Regarding 3/4" plywood being thinner, the world has gone metric and plywood imported from other countries comes in 6, 9, 12, 15 & 18mm each of which is thinner than 1/4", 3/8", 1/2", 5/8" & 3/4"
3/4" is 19.05mm so the plywood is 1.05mm thinner, approx 40thou.
UK started with metric 35 years ago but many still prefer imperial measurements.
Very few 30 year olds have ever known inches as all they were taught at school was metric.
Because most routers still come with 1/4" or 1/2" collets we can use bits made for inch as well as metric.
To cut dados for 18mm sheet material I have an 18mm cutter.
It can often be confusing having both metric and inch sizes but I often find it helpfull such as when cutting a 1/2" mortice and starting with a 12mm bit then cut to finish size with a 1/2" (12.7mm) cutter.
3/4" is 19.05mm so the plywood is 1.05mm thinner, approx 40thou.
UK started with metric 35 years ago but many still prefer imperial measurements.
Very few 30 year olds have ever known inches as all they were taught at school was metric.
Because most routers still come with 1/4" or 1/2" collets we can use bits made for inch as well as metric.
To cut dados for 18mm sheet material I have an 18mm cutter.
It can often be confusing having both metric and inch sizes but I often find it helpfull such as when cutting a 1/2" mortice and starting with a 12mm bit then cut to finish size with a 1/2" (12.7mm) cutter.
