Mortise or tenon, that is the question when turning or making a wood bowl. For some, there is no preference, for others, it’s either mortise or tenon, but not the other.
You’ve set up the bowl blank, begun turning and it’s now time to decide how to attach the bowl to the four jaw chuck. It’s time to make a decision. Unless, of course, you’re turning a wood bowl without a chuck. But for this article, we’re dealing with a chuck and how to attach to that chuck.
So how do you decide which to use, a mortise or tenon?
There are some factors that can be considered to come up with an answer. In this article, we will look at these factors and hopefully you will come away with a better grasp of when to best use a mortise and when to best use a tenon.
What Is A Mortise or Tenon
Before we dive too deep into this baffling question, let’s clarify what we are discussing. A mortise or tenon are two different ways to attach a wood bowl bottom to a four jaw chuck.
Usually, when turning a bowl, the bowl bottom sides and base are turned first, then the bowl is reversed, and the interior of the bowl is then cleared out and finished.
The terms mortise and tenon are traditional woodworking terms used to describe two opposite interlocking joints. The tenon is an extension of wood material, and the mortise is a recessed cavity in wood.
In woodworking joinery terms, a tenon is designed and cut to fit snuggly inside a mortise, and the two are glued or fastened together.
For our use, we only need a mortise or tenon, but not both. The bottom of the bowl, whether fitted with a mortise recessed area or a tenon extension will be attached to a four jaw wood chuck
The four jaw chuck jaws will contract to hold a tenon or expand to grasp a mortise.
How To Make A Mortise
The process of making a mortise or tenon starts by sizing a four jaw chuck to the bowl blank. When sizing a mortise, the chuck jaws should contract shut, and the mortise should be slightly larger to fit the chuck. With a tenon, the jaws need to contract down on the tenon but not close completely.
To make a mortise, the sized area of the bowl blank needs to be cleared out. Cutting the mortise can be done with a parting tool, bowl gouge or and combination of tools that work best for you.
With a mortise recessed area shaped, the dovetail undercut needs to be shaped along the outside edge. A skew chisel used on center works great for scraping a slightly angled undercut.
For all the details on making an excellent mortise recessed area, check out this article.
How To Make A Tenon
With the chuck size marked on the bowl blank bottom, the material around and up to the tenon is removed. I typically remove this material with my large bowl gouge.
Once I’m up to the tenon line, I will slow down and make nice clean cuts squaring up the cylinder of wood protruding from the bowl blank. I can’t stop there because a cylinder-shaped tenon will not be held well by the four jaw chuck.
I use a detail spindle gouge to turn a gently angled undercut in the bowl tenon. Starting on the tenon cylinder edge, I make a slight inward push cut until I reach the tenon shoulder. And speaking of that shoulder, it needs to be level and smooth as well for an excellent fit to the chuck.
To learn all the ins and outs of making a perfect wood bowl tenon read this full article. And whatever you do, don’t make tenons like these!
Personal Preference
Ok, so back to the question, mortise or tenon?
Why all the moralizing around the base of a bowl blank? Well, that’s a great question. I guess for some it becomes a set routine way of doing something.
We all know what happens when some people prefer one thing over another thing. For some reason, they feel compelled to defend their position at all costs.
The debates are long-running and storied. Ford versus Chevy. Bud Light versus Miller Lite. Apple versus Microsoft. Coke versus Pepsi. Democrats versus Republicans. John Deere versus International. And now we will add Mortise versus Tenon. LOL
Do What Works
Now, I must say I do prefer using a tenon most of the time. I’m not a staunch “tenon only” guy, however. I will make mortises on occasion, but I prefer using tenons usually. I think you’ll see why as you continue reading.
Instead of taking a one-party ticket approach when deciding which connection to make for your bowl bottom, consider what makes the most sense for each bowl.
It’s easy to get into a routine of making only mortises or tenons and not genuinely considering the alternative. A better approach is to determine whether a mortise or tenon is best for each particular bowl you turn.
Mortise Advantages
One of the advantages of making a mortise recessed area is simplicity and speed. Turning a recessed area is relatively simple and straightforward.
Little waste material needs to be removed to create a mortise, just the mortise area itself. Make the cuts to eliminate this area with a parting tool and bowl gouge.
If a particular bowl blank is thin, a mortise works well by not wasting material around the base. Platters, especially work well with a mortise connection.
Mortises are great for beginners first learning to make a wood chuck connection to the lathe. The process to make a mortise is quick and straightforward.
Another advantage of the mortise is it is easy to remove and reattached to the chuck later. Easily reattachment can be a plus for applying finishes and not tying up the lathe for other projects.
