Kind Readers,
I’ve been making some mortise and tenon joints for an exterior gate. I’m marginally satisfied with the results for a gate, but hardly think my skills are ready for furniture. Some questions…
1) When I was dry fitting the pieces, a couple of joints got awfully tight with the tenon only about 1/2 way in. Visual inspection made it easy to see that the top of the mortise was not the culprit. No real surprise there since I had used a caliper to check the thickness of the tenon and it seemed acceptably uniform. But… I had also used a caliper to check the mortise width and length and had deemed both to be acceptably uniform as well. Obviously something was wrong! My question is this… does anyone have any tricks (other than an MRI) to figure out what needs to be trimmed in situations like this?
2) While making the mortises, I felt like it was serious “guess work” to get the walls of mortise parallel and perpendicular so that the pocket would not be narrower (or wider) at the bottom and the top. Moreover, the calipers only gave me some reassurance since I could have created a parallelogram (only a slight one, my eyes aren’t that bad!). What’s the trick here? How does one check to make sure you have chopped a nice square, parallel, perpendicular mortise? (Note: I used a tri-square to check that the two ends of the mortise were perpendicular – I wasn’t as convinced that the tongue of the tri-square would be an accurate indicator for the side walls)
3) It took me a really long time to make 4 M & T joints in a soft wood (redwood in this case). My tools are all nice and sharp so that’s not the problem. I admit I’m inexperienced; but I must be doing something wrong! It can’t take this long to make this type of joint by hand can it? I cut the tenons by making multiple cross cuts on the table saw and removing the remaining waste with a chisel. Other than the time spent making sure the shoulders were perfectly aligned, I felt the tenon work went reasonably fast. Any tips for a relative M & T novice?
Thanks in advance,
— David
Edited 9/19/2005 3:30 am ET by DIBL
Replies
Hi David,
The speed issue is easy enough, it sounds like you are a relative beginner at Mortise & Tenon joints.
Your speed of both laying out and executing the joint will improve by practise. There are a bunch of tips, shortcuts for laying out like putting all of the stiles clamped together face to face and marking all of the mortise ends at one time, ditto the tenon shoulders. There are dozens of articles around. If you do lots of them you will learn naturally how to go about it expeditiosly.
Chances are, at least a part of the extra time it has taken is due to checking everthing multiple times out of nervousness in a quest for perfection.
As for the fit, in machinery work if I were to drill a hole exactly .500-inches in diameter into steel and try to insert a steel shaft exactly .500-inches in diameter it would be a force-fit and require a press. Some clearance is needed to make a running fit.
Woodworking is more forgiving because the wood will compress a bit, but a M&T joint should not be so tight- you need room for glue. If you are sure that your layout is correct, and that the mortise is plumb, relative to the edge of the board and that the sides are parallel, then pare back the tenon cheeks until the joint fits.
I may be wrong here, but it seems to me that for furniture the M&T joint is important as much for increasing the gluing surface as the mechanical stength of the joint. Different from the same joint in timber framing where no adhesive is used, just trunnels or pegs.
To find a troublesome spot inspect the tenon, if you see any burnished, shiny spots then the joint is tight there and either the mortise or the tenon needs paring.
Regards,
David C
Edit: MortiCe or MortiSe? Who knows? I went with MortiSe so had to clean up a bit-DC
Edited 9/19/2005 8:22 am ET by DCarr10760
Ditto. The strength of a M & T comes partially from the mechanics of the joint (shoulders etc) but especially from the gluing. By gluing side grain instead of end grain, a much stronger joint is created. Hence, the joint should not be starved for glue- so if one side is pinched tightly (shiny) it is unlikely that glue will flow there. You should be able to dry assemble and pull apart an M & T by hand without strenuous effort.
