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For example - I am installing a fold up table from Ikea, it needs to hang from the wall, as shown below.

enter image description here

It explicitly says to use pan head instead of flat screw heads like shown in the picture, I would drill into hollow concrete and will use nylon anchors but my question is, would a washer on a flat screw head be a hack here to do the job of the pan head screw?

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  • $\begingroup$ It's not just about the shape of the head, but the flank angle of these two screws are different, also those have two different threads, anyway as far as the construction is static, and you use steel ring (washer) not rubber, then yes the ring provides enough surface for torque. $\endgroup$ – Sam Farjamirad Oct 13 '18 at 9:25
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It seems reasonable to believe that the flat head (countersunk) screw would apply enough force to split the wood, hence the restriction.

If you use a flat head screw and the washer prevents the countersunk portion from exerting wedge-type force on the wood, you will have accomplished the objective.

Consider also that if you use a fender washer (large diameter), the compression force is going to be distributed over a wider area, providing more confidence in not damaging the wood brace.

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  • $\begingroup$ Hey, that is not wood, its actually metal, pretty hard one. Also, I was wondering why they do not even use washers in their example, even though its pan head, wouldn't that be better? $\endgroup$ – appwizcpl Oct 13 '18 at 9:47
  • $\begingroup$ I think using washers in the kit would be better, but for a manufacturer, it's an additional expense for product and handling. Even though the brace is metal, a countersunk head can distort the hole, resulting in a loose fastener over time. You'd have to check the tightness of each fastener at least once a year if you used countersunk screws. $\endgroup$ – fred_dot_u Oct 13 '18 at 10:37
  • $\begingroup$ ^this is the correct answer. A thick washer that will not distort under continuous tension like the thin metal of the bracket would) with a countersunk screw will work fine. A Pan head isn’t so hard to come by, however, so I’d just follow the guidelines, personally. $\endgroup$ – Jonathan R Swift Oct 13 '18 at 11:13
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If you use a washer under the head of the flat head wood screw, get you a cup washer. these are intended to let you use flat head screws as if they were pan heads. They hold the wedge profile of the flat head screw up and out of contact with the wood so it will not split the wood as you screw it in, and they hide the sharp rim of the screw head so it will not cut your hands or get snagged on things.

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I assume that the 'leg' is tubular steel with pre-drilled holes.

The problem with using countersunk screws is twofold, firstly that countersunk they will only make contact with the very edge of the hole and are likely to deform it over time and effectively become less tight. In this sort of situation you want the fixings to be providing a clamping force rather than being loaded in shear.

The other issue is that the screw heads won't sit flush with the surface which doesn't look very neat and can leave a sharp edge protruding which can snag on things.

Using plain washers may help with the first issue, at least to a degree but not the second. You can get cup washers which are have a recess to allow countersunk screws to sit on a flat surface enter image description here but then again anywhere which sells cup washers is also likely to have flange or pan head screws whcih is what you really want.

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