I recently decided to try using lock miter joints for drawers that don’t need dovetails, in this case for some storage drawers in my shop. I bought an Infinity 1/2″ Baby Lock Miter joint and on poplar they were fine. Then I tried using it on 3/4″, 4″ wide maple with poor results.
With these bits, you run the end of one piece flat across the bit and the other piece vertically. I found that the maple is too hard (it was soft maple) and that the bit grabs and is very difficult to keep the wood flat against the fence, despite using various backer and pusher boards, burying the bit in a sacrificial fence and using a double height fingerboard. The result was a profile that didn’t run true across the board and with some of the thinner parts chipped out badly.
Is it just a bad idea to use this technique on harder woods? Or is their a way to get a good cut on the vertical board? I feel like even if I built a jig, I’d run into the same problem — the harder wood doesn’t want to feed through the profile cleanly.
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Those bits are a menace. Mine was huge and sounded scary even at the lowest spin speed. The single-pass thing sounds like a good idea, and once it's dialed in it's kinda cool, but really sketchy too. I used it for a single project, then it sat for 15 years before I threw it away. I just don't think they're safe.
The large opening required makes it almost impossible to cut narrow pieces like drawer sides. If you're committed to using it I suppose you could cut wide boards and rip them after... or just go with a lock rabbet joint, easy-peasy on the tablesaw.
Sounds like too much material removal per pass for your setup. Try using the fence to make multiple passes. The rule of thumb I was taught, even for monster routers like the Milwaukee 5625, is a square 1/4" per pass.
For involved profiles this can take some visualization but erring on the side of conservative will generally work better than hogging things out. Shapers can take huge bites out of things, router tables not so much.
You might try cutting a 45 degree bevel along the edge using your table saw prior to making passes on the router table.
I don't think the hardwood should be a problem (maybe something exceptionally hard but not soft maple). geedubbee's comment makes sense. Do the joint in steps. Lock miter joints are a bit sensitive and must fit essentially perfectly. If it was your first lock miter joint I'd say maybe practice a bit more on scrap till you get the set of steps that works for you best. Also, I don't know that I've tried this but seems like you could do the final dimensioning of the width of the pieces after the joints are cut, possibly giving you a wider edge to run against the table. I do think that the most important is not to take too big a bite with each pass.
Every instruction manual or article I have ever seen has the bit setup first and each cut made in one pass, that's why I'm a hater.
How would you set up for multiple passes? I suppose if you got the height perfect first you could bury the bit and slowly bring it out of the fence? Would it work for both parts? The final-pass cuts would be putting a ton of pressure on a pretty thin point of material...
A couple of folks above have suggest multiple passes, have you ever tried it with a lock miter bit?
Cutting at 45° first is possible, but you can't take very much because both sides of the cut protrude past the miter surface to create the locking tongues. I suppose there's a small advantage there.
I confess that I've never done a lock miter joint in multiple passes because the only use I've ever put the bit to is making an Arts & Crafts style leg joint 4 quarter sawn board ends together. The joint would be cut along the grain with board flat on the router table, so much easier to hold and keep in place.
Part of the problem, I'm sure, with using this joint for a drawer box is that it is difficult to hold a 4" board securely to cut the joint on end grain.
I have never thought of using a lock miter joint on drawer boxes. I now use either my Domino, dovetails, or a rabbeted joint (mostly Domino) for shop drawers and dovetail for furniture.
If the lock miter joint is cut on the edge of a board along the grain, it's much safer, more easily held in place, and the result, I'm sure, much more like what the OP wanted.
So, after more thought, I take back my multiple cut suggestion and recommend using another joint that is safer and easier to cut. Since the drawers are for shop storage, I'd suggest dovetails or even a rabbeted joint of some variation. These are very strong. Also, if you want to learn how to cut dovetails, a great joint to use for many projects, it's great practice or, it's a good excuse to buy a dovetail jig.a
I got suckered into them too. Never got it to work right.
Dang StumpyNubs.
Always thought it was just me being too stupid or lazy.
Been sitting ever since.
I find other methods more enjoyable, easiser, and faster anyway.
I don't think that the problem is the hardness of the soft maple. I think it is maple's tendency to come out in big chunks (unlike poplar). A sharp rotating cutter should naturally hold the board against the fence (or table of a jointer or table saw.) Multiple lighter cuts are the answer. FWW had an article a few years ago about setting up a router table for the final cut with the usual fence, and then attaching thin sheets of material to the fence to create lighter cuts. You can clamp, screw, or double sided tape the pieces to the fence. I made multiple fence additions with the same pattern, and same flat head bolt holes (countersunk), with a wing nut on the bold against the back of the fence.
My lock miter cutter is a 3 wing shaper cutter with a 3/4" bore; much more solid than a router bit with 1/2" shank. I still use a table saw to remove some of the material, and use multiple passes, all for a better quality cut. I've only used lock miters on long edges, but on red oak and walnut (much harder than soft maple), without any problems.
Microjig has a lock miter bit and a setup tool that would appear to guide the user to a quick and easy setup.
Link - https://www.microjig.com/products/lm-bit
Up front, I don't own the Microjig bit or setup tool so I can't tell for sure whether it's as easy as the video shows.
I've seen videos of woodworkers making lock miter joints in white oak for Arts & Crafts table legs. If it works in oak I would guess it should work in most hardwoods.
What is needed is a secure way of holding the piece while cutting. Something else, the cut can't be hurried; steady and slow.
I've given up on lock miters a couple of times because I could not get a consistent edge even using the set up jigs. It's that vertical piece thats trouble. The one thing I tried that was helpful in keeping that vertical piece steady is to use a wider piece than you need and then cutting it done to size.
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I've had success using them for edge grain. Making long boxes or table legs with 4 quartered faces. 0 success using them on end grain it always seems to chip or chunk out at some point. "Dialing-in" is a big problem. It takes a lot of trail and error. Once dialed in, if you can reliably end in the same place, you can take multiple passes by moving the fence.
Thanks for all the ideas. I'll try making successive light passes; I'm not sure that will work -- can you really sneak up on the joint? But I'll do some test pieces and see. All in all, very disappointing as I got this bit for drawers where I don't want to or need to use dovetails, like for shop storage. It was supposed to be a quicker and easier alternative, especially for drawers with half-inch thick sides that aren't that amenable to dominoes. Oh well, live and learn and waste $100.