I'm refurbishing my 70s vintage Black & Decker Workmate. It’s seen a lot of abuse, but the only thing that ever broke, besides working corners of the plywood vise jaws (which I'm replacing) were the screws that held the plywood to the 1/16" metal bracket underneath (2 screws on each jaw, per side). So I'm looking for ideas on a better, stronger method than the manufacturer used. I'm thinking of Ikea furniture I've seen, where they've used a machine screw that screws into the side of a larger tapped shaft, that you insert into a hole that's drilled perpendicular to the machine screw/hole — in my case, a long hole drilled into the vise ends (see photos). Seems to me it might suffer abuse a lot better than a dinky little, 3/4” long, wood screw? Any other suggestions out there? 1/16” metal plate into 1” Baltic birch plywood. I'm excited to hear what other ideas y'all have! Thanks in advance.
Honestly I think you're overthinking this, after all how long does the original screw arrangement last in this model of Workmate generally? It's only once they begin to fail that there's a problem and I presume this takes years and years even with constant use. But I'm all for over-engineering something if it's quick and doesn't cost much! And that's certainly possible with this.
There are multiple ways you could go here, including my first thought which is using through-bolts (the heads recessed in the top) but I think the ideal solution is simply to add more screws. All this requires is drilling a few extra holes in the steel supports. Flip over and drill from above to do this. Keep the old jaws in place to support the brackets and simply drill through.
Just one extra screw in each bracket should be enough TBH but if you want to go the extra mile drill two per, for a total of six screws per jaw if you want to also use the original holes but I can't imagine four each wouldn't be perfectly sufficient.
Just an extra point, you mention in the Comments that you've already bought the plywood but while standard Baltic birch is plenty strong it's not ideal for this type of thing. One great alternative is phenolic ply, which in addition to the phenolic glue used throughout also has films of phenolic resin on both faces, making it incredibly tough and long-lasting and highly water-resistant which might prove useful. I think this is the type of plywood that Paul Sellers uses to line his vice jaws.
If you really want a more solid attachment, drill a few more holes in the metal brackets and just add more screws. It looks like there's space for at least two more screws on each side of each bracket, so you could have up to six screws per bracket instead of the current two. Routing recesses into the bottom of the top boards to accept the brackets could add some more strength as well, since some of the lateral force during clamping would be taken by the edge of the bracket meeting the side of the recess.
In my experience, you generally don't get a huge amount of clamping force from the jaws of a Workmate. It's enough to hold work steady, like clamping a board while you're cutting it to length, but I wouldn't choose a Workmate for clamping a panel made from gluing several boards together. So while it might make sense to add a few extra screws to increase longevity, you probably don't need to do more than that.