Poor results with M&T joints

[Robert Opalko]

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!??

Frustrated!
Robert Opalko

[Neal Clayton]

the fence on the mortiser only needs to be square to the bit, the table doesn't matter (unless you're cutting mortises from front to back rather than side to side).

but a few things...

a) don't cut the mortise first, that's near impossible to make a tenon to line up to. just cut the tenons first.
b) tenon width needs to be about 5 thousandths less than the size of the bit you intend to use in the mortiser. use a micrometer to measure it, you can't tell with a tape measure or ruler or other means.
c) once the tenon is cut lay the piece with the tenon next to the piece that will be mortised, flat on your table saw top. then you can mark the location of the mortise with a pencil by butting the tenon up against it, assuming the pieces are flat. flip both pieces over and do the same thing on the back. this will account for any amount that the tenon is off center and give you highly accurate marks. as long as the mortise perfectly splits the marks, it will fit.

[Prashun Patel]

I am having problems understanding where yr going wrong. But I offer how I do it:

I cut my mortises first, since I find that trickier. Then I nibble away at the tenon as you do to get a good fit.

I nibble the wide faces first on a test piece cut to the right thickness. Then I take that piece to the mortise and test the fit for width. If it's shy by a lot, I raise the blade and recut and retry. Once it's within 1/64 - but still a little wide, I stop. I then clean up the tenon with a shoulder plane, which removes my blade marks and gets it tight but fitting.

Then I cut the REAL tenon (wide faces only).

Then I use the test piece to sneak up on the width (narrow faces) of the tenon the same way.

This method allows me to a) not have to use a dado blade, b) not have to use a tenoning jig, c) only have to reset the blade height once.

I also cut the tenons a little taller than the mortise depth so they can be trimmed later to fit perfectly.

A shoulder or rabbet plane is really invaluable for this kind of fitting.

This method takes longer than using a dado blade or a tenoning jig, but I just find it more controllable.

Of course, before I start, I take an s4s piece, and then cut a kerf all the way around, rotating each time, and keeping the end butted against a stop or the fence. This identifies any significant errors in runout.

[Robert Opalko]

How do you guarantee to make a mortise a few thousandths larger than the tenon? I see no easy way to make the mortise wider?

[Neal Clayton]

well if you have a 1/2" mortiser bit/chisel then you want to make the tenons about .495. you tweak the table saw blade until that's what you wind up with.

[Robert Opalko]

As I have said in another post: how do you gauge how deep to make the initial cuts with the 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 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. I guess I need a shoulder plane but am out of money right now after spending so much on wasted stock!...argh.

[Lee Schierer]

When I make my shoulder cuts on pieces longer than the fence on my crosscut guide, I use a stop block against my table fence to set the spacing I need for the shoulders. By pushing the piece to be cut against this stop block, all four side cuts come out the same and unless I move my fence I can get back to my original setting for shoulder cuts using the same spacer against the fence.

I always cut the mortises first and clean them up before cutting tenons. I can easily adjust a tenon thickness with my tenon cutting jig to get the exact fit I want. If I were to nibble the sides of the tenons, I would make a test piece that matches the length of the mortise and cut the sides to my best guess height to make them slightly over size and then adjust the height until the test piece (when cleaned up of saw marks) fits properly. Then use that blade height setting for the real pieces. Do the same thing for the sides once you get all the thickness cuts done.

If you get a tenon too small, one advantage of a tenon cutting jig is that you can use the face cut offs to glue back on the tenon face on each side to thicken up the tenon and then re-cut it to the proper dimension once the glue sets up.

I don't have a good shoulder plane so I use a "bastard" mill file to remove the saw marks. It has an aggressive cut so it removes material pretty fast.

[JohnT Fitzgerald]

I guess there are a few things that could be going wrong...

- There could be a lot of play in your miter gauge, or it could not be accurate - or whatever it is you use when cutting the shoulders. Check that and see if there's a way to improve it or get a better gauge. You could also use a sled to make more accurate cuts.
- lumber not square (all 4 surfaces with respect to each other).
- inaccurate positioning when cutting adjacent shoulders. This can be helped byt clamping a stop block to your fence and start the piece against the stop block before cutting. Note that the piece should contact the block only at the initial start - once cutting, you do not want the piece to ride against the fence or anything else.
- I would suggest that you do not move the fence to make minor adjustments. One method I have used is to use a screw tht is screwed into the stop block, for the initial positioning. If you need to take off a little more material, turn the screw a slight amount to move the piece over just a little.
- final fitting can be done using sandpaper on the cheeks, making sure to keep the shoulders nice and square and clean.