If a joint is too tight, coat the tenon with chalk or pencil lead and try to assemble it. Pull it apart- the areas where the chalk or lead have all worn away need to be addressed with a sharp chisel or shoulder plane. Take a few shavings and try again. Remember when you glue, the wood fibers will begin to swell, so a joint that is too tight on dry fitting will be difficult to assemble when wet with glue. As long as the shoulders are square to the mortise, and the joint is aligned, the M & T will work well. When you glue there should be some squeeze out to ensure that the joint is not starved. Leave it be and come back in an hour and remove it with a sharp chisel ofr chisel plane. Good luckGlaucon
If you don't think too good, then don't think too much...
David, you didn't mention how you made the mortises but from your description I assume that they are chiseled and the mortise walls are probably causing the binding. There are several approaches making mortises to keep the walls perpendicular. A guide block a simple jig make from a a block of wood clamped to the stile and by pressing the chisel against the face of the guide block you can pare an even and perpendicular mortise wall. The other approaches are variations on a mechanical theme using either the drill press or a router.
There are designs around for shop-made mortising router jigs that will make perfect mortise slots using spiral up cutters. You can either square the ends of the mortises or round the tenons to match the slots This is my preferred method for M&T. The other way is using the drill press to drill a series of overlapping holes and then clean up the walls with the chisel. Using a guide block can be helpful in this process.
A shoulder plane or sandpaper are useful tools for cleaning up tenons when the fit is a mite too tight. Conversely, if you the tenon is too loose, you can shim the mortise using scraps of veneer as filler.
Since this is for exterior use, I would recommend an exterior epoxy to glue up the joinery. You may also consider pegging the M&T's to further secure the joints since there will be a great deal of stress from use as well as wood movement caused by changes in the weather.
Good luck.
Doug
Use a drill press for the mortices. If that's not available, square up the drill bit in your your drill, and clean up with a gooseneck chisel. Mortice first,tenons second.
A hard block,as in a loose tenon, helps to ensure a good fit of your mortice. Leave at least a 1/4" extra depth in the mortice for glue squeeze out.
The gent who taught me used a selfmade "widget" to check that the sides of mortises are square to the surface. Essentially it is a "dogleg" made of hard wood, with a hole drilled thru the upper section, via drill press, so that it is normal to the registration plane. The gizmo is then fitted with a length of drill stock that is a very tight fit to the hole, but it can be moved up and down. This rod is "perpendicular" to the surface of the project in both "x" and "y" directions.
The "dogleg" feature enables one to better see into the mortise. I am certain my description is not really adequate, but hopefully you will get the idea.
Hi David
Being in a very similar boat to the one you are in with my M&T's and no Grey old man with a pencil behind his ear to say "no you fool, do it like this!" to help me. In sheer frustration I found a Lee jig to help me see sanity again. Its called the FMT and is sadly a little dear on the pocket. Why I love it is mainly because wood is so very expensive in South Africa and I havent botched a single lentgh of timber since I bought it, and also because its so very very accurate. I now seem to think up complicated constructions on purpose to just to use this new "toy". It does sadden me that I cant make M&T's like my grandad did, but I suppose that times do move on and the dovetailing jig may be my Christmas presesent even if its only half as good as the FMT.
Good luck
Regards
Neil
Hello,
Making a mortise and tenon is a very coordinated effort, for a misstep in producing one affects the other. Years ago when I studied woodworking, we purchased just a few tools in the beginning: a marking gauge, a back saw, some bench chisels, some mortise chisels, a mallot, a plane, and sharpening stones. I couldn't imagine making a mortise and tenon without using a marking gauge and a mortise chisel. When you choose the size of the mortise, it is based on the size of the mortise chisel you will be using. The marking gauge is set to that size, and is used to mark both the mortise and tenon. When the subsequent mortise is chopped to the line (it can't be wider because the width was set to the chisel itself), and the tenon is sawn to the line, the fit is wonderful. Tight to hand pressure is the desired result.
You mentioned that you chopped the mortise, but I am curious did you use a mortise chisel? There are several ways to make this joint, this system may be slower, but has a very high success rate.
Gottlieb
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