Production work of many wood bowls can be executed more quickly utilizing mortise recesses compared to tenons. Tenons usually need to be removed later, which adds a production step.
Also, the recessed area of a mortise is a great place to hide a surprise for a wood bowl admirer. Decorative lines can be turned, patterns, colors, woodturning, or even inset items may be epoxied within the mortise area as a visual treat.
Mortise Disadvantages
The mortise, by its very nature, requires real estate inside the wall thickness of the bowl. Because of this intrusion, the final bowl thickness usually can’t be very thin.
Another big disadvantage is the mortise does not make shaping the final bowl foot easy. The large recessed area dictates the final foot design and makes alterations more complicated.
If the base of a particular bowl is narrow and the amount of wood around the mortise is thin, the wood chuck might add too much pressure to the surrounding wood. When there is not enough wood around the mortise to support the pressure of the four jaw chuck, an area of the side wall mortise will likely fail.
My big personal objection to the mortise is visibility. When a bowl with a mortise is flipped over the realization of the woodturning process is immediately evident.
I really prefer a bit of a mystery for the non-woodturner when they explore a wood bowl. It’s much more satisfying to have someone ask how a piece was made.
I guess, for me a mortise circle makes a bowl look and feel unfinished. But again, that is my preference only.
Tenon Advantages
A tenon can be turned on a bowl blank and create a secure, stable connection for almost any bowl. Narrow bowls with smaller bases do well when turned with a tenon.
Thin-walled bowls are easier to turn with tenons rather than mortises because the tenon is not interfering with the overall wall thickness. The tenon is an extension of the base rather than an intrusion.
Tenons can be initially created larger than needed to support the turning process and then reverse chucked and turned down to a much smaller profile.
Also, because of their ease of later alterations, tenons can be reshaped to match almost any design or final look needed. The portion of the tenon gripped by the wood chuck can also be included in the final base.
A bowl tenon allows for the entire area of the bowl base to be exposed both for visualization of the final shape and turning purposes. The final foot of a bowl can be turned while still maintaining the tenon joint. Later the tenon can be cleared from the bowl foot area.
Reverse chucking and reshaping the tenon after the bowl interior is complete can be total. In other words, the entire tenon can disappear, and the area sanded revealing no clear connection between the bowl and the lathe. The mystery of the lathe connection is what I like most about using a tenon.
Tenon Disadvantages
Occasionally, if wood is too dry and brittle, a tenon can break off. A tenon coming lose has only happened a couple of times to me with very dry pecan wood.
When turning a side-grain wood bowl, it is possible that the grain lines up cleanly with the base of the tenon which can increase the chances of separation. Again, this has only happened a couple of times with very dry wood.
To prevent a tenon from breaking off, with the bowl off the chuck, I will run a small bead of very thin CA adhesive glue around the base of the tenon. The CA helps by soaking in and bonding the wood fibers together.
If a particular piece of wood is already thin, removing waste material and forming a tenon will make it thinner. Removing around a tenon can waste a bunch of material.
Another disadvantage of the tenon is it needs to be removed. The removal process takes a bit of time, not a lot but some. There are several ways to remove a tenon, but they all take a little extra time compared to the mortise.
No-Nos
If you turn a mortise or tenon in the tender sapwood along the outside of a particular piece of timber, the connection might be compromised. Of course, this depends on other factors like species and dryness, but in general, it’s best to move away from tender, soft sapwood for a mortise or tenon.
Another thing to be aware of is end-grain turned bowls. An end-grain bowl blank should never be attached with a mortise. The outward pressure from the four jaw chuck will expand and break the blank along the grain lines and result in a loose fit a best and a flying bowl in the worst case scenario.
Mortise or Tenon Conclusion
Both the mortise and the tenon have their places in wood bowl turning. There is no need only exclusively to use one chuck joint over the other; both have value at different times.
Now that we’ve covered many of the advantages and disadvantages what do you think? Do you currently only use one over the other, or do you use both? Please share your wood bowl connection preference in a comment below.
Bowl blank attachment is important. Check out these articles now:
• WOOD BOWL MORTISE – MAKE IT RIGHT
• WOOD LATHE FACEPLATE – NEVER DO THIS – 8 THINGS
• 5 WORST TENON SHAPE WOOD BOWL (FOOT, SPIGOT, ATTACH)
• WOOD BOWL TENON REMOVAL – 3 EASY WAYS
• BOWL TENON – CREATE PERFECT SECURE WOOD BOWL FOOT
Happy Turning,
Kent
46 Responses
Love your site and YouTube channel. I had been using a mortise but using a drill press with a 2” Forstner bit instead of turning on the lathe. I didn’t know the importance of the dovetail shape before reading your articles. I’ll stop doing that and take the extra time to make it the proper shape from now on. Thanks for taking your time to help out novices like myself.
