Replies

1. 
   ring | May 07, 2007 06:34am | #1

   No contest. This is the classic situation that demands M&T joints. The lap joint cannot resist sagging over time.

   Size of tenon? Depends on the technology you're going to use, but about 3/8" to 1/2" will be fine. If you're doing the mortises by hand it will depend on the mortise chisel you've got.

   David Ring

   http://www.touchwood.co.il/?id=1&lang=e

1. 
   allenb | May 07, 2007 06:51am | #2

   Thanks Ring

   My first thought was to go Mortise and tendon but I have a plan that I am following, with modifications as I go.  The plan shows lap joints and it made me think twice.  I will cut the mortise with a router so 3/8 or 1/2 could be done.  The 1/2 may be a little stronger.

1. 
   DustyGeorge | May 07, 2007 05:13pm | #3

   Allen,

   Half inch tenons may actually be a little weaker.  I am not an expert on the mechanics of a M&T but I have always felt that it is the shoulders that give a M&T its strength and resistance to racking.  The purpose of the tenons is to hold the shoulders firmly in place.  The 3/8 inch tenons would provide just as much glue surface as 1/2 inch tenons.  Just my humble opinion.  Others with more expertise may contradict me.

   Good luck, George

   You don't stop laughing because you grow old.  You grow old because you stop laughing. - Michael Pritchard<!----><!----><!---->

   <!----><!---->

   Edited 5/7/2007 10:16 am ET by DustyGeorge

2. 
   MikeHennessy | May 07, 2007 05:52pm | #4

   David Ring is a more experienced woodwright than I, so I'd have to give him the nod -- but my rule of thumb is that tennons should be about 1/3 the thickness of the mortised stock. Under that theory, 1/2" would be a bit much, leaving the cheeks of the mortise weaker than I'd like to see. That said, you would probably be OK with lap joints per your plan, given the strength of modern adhesives. A bridle joint works well too, and is pretty easy to make with only a dado blade on a table saw. It will really come down to a design issue, i.e., what pleases you the most.

   Mike HennessyPittsburgh, PA

1. 
   allenb | May 07, 2007 06:19pm | #5

   Thank you!

   Given your 1/3 rule and the advise from a previous poster I think the 3/8 tendon is coming out on top.  These doors are going to be heavy (in my opinion) and I would like to design in as much strength as possible.

1. 
   jackplane | May 07, 2007 07:21pm | #6

   FWIW, I agree with Mike and Dusty. I learned and always use the one-third rule.Expert since 10 am.

2. 
   BruceS | May 08, 2007 02:17am | #7

   Well,  We agree on the 1/3 rule  ;-)Work Safe,  Count to 10 when your done for the day !!

   Bruce S. 

    

2. 
   ring | May 09, 2007 01:30pm | #16

   Mike,I agree with the 1/3 rule also, but the practicality is that one makes mortises with the tools one owns. If his stock is 1" thick, then we all know he's not going to make a mortise that's 21/64" just because of a rule of thumb. I'd go with 3/8", but if he's got tooling for 1/2" then it'll work fine as well. The 1/4" shoulders in oak will suffice.

   regards,
   David Ring

   http://www.touchwood.co.il/?id=1&lang=e

1. 
   MikeHennessy | May 09, 2007 01:55pm | #17

   David:

   I agree -- 1/2" will work fine, particularly since the stiles are over 1" thick. (I had originally thought that the stock was 1" nominal.) Still, if tooling is the limiting factor, I've used bridle joints on doors like this with full glass panels (the OP's are only 10") and they've worked fine. A bridle joint also has the advantage of having even more glue area than a M&T. A decent stacked dado set on a TS is all that's needed to make this joint whatever dimension you wish.

   Mike HennessyPittsburgh, PA

2. 
   MikeHennessy | May 10, 2007 03:14am | #18

   Following up on my previous post that a bridle joint would be OK for this, here are some (crummy) pics of some kitchen cab doors I made -- glass panels and bridle joints. The pins are just for show, and don't go through. These have held up fine for about six years now.

   Mike HennessyPittsburgh, PA

    

   
3. 
   WillGeorge | May 11, 2007 10:32pm | #20

   Mike Hennessy..I agree with you for your project (By the way, nice work!)..I read the original post as a actual door as in a (front door or something like that)I use to make alot of custom doors and the more I think about it these days, the modern glues we have available a 'lap joint' just may work as well?

