Poor results with M&T joinery

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Forum topic by opalko posted 03-04-2011 05:49 PM 1639 views 0 times favorited 20 replies Add to Favorites Watch
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148 posts in 3004 days

03-04-2011 05:49 PM

Hi all, I am having poor results with my mortise & tenon joints, looking for advice on better ways to do these.

I am using a new Delta dedicated mortiser (which I have found out has a fence out of square – having Delta send a replacement after they told me “makes no difference if fence is square to table or not..”??).

For the tenons I make the cuts on a Delta Unisaw, single blade, no tenoning jig – just nibbling away the stock one pass at a time.

What happens is that after I make the mortises I then make the initial cut on all 4 sides to define the shoulder. I then nibble away one sawblade width at a time the edges on the two opposing sides to define the wide faces of the tenon. I then change the sawblade height to define the tenon side faces (narrow sides). I check the fit with the mortise. It is almost always too wide at this stage. So, back to the tablesaw. Lower the blade first to original height, then raise it a hair. Of course, the initial cut on all 4 sides has to be cut again, this time with the blad higher.

Invariably at this point I mis-cut and the line is now out of square along one or more edges (in other words if the piece were flattened to a two dimensional piece, and you followed the shoulder line, it would no longer be straight. Now, even if this step is done correctly, and the piece still is too wide, it must all be done again. On some cases I gest the shoulder line square/straight all the way around, but I make the tenon too thin! Now I have to start over….

The possibility for introduction of error seems almost insurmountable! How does anyone manage to get these right on the first try, or even the second try? What always seems to happen is I get a clean fitting joint on one side (hopefully the side showing!) but the opposite side is 1/32” or more too deep, so that there is a gap showing. Argh….! Help! Will a Leigh FMT jig make all these problems go away! Should I switch to dowels? Biscuits!??

Robert Opalko

20 replies so far

View pintodeluxe's profile


5623 posts in 2782 days

#1 posted 03-04-2011 06:05 PM

Keep at it, there is no more satisfying joint that a mortise and tenon joint that fits well.
1. As far as the mortiser – just make sure that the chisel is chucked square to the face of your workpiece and you should be fine. On my Delta, there is no automatic lock to square the bit, you have to do it manually.

2. When cutting your tenons, make sure that your miter gauge is square to the blade. Also check that there is no slop in the miter gauge runner. If you detect slop in the runner, it can be tightened up by striking the side with a nail punch to create small raised dimples. Otherwise you can add slick tape to the sides of the runner.
3. Once the above two items have been checked, you will see square shoulders on your tenons. It will be a lot easier once you add a dado set to your collection. You will get smoother tenon cheeks with a dado blade. I get the fit very close, then use a sanding block (with self-adhesive sandpaper on two adjacent sides) to fine tune the fit.

FYI: once you have the dado blade, you will not need a tenoning jig.

Best of luck with your projects!

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Bertha's profile


13521 posts in 2661 days

#2 posted 03-04-2011 06:09 PM

I built a dedicated tenoning jig for my old $99 Delta table saw. I’ve used chisel mortisers & pre-drilled mortises on the drill press but I was never quite happy with the fit. For me, the combination of a sharp quality mortise chisel & shoulder plane works best. I’m still no expert but I can get by.

LOL at Delta. Why are their fences so expensive if squareness is unimportant?

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View opalko's profile


148 posts in 3004 days

#3 posted 03-04-2011 06:12 PM

Thanks – how do you gauge how deep to make the initial cuts with the dado blade? Obviously the width of the mortise will make each shoulder cut slightly less than half that amount, but again, going from measuring that width, transferring that amount divided by 2 minus a small amount to the tablesaw (dado) blade height seems tough to get right the first time! Now you have to go back, recut a little deeper (higher blade height). And you have to go all the way to the shoulder edges on all 4 sides! Again, more room for a mis-cut! There has to be an easier way.

View Loren's profile (online now)


10278 posts in 3616 days

#4 posted 03-04-2011 06:27 PM

Try doing your final fitting on the router table, were the fence and
single-point cutter makes wrecking the shoulder line of the tenon
much more difficult. You’ll never get great results every time trying
to do accurate shoulder cuts on a standard table saw.

With the router method paper shims can be placed underneath
the work and removed to “sneak up” on a piston fit.

View Alster's profile


101 posts in 3182 days

#5 posted 03-04-2011 06:30 PM

Frankly, the fastest and easiest way to get a perfect fit is to cut your tenons just slightly oversized and then sneak up on a perfect fit with a shoulder plane. You have a LOT more control when you’re only removing .001” at a time. That degree of control is almost impossible to achieve on a tablesaw.