Right on, Andy! Sounds like a great plan. All the best to you and Happy Turning!
// My big personal objection to the mortise is visibility. When a bowl with a mortise is flipped over the realization of the woodturning process is immediately evident. I really prefer a bit of a mystery for the non-woodturner when they explore a wood bowl. It’s much more satisfying to have someone ask how a piece was made. //
I don’t really buy this particular objection, because the non-woodturner, viewing the bottom of the bowl, typically hasn’t a clue what a four-jaw chuck is or does — they still typically want to know how the piece was made, even when it was turned with a mortise.
Fair enough. 😉
Happy Turning!
Kent
I turn a lot of Burl. If it has voids, the tenon foot helps hold the bowl together. I personally don’t like the design compromises of a mortice that usually results in fat bottomed bowls. I prefer to turn thin bowls. Removing evidence of a tenon foot can be done with zero loss of the thickness of the blank. Removing a mortice foot means you lose at least the depth of the mortice. I would use a mortice less than 5% of the time and usually only on platters and plates. The only time I’ve had a tenon come off was when I cranked the 4 jaw chuck closed too tight and cracked it off. I agree with your advice that turners should think carefully about which technique they use in particular circumstances.
Craig,
Well said! I agree with your sentiment! I’m a tenon fan as well for the reasons you listed.
All the best to you and Happy Turning!
Have been attempting quarter sawn green red oak and started with a tenon on two pieces. They both came apart. I salvage both. One by using the screw for my chuck and the other I attached a face plate and turned a mortise on the base and was able to complete the bowl without it splitting. I’m now drying the pieces for my final turning.
Hoping the mortise will continue to hold. The screw fixture is okay but I turned the inside too much and hit the drill hole.
Anyway, enjoy your articles and thought I’d offer my experience.
Richard,
Thank you for writing and sharing!
Yes, red oak has the characteristic of being a bit brittle and breaking easily at times.
Happy Turning!
Kent
I tend to gravitate toward a mortise. I burn my “brand” in the recess. One benefit is that they bowl can always be re-mounted on the lathe to touch-up or refresh friction polish.
John,
Thank you for writing and sharing!
Those are good advantages of the recessed mortise.
Happy Turning!
Kent
Hi Kent:
Absolutely love your YouTube Channel! We never miss an episode and are learning a great deal from you. By far you are the best teacher that we’ve found in the YouTube world. You actually teach, not just let us watch you turn a bowl.
My husband and I have just ventured into the world of turning bowls. I’m only on my 3rd bowl and already have a huge problem. I’m hoping you can advise me on how to save this bowl. I will do my best to explain what I’ve done. Wish I could upload a picture.
This is just a small bowl that is meant to be a candy dish when finished. It’s being turned out of a purchased red elm bowl blank.
I started out by creating a mortise for the bottom of the bowl. We haven’t tried tenons yet.
As I was creating the outside of the bowl decided that I would like to have a nice base or foot on it that is a protruding ring around the mortise. The ring is about a quarter inch wide and the same depth. I proceeded to shape the rest of the bowl and so happy with the way it’s shaping up. Here’s my problem. After I did this my husband realized that there will be an issue when I hollow out the bowl. He thinks that it won’t be stable enough and the pressure from the chuck will break the wood on my pedestal, probably having the bowl fly off the lathe. My heart sunk and I do believe he is right. Is there anyway to solve this problem without having to start my bowl all over again?
Being so new to turning bowls, what I’ve accomplished so far took a great deal of work and thought. I would hate to have to do this over again. I really would like to keep the pedestal. The bowl won’t look the same without it.
One solution we thought of was going deeper into the bowl with the mortise so that there’s more wood to support it and then plugging it with a wooden disc when the bowl is complete. Won’t look the same, but I suppose it would be better than starting over. Any advice would be greatly appreciated. Thank-you
Michele,
Thanks for writing and sharing!
The issue you are explaining is exactly why I don’t like to use mortises too often. You are limited to how the final base can appear and you need to have plenty of “meat” around the mortise to support the chuck.
One option is to remove the mortise ring and turn a tenon. This will reduce the height of the piece. Another option is to turn a match insert blank from scrap wood and glue it into the mortise area. Let that dry over night then form a tenon on the scrap area.
I believe you will look back on this as a nice learning lesson down the road and I completely know what it’s like to make that first bowl, but they don’t all turn out, especially at the beginning.
