Machine Setup for Lock Miters
Lock miter setup requires a lot of fiddling, so a permanent dedicated machine can be most efficient. April 6, 2011
Question
What is the correct way to set up a lock miter to not have to use a spacer on the fence? I have used up many scrap pieces trying to get it right. Fence in and out and height changes on the bit - what else is there?
Forum Responses
(Cabinetmaking Forum)
From contributor L:
Setting up a lock miter is a pain. Once correctly setup one part is run flat on the table the other is run on edge. No spacers! Use a heavy wide board for a fence that goes all the way through. Though small parts may be run manually or with feather boards you will have the best luck with a power feed. We just leave a heavy old shaper setup with an inserted mock miter cutter and two power feeds. Two because changing a feed from horizontal to vertical takes too long. Swing one out of the way and the other into place. Reducing setup time is the goal. If you can't afford the dedicated machine, once you are setup make a set of reference jigs to allow you to come back the same location (relatively) quickly. Use the miter slot as reference for the fence by attaching a board to a stick that fits snuggly in the slot and rests against the fence. The elevation of the cutter can be done using a gage block or a sample of the lock mitered wood. A real ht. gage is the most reliable. We run a lot of both solid lumber and veneered MDF panels. We have even run laminated slatwall but that is a real challenge.
From the original questioner:
Thanks for the info the scrap is piling up.A pain is putting it mildly. We have it dialed in on our newly dedicated shaper.
From contributor C:
Try a single tongue lock miter. If you do you will never go back to the other. Both pieces are run flat. One on the shaper and the other on the saw with a dado blade. We leave one shaper set up with this setup and never change it until the bit is dull. You can even run different thickness material and the corners will line up.
From contributor C:
Run one flat and the other vertical. The trick is getting the material centered in the middle of the lock miter.
AI enhanced answer (added Jan 14, 2025):Setting up your machine for lock miters involves precision and attention to detail:
1.
Blade Selection: Use a lock miter bit designed for your router or table saw. Ensure it's sharp and clean.
2.
Machine Setup:
-
Router Table: Adjust the height of the bit so that the centerline of the bit aligns with the center of your workpiece thickness. The fence should be set to cut at a 45-degree angle.
-
Table Saw: If using a dado set or a lock miter blade, set the blade height to half the thickness of your stock. The blade should be tilted to 45 degrees.
3.
Fence Alignment: The fence must be perfectly square to the table. For a router, the fence should be set so that the bit cuts at exactly 45 degrees. Use a square to check this.
4.
Test Cuts: Make test cuts on scrap wood of the same thickness as your project material. Check the fit:
- If the joint is too tight, adjust the fence slightly away from the bit or lower the blade.
- If too loose, move the fence closer or raise the blade.
5.
Consistency: Ensure your workpiece is always fed in the same orientation relative to the bit or blade to maintain consistency in the cut.
6.
Safety: Always use push sticks or blocks to keep your hands safe, especially when working with small pieces.
Remember, patience and small adjustments are key to achieving a perfect lock miter joint.