[Steve Jenkins]

If you are making your shoulder cuts first I don't think it matters if they are just a hair deeper than the thickness of the tenon so I set the saw that way then reset to cut the actual tenon if I'm using the table saw for that. Usually I cut the tenon on the band saw after cutting the shoulders on the table saw. always test test test on scrap

[Matt Day]

I used the tools as you recently to knock out some M&T joints. Here's what I did:
1) cut mortises with mortiser (make sure you're using proper technique like not starting from one end and moving to the other with overlapping cuts)
2) clean up mortises with hand chisel if necessary
3) Use just the end most 1/4" or so of the soon-to-be-tenon (or with scrap of the same size) to fit to the mortise using the TS. There's no reason to go all the way to shoulder for test fitting. Once you have it fitting well, cut the whole thing.

[Dan Schocke]

There's no law that says you have to cut the entire face of the tennon when trying to get the correct thickness... Start small -- one or two blade widths with the height of the blade set to give you something close but oversized at first. Keep raising the blade in small increments until that test area (again, one or two blade widths) fits well into the mortise. At that point you can be confident enough to cut all the way to the shoulder of the tenon. As others have said, use a stop block and the fence to make sure you are able to locate the shoulder precisely on all faces.

--Dan

[John TenEyck]

An alternative to all this fit and fumble is to cut mortises with a router and use loose tenons. Really fast. Really accurate. You will never be off more than the variance in your stock, and that won't matter as long as you reference from the face side. I still cut traditional M&T joints occassionally, but most of the time I use loose tenon joints for the above reasons. Sometimes the best solution is to take a different approach.

[Bill Edwards(2)]

Isn't this why they make shoulder (tenon) planes?

[shane lyall]

Isn't this why they make shoulder (tenon) planes?

+1 on shoulder plane. I made a tenon jig out of scrap 1/2 ply with a cheep HF toggle clamp. Cut shoulders with miter guage then cut 'em a little fat and fine tune with a plane. Takes a little practice but stay with it.

[keith micinski]

I think he number one thing to take away from this is that no one sets up a tenon and cuts it the first time. You have to sneak up on the width using some form of a tool, your choice, and that's all there is to it. Also if the shoulder is a little small who cares. I like to have a little bit of up down movement for adjustments anyway. Once you glue the tenon in it's not going anywhere. That having been said now that I have started using hand Planes a little if there is something a little off it sure does make it easier to fine tune things.

[Paul Murphy]

Mortise and Tenon is not rocket science, but “everything depends on everything else”, and so a lot can go wrong if you are not consistent in your methods.

Start with your stock. All your stock should get the final pass with the same planer setting, meaning don’t touch the planer thickness setting until all your stock is planed at that setting.
Now your stock is the same thickness, and if you are careful you stand a chance of matching a rail face to a stile face, and if that happens the back also matches.

Cut a test mortise to discover how thick your tenon needs to be, for a centered tenon (zero offset) subtract that thickness from stock thickness and divide by 2 for shoulder thickness.
Carefully set the fence for the desired offset.

However you decide to cut your mortises, place the same face of all parts against the fence. If you decide to mortise the first stile with the show face against the fence, then all the stiles should be mortised with the show face against the fence at the same setting.
Now that ALL your mortises are the same distance from the face, you can cut your tenons to the correct thickness.

There are many ways to cut tenons, so let’s look at a couple. You can dado or “nibble” both wide tenon cheeks until you have the proper thickness, but each time you raise the sawblade you cut both faces for double the material removed. If you neglected to thickness your stock identically, your tenons will vary in thickness by the variation in stock thickness.
A second way to cut tenons is to use a vertical tenon jig that can either be purchased or shop-made. A “trick” to this method is to make a shim equal in thickness to saw kerf + tenon thickness. Carefully set the jig to cut the proper offset for the tenon face farthest from the jig face. After cutting the first tenon face, place the shim between the jig and workpiece, and cut the second tenon face. The beauty of this method is the tenon is uniformly thick and identically offset from the reference face, and any variation in stock thickness shows at the rear face.
You can use the bandsaw to cut tenons if you want, or a combination of machines. Pay attention to the proper reference face, stock thickness, and setup, and whatever way you choose has a chance of working well. Think of the benefits of various methods that work in your shop, on your projects.

