Lock Miter Bit & Large Cabinet

[Jerry Todd]

Need some advice on using a 45 degree lock miter bit for the miter corners for a large cabinet made of plywood. Will It work on plywood? The cabinet will be constructed with 3/4 inch cabinet grade plywood with a face frame front. It will be approx 6 feet tall by 2 feet deep by 4 feet wide. I can see problems handling the bulky pieces on the router table.
My second choice would be to use pocket holes or dadoos.
Jerry

[Gary Max]

I tried that bit and never had any luck with it. Seemed like the joint always had a wave in it and never matched up right. --- Sold it on ebay

[Jim Becker]

Conceivably it will work. But as Gary says, it can be touchy. You really need to use featherboards and other hold-downs to keep the panels moving though the cut in EXACTLY the same plane...kinda the same issue with cope and stick. Even a tiny variation in the panel up or down will affect the joint and its ability to mate with its partner once both sides have been cut. Cutter height also needs to be "exact".

[Don Abele]

Jerry, I have both a Lock Miter and the Lock Miter Jr. I have used them both in solid wood and the Lock Miter in 3/4 inch plywood as well. The key to getting a good fitting joint is to use feather boards. The piece must be absolutely flat against the table for one cut, and absolutely flat agains the fence for the other. Gary, this may have been why you got a wavy fit.

As for the size, I've never run pieces through that big. Just taking a guess here, but I'd say you'd be hard pressed to make the joint accurately on something that large. Just too unwieldy to handle. Now if you have a router table that's 4x6 feet with a 6 foot fence, then go for it :D . Whatever you do, don't be tempted to use this bit hand-held.

Be well,

Doc

[Jamie Buxton]

Like the other guys say, it'll be difficult to get a lock miter right on something that big. Another issue with that approach in plywood is that even if you get it perfect, the corner is going to be delicate. There's no thickness to the veneer, so you can't even slightly round over the corner. Any ding at all will penetrate through the veneer into the substrate.

A better approach is a piece of square-cross-section lumber at the corner. The plywood panels butt into it with nice 90 degree edges -- not that tricky 45 degree stuff.

Besides, if you're putting a face frame on this cabinet, where are the edges you want to lock miter? Are they the horizontal edges at the top, going front-to-back? If so, the top of the joint is above eye level. You could just do a butt joint between the top and the sides, with the sides running the full height. Or if you don't want the stark-modern look, wrap the top with a little molding. It will cover your joinery, and it will help make the piece look finished, instead of being chopped-off.

[Charlie Plesums]

Lock miters are hard to get set up in addition to the precise horizontal and vertical required. However, this page shows how it was done on a shaper with a sliding table and a monster jig, cutting in plywood...
http://www.stonehorsefarm.com/LockMiterJig.htm

I would be a little concerned about just butting plywood into a solid corner board, but some biscuits or a tenon would be my choice.

[Gene Collison]

Need some advice on using a 45 degree lock miter bit for the miter corners for a large cabinet made of plywood. Will It work on plywood? The cabinet will be constructed with 3/4 inch cabinet grade plywood with a face frame front. It will be approx 6 feet tall by 2 feet deep by 4 feet wide. I can see problems handling the bulky pieces on the router table.
My second choice would be to use pocket holes or dadoos.
Jerry
________________

Jerry,

John Lucas has an excellent setup guide for that bit at his site. http://www.woodshopdemos.com/cmt-lm5.htm But I wouldn't advise using that bit on 3/4 ply. I would rabbit the sides top and bottom and cut a back panel to fit and glue it in. Clean and easy.

Gene

[Jim Becker]

Another thought...if you want "clean corners", bevel them at 45º and use a spline or biscuits to keep things lined up along the joint. A few glue blocks internally and out of the way will keep it super strong. I made some display cubes a few years ago for a sculptor friend using the method and they turned out great. If you plan it out right, you can also get the grain to "wrap" around the box.

[Chris Padilla]

I used a lock miter on my cabinet construction for one section of my EC. One problem I had is when you route on the vertical section, a fair amount of the plywood plys were blown out--the "tongue" for lack of a better word. Now maybe my plywood wasn't all that great (maple A-1, yeah, right) but I was dissappointed with the blow-out...nearly made all that great glue surface pretty much disappear.

Let me put it this way, I don't think I'll use the lock miter bit on large panels again...they are difficult to handle. I ended up routing a rabbet on the corner and gluing is a strip of wood to clean up the corner.

Also, I've followed and emailed John Lucas on the set-up of this bit and I'm no dummie but I still have a helluva time setting this bit nicely and I go through lots and lots of test cuts. It is fussy as heck.

[Mike Kelly]

Jerry, a zero clearance fence insert helps tremendously with this also, especially with plywood. But six feet of no blowout is questionable after perfect setup with plywood. I have successfully built small boxes with plywood using this bit.