Replies

1. 
   pauld | Aug 23, 2003 07:39pm | #1

   Jay,

   As to biscuits - I save them for alignment chores; they're just not stout enough for structural duty IMHO, especially in a piece like a porch swing that will be subject to high stress.

   You're right about the strength and surface area of multiple dowels being roughly comparable to floating/loose tenons. However, I find M & T joinery more satisfying because dowels can be difficult to align precisely and can wiggle around a little too much for my taste. Matching dowel and hole diameters can be challenging, especially when glue is applied, and a little error when drilling dowel holes can multiply during clamp-up and lead to misaligned parts and unsightly gaps.

   FWIW, some of my first wood projects used hand-cut mortise & tenon joints that are still holding strong 30 years later. They weren't difficult (patience can be more valuable than skill in many woodworking tasks), just remember to cut your mortises first and then cut yout tenons to fit the existing mortises. I like to cut my tenons slightly oversize and trim them to achieve a perfect fit. Take particular care to make precise cheek cuts or you'll have visible gaps where the tenoned parts meet other pieces.

   The strength of these joints depends on good proportions: make the mortises too large, and you'll weaken the surrounding wood fiber; make the mortises too small, and the tenons will be weak. I usually shoot for mortises that are about 1/3 the thickness of the material in which the tenon will be inserted.

   I'm sure I've forgotten some stuff, and that other Knotheads may disagree with my opinions, but I hope this is helpful to you nonetheless.

   Good luck,
   Paul

1. 
   JTBelcher | Aug 24, 2003 03:31pm | #5

   Thanks for all the answers!

   So for strength applications, dowels or mortise and tenon will work well.

   I was surprised to hear that dowels have been difficult to make work properly.  I figured the M&T joint would be much more difficult.

   Here's a follow-up question.  I don't see a particular difficulty in cutting the tenon, but the mortise I worry about.  I have no mortising machine, so what's the best way to get a good cut?  I'm imagining the thing to do is to drill holes inside the layout lines and then clean it up with a sharp chisel.  I'm I on the right track?  Are there any other tricks?  I just picture that mortise being difficult to keep nice and straight from the face to the bottom.

1. 
   IanC | Aug 24, 2003 07:25pm | #6

   M & T, you've made the right choice!  Dowel joinery isn't great for furniture like chairs and beds that experience racking.  With virually no flat glueing surface, the glue can fail, then the wiggling of the dowel will crush the surrounding wood fibers until it's loose.  That's why there are so many factory made kitchen chairs falling apart.  They use dowels for speed and they can do a better job than you of installing them accurately, but they still fail.

   I'd suggest you cut the mortises first and then the tenons to fit.  It's easier to shave a bit off a tenon than to slightly enlarge a mortise.  Cutting the mortise will be easier than you think.  Clamp the workpiece solidly,  mark out the mortise with a knife, not a pencil as this will give you a groove to set the chisel.  Your chisel should be razor sharp and the same width as mortise. Start at the short ends, hold the chisel perpendicular, bevel side in, and just slightly inside the line because when you strike the chisel, the bevel will cause it to move outwards slightly.  Do the same at the other end, then a series of shallow cuts in between about 1/16th apart, then clean out the waste using the chisel at an angle.  Repeat until you reach desired depth.

   Oh yeah, you were going to drill out the waste.  Even easier!  Use a bit slightly smaller than the width of the mortise, drill out all you can and clean up the ends and sides with a sharp paring chisel.  I'd still mark it out with a knife (utility knife will do). 

   This is part of the technique that works for me.  I'm sure I left out some details and  as in cutting dovetails, everyone develops their own routine. Have fun.

   Ian

   Edited 8/24/2003 12:27:20 PM ET by IANCUMMINS

1. 
   JTBelcher | Aug 25, 2003 04:03pm | #9

   Thanks for the suggestions.  It sounds like something I can do.

   Are there any rules of thumb for the proper depth of the mortise?  As deep as possible?