Ok, now to your mortise machine. They are problematic and fussy to setup, but you can help them some. You might screw an aux face-board to your mortise fence and carry the fence+face-board to your jointer…reference the table side of the mortiser fence to the jointer fence (protect the jointer fence with a scrap board if necessary) and joint the face-board (make sure you do this safely-and don’t cut into your screws or metal fence!). You now have a square fence for your mortiser. Sometimes it helps to cut a setup shim to your offset dimension, and place the shim between the fence and chisel. Fine tune with sheets of paper until your offset is perfect, and then lock your fence. Test pieces thickenessed with your other stock, and you are on your way.
185139

[John Morrison60]

I am a comparative newby to this, I machined M&T several ways, (mostly with drill press and Table saw attachments)
and quickly realized that small inconsistencies magnify thhemselves.
I had good results, but it was stressful for me making all decisions and executing all the machining.

I did that for a year or so until I saw a demo of a Domino, not even looking back now.

I now prefer to spend my time putting a good finish on my projects.
I am learning this hobbly one step at a time.
The traditional M&T just takes too much time for me.

I only mention my path because you indicated you were looking at new equipment to assist your projects.

Good Luck
John

[Ole Anderson]

1) cut mortises with mortiser (make sure you're using proper technique like not starting from one end and moving to the other with overlapping cuts)


I just did sixteen 3/4" x 2-1/4" mortices with a Delta mortising attachment on my Craftsman DP using a 5/8" bit and two overlapping passes. (Hickory and soft maple) I definitely didn't get a smooth cut that was even by thousandths. I did start at one end and made overlapping cuts. What is the correct method for next time? Ended up trimming each mortice with a chisel and a jig to get a decent fit. Tenons were consistent as I used a tenoning sled on my TS.

[John TenEyck]

I am a comparative newby to this, I machined M&T several ways, (mostly with drill press and Table saw attachments)
and quickly realized that small inconsistencies magnify thhemselves.
I had good results, but it was stressful for me making all decisions and executing all the machining.

I did that for a year or so until I saw a demo of a Domino, not even looking back now.

I now prefer to spend my time putting a good finish on my projects.
I am learning this hobbly one step at a time.
The traditional M&T just takes too much time for me.

I only mention my path because you indicated you were looking at new equipment to assist your projects.

Good Luck
John

Good on you. No one sees how your joints are made. Everyone sees the outside results. There are a few occasions where traditional M&T joints might be the best or only option, thru tenon joints being one obvious one, but for most applications loose tenons are every bit as good, and easily better than a poorly cut M&T joint. Enjoy your Domino - and the beautiful joints and furniture you make with it.

[Paul Murphy]

As long as we are talking about other options, I also like the loose tenon method. If I had the budget, I would buy a slot mortiser, or a multi-router.

Last time I came close to buying a slot mortiser, the nicest sawmill in my area had some curly walnut that I couldn't resist.

[John TenEyck]

If I had the budget, I would buy a slot mortiser, or a multi-router.


No reason not to have one. I made this for less than $50 in less than 8 hours. Does everything I need on all but huge parts.

https://picasaweb.google.com/JohnTenEyck54/SlotMortiser?feat=directlink

[Steve Schoene]

The question was asked about what the correct way of making the mortise chisel cuts if it isn't starting at one end and making overlapping cuts. The answer is that you first make non-overlapping cuts. When the chisel is completely surrounded by the wood it has no forces want to make it bend. Then after athe non-overlapping cuts have been made, then the non-cut areas can be cleaned out with the chisel then being open on two sides, again not putting on forces that tend to flex the chisel.

[Paul Murphy]

OK, I’m going to try to explain once again why some M&T methods work better than others. I struggled with some of this for years until I decided I had had enough, and was going to find a better way. Here we go…

Lets look at why so many people like loose tenon construction, whether it’s by a slot mortiser, Domino, multi-router, or mortise-pal.
If you cut mortises referencing the show-face in two different pieces and then join them with a floating tenon, the joint is flush at the reference show face. If the pieces are the same thickness, the joint is also flush at the back face. The floating tenon eliminates the need to accurately cut a tenon with the proper matching offset defining the shoulder. The floating tenon eliminates setup error, and the mortise can really be set to any approximate location as they will all match when referenced to the same face. One setup, cut your mortises, assemble with floating tenons, done! People love it because it is error proof as long as you reference the proper face.

OK, now we look at the traditional M&T using the hollow chisel mortiser and simple tablesaw tenon jig. More setup, but you can refine it to reduce the chance for errors, and once you streamline this operation it works nearly as well as floating tenons.
Cut all your tenons using the same reference face. Most times the first saw cut will define the rear face of the tenon, so use test pieces until the rear tenon shoulder matches the rear mortise shoulder. Shim the workpiece by blade kerf + tenon thickness, and cut the second face of the tenon.
What is this method all about? It is all about referencing the same face against all jigs, thereby making tenon offset less critical. [if you dado your tenons referencing both faces, you have to center your mortise to achieve a flush joint] By shimming the tenon for the second cut, you are only adjusting the jig once, to set shoulder offset. Keep that shim, and whenever you cut tenons of that thickness you are good to go after setting the tenon shoulder offset.
When setting the tenon shoulder offset, you can fine tune it with sheets of paper, which are about .004” thick. Some guys use post-it notes because they stay in place well.
When setting the shim thickness, you can also refine that thickness with post-it notes.
The next time you cut tenons of the same thickness, all you are adjusting really is shoulder offset.