View SST's profile


790 posts in 4163 days

#6 posted 03-04-2011 06:31 PM

Have you thought of getting a good tenon (hand) saw and doing it that way. If you spent as much time practicing that as you do on the table saw, you might get good tenons & lots of self satisfaction to boot. Also, you might try final sizing with a good shoulder plane.

-- Accuracy is not in your power tool, it's in you

View opalko's profile


148 posts in 3004 days

#7 posted 03-04-2011 06:35 PM

Yes, I like the idea of a shoulder plane, and (possibly) cutting the tenons by hand. I’ve been under the New Yankee power tool school of thought for so long I haven’t tried anything else. What shoulder plane is recommended that is reasonable? (if any)

View Bertha's profile


13521 posts in 2661 days

#8 posted 03-04-2011 06:49 PM

Shoulder planes are expensive but nothing else works as well to shave a tenon. I have an older Clifton that was quite expensive. Of course Lie Nielsen & Veritas make nice ones. Some of the older Stanleys are very nice but sought after (=$$$). Avoid the modern Stanleys. There’s a very inexpensive wooden shoulder plane either at Rockler or Veritas (someone can correct me) that works quite well for the money.

I should issue a warning, however. If this is your first hand plane, beware of the disease.

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View Howie's profile


2656 posts in 2891 days

#9 posted 03-04-2011 06:54 PM

Make sure your fence isn’t slightly wobbing.

-- Life is good.

View David Craig's profile

David Craig

2137 posts in 3077 days

#10 posted 03-04-2011 07:05 PM

I am far from an expert but, from your description, I am questioning your method of “sneaking” up on the cut. You are raising the TS blade up a hair, but you are also making 4 cut which multiplies the effect of that attempt to sneak up to it. If the cuts are minimal, you might want to try cutting one side of the tenon, dry fitting it, if it is still too large, then trim the other side. This might work better for you than making 4 cuts then fitting it. If the blade height is only being raised a smidgeon, then it should not be noticeable if the tenon is not 100% perfectly centered.


-- There is little that is simple when it comes to making a simple box.

View Loren's profile (online now)


10278 posts in 3616 days

#11 posted 03-04-2011 07:05 PM

I recommend spending for a big 4 pound shoulder plane. The mass helps.

If you do especially small work smaller shoulder planes may be useful,
but for general work the lighter the shoulder plane is, the harder
it is to get a clean end grain cut with it.

View Rick  Dennington's profile

Rick Dennington

5809 posts in 3163 days

#12 posted 03-04-2011 07:10 PM

One thing that hasn’t been mentioned, and it’s very important, and that is to make ”Test cuts” on scrap pieces of the same size. You don’t just jump in and start cutting mortises and especially tenons without making test pieces…. that’s how you come up with the final solution for your projects…..the test cuts get the bugs worked out for your final finish cuts......practice, pratice, and and more practice......and don’t take it for granted that all the wood is the same size.....their not….....

-- " At my age, happy hour is a crap and a nap".....

View opalko's profile


148 posts in 3004 days

#13 posted 03-04-2011 07:13 PM

I have made test cuts on scrap pieces, but I guess you must not make the cuts on the shoulder edges until after you have the width of the tenon correct? Otherwise you will still have to go through a re-setup even after getting the scrap piece correct..?

View pintodeluxe's profile


5623 posts in 2782 days

#14 posted 03-04-2011 07:40 PM

Correct, just make the test cuts on the two faces of your scrap piece. Test the fit in your mortise, and once it starts to slip in with a snug fit stop cutting on the saw and switch to sanding block or a plane.
I can understand your frustruation with a single width blade. Once you use a dado blade, you can adjust the tenon size in a matter of seconds.
Also when I’m planning a project, I will shoot for an equal tenon reveal on all four sides if possible. IE: the dado blade height is the same setting for all four sides. One setup, four cuts. Check fit, repeat.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View NathanAllen's profile


376 posts in 3113 days

#15 posted 03-04-2011 09:51 PM

Tenon jig and a dado set if you want to make them quick and easy. Handsaws, chisels, planes and coping saws can result in great and satisfying results; but depending on the amount of time you have a dedicated mortiser and tenon jig will make the project much easier.

Delta is right that the fence doesn’t have to align to the table; justthe bit to the fence. Keep the bit collet a bit loose, move the arm down and pull the fence against it. Align the chisel and lock the collet then re-adjust the fence to the needed position. As long as the cam is straight the relationship won’t change.

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