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am designing an electronic enclosure for a medical device. For assembly reasons, the enclosure is split into two halves, with the bottom half having a depth of 200mm and top half of depth 50mm. I want the enclosure to certified for IP62, hence I want the screw to be mounted from the bottom, so the screw holes are not exposed from the top. The issue I am faced is that I would have to move the screw driver over a length of 200mm, to mount it onto the corresponding threaded insert in the top cover. There will be risks of screw falling off or getting stuck and the assembly time increase due to this step. I have ten screws to be mounted and this is going to be a major problem when we productise this. I cant seem to find any solution that will help solve the assembly issue while still keeping my other requirements intact.

Thanks

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    $\begingroup$ Use a longer screw with a long smooth shank to reduce travel. Use molded in snap fits to reduce fastener count and align and hold parts while running in mechanical fasteners. You can also use a hinge tab to do that. $\endgroup$
    – Phil Sweet
    Commented May 22 at 10:02
  • $\begingroup$ what size of screws? $\endgroup$
    – Pete W
    Commented May 22 at 12:50
  • $\begingroup$ use tubes to guide the screws $\endgroup$
    – jsotola
    Commented May 22 at 23:15

3 Answers 3

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So, one option is to make bulges on the sides and end to have the screws - a technique used on many items from plastic boxes to engines.

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  • $\begingroup$ Constraint I have is that the visible surface must be smooth and both the halves of the covers must be flush to each other without any projections on the sides $\endgroup$
    – Sengalraja
    Commented May 22 at 9:10
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    $\begingroup$ @Sengalraja That constraint turns out to be crucial information you should have stated in the original question. $\endgroup$
    – Solar Mike
    Commented May 22 at 9:45
  • $\begingroup$ Flip the box over before inserting screws during assembly? $\endgroup$
    – Rich
    Commented May 22 at 14:04
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Another option would be have counterbore holes on the bottom half so that you can use a "normal" screw. if necessary, you could look at blanking the holes on the bottom half with some sort of screw/hole cover. You would need a long handle Allen key to to do up the screw, but that should be doable.

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  • $\begingroup$ HI AM304 This is how its designed right now. With this, what I identified as the risk was that the assembly time increases as I would have to move the screw through the length of 200mm at the final stage of assembly when all other internal components are assembled and from the bottom, which means I would need a fixture. There is the additional risk of the screw falling off while assembling or unable to hold the screw In place as I move it upwards the counterbore. $\endgroup$
    – senthil kumar
    Commented May 22 at 10:03
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    $\begingroup$ this is an attractive solution, if space allows. If the parts are molded, would probably want the "20mm" dimension shown here reduced to the standard section thickness for molding, and the counterbore feature being a molded cylinder, possibly with support ribs etc $\endgroup$
    – Pete W
    Commented May 22 at 12:52
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Short screws can be used to hold thick pieces together in the following way: we redesign the half of the box through which the fastening screws will be driven by replacing the simple clearance hole for the screw with a hollow cylindrical recess (a flat-bottomed counterbore) with the same wall thickness as the box itself, and a clearance hole in it to pass the threaded end of the screw.

The screw then engages a pilot hole in a molded-in cylindrical boss extending up from the other half of the box so that when the box halves are brought together, the two cylindrical protrusions just barely come together. Then you thread a short screw down through the hollow recess on one half of the box until it passes through the hole in the bottom and engages the pilot hole in the other half.

Tightening the screw then cuts threads in the hollow boss and pulls the two halves of the box together. You use a TORX-profile self-tapping screw which sticks into a powered screwdriver TORX bit containing a magnet to retain the screw as you insert it into the hollow recess.

It is prudent to chamfer the end of one of these cylindrical features and equip the other with a flange that slides over the chamfer to guide the features together in proper alignment during assembly.

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