Well, I’ve really said the same thing as in my first post, just from a different perspective. Once people see the benefit of using the same reference face, they start getting better results in less overall time.

Also, thank you to John TenEyck for posting your slick router mortising jig. I'm going to have to try that out, so please post your plans if you still have them.

[Darin Higginbotham]

John, I would also like a set if you have some, thanks.

[Larry Edgerton]

The question was asked about what the correct way of making the mortise chisel cuts if it isn't starting at one end and making overlapping cuts. The answer is that you first make non-overlapping cuts. When the chisel is completely surrounded by the wood it has no forces want to make it bend. Then after athe non-overlapping cuts have been made, then the non-cut areas can be cleaned out with the chisel then being open on two sides, again not putting on forces that tend to flex the chisel.

I disagree, to a point. I agree that both ends of the mortise should be done as a plunge in undisturbed wood to ensure that they are straight.

After that I work from one end to the other so that the side of the chisel that has the chip ejection slot is exposed is free to drop the chips in the mortise. This is because of heat, the bit stays a lot cooler doing it this way and will last much longer.

[McKay Sleight]

Having used a multi router at the school that I used to teach at, the thing is the bomb when it comes to cutting mortises. I had a student that did an Arts and Crafts head and foot board with 8 million mortises. Not having an extra 2-3 grand, I do not have the multi-router and John, that thing looks really nice to use.

[John TenEyck]

Hi all. You can download a SketchUp drawing of my horizontal mortiser at the bottom of this page: https://sites.google.com/site/jteneyckwoodworker/current-projects A few details might be missing, but it's pretty close to the picture I showed above. I took many of the design concepts from two designs I saw in two FWW articles. I designed it to be cheap. The major parts are made from a single 2' x 4' piece of MDF, the runners are maple, the router plate is tempered Masonite. Clearly you can use higher quality materials but I don't plan to because it works just fine. The key is to fit the runners to the sled slots carefully and to make sure everything is square. The bottom risers are there primarily as support and alignment for the back. Take note that there is a small fence on the back of the work table, which is there for registration of the workpiece. Depth of cut is controlled by how far the router bit is protrudes beyond the fence, so there is no need for a separate stop. In use, the "machine" has two axis motion, in/out and left/right. Left/right is controlled by the two adjustable stop blocks. There is maximum left/right travel of about 4", which meets all my needs, but if you needed more you could either reposition the work or build a wider base unit to start with. Bit elevation is set by moving the router plate up/down. The vacuum system shown in the photos didn't work too well, and I've since replaced it with a Rockler Down Under Dust Port which works quite well. My out of pocket cost to build this was less than $50, not including the Rockler dust port added later at around $15. Clearly, this is no JDS MultiRouter but it works great for cutting mortises and dowel holes. Dowel holes, you ask? Why yes. Just align your workpiece to the bit, and then set the stops tight to the bottom table so that you can only move in/out.

If you have any questions, or something wasn't clear, I'll be happy to try and answer them.

John

[Harry Niemann]

I make my mortises with a mortising machine, but I cut all the tenons with a radial arm saw. You can see exactly where the blade is cutting. I use a stop block on the ras fence to make all tenons the same length and nibble away.

[Paul Murphy]

Thank you John TenEyck for letting us download your mortiser plans. It looks to be a very practical jig.

I noticed you also have a vacuum setup, which is something I've been thinking about for some time now. Your curved doors look very cool!

[hank dekeyser]

Years back when I worked in a custom shop we cut tennons on a saw w/ a dadoe blade and a fence- quick and easy. MOrtising was done on the drill press- That was the only thing these 2 machines did. We built thousands of cabinets like this and they still do to this day.

In my shop I have the Jet dedicated mortiser and cut my tennon cheeks on the table saw, then go to the band saw for the rest. Too many people get caught up in wanting it to be "a perfect fit" when it needs to be, I do it by hand. otherwise down and dirty quick and easy. you'd be amazed how tight you can get them on the band saw.

