Question about Lock Mitre Joint

[Eric Scantlebury]

Hello,

Let me first start by saying that I am by best accounts a novice woodworker who has decided to take my ability to do DIY projects around the house (molding, thresholds, etc) to the "next" level. I have decided that I want to try to build the Miter Saw Stand featured in Popular Woodworking for my Dewault 703. Here is the link to the plans:

that plan the carcass is assembled by butting the end of a board into a rabbit and held with glue and screws. Seems simple enough. However, I just finished reading an article about locking Miter Joints in the February issue of Popular Woodworking and now I'm leaning towards using that method to assemble the cabinet carcass (top, bottom, sides and back). With that in mind I have a few questions.

1. Is there a strength difference between the two types of joint? And if so which is the stronger joint? It would seem to me that the miter joint would be stronger than the butt end joint.

1. If it is feasible to substitute the Miter joint - is it possible to miter the back in the same manner? In other words creating a "square" cabinet seems simple enough but what about attaching the back using the same method. Is this possible? If so is their any special considerations when routing the panels at the intersection of the "corners" of the carcass where, say, a top meets a side and the back? If that description makes any sense at all.

2. If all is well with this method - is it possible to run that type of bit effectively in a PC690 using the PC router stand and still get good results? Or does a bit like that need a heftier router?

Thanks for any input and answers.

Eric

[Swingman]

Joint strength is relative to the type, and proposed use, of the end product. On a plywood shop project, I personally would go with the glued rabbet joint and screws. It is more than strong enough in plywood, fast, and minimum or no clamping.

I am not a fan of miter joints on most shop grade plywood projects unless there is a real need for them ... but then I don't own a locking miter joint router bit. As they say, when you only own a hammer, everything looks like a nail.

BTW, if you decide to use the locking miter joint, they can also be cut on a table saw.

FWIW ...

[Steve Turner]

I've built several things out of plywood (of varying qualities) where the corners are connected with lock miter joints, and I've been pleasantly surprised with the results. I really just started doing it as an experiment; I'd never seen anybody else doing and I figured it wouldn't work very well, but I can't really see any downside. I haven't seen that PW article, but I'm curious about it. I wonder where they got the idea?

I don't have any proof to back up my claim, but it seems to me that you are right; the lock miters I've done with plywood are very strong, and my guess is that they are stronger than a butt joint with screws. Be sure to use a good healthy coating of Titebond II (or better yet, Titebond II Extend) on both male and female surfaces of the joint.

Sure; all four corners can be lock mitered. I would run the longest panels through horizontally (easier to manage), and the shorter ones vertically. It helps to build yourself a very tall router fence for this purpose. Lots of good clamps with square, flat faces (like Besseys) will make your life much easier! Start clamping in the center of the panel and work your way out to the ends so the excess glue has somewhere to go (and be ready to clean it up; it's easy to get too much glue in the joint channels, and it will come out in globs when the clamping commences!) Check the carcase with a good framing square as clamping progresses, and it's a good idea to orient the clamp handles in an alternating fashion to counter any tendency to pull the carcase out of square.

Sure, most lock miter bits aren't that big and you don't need a 3HP hog to spin them successfully. Make multiple passes to get a clean cut. Search this group for subject line "lock miter bit" and look at the posts from 1/15 or so; we discussed methods for getting good results from lock miter bits in that thread.

And oh yes: Try this all out on some scrap pieces before diving right into big project! Good luck.

[charlie b]

snip

You're doing this in ply rather than solid wood?

If ply (or MDF) my gues is 3/4" right?

Assuming ply or MDF, the answer is the lock mitered joint will be stronger than the rabbet, glued and screwed. Screws don't hold real well into the sides of plywood.

The lock mitered joint is, if cut properly, self aligning and as noted in the article, somewhat self supporting. It also almost doubles the glueing (sp?) surface area - thus more strength.

The lock miter joint will accomodate your idea -but the parts have to be cut very accurately and the lock miter joint must be cut accurately on all four edges of all six pieces. The sides and the top and bottom are easy. As long as the sides are the same length and width and the top and bottom are the same length and width you'll get an open ended box without too much trouble. It's cutting the front and back to exactly match the opening they must fit into that's the critical part of the process.

But, if you do all the cuts on all the parts that use each fence set up or cross cut stops, you're half way there. When you cut the lock miter joints on the router table you've got to use feather boards for holding the stock firmly against the fence for the vertical cuts and feather board to hold the stock down flat on the table for the horizontal cuts. Any wandering of the stock while routing will definitely show in the resulting edges of your box.

And there's the rub. The Baby Lock Miter bit is 2 inches in diameter. The Lock Miter bit is about 2 1/2 inches in diameter. That's a chunk of metal to spin at 22-28K rpms and remember, on half inch stock it's eating a half inch on a side triangle in one pass. Works fine with a 2.25 HP Dewalt 621 plunge router in my router table. The 690 might work.

Now you've got me curious. Have more baltic birch ply. Will think through the cutting set ups and cutting sequence and give it a try. Will post the hows, whys and a piciture or two to a.b.p.w. when I've either got it or have given up.

charlie b

[Eric Scantlebury]

Thanks all for your input. I was thinking of using birch ply as well. And since this is just a piece to hold my Miter saw I though it would be a good place to also practice this type of joinery (i.e. if I mess up it's ok if it doesn't look perfect because it's not a presentation piece). I would be interested in your response if you do try (especially the hows and whys). Now another question. Are the CMT Miter bits good or should I look to some other brand? Thanks again from a newbie.

[Eric Scantlebury]

Thanks for the reply - I do plan on trying on scrap (most likely many times LOL).

[Eric Scantlebury]

Thanks for the input. I do realize you can do that on a table saw (the article also articulates joining with biscuits or a spline). I just thought it may be good to practice this type of joinery on a piece that doesn't have to be "perfect".

[Rodger Pevehouse]

Eric, If you would, let me know if you build the Miter Saw Station. I love the space saving feature of this stand. I would be interested in any problems you run into.

[Swingman]

LOL ... if you're a true wooddorker, it will be "perfect" ... whether it needs to be or not. ;>)

Good luck on your project.

[Eric Scantlebury]

Will do. And when I get around to it (I'm still in the "how do I want to build it and how might I change it stage") I'll be sure to post pictures as well. I'm about 90% sure I'm going to try the lock miter joint. I need a couple of more tools in order to start - the miter bit and an edge guide for my PC. I have a feeling At least the edge guide will be purchased this weekend.

[charlie b]

Have posted diagrams of how a closed box with all lock mitered edges can be done in alt.binaries.picture.wood- working. May actually try it on some half inch baltic birch ply since the bit is already set up for that.

Will post pics of results, if and when, to a.b.p.w.

charlie b