Making 4 ft Lock Miter Joint

[George Bokros]

I want to make / use a lock miter joint for a cabinet I will be making. The joint, actually 2 joints / corners, will each be 4 ft long. I have done some a while back that were approx 2 ft long successfully. I have Infinity Tool router bits and their set up tool.

Has anyone done one this long successfully? Any tips / secerets to doing so?

Thanks for any suggestions you have.

[John TenEyck]

George, I don't see the issue. If your stock is flat and the edges are straight a 4 ft long miter, lock miter, etc. should be no different than one 2 ft long. I've made many 4 ft long bevel joints on my table saw that line up perfectly. Flat stock, straight edges = success.

John

[Mel Fulks]

Many times, and in quantity to be a stock item. The only thing that would make the longer one more trouble is failure to get the edges nice
and straight with saw or jointer. I always use a 3/8th round over bit on the inside corners of each piece ,using a “climb cut”. Then use the lock mitre cutter
at highest speed and running forward (not climb cut) to make the lock edges. When using the LM-cutter leave s a little flat at the pointed
corners, it stops tear-off there. When you sand the glued boxes and slightly round the corners the small flat disappears.

[Jim Becker]

The biggest challenge is going to be the cut that has to be vertical to the fence...you'll want a very tall, well supported fence that is perpendicular to the router table surface and some way to insure that the panel stays flat to it. Even the most minor deviation can really whack the quality of the joint with lock miter tooling.

[Ken Andersen]

I've done 4' without problems. For me, length is usually not the issue but rather sometimes I get a slight "snipe" on the ends if the infeed and outfeed fences are not perfectly aligned. I've learned to leave the material long by 4-5", machine the mitres, then trim to length.