In my online turning course, we all turn inexpensive lumber bowel blank specifically to not be too concerned about the wood. It also takes the pressure off of being perfect, which nobody is at first.
I completely empathize with your situation. Remember we can always turn another. But more importantly, enjoy and learn from the whole process.
All the best to you!
Happy Turning!
Kent
I’m new to wood lathe and bowl turning, but I have a long history of metal fabrication. I would like to comment on the problem Michele had with the bottom of her bowl being to thin, and possibly breaking when she flipped the bowl to mount into the chuck. I had the same issue and here is what I did, hope it helps.
I wrapped the bowl base with a few wraps of heat tape, to give it added strength. Ok, now to explain heat tape. It’s used in heated areas like carbon fiber repairs that use vacuum and high heat. (400 degrees). It’s also used in t-shirt heat presses to hold the decal in place during the heating process. You can find it on Amazon for about $6 a roll. It’s very strong and does not easily expand/stretch. It’s easy to remove and makes a great smoothing layer over epoxy fill ins as well.
It worked for me and saved my small red cedar bowl.
I’m hooked on bowl turning and Kent’s site is my go to source for all things bowl turning.
Yes, I dream of bowls at night already. Always looking for my next bowl.
Rex in Florida
Hello fellow bowl dreamer, Rex.
Thank you for writing and sharing! I’ll have to check out this heat tape.
Thanks for sharing.
All the best to you and Happy Turning!
Kent
I’m a regular watcher of your You Tube channel and as a new woodturner I’ve learned a lot. Thank you for sharing. This is my first time checking out you web site and the main reason was to read up on mortises versus tenons. As a new turner I’ve had much more success with mortises. I know it is all related to skill and technique and that will probably change over time.
Philip
Hello and welcome, Philip.
Thanks for sharing and visiting the website.
Yes, do what works best for you. Always!
Be willing to experiment and you will go far.
Happy Turning,
Kent
I think that saying that the fact that a mortise remains is a bit of a misnomer. An advantage of a mortise is that it *can* remain, but doesn’t *have* to. I use a mortise more than a tenon, and I nearly always remove the mortise. If removing a tenon is a benefit to having a tenon (because it can’t be seen), then a mortise falls into the same category. I don’t find removing a mortise to be any more difficult, and I generally add some detail on the bottom as I do it.
Hello Scott,
Thanks for writing.
Yes, I can see how mortises can be just as good as tenons, especially if you shape them after the bowl is complete.
It is a personal preference and more power to you and your mortises. 😉
Happy Turning,
Kent
Just returned from a training class on bowl turning held at one of the better known wood craft supply stores. I am new to turning and have only attempted 3-4 bowls to date. We were turning walnut, wet approx. 5″-6″ dia and approx 4″ thick; not big, END GRAIN. We were instructed to cut a mortise to attach to our 4 jaw chucks. As my wall thickness became smaller, my bowl split from the bottom up the side all the way to the top edge. A few other students had their bowls fly off the lathes on more than one occasion. The moral to this story is, I wish I had read this article yesterday rather than today. Might have saved a nice bowl and several hours work. Guess that’s why they call it live and learn!
Steve,
I’m sorry to hear about your loss. And I’m a bit surprised to hear they had you make mortises in green wood. Green wood requires continued tightening of the chuck because the fibers move and compress so easily. As you keep tightening or expanding into the mortise, the chuck acts like a splitting wedge and will eventually break the mortise or the whole bowl.
Wet wood is a perfect time to use a tenon. Unfortunately, turning a tenon requires a bit more time and practice, but it’s well worth learning and using on a regular basis.
Probably 95% of everything I turn is mounted using a tenon. I highly recommend tenons over mortises. But it is good to turn a mortise or two so you have the experience. It sounds like you have the experience now. 😉
Happy Turning,
Kent
Kent,
I usually start out with a tenon. When I think I am finished, I remove it. More often than not I decide to make changes of some sort so I am left with a mortice that I can use to make the changes. It seems I am always doing this, usually because I have read something from your web site:)
Wow – what an awesome website -first time I’ve visited and I am already dying to go try some new ideas… I use both – often I resort to a mortise after I cut my tenon too small 🙂
Thank you Erik!
I’m thrilled you love this site and I’m glad to help.
Good luck with the tenons!
Happy Turning,
Kent
I use a mortise in larger bowls and a tendon on smaller. For the first time I am going to core some large (11” to 15”) blanks. I went to my local guild to use their larger lathe. I was making a dovetail mortise and one of the mentors told me I had to use a tendon. I said I disagreed and he then refused to help me, so, I went looking for pros and cons and I will stick with mortise for bowls over 6”. I’ve been turning for 40 years but mostly bowls for about 10 years and lost count about 1,000. Thanks for a fair comparison.