[Larry Edgerton]

No reason not to have one. I made this for less than $50 in less than 8 hours. Does everything I need on all but huge parts.

https://picasaweb.google.com/JohnTenEyck54/SlotMortiser?feat=directlink

You do nice work John.

[Paul Murphy]

Another way to cut tenons is on the router table [or shaper]. CMT makes a router bit that will cut tenons up to 1-1/16 long in a single pass, although you will have to make any haunch cuts seperately [I used the bandsaw, but there are many ways you could use]. The CMT bit comes with shims, and so you can set it for a very precise fit. If you have a router table with a variable speed router this can be a good option for making your tenons.

http://www.mcfeelys.com/product/TG5-8627/Tenon-Cutting-CMT-Router-Bit-800627

[Charles Lent]

Robert,

I used to make M&T joints on the drillpress and tablesaw, the same way as all of these other posters, and did so for many years. The key is to have all of your stock exactly the same thickness and then work from only one reference side/edge, doing all of your measuring and cutting from this one side/edge, but it isn't possible to do this when using the table saw to make the tenons because it's necessary to flip the part over to cut the opposite side, and your reference surface is then is on the wrong side. If the material isn't all the same thickness or your mortise isn't centered, your tenon will be the wrong thickness or it will be in the wrong position to mate with the mortise. Even by following this method perfectly it is still very time consuming and difficult to get repeatable results and almost every joint usually must be hand fitted for good results. I hated making M&T joints this way. Then I tackled a project that needed about 1200 M&T joints and decided that I had to find a better, faster way or I would likely never finish the project. I bought the Leigh FMT jig and with just a couple of hours practice I was making M&T joints so accurately that they were all a repeatable snug slip fit (you don't have to hammer them together and they don't fall apart if tipped so gravity can pull on them). They fit so well that when they are dry fit together they just push together with slight pressure and when pulled apart the vacuum created in the joint makes an audible pop. I completed all of the M&T joints in that project in less than 1/3 of the time that it would have taken me if doing them with the drillpress and tablesaw, and every part of my project fit together perfectly. The original FMT is expensive (now called the Pro FMT), but they now offer a lower priced version for hobby use. It uses the same bits and guides as the Pro FMT, but is made from sheet metal instead of being machined from aluminum plate. There are now also several methods available for using a router to make floating tenon joints and these work very well. The Mortise Pal is one of them. With these you will need to make your tenon stock the correct thickness with a planer, then cut it to width on a tablesaw, and then round the edges on a router table to fit your mortise joints. You should make this stock tenon material ahead of time and then cut to length as you need it for the project. This works well and costs significantly less than the FMT jig, but will take a bit longer. Even with these jigs you need to always work from one reference side/edge or you will have problems.

In my opinion, the router is the best and quickest way to make good fitting M&T joints. It's up to you to decide whether to go with an FMT jig or with one of the floating tenon type mortising jigs.

[Paul Murphy]

Robert,

The key is to have all of your stock exactly the same thickness and then work from only one reference side/edge, doing all of your measuring and cutting from this one side/edge, but it isn't possible to do this when using the table saw to make the tenons because it's necessary to flip the part over to cut the opposite side, and your reference surface is then is on the wrong side.

Charles, your post is mostly true, and very helpful. The one part that isn't true is that you can in fact cut tenons on vertically on the tablesaw referencing only one face. You have to make a shim to space the the workpiece for the second cut, shim thickness = sawblade kerf + tenon thickness. I describe it in my earlier posts, and have a picture to help explain.

Anyway, your experience is very similar to my own early days cutting tenons on the tablesaw. I always wondered about the Leigh FMT, I'm glad to hear it is working so well.

[keith micinski]

I also agree about using one reference face but one thing that isn't true is that if the stock is of differing widths the tenon wont be centered. Flipping the piece over and using both side will always center the tenon. If you use only one face and you cut the tenon then it wont be centered but the reference face will all be the same which is whats really important. Norm always use to flip his boards when cutting a dado to center it and I have always thought that was a waste of time. I usually make my table legs and 1 1/2 at the top. I cut my mortises roughly to be centered on 3/4 but if they are off a little either way what do I care? You can't see the inside face let alone get something in there to measure it and see that it is a 64th off one way. Same thing with my tenons. I get them as close to center of my 3/4 stock as possible but if they end up slightly off again it doesn't matter. Now obviously if your trying to flush the leg up with apron on the outside then you have to be spot on but anymore I find myself making the aprons a little fat and then planing them back so it is a perfect fit every time no matter what mistakes are made. I hate to say it but I am finding that a couple good hand planes are really the key to making high quality joinery which is something I would have never said until recently. Unless of course you want to spend a boat load on a slot mortiser or a domino.