THE MASON'S MITER, MAYBE THIS IS JUST YOUR STILE!...

WHAT IF....you want a rail and stile connection on a door to have only a slight edge detail such as the diminutive chamfer in the picture shown at right?   Several problems come into play:  If you use a router bit set with mating male and female sides, you are stuck with the mini tongue and groove the bit set creates- which I question for its overall strength and reliability.  You're also stuck with the exact profile of the bit set with little variance.  Also, if you deepen the groove at the location of the joint, there is no way to lengthen the mating tenon.  So, skip the bit set and just use a mortise and tenon joint for great strength, but you then need a little molding to create the profile.  That is an added step you may not want, and how would you get the profile shown above?  You can route the profile into the door edges, planning on a mortise and tenon joint,  then miter  the edge detail at the rail/stile connection.  BUT, this then requires  removing the profile at the joint line of the two pieces.  This last method  has been used in antiquity and looks great but is a fair amount of work, and you still have to coordinate cutting the groove in all four sides to let in the inset panel.  The complication there becomes whether to use a haunched tenon or a stopped groove in the stiles?  The stopped groove is easy enough with a router table approach, but not so easy when done by hand and impossible with the table saw,  either of which appeal to me more than using a squealing router. Using a  haunch  allows the grooving plane to run to the end, though the mortise is of course much deeper.  For a haunch to be used, sometimes the groove has to be deeper than needed or the haunch will disappear when the profile portion is removed along the joint line.  Complicating this is that the necessary groove for 1/4 inch birch ply (as shown) is less than 1/4 inch and more like 5mm. I own a hundred router bits, but none that perfectly fit  1/4 inch (so called) birch ply. The closest imperial size is 3/16.  I don't as yet own any grooving or plow planes, and may never get a 5mm blade unless I buy a newer variety such as the Veritas model. All approaches are very doable, but alot to keep track of when constructing a simple cabinet door! As usual, simple looking assemblies are hardly ever simple.  If time were of no issue, then I would use the older approach and end up with a regular miter at the inside corners, instead of the mason miter shown above.  I have done this for window trims with period type "t-style" butt joints but mitered edge profiles at the inside corner ( I used biscuits for the joint which I have come to dislike in general).  Very pretty to be sure, but still requires alot of finesse to create a tight miter,  even without  the added complexity of the groove for a panel.  Adding the groove, adds the haunch, which adds strength and quality, and resists any twisting in the rails which is a factor in larger doors for built-ins.

Shown above is one solution to all the issues concerned.  To recap, those issues are:   I want a decent mortise and tenon joint in my connection (1" deep or more!)  Two, I want the tiny little chamfer because that's what my customer wants. Three,  I want the groove to be created fast and repeatable and also be the same dimensions as the mortise, so it all flows as one operation.  Four, I insist the chamfer turn a sharp corner and not look rounded as would be if you assemble the door and then route the edge. The chamfer in the photo above was in fact routed, but was stopped before I reached the inside corner where the joint meets. The remainder was then chiseled in tight very easily thus creating what has in earlier times been called a "mason's miter".  You may  not prefer this look, but it does have historical precedent as an acceptable, if not desireable joint.

So what were the steps involved?   First, cut the pieces to length, taking into account the added tenon length to each end of the rails.  For me this was one inch each end, or two inches total extra.  Next, cut the groove for the inset panel using a table saw and regular blade.  You can get a groove to be both the perfect size for plywood, and also be centered if you do a trial piece on a same-size scrap.  You want to be able to push the stock through, flip around, and push through again.  Using a thin kerf blade this reqires me to remove the sliver in the middle.  I did this by pushing a small flat screwdriver through the groove, but you could also make an extra pass with the fence set to put the blade centered on the sliver. Next, create the tenons any method you prefer, which for me is a set up with regular sawblade in the table saw set to make the shoulders and then nibble away the waste.  I know I will pare the tenons anyway, so I just nibble to a snug fit and then pare to fit.  If you do the grooving first, it gives you the guidance on cutting the tenons.  I pare with a bench chisel and a rasp on hand and it goes fast.   I know alot of guys who like making verticle cheek cuts with a tenon jig.  I've never liked this because my tenons end up too loose, or are fat and then I have pare them anyway saving no time at all.  If you like this method, but struggle with it, try cutting the cheek  with a setting you know will cause a fat tenon which allows you to fine tune with shims to make a thinner tenon, if needed.  If you cut the sides starting with the lefthand  cheek, you can then shim the stock into the  blade on successive trial cuts.  By shimming, I mean a thin business card or some such material between the stock and the jig. It may be as thin as masking tape between the stock and the tenon jig.  Too fiddly for me, though you may not mind at all

As a sidebar, I again advocate at least hand sawing the tenons though guys in business think their whole financial world will be ruined as the result.  Hand cutting is infinitely more enjoyable (for me), and my skills are honed to do this very quickly and tightly (and so will yours be).  Whenever people reject a hand method, they often do so because they refuse to acquire the genuine skill that the machine replaces.  (I will say that they may realize too they've been acquiring tthe wrong tools and behold, they have the machine, and not the correct hand tool!  I too have this problem and resort to the router since I am sadly underequipped in molding planes)   Many will say "it's too slow" but that's only true relative to their lack of skill.  I say, speak for yourself as to what's slow, because I've seen Paul Sellers cut a dovetail box all four sides in under ten minutes.  And there are others as well, Rob Cosman, John Bullar, Frank Klausz, etc.  Most guys couldn't even get their router set up in twice that time.  I'm not quite that fast at hand dovetails but will be eventually in another few years.  As to the dollars and cents (if you make your living from the craft) YOU tell me which product garners the higher price- the true handmade stuff, or the machine made stuff.  I know price isn't the same as PROFIT, but I just want you think this through as I have begun to in my business.  If always using a machine and doing it the "fast" way was more profitable, I should be rich by now.  Maybe I missed something along the way in my quest to make a living.  Maybe I missed the part about always doing my best work.  Maybe I missed the part about being in the wrong price range to start with and always being the cheap guy.  Maybe I never wanted to charge more for my work because deep down, I knew it wasn't done the best way, and certainly wasn't my best work.  Maybe I tied my hands at the outset by predetermining the price which then predetermined my approach to the work.  Maybe I had it wrong way around.

.  If I've learned one thing in thirty years, it's that quality is a better business strategy than CHEAP, though it doesn't seem like it to the small business oftentimes.

.The last steps are easy...First, dry fit your doors with no panel. Seems to me I would have to do this step regardless which method I use.  I like hand paring or rasping my tenons to perfect fit.  Good fitting joints are the basis of honest workmanship.  Next, with the door dry fitted, make a pencil mark on the stiles 1cm or so back from the connection so you know where to stop routing the chamfer.  If you plane your chamfer, you'll need to stop farther back and do more chisel work into the corners.  Now, having created the chamfers on the disassembled parts, assemble the doors, with inset panel , glue and clamps.   Don't forget to put some glue on the plywood panel which hurts nothing and adds even more strength overall.  I leave very little clearance in the panel groove for expansion, because in my world,  everything seems to shrink and never seems to expand.  Well, that could be different in your world, or maybe you build in extremely low humidity and then it expands later.   Use your best judgment in regards to expansion in all your projects. Once the glue sets, you can do the chisel work into the corners creating the "mason's mitre".  You can do it with the clamps on, but the door is heavier to flip around as you chisel or pare into the miters.