Great idea George thanks my first preference is a forstner bit these also give grief with that long tip never ever thought of reducing that as well different types vary in that regard. I have sure had rubbish Forstner bits as well. Noting you live in Busselton I guess you count your lucky stars finding someone there to do the mod.
Did you know the mint in Canberra and perhaps Perth have a commemorative Kangaroo Penny slightly larger that covers a lot of other years at 5.00 bucks each.Similar to the kangaroo on one side but you stick the other side down so who cares.
When I polish them I cut a recess neat fit in an oversize dowel on the wood lathe to hold the penny while I polish them. Last night on You Tube gazing a way to hold a penny to facilitate scroll saw cutting and also holding the coin to reduce the thickness for making jewelry and I figured thinner to assist making pens. Welcome to the frorum from 3000 miles away mate.
Give me a pm with your E Mail I figure we can help each other more also including Mark up in Tennant Creek who I talk to often on Skype.
Peter.