Originally Posted by
YNWaN
It looks like the first armboard was acrylic which is more brittle than people often appreciate. It’s not so much that you needed a pilot hole as you need a sharp drill (or forstner bit), not a spade bit as you may use for wood) and a gentle drilling pressure with the acrylic backed by a bit of waste wood to stop cracking as the drill goes through the last bit. The second armboard looks like an acrylic/stone mix like Corian or Hi-Macs. This is significantly heavier than acrylic, but is also a lot stronger and less likely to crack.
Edit: it could be Staron too but all these silica/acrylic composites are very similar.
More editing: looking at the two armboard the position of the arm mounting hole appear to be in very different positions with the new one being much more toward the edge....?