Even at the best of times, the Lock Miter is a tricky joint to master, and I often get requests for tricks to help improve cut quality when using lock miter bits on difficult species of wood or finicky end grain. The Lock Miter bit was originally designed to create box beams, posts, and other long grain projects. However with such a lovely and strong joint the bit has been adopted for many applications beyond it’s original intent. Trial and error is always going to be a factor when working with the lock miter joint, but there are some tricks that can lead to a finished joint more quickly, even in the most difficult pieces.
1. Slow the bit down
If you are having problems getting a clean cut, always try slowing the bit down first. This helps soften the impact of the bit on the fibers of the wood and can help the bit cut more cleanly. Less impact on the material means reduced vibration and better cuts all around.
2. Use Feather boards!
Use as many feather boards, hold downs, backup blocks, and sacrificial fences held in place with double sided tape as possible. Anything you can do to eliminate vibration and allow for smooth feeding through the cut will help produce the best possible result. The JessEm Clear Cut Stock Guides are far and away the most helpful hold down/feather board I have ever had the pleasure to use and I highly recommend them. You’ll see them in use here alongside the Milescraft feather boards for a rock-solid hold against our fence.
3. Always use a backer block
A backer block is a must whenever routing end grain. The block will support the workpiece at the exit of the cut and greatly help eliminate excessive blowout. This tip helps whenever routing or cutting end grain, not just when creating lock miter joints.
There isn’t a lot of waste that can be removed before the lock miter bit does it’s work, but every little bit helps. Lock miter bits cut on a 45° so making a clean chamfer cut and removing as much waste as possible before the lock miter cut is made can help ease the work that the bit must do. A Chamfer Router Bit can do the job perfectly.
5. Dampen the End grain.
Using solvent or even water to dampen the end grain before routing can help soften the fibers and improve the cut quality. When all else fails, this trick combined with the others can make the difference between completing a tricky project or having it end up in the scrap bin.
The trickiest part of making perfect lock miters is setting up the bit in the first place. Our Lock Miter Master Setup Jig helps eliminate much of the guesswork and confusion that is associated with this wonderful bit. If you have not seen the Lock Miter Master Jig in action take a look this blog post Gettin Jiggy Wit It I’m sure it will help dis-spell some of the mystery that goes along with using the lock miter bit.