Jim,
Thanks for the comment. Yes, it’s really a personal preference unless there isn’t enough wall for a mortise or if its an end grain turning. It’s sad that some people get so set on something being one way or another.
I think it all goes back to how they are trained. My mentor really doesn’t like oak, so I’ve avoided oak without question. I just came across some Holm Oak, and OMG it is amazing. We have to have open minds!
Thanks again and Happy Turning,
Kent
Like to learn how turn bowl
Hello Arthur,
You’ve come to the right website.
Check out this article, How To Turn A Wood Bowl, for all the steps in turning a wood bowl. Enjoy!
Happy Turning!
Just found your site. Nice.
I use a recess most of the time but also use tenons. Mine are almost always practical bowls so I follow the 1/3 or golden rule for the base.
If you remember your pi r squared.. even deleting the center area there is 3X the amount of wood to break away with a 2″ recess surrounded with 1″ compared to a 2″ tenon. Never had a recess shear off like a tenon.
In the “No Removal Required” I would rate them the same.
In the “No attachment Evidence” I would also rate them the same.
You can leave both or remove both. Not a problem with either.
Thanks, Mike! I like your reasoning.
I like your reasoning too. I’m fairly new to turning and have been struggling with the attachment protocol. Lean toward the recess for bowls.
Steve,
Do what works best for you, but be open to trying new things and you’ll go far!
All the best,
Kent
Reverse chucking remains a challenge for me with removing or shaping tenons. What method for reverse chucking do you recommend?
I mostly use a simple scrap wood jam chuck with a piece of carpet padding to prevent scuffing the bowl interior. The tailstock is pulled up and the bowl gets centered on the tailstock. I will use pull cuts to remove the tenon and make the final bowl bottom shape. In this configuration, I will also power-sand the newly shaped area to match the rest of the bowl exterior sanding. I carefully recess and shape the area inside the bowl foot until there is just a small cone connecting the bowl to the tailstock. I will then remove the bowl from the lathe, chisel off the cone nub and carefully sand the inside foot area, usually with a 2″ sanding disk.
Another great way to approach this is to use the vacuum chuck. Everything is the same as above, except when you get to the little remaining nub, you remove the tailstock and cleanly turn away the inside bottom foot area while the vacuum chuck holds the bowl in place. I hope this helps. Happy Turning!
Hi Kent- an excellent description and critique of the tenon and mortise. I teach woodturning and cannot emphasise enough of how important it is to make a “perfect”tenon. I also recommend that the face (ie where the faces of the chuck jaws meet the wood)of the tenon is slightly undercut- this also helps with a square fit. A poor fit of the tenon/jaws results in having to reshape the outside of the bowl- a lot of wasted time, particularly if sanding has been performed as well!
My choice is the tenon most of the time as it allows a variety of foot designs and if making articles with small diameter bases the tenon wood can be used as well as you point out.
Brian, Thank for sharing your comment. Yes, the tenon is the critical foundation to a quality turned bowl. And it offers so many options for final appearance. Thanks again!
I would consider myself to be a beginner turner with my training being watching many episodes of Tim Yoder. I’ve had my lathe for just over a year. I have mostly used the mortise method because it creates a foot on the small bowls I’ve turned. I will be more conscious of selecting my mounting method now after reading this post. Thank you.
My teacher is one who does both but always uses the ” X ” pattern when mounting.. ” X ” referring to grain orientation. Spreading the expansion / compression of the jaws as equal as possible and always uses the tail stock for safety / support ..
Sounds interesting. Can you explain the “X” pattern in more detail?
Look at the chuck jaw… 10 — 2 — 4 — 8 position… Now orient the grain in a X 10 … 4 2 ….. 8 a X .. spreads the force equally.. either in expansion or compression
OK, that makes sense. Thank you for sharing!
My teacher uses a box of soda straws glued together to form a log.. the straws the grain of the wood.. and it shows expansion / compressor very well as a teaching tool
Great idea!
I use Both, After learning by Trial with Flying Bowls, I am Much more inclined to pay a lot of attention to the Wood I’m turning. I prefer a Tenon, But, I have had more occasions of Losness, or having to re-tighten the jaws using a tenon. I Use a Mortise quite Often now on Bowls, and do some embellishment, and sign the project in this area. K-ray
Thank you for sharing! Happy Turning
Very good info. It verifies everything I learned yesterday at a “hands On Demo/class at our AAW sponsored event.
I us both most of the times.Or try to.