4. 
   user-200815 | Jun 17, 2007 10:18am | #21

   Am getting into this thread very late but here goesA lap joint and even a bridle joint won't do what a mortise and tenon joint does do - limit 5 of the six possible motions you'd like with a joint (yes SIX - in/out, left/right. up/down AND rotation around each of the three axis). So when you dry fit the parts, or go to glue them up, the lap joint can't be dry fit and have things hang together without clamps. The bridle joint will let you put things together - but allows sagging. And neither is automatically self aligning. The mortise and tenon joint - or easier yet, and nearly as strong - the loose / floating tenon mortise and tenon joint - takes care of everything - no twisting, nor racking, nor parts coming of alignment. It allows only movement on one axis - pull apart - everything else is fixed.And the tempation with doors is to go with one tall tenon - which may be a mistake if it's too tall. You've got grain joined at 90s - the tenon wanting to expand and conract far more than the side grain or face grain the mortise is cut in. Much past an inch of tenon height and you probably should break it up into two shorter tenons.And with a doorway door (as opposed to a cabinet door) - you might want to go with a haunched tenon to help with twisting.You may find this stuff of use - now or for some future project
   http://web.hypersurf.com/~charlie2/MT/MTPrimer0.htmlBTW - unless it's for something bigger than furniture scale - I've gone to loose tenon mortise and tenons. Much less risky, no "visble length PLUS the tenonS lengths, no shoulders to tune, not gaps to fill when I screw up. Cut things to their visible length and mortise both parts - with a router jig or, better yet, the new Festool DOMINO that makes cutting mortises - especially in end grain - and more importantly - in the end grain of L O N G parts quick, easy - and accurate.For your door project - four or even 6 loose tenons for each joint would give you more strength than you'd need - and done very quickly - with no layout lines and almost no tool set up.http://web.hypersurf.com/~charlie2/DOMINO/DOMINO_TableOfContent.htmlcharlie b

2. 
   sapwood | May 08, 2007 08:13pm | #13

   I have to agree that this situation seems to call for a m&t joint. At least that is what is classically taught. But why would a half lap necessarily give way over time? What mechanism is failing to allow the sag? Is the glue flowing? If so, then a rigid (urea formaldahyde) glue could be used. Or is there something else? If the joint is pinned, as was suggested for the m&t by another poster, would the joint still fail? How could that be? Is there any emperical evidence that would back up the choice for m&t?

1. 
   mwenz | May 08, 2007 10:51pm | #14

   Only a couple reasons why I would use M&T versus half-laps--and I do make a lot of things using lap joinery of different stripes.

   One reason would be that the tenon is held captive by the side walls of the mortise. To me cabinet doors receive the most abuse of any other furniture style [darn near any way]. It is the side loads of a door being shut none too gently that is the issue.

   Another reason is the shear weight of the panels and glass. Still don't know what the dimensions of the doors are, but the safety glass poundage out 20" from a hinge is plenty. Worse the wider and taller a door is. Again, the issue is twisting shear by not having a tenon captured in a mortise.

   All that said, I have also used reinforcement like Pat shows. That was on a "modern" styled AV cabinet where I think the brushed metal looked nicely [SS in my case].

   Take care, Mike

1. 
   allenb | May 09, 2007 06:28am | #15

   I'm still reading along so you guys just keep talking.  Just for reference these doors are 53" tall by 17" wide.  The frame is 2 1/2" wide 1"+ thick (actual).  They will have a 10" glass window at the top and the rest will be filled with a wood panel.  The panel will be 1/2" thick or a little less but not less than 3/8".  All QSWO.

   Thanks,

   Allen

2. 
   Routerman | May 08, 2007 05:47am | #8

   Would lap in a minute if you'd allow some steel or aluminum mending plates across the connection.

    

1. 
   allenb | May 08, 2007 06:05am | #9

   Interesting suggestion.  We would need a change order so we could bill more.  Could you elaborate on how you would clear that design change with the customer. (the wife) 

   Thanks,

1. 
   Routerman | May 08, 2007 03:59pm | #11

   Tho not a great pic, the hardware shown mends two sticks in length.

   Tell her, the joint may get flakey with time,  but it takes > 500 pounds to pull out that screw and the aluminum is weather proof. Like Walter Williams giving his wife useful gifts, get her some polish to dress that metal, thus saving money. If you want to charge more, do that too.

    

    

   Routers

1. 
   allenb | May 08, 2007 04:15pm | #12

   That's a little nicer than I was envisioning.  I was thinking more along the lines of a Simpson truss tie style affair.  Where would one find a connector like you have pictured.  It's not going to work on this project but on others it might work very well.

   Thanks,

3. 
   mwenz | May 08, 2007 03:47pm | #10

   Especially seeing that there will be glass in some of the doors, do the M&T. My preference would end up being 5/16" to 3/8" tenons--but that's because I would use my mortise chisels.

   Further, I would pin the tenons. Depending on how wide the individual doors will be, there will be a lot of stress on them. If you opt for this but don't want to see the pinning [actually wood dowels through the stile and rail's tenon] you can pin them from the back side all the way through the tenon and just a bit into the opposite side of the mortise wall. Don't use too much glue else the hydraulic force will blow out the "show" side.

   As an aside...If the cabinets are a type of A&C cabinet, pinning all the way through would be visually a design detail I would use anyway. If a Greene & Greene version, I would set the pins down from the show surface and cap them with a square plug so they can be beveled.

   Take care, Mike

4. 
   WillGeorge | May 11, 2007 10:27pm | #19

   No contest. This is the classic situation that demands M&T joints.

   I agree for what that is worth. I posted some pictures of some HUGE doors from China that were HUNDREDS of years old with M&T joints.
   NO SAG AT ALL. I'm sure a 'lap joint' would have NEVER worked that long! These doors were 20 feet tall by 8 feet wide.. Just my guess at the actual size. Oh, byt the way, about 6 inches thick!