is there a disadvantage to create a m&t joint by cutting two mortises and using a separate piece of wood as the tenon? the reason i am asking has to do with efficiency: i am thinking a bout buying a slot mortising attachment for my jointer/planer and my thinking goes something like this:
with a slot mortiser i can quickly and quietly cut two perfect mortises, then thickness the floateing tennon for an extremely accurate fit. this will take less time than cutting the tennon with my dado blade or router and will probably produce a better fitting joint.
Edited 8/3/2002 2:30:24 PM ET by DJBRACH
Replies
DJ,
You've described a "floating tenon" construction. For many, many projects such a joint is perfectly acceptable. The joint is theoretically weaker than a true M&T joint, but frequently so far exceeds the stress that will ever be applied to the piece as not to matter.
An example might be a small cabinet door of frame and rail construction, or even a leg to apron joint of a table.
One of the problems with such a joint is that if the fit is sloppy, the joint is "twice as weak" as a true M&T joint with equal sloppiness of the one true mortise to tenon glue surface. So do the joint well.
An example of a poor use of such a joint might be a heavy entrance door where all the strength of the true M&T joint is necessary.
Rich
Anydown side to using epoxy with M+T?
Paul,
I don't know. I've never used epoxy. But I don't think there would be any reason not to use it. Some others who have might be able to give advice about the tightness of the joint before glue-up compared to "classic" glue up.
I like to make my M&T joints tight enough that it takes some upper body weight to fit them together. That fit is good for Titebond, but might be too tight for epoxy.
I don't like working with epoxy at all. Titebond and hide glue are my favorites.
Rich
Most epoxies are gap filling glues that actually require a looser fit in order for them to bond at full strength. For this reason I'd say that it would be your best bet to fit loose if you were going to join the members with epoxy. It's a matter of personal preference, but I don't like to use epoxy -- I'll stick with good old Titebond, with which you can fit the joints nice and tight.
Happy joinery,
Tim
BAsed on a article in FWW, I built a series of garden benches of Spanish cedar. I used all M&T joinery, and used the WestStytem epoxy, as recommended, and after 1 1/2 years outside, no problems at all. Actually pretty easy to work with, although that was my first time.
Tim,
Thanks
S4S,
Thanks, did you thicken the epoxy?
Edited 8/3/2002 8:11:55 PM ET by PAULPARADIS
No, not at all. The joints were all hand tight, without any signifigant gaps. Because this was an exterior application, I was careful to seal all of the interior end grain to prevent water impregnation, although on Spanish Cedar this may have been unnecessary. The nice thing about the WestSystem stuff is that using the slow hardner, I had plenty of open time, which was needed as I used a curved top rail, and the slats went into a 3/4" groove, and then the recesses between the top slats were back filled with spacers, precut and fit. 12 slats, 11 gaps, 12 M&T on the bottom rail, and the top, bottom, and seat stretchers. Assembly during glue up took 45 min. plus; no problem. Also, with the pumps they sell, one squirt of each (resin and hardner) made measuring simple.
Edited 8/5/2002 7:58:30 AM ET by s4s
I too am building the bench in FWW147 using loose tenon joinery, If I use westsystem epoxy how tight should the tenons fit in the mortise? did you groove the tenons? I've never worke with epoxy before so any help is greatly appreciated.
tom
The ones that I built were based on the print and article in #130. Don't recall the one in # 147. I don't use floating tenons unless the ceiling height in my basement does not permit real tenons. 4 ft. or so is my limit.
As to the epoxy, works quite well. Do spend the $ on the measuring pumps; they are a pleasure. As far as I can tell, the joinery for epoxy is the same as for titebond. The tenons should be snug, but not hammer tight. I used no groves. I generally make my tenons a bit tight, then bring them into a fit with a rabbit plane. I find this easier and quicker than trying to adjust the mortises. By the way, I use a hollow chisel mortiser on a drill press for the mortises, and this cut is a bit raggedy (sp?) on the sides, which may substitute for the grooves you asked about.
I think I'll try to remeber to photograph one of mine, and post it. (I haven't done this before, and it amy be a bit painful; we'll see.) I changed it a bit, by making the top back rail curved (29 1/2" radius, as I recall). And, agaisnt the author's advice, I used M&T on the slats. I don't think this will be a problem, as they are quite well fit and should admit no water.
On the top of the back, the curved part, I used a slotting bit in the router, ploughed a full mortise, and them cut and shaped individual backfill pieces. 12 slats; 11 fill in pieces. A bit of a pain, but my wife loves curves, as do I. I should have laminated 2 or 3 boards before cutting the back rail, which is 1 3/4" thick. Will have to see how it stands up to the weather as is, but could do a bit of splittiing with the weather in Pa. One now lives in Boston, and one in Portland OR as well.
Made 5 all together. A bit of a production run. I like the making of fixtures, and for all of that work, I sometimes do a few of one thing. The hardest part was getting the shoulders right on the curved rail, which I finally figured out after # 3.
The family appreciates the extras, although this bench has drawn a few requests for copies, and for money (believe it or not).
Edited 9/2/2002 1:25:38 PM ET by s4s
Edited 9/2/2002 1:31:01 PM ET by s4s
thanks for taking the time to answer my questions, you have been most helpful! by all means post some photos of those benches, I'd love to see them.
tom
Paul, issue #147 (Aug. 2000) has a garden bench on the cover that is assembled with floating tenons and epoxy. Check it out.......
A properly fitted M&T joint has enormous strength, and chairs are the only furniture I can think of where stresses in use might be a concern. Rich has pointed out the (in my view, disappearingly small) disadvantage of the loose tenon.
As for type of glue, consider the history of timber-framed structures. Mortise and tenon joints are the mainstay of the timber framer, and they aren't glued at all; the mating pieces are simply pegged to prevent withdrawal of the tenon (I blush as I write this), and the mechanical properties of the joint take it from there. Many timber frame structures are still standing after centuries of use, and they are continually subjected to the severe stresses of widely varying environment, snow and rain loads, high winds, earthquakes, and the like.
Edited 8/2/2002 7:50:49 PM ET by Donald C. Brown
I guess making two square holes and using a square dowel would work very nicely but lets face it , it is not a mortise and tenon. As for the glue titebond is my choice, no matter which if joint is tight you should groove internally to allow for glue to become part of project. jack
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