hole that would cost too much to drill or punch?

          Sent from my SM-G900V using Tapatalk

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          • #6
            The switch will have a nominal size of 20mm but has a tolerance range. They specified the hole size after and just added 0.2 so it'll always fit.
            Just drill 20 and it will be fine.

            Comment


            • #7
              Here you go-metric unibit-

              http://www.ebay.com/itm/4-22mm-Metri...UAAOSw3ydVrzgp
              I just need one more tool,just one!

              Comment


              • #8
                It's just a clearance hole... with tolerances applied. The probably have a min-max on the data sheet that makes more sense.
                Last edited by lakeside53; 05-27-2017, 11:13 AM.

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                • #9
                  It is an NTE Electronics switch and I bought it from MCM Electronics so I wasn't even sure that there was a data sheet. I got the 20.2 mm mounting hole from their item description. But I checked again and lo and behold, there is a data sheet - of sorts. All it shows is a two view drawing of the part with English/metric dimensions and a two line "Device Type" table. That's absolutely all it has. Not even the manufacturer's name.

                  Anyway, it does appear that the diameter of the part that goes through the hole is 19.8 mm. So I suspect, as ikdor suggests, that 20 mm will be fine. And I already have one of those metric step drills. They are my go-to tool for holes like this in sheet metal. I have at least five of them in various size ranges.

                  But I still have to wonder just where that 20.2 mm number came from. Perhaps a computer geek at MCM who THOUGHT he knew what he was doing.
                  Paul A.
                  SE Texas

                  And if you look REAL close at an analog signal,
                  You will find that it has discrete steps.

                  Comment


                  • #10
                    I thought 20 mm was a standard metric hole size for industrial switches, but it seems that they may be 8, 10, 12, 16 (5/8"), 22, and 30 mm:

                    http://us.idec.com/Catalog/ProductFa..._Pilot_Devices

                    Other sizes may be 22.3 mm and 25 mm:

                    https://www.ia.omron.com/products/fa...dimension.html

                    Maybe someone said the hole size is twenty-two millimeters and it was interpreted as twenty point two?
                    http://pauleschoen.com/pix/PM08_P76_P54.png
                    Paul , P S Technology, Inc. and MrTibbs
                    USA Maryland 21030

                    Comment


                    • #11
                      Might be a knockout punch size..

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                      • #12
                        Not if you are talking US conduit sizes. A 1/2" KO punch is 7/8" actual diameter and the is the smallest one. Yes, I have one. 7/8" is slightly over 22mm, not 20.2mm.

                        Perhaps conduit in some other country would use that size hole, I just don't know.



                        Originally posted by 754 View Post
                        Might be a knockout punch size..
                        Paul A.
                        SE Texas

                        And if you look REAL close at an analog signal,
                        You will find that it has discrete steps.

                        Comment


                        • #13
                          I have mounted quite a few push button switches in panels and they mostly call for a 22mm hole. I think you all are beating a dead horse here. Paul measured and came with 19.8mm so the call out should be 20+/-.2mm. Simple as pie!
                          Location: The Black Forest in Germany

                          How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                          Comment


                          • #14
                            It's possible it was supposed to read 20.0 mm and the persons finger just slipped. The zero is a double width button on a numeric keypad
                            overlapping both the 1 and 2 buttons.
                            Location: Long Island, N.Y.

                            Comment


                            • #15
                              Originally posted by Black Forest View Post
                              I have mounted quite a few push button switches in panels and they mostly call for a 22mm hole. I think you all are beating a dead horse here. Paul measured and came with 19.8mm so the call out should be 20+/-.2mm. Simple as pie!
                              No!! we should discuss and argue for 10 more pages instead of making something!

                              You are of course, correct! The 20.2 is just the max recommend hole size for the 20mm nominal switch.

                              Comment

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