Lock Mitering Cabinet Corners

Practical advice on the process of lock-miter joinery for cabinet corners. October 28, 2014

We use a lot of pilasters on our jobs. I'm not sure if this is the correct term but an example would be a 3" wide x 96" tall x 26" deep MDF column mitred together at the front corners. Currently we cut the blank rectangles on the router and have a dedicated table saw set up to cut the miter, then miter fold the pieces together. My only complaints with the current system are that if you aren't very careful to hold the MDF flat on the saw it will show in the miter, especially if we are staining the column. Also, with miter folding the glue takes a long time to dry and sometimes the glue seeps out of the mitre even though the seam is taped, and once it dries itís a pain to get off, especially with stain grade because it is not hard to sand through the veneer while trying to remove the glue.

One thing that I could do to make this easier would be to cut the angle on the CNC, but the problem with that would be that a lot of the columns have flutes that are cut on the CNC and I would have to have a jig and machine both sides which is not really ideal. I would be open to investing in a dedicated shaper with lock mitre tooling but I have heard that this has its drawbacks also. I have also tried butt joining a 3" piece of solid wood for the face piece but that didn't work out well at all. The seam took forever to get right. Does anyone have any ideas other than those mentioned above?

Forum Responses
(Cabinetmaking Forum)
From the original questioner:
Let me add one thing to this: If I have the space and funds to justify two dedicated shapers, each with power feed, one for the vertical pass and one for the horizontal pass of a lock miter, would this then be the ideal system?

From contributor L:
We have a lock miter permanently set up on a shaper. We have two power feeds on it - one for vertical and one for horizontal. Itís quick to swing in and out. I wouldn't do it with one feed because they are such a pain to change over. The problem with MDF veneered is it is so fragile on the sharp edge. Most of what we run is solid lumber. We have run laminated slatwall on it, mostly successfully.

From contributor D:
We use lock miters a lot. We use two shapers, one dedicated to vertical and one dedicated to horizontal. We also use a custom fabricated clamping jig based on the concepts of the Hess Mobile, only better. The key is to use solid wood on at least 1 side of the joint. If you're mitering veneer only, then you're better off not using a lock miter.

The secret is to slightly offset the joints. By doing this you can apply as much clamping pressure to the joint as you'd like, and by moving the joint "around the corner" it is less likely to separate and if it does it is easier to deal with.

From the original questioner:
I could use solid wood for the 3" nosing piece without adding a lot of cost and then sand off the burr on either side.