1. 
   IanC | Aug 26, 2003 05:12am | #10

   Jay, Here's a few rules of thumb for tenon dimensions.

   The thickness of the tenon should be approximately 1/3-1/2 the overall stock thickness.  So in 3/4 stock, a 1/4" to 3/8" tenon thickness is recommended.  I like 3/8".   In a porch glider I suspect you'll be using some 1 1/2" thick stock so the tenon should be 1/2" to 3/4'" thick.

   As far as depth, you can use a through M&T as recommended by Stein, used in a lot of Arts & Crafts style furniture and great for outdoor stuff, or a blind mortise which should extend to about 2/3 of the stock width.  So if the stock is 1 1/2" wide, the mortise would be 1" deep, 3" wide would be 2" deep.

   When you test fit the tenon in the mortise, tap it with a hard rubber or wood mallet.  It should slide on snuggly but you should always be able to tap it back off without a great deal of effort.  If it feels so tight that it may bind up, stop, take it off and trim the tenon.  The fewer times you have to test fit, the better cause you're compressing fibers everytime you do it.   I'd suggest finding some woodworking books or mags that explain M & T joinery a lot better than I can.  Good luck.

   Ian                   

2. 
   JTBelcher | Aug 26, 2003 01:47pm | #11

   Thanks for your advice.  I think above all I just need some practice!

   Also I'll look into picking up a book with some M&T basics.

3. 
   IanC | Aug 26, 2003 03:11pm | #12

   You're welcome, and I should apologize to Paul D.  After re-reading this thread, it appears I jumped in where I wasn't asked with duplicate info.

   Ian

2. 
   Steinmetz | Aug 23, 2003 08:28pm | #2

   Jay, porchswings are best made with through mortise and tenon joints

   If you want to eliminate using glue, then 'pin' the finished joints with dowels.

   This was done one hundred years ago on post and beam joinery for barns

   the two through holes for pins (Pin oak) are offset and bored through the mortises

   then, the tenon is put into the mortise. While assembled, mark out the centers through the bored holes onto the tenon.   next ,disassemble the joint to bore out the two mating holes in the tenon, BUT! prick punch the centers 1/16" CLOSER to the CHEEK.

    The pins (or, dowels) when driven in, will draw the joint in really tight.

    Note: it's a good idea to  'Bolster'the work and use a wooden mallet .

   Bolster, means backing up the work with a wrapped hunk of steel/lead/brick with your left hand and driving the pin in with your right hand.

   I guarantee this will NOTwork loose. Stein.

   To make the pins easy to start their 'Journey', I taper the tips slightly with a block plane or a rasp.  To REALLY show off your craftmanship, Make the pins about 1/4" longer than the thickness of the wood and slightly chamfer both ends.

   Drive them in so that 1/8" protrudes on each side. Stein.

   
   

   ---

   Edited 8/23/2003 1:42:48 PM ET by steinmetz

   
   

   ---

   Edited 8/25/2003 11:19:17 AM ET by steinmetz

3. 
   RANGERP75R | Aug 23, 2003 10:12pm | #3

   Jay

      Ditto stein on what your doing with the through mortise an tenons pinned. Or you could just put about 50 lag bolts in that thing an be sure to add some duct tape. ha..ha..

      Good luck with it an let us know when we can come over an swing in that thing. ha..ha..

   Regards for success...

   sarge..jt

1. 
   DavidP52 | Aug 24, 2003 11:01pm | #7

   . . . . . The best joint is the one you don't have to make . . .

1. 
   RANGERP75R | Aug 25, 2003 12:22am | #8

   boatman

      Ha..ha... Florida sun or Oriental Philosophy? < G >

   sarge..jt

4. 
   Kevin | Aug 23, 2003 10:22pm | #4

   Hmmm.... best joint? Well... back in the day we used to be pretty fond of Columbian Gold's slightly musty, very distinctive scent... Wrong kinda joint? Ooops, my bad. LOL

   <G>

   Regards,

   Kevin