Hi,
I am ready to do the glue-up on the base of a large table i am making made with only mortice-and-tenon joints. Conventional wisdom dictates i would require 8 large clamps to put presure on all the mortise-and-tenon joints that connect the legs and the aprons. Four from front-to-back, two on each side. Four from left to right, two on each side. Are these really necessary?
The simple fact is, i don’t have that many large clamps, and I was thinking where i could borrow the missing clamps when i realised … do these clamps actually put usefull pressure on the joints? They do push the shoulders of the tenons to the legs of the table, but these shoulders are end-grain. The only long-grain connections are inside the mortice-and-tenon joints, and the legs are to thick to allow the clamps to exercise any pressure in there.
So in short, when glueing up a table base, do you need all those clamps, or are a couple that just press the tenon-shoulders to the table legs sufficient?
Jan
Replies
Clamps
Consider glue up in stages - ends first.
SA
How many clamps?
Infinity + 2. ;-) (A fella can never have too many clamps, ya know.)
I agree with Westchester - consider gluing in sections, ends first, then combine the sections. You do want good clamping pressure holding the tenoned stretchers into the mortices in the legs. .
consider pegging
You really don't paint a full picture based on just m&t being the joint. Is it also containgin long grain to long grain as well. Over the years i've managed to pick up 1 clamp here one there and now have about as many (you can never have too many) clamps as I need for any given glue up But someone taught me a long time ago, that if you do a m&t and do a peg with it as soon as the peg is in i remove the clamp and it's never failed as the beg holds it together. If you don't want the peg to show on the ousite facing face just stop short of going through. If you realy want to do it do a drawbore. I have seldom faced an engineering requirement for the drawbore. Now for christmas and holidays, I've asked the kids for clamps I got two of the really big bessy's that was a fantastic gift. Good luck and post some pic's
If yer asking the question "are these really necessary" , yer in trubble already.
Example..You do the glue up with the bare minimum of clamps, but when you check the diagonals of the table legs, you noticte that one diagonal is longer than the other, you have to torque your whole assembly so that the table legs are parallel. Opps no more clamps.. and glue is setting.
Or if you have the clamps to do that, you notice torquing the legs has warped the apron off of your flat surface. Oops neet some clamps to keep the apron planar!. on how can I do that without more cllamps. Glue is setting
Oops Apron ain't square, neeed to give it some torque to get the whole assembly back in square. Don't have clamps long enuf. Glue is setting.
Buddy, you need more clamps than you think you will need. If all things work perfectly, bare minimum works, but when things go south and the glue is setting, you need s few more RFN. No amount of JIT or miniimalist cost management will get them to you before the glue sets.
The axiom of "you never have enuf clamps" ain't just folly, and has withstood the test of time! Ignore it at yer own risk!
Pipe clamps is cheap and can go up to 12 feet, longer with pipe couplings. Black pipe used to be a buck a foot and 15 bucks gets the pipe clamp heads and tails. (get good smooth threaded ones!- not rough threaded imports!)
But I gotta ask why you don't use KD fittings for the table legs of are you never gonna move? There's centuries of usage of that methodolog that has proven pragmatism.
just wondering!
Eric in Calgary
Hi Guys,
Thank you for your replies. I should have known better then to mention 'clamps' in the title ;) In short, i do have lots of clamps, but not enough (never enough). I will glue up in stages due to the lack of very long (>1m) clamps.
My real question was about the clamping of mortice&tenon joints. IMHO you can not put pressure on the relevant surfaces (those of the sides of the tenons).
Thanks for your time ... Jan
The "C" Word
Yep, it's almost as much of comment-magnet as the "S" word (sharpening). ;-)
Like Hackmeister, I clamp M&T joints parallel to the tenon, just to keep the shoulders snug until the glue dries. The rest of the joint depends on a tight fit. It is important to keep the clamp exactly parallel and centered, so as not to inadvertantly skew the joint.
CLAMPS!!! DID SOMEONE SAY CLAMPS!!!!!!
Sorry, couldn't resist the title.
For mortice and tenons, I usually put a clamp on parallel with the direction of the tenon for each joint, mostly to keep glue pressure from pushing out the tenon. If the diagonal needs one to square up then maybe one in that direction.
If I was short of clamps, after gluing and clamping, I would pin the mortice with a dowel, wait a little bit and then pull the clamp off. Gluing in stages is good too, even if you do have enough clamps, because it slows down the part of the project that is easiest to mess up.
On a side note, after making a rack for mounting C clamps, for fun I counted my collection of various clamps and came up with about 80. And I still run out!!! I realized that the most I have of any one size is 8, and it is easy to run out with only 8 clamps.
Under Pressure
Like Hackmeister and RalpBarker replied, the clamps are there to keep the shoulders of the apron snug to the leg until the glue dries. The rest depends on a tight fit. This is a very different type of pressure on the glue joint then say with a table-top glue-up where all kind of tricks are used to put maximum pressure on the joints.
Unfortunately, using a dowel to pin the joint is not really an option in this table leg since the tenons of the two aprons meet inside the leg and there just isnt room for the two dowels without boring out pressious support wood.
On the other hand, tables have been build like this for a very long time, so i guess everything will work out.
Thanks ... Jan
I think the question is more one of how many clamps does YOUR table require.
When I'm building a table for myself or a client there comes a point where a choice has to be made about the tightness of the joints verses the ability to keep everything straight and flat. The finest tables are built so everything is perfectly fitted and very little clamping pressure is required to keep everything together while the glue dries and it's not uncommon for a simple brad in each joint to hold things with no clamps used at all.
On the other end of the spectrum I enjoy building craftsmen-style tables with rather thick oak approns and legs....one of my favorites for things like builtins, islands, bath vanity tables, and whatnot. The oak is hand selected and quite flat so it's possible to get great results without jointing all the boards perfectly flat. I'll run them through the thickness planer and use them as is, which requires some of the mortise and tenon joints to have additional clearances so any slight board twist doesn't keep the entire assembly from laying flat. In these cases I need a lot of clamps to pull things together tight until the gap filling epoxy or polyurethane sets up hard.
Don't forget about alternatives to clamps.....nylon strap clamps can work well if everything stays tight and flat when you test clamp it all. Just make sure to protect the wood edges, which is the main reason I don't care to use this method. On projects that require more production than I have clamps for I'll resort to straps or even nylon mason line tied tightly. Mason line is relatively cheap, is small enough to stretch easy with hand pressure and applys 50 lbs or so of clamping pressure with every wrap and there's no limit to the number of wraps that can be used. Of course thicker nylon rope can be used if some method of tightening the rope is used such as a stick used tuniquet style.
All and all, strive to use as few clamps as possible and as many as is necessary!
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