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What size router bit to use?


Established Member
Forgive me if this sounds like a daft question but I've just bought a new router and I'm thinking of routing grooves for shelves to go into for a wooden book case I'm making. The shelf is 18mm thick. Should I use an 18mm router bit or a 19mm bit? Just wondering if the 18 would be too snug a fit.


Established Member
I havent bought the bit yet. Didn't really want to buy 2 as it'll be only a one off job.


Prominent Member
Is your router a 1/2" collet? Not sure I'd trust an 18mm cutter in a 1/4" collet :eek:
Does the fence have micro adjustment? You could tweak the groove with the micro adjust if a tad too tight.
I'd probably go with making a jig, batch out the cuts, use a 12mm cutter and strip of wood/packer to make up the difference to 18mm, or whatever the measurement needs to be.

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