Milling coins to half thickness then gluing or sweating two tails or two heads together to make a double headed/tailed coin was fairly common. In recent years I have used these as bronze washers in boat building and repairs since they were cheaper than bronze washers.
I actually collect the Half-Pence and One Pence coins, and willing to pay you for them (at least 1 cent above the cost of a washer!!!).
If you have any specific years that you want, let me know and I'll have a look. If it is valuable, doubt I'll have it.
I have about 5000 to pick through, sorted into reigns. They are just too heavy to ship to anywhere